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Important Questions for Class 12 Biology Term 2 with Answers

Important Questions for Class 12 Biology Term 2

If you are searching for CBSE Class 12 Term 2 Biology Important Questions then you are in right place. The students appearing in the CBSE Class 12 Term 2 examination can consolidate their preparation with the help of the CBSE Class 12 Term 2 Biology Important Questions are given on this page. The Central Board of Secondary Education has announced the Term 2 exam date, the CBSE will conduct CBSE Term 2 examination from 26th April 2022 onwards. Go through the whole article and bookmark this page to get all the latest updates from Adda247 School regarding CBSE Term 2 Exam 2022. 

Important Questions for Class 12 Biology Term 2 – Pattern

Here we have given the exam pattern of CBSE Class 12 Term 2 Biology. The exam pattern given here is based on the sample papers released by the CBSE on its official website. Check out the exam pattern of CBSE Class 12 Term 2 Biology given below: 

  1. Section A: Section A consists of 6 questions. Each question carries 2 marks 
  2. Section B: Section B consists of 6 questions. Each question carries 3 marks 
  3. Section C: In this section, a case-based question of 5 marks will be asked. 

Important Questions for Class 12 Biology Term 2 with Answers: 2 Marks 

Here we have given the 2 marks questions of Class 12th Term 2 Biology. The candidates must go through all the questions given below:

Human Health and Disease

Q. Name the two types of cells in which HIV multiplies after gaining entry into the human body.
Ans.HIV multiplies first in macrophages and then in helper T-cells or lymphocytes

Q. In what way are monocytes a cellular barrier in immunity? 
Ans.Since, monocytes can phagocytose and destroy the pathogens in blood, they act as cellular barrier

Q. High fever, loss of appetite, stomach pain and constipation are some of the symptoms seen in a patient. How would the doctor confirm that the patient is suffering from typhoid and not amoebiasis? 
Ans.Typhoid can be confirmed by widal test.

Q. Give the scientific name of the pathogen causing malignant malaria in humans.
Ans.
Plasmodium falciparumcauses malignant malaria in humans.

Q. It was diagnosed by a specialist that the immune system of the body of a patient has been suppressed. Name the disease the patient is suffering from and its causative agent.
Ans
.Patient is suffering from AIDS disease. Where in the immune system gets suppressed making the person susceptible to infections caused by pathogens. The causative agent of the disease is HIV (Human Immunodeficiency Virus).

Q. How do virus infected cells provide innate immunity to healthy cells?
Ans.Virus-infected cells secrete proteins called interferons, which protect non-infected cells from viral infection. Thus, providing innate immunity to healthy cells

Q. Why is secondary immune response more intense than the primary immune response in humans?
Ans. Since, the secondary immune response is based on the memory of primary response,i.e. first encounter with antigen. The second generated immune response is more fast having higher affinity for antigen, and therefore more intense than primary immune response.

Q. Name any two types of cells that act as ‘cellular barriers’ to provide innate immunity in humans.
Ans.Certain type of leucocytes (such as PMNL- neutrophils, monocytes) and natural killer cells are two types of cells that act as ‘cellular barriers’ to provide innate immunity in humans

Q. What is it that prevent a child to suffer from a disease he/she is vaccinated against? Give one reason. 
Ans.Vaccination produce antibodies in large numbers, which protect the child by neutralising the pathogenic agents during infection.The vaccine also generate memory B and T-cells.

Q. How does malaria differ from chikungunya with reference to their vectors?
Ans.Malaria is spread by the vector, i.e. Anopheles mosquite, whereas chikungunya is spread by the vector, i.e. Aedes

Q. Malaria, typhoid, pneumonia and amoebiasis are some of the human infectious diseases. Which one of these are transmitted through mechanical carriers.   
Ans.Amoebiasis is transmitted through mechanical carrier, i.e. houseflies

Q. How does colostrum provide initial protection against disease to newborn infants? Give one reason.
Ans.Colostrum contains antibody IgA that provides protection against disease, thus protecting the newborn infants

Q. Some allergens trigger sneezing and wheezing in human being. What causes this type of response by the body?    

Ans.Immune system of the body produce exaggerated response (allergy) against allergens and release chemicals like histamines and serotonin from mast cells. This is the cause of sneezing and wheezing, in response to these allergens.

Q. Name the type of cells, the AIDS virus enters into after getting in the human body.          
Ans.AIDS virus enter into macrophages after getting in human body

Q. Where are mucosal associated lymphoid tissues present in the human body and why?
Ans.The Mucosal Associated Lymphoid Tissues (MALT) are present in the lining of the major tracts,i.e.
respiratory, digestive and urogenital tracts. MALT constitutes about 50% of the lymphoid tissue in human body that elicits immune response to antigens along mucosal surfaces.

Q. A boy of ten years had chickenpox. He is not expected to have the same disease for the rest of life. Mention how it is possible?
Ans.(i)The antibodies developed in his body would circulate in body fluids and neutralise the pathogenic agent during subsequent encounters.
(ii) Further memory B-celis and T-cells are retained in the system, which trigger a more intense and quick response against the same antigen, thus preventing the occurrence of same disease in his life

Q. What types of virus causes AIDS? Name its genetic material?
Ans.Retrovirus causes AIDS. RNA is its genetic material

Q. What causes swelling of lower limbs in patients suffering from filariasis?     
Ans.Wuchereria bancrofti and Wuchereria malayi, the filarial worm lives for many years in the lymphatic vessels of lower limb, cause inflammation and swelling.

Q. What role do macrophages play in providing immunity to humans?
Ans.Macrophages destroy the microbes (by phagocytosis) and provide protection against diseases.

Q. How do neutrophils act as a cellular barrier to pathogens in humans?
Ans.Neutrophils in blood can phagocytose and destroy the microbes thus acting as cellular barrier to pathogens.

Q. Name the two intermediate hosts on which the human liver fluke depends to complete its life cycle so as to facilitate parasitisation of its primary host
Ans.The human liver fluke requires two intermediate hosts, i.e. freshwater snail and fish to complete their life cycle and facilitate parasitisation of its primary host

Q. How does haemozoin affect the human body when released in blood during malarial infection? 
Ans.The release of toxic haemozoin by the ruptured RBCs during malarial infection accounts for recurrence of high fever and chill every 3-4 days.

Q. What is an autoimmune disease? Give an example.
Ans.The abnormal response of an immune system in which it fails to recognise ‘self and ‘non-self’ and start destroying its own cells and molecules is called autoimmune disease. Rheumatoid is an example of autoimmune disease which destroys articular cartilage and fusing bones

Q. When does a human body elicit an anamnestic response?
Ans.Second encounter of the organism with same antigen or pathogen elicits anamnestic or secondary response for which body have memory of first encounter.

Q. State two different roles of spleen in the human body? 
Ans.The two roles of spleen in human body are:
(i) Spleen acts as a filter to trap blood-borne microorganisms.
(ii) It is also a large reservoir of erythrocytes

Q. How do interferons protect us?
Ans.Interferons produced by virus-infected cells protects the non-infected cells from viral infection by inhibiting its replication and making cells resistant to viral infection

Q. Why do pollen grains of some flower trigger sneezing in some people?
Ans.Pollen grains are allergens and cause allergy in some people due to release of chemicals i ike histamine and serotonin from mast cells

Q. Mention the useful as well as the harmful drug obtained from the latex of poppy plant.  [Delhi 2013]
Ans.Morphine is obtained from latex of poppy plant. It is useful as a sedative and harmful when used as opioids

Q. How does smoking tobacco in human lead to oxygen deficiency in their body?       [Delhi 2012]
Ans.Smoking increases carbon monoxide (CO) content in blood and reduces the concentration of haem-bound oxygen. This causes oxygen deficiency in the body

Microbes in Human Welfare

Q. BOD of two samples of water A and B were 120 mg/L and 400 mg/L,Which sample is more polluted?
[Foreign 2009]
Ans. Sample B(BOD 400 mg/L) is more polluted as higher the BOD, more is the polluting potentialQ

Q. Given below are a few impurities in urban wastewater. Select two colloidal impurities : ammonia, faecal matter, silt, bacteria, calcium. [All India 2009c]
Ans. Faecal matter and silt are the colloidal impurities in urban wastewater.

Q.  Why is sewage water treated until the BOD is reduced? Give a reason. [Delhi 2010c]
Ans. The greater the BOD of sewage water, more is its polluting potential. So, the sewage water is treated, till its BOD is reduced to reduce the organic matter present in it.

Q. Milk starts to coagulate when Lactic Acid Bacteria (LAB) is added to warm milk as a starter. Mention any other two benefits LAB provides.[All India 2009]
Ans. Two benefits of LAB:
(i) They improve the nutrient quality of curd by increasing the vitamin-B12 content.
(ii) LAB also check the growth of disease causing microbes in the stomach.

Q. Write the scientific name of the microbe used for fermenting malted cereals and fruit juices.[Delhi 2011]
Ans.  Saccharomyces cerevisiae also, commonly called brewer’s yeast is the microbe used for fermenting malted cereals and fruit juices.11]

Q. Mention the information that the health workers derive by measuring BOD of a waterbody.  [All India 2010]
Ans. Higher the BOD of water body, more is its polluting potential and vice-versa. BOD indicates the presence of organic matter in the water.

  1. Give the scientific name of the source organism from which the first antibiotic was produced.  [Foreign 2014]
    Ans. The scientific name of organism, i.e. mould from which first antibiotic was produced is Penici Ilium notatum.

Q. Which of the following is the baker’s yeast used in fermentation? Saccharum barberi, Saccharomyces cerevisiae and Sonalika. [All India 2011,2009,2012]
Ans.Saccharomyces cerevisiae is the baker’s yeast used in fermentation.

Q.  Name the type of association that the genus Glomus exhibits with higher plants. [All India 2014]
Ans. The genus Clomus exhibits symbiotic association with higher plants.

Q. State one reason for adding blue-green algae to the agricultural soil. [Delhi 2014C]
or
Mention two advantages of adding blue-green algae to paddy fields.
[All India 2011C]
Ans. Blue-green algae are added to agricultural soil because they add organic matter to the soil and also increase its fertility.

Q. Mention the role of cyanobacteria as biofertilisers. [AilIndia 2012]
Ans.Role of cyanobacteria as biofertilisers Cyanobacteria fix atmospheric nitrogen and increases the organic matter of the soil through their photosynthetic activity,

Q. Name any one symbiont, which serve as biofertiliser. Mention it specific role. [All India 2010C]

Ans.Rhizobium is a symbiont bacteria that serve as biofertiliser
The bacteria fix the atmospheric nitrogen into organic forms, which is used by the plants as nutrients.

Q. Which of the following is a free-living bacteria that can fix nitrogen in the soil? Spirulina, Azospirillum and Sonalika.           [Delhi 2009]
Ans. Azospirillum

Q. Which of the following is a cyanobacterium that can fix atmospheric nitrogen? Azospirillum, Oscillatoria and Spirulina.             [All India 2009]
Ans. Oscillatoria

Q. How is the presence of cyanobacteria in the paddy fields beneficial to rice crop?       [Delhi 2009C]
Ans. In the paddy fields, cyanobacteria such as blue-green algae fix atmospheric nitrogen to enrich the nitrogen content of soil. Therefore, the entire need of nitrogen to rice crop can be supplied by blue-green algae, leading to increase in yield.

Q. Name the group of organisms and the substrate that act on to produce biogas.       [Delhi 2009]
Ans. Methanogens are the group of organisms that acts on cellulosic materials/cow dung to produce biogas.

Biotechnology – Principles and Processes

Q. Write the two components of first artificial recombinant DNA molecule constructed by Cohen and Boyer. [Foreign 2014]
Ans.The two components of first artificial recombinant DNA molecule constructed by Gohen and Boyer are:
(i) antibiotic resistance gene
(ii) plasmid of Salmonella typhimurium

Q. Name the host cells in which microinjection technique is used to introduce an alien DNA. [Foreign 2014]
Ans. The microinjection technique to introduce alien DNA is usually carried out in animal cell, i.e. directly into the nucleus.

Q. Name the material used as matrix in gel electrophoresis and mention its role.        [All India 2014C]
Ans. The material used as matrix in gel electrophoresis is agarose.
This agarose gel acts as a sieve to separate the DNA fragments according to their size.

Q. Write any four ways used to introduce a desired DNA segment into a bacterial cell in recombinant technology experiments. [All India 2013]
Ans. Ways to introduce desired DNA into bacterial cell are:
(i) microinjection (ii) disarmed pathogen vectors
(iii) portion by bivalent cation such as calcium
(iv) bidlistic or gene gun

Q. Name the enzymes that are used for the isolation of DNA from bacterial and fungal cells for recombinant DNA technology.
[All India 2014; Foreign 2014 ]
Ans.The enzymes used for the isolation of DNA from bacterial cells is lysozyme and fungal cells is chitinase.

Q. How can bacterial DNA be released from the bacterial cell for biotechnology experiments? [Delhi 2011]
Ans. Bacterial cells are treated with lysozyme to digest the cell wall for releasing DNA.

Q. Why is the enzyme cellulase used for isolating genetic material from plant cells but not for animal cells? [Delhi 2010]
Ans. Cellulase is used for digesting the cellulosic cell wall of plant cells. Animal cells do not contain cell wall, so cellulase is not required.

Q. What is the host called that produce a foreign gene product? What is this product called?    [Foreign 2010]
Ans. The host cells that produce foreign gene product are called transgenic organisms or Genetically Modified Organisms (GMOs). The product is called recombinant proteins.

Biotechnology and its Application

Q. How does ds RNA gain entry into eukaryotic cell to cause RNA interference? [Delhi 2011c]
Ans. dsRNA gain entry into eukaryotic cell either through:
(i) infection by virus having RNA genome or
(ii) mobile genetic elements (transposons) that replicate via an RNA intermediate.

Q. Name the source organism of the gene cry IAc and its target pest. [Foreign 2011]
Ans. Source of gene crylAc is Bacillus thuringiensis and its target pest-cotton bollworms.

Q. What is the host called that produces a foreign gene product? What is this product called? [Foreign 2010]
Ans. Transgenic organisms or genetically modified organisms are hosts that produces a foreign gene product.
Recombinant proteins are the product.

Q. How does silencing of specific mRNA in RNA interference prevent parasitic infection? [Delhi 2008C]
Ans. Parasitic infection can be prevented by using RNA interference (RNAi) process, as the nematode cannot live in the transgenic host that expresses the specific interfering RNA thus, making it double stranded and unable to translate the protein or product.

Q. How are tobacco plants benefited when nematode specific genes are introduced into them using certain vectors? Name the vectors used. [Delhi 2008C]
Ans. Nematode specific genes when introduced into the host plants, initiate the process of RNAi and hence, silenced the specific mRNA of nematode. The parasite cannot survive in transgenic host, so prevent the plants from pests. Vector used is Agrobacterium.

Q. A multinational company outside India tried to sell new varieties of turmeric without proper patent rights. What is such an act referred to? [All India 2008]
Ans. This is called biopiracy. It refers to the use of bio-resources by multinational companies and other organisation without proper authorisation from the countries and people concerned without any payment.

4. What does the organisation GEAC do? Check with reference to genetic
engineering.[Foreign 2008; Delhi 2008C]
Ans. GEAC (Genetic Engineering Approval Committee) is an organisation set-up by the Indian Government to make decisions regarding the validity of GM research and the safety of introducing GM organisms for public services.

Organisms and Populations

Q.Write the basis on which an organism occupies a space in its community/natural surroundings.[All India 2013]
Ans.An organism occupies individual or species level in its community. This level is occupied on the basis of ecological level of organisation or ecological hierarchy. Individual-> Population -> Biotic community -> Biome

Q.Why are some organisms called as eurythermals and some other as stenohaline? [Foreign 2011]
Ans.Organisms, which can tolerate and thrive in a wide range of temperatures are called as eurythermal while organisms, which can tolerate and thrive in a narrow range of salinities are stenohaline

Q.Why are green plants not found beyond a certain depth in the ocean? [HOTS; Delhi 2011]
Ans.Beyond a certain depth, green plants are not found, because light is unavailable in that zone.

Q.Mention any two activities of animals, which get cues from diurnal and seasonal variations in light intensity, [Delhi 2011 c]
Ans.The two activities of animals which get cues from diurnal and seasonal variations in light intensity are:
(i) Timing their foraging
(ii) Migratory activities
(iii) Reproduction (any two)

Q. How do animals like fishs and snails avoid summer related unfavourable conditions? [Delhi 2010]
Ans.Fish migrate and snails go into aestivation or summer sleep to avoid summer-related problems.

Q. How do prickles help cactus survive in desert? Give two methods.[All India 2010 C]
Ans.The two methods by which prickles help cactus survive in desert are:
(i) By reducing and altering outer surface to reduce evaporation of water.
(ii) By providing defense against grazing animals.

Q.Which one of the two, stenothermals or eurythermals shows wide range of distribution on earth and why?[HOTS; Delhi 2008]
Ans.Eurythermals show a wide range of distribution on earth, as they can tolerate and thrive in a wide range of temperatures

Q.When and why do some animals like snails go into aestivation?[All India 2008]
Ans.During stressful conditions of the habitat and inability to migrate, animals like snails undergo aestivation and protect themselves

Q.When and why do some animals go into hibernation?  [Foreign 2008]
Ans.When unfavourable conditions are for a short time and if the animals could not migrate, they undergo hibernation to avoid stressful winter conditions.

Q.List any two physiological responses that help you to gradually get acclimatised to high altitudes when you go from the plains. [Delhi 2008 C]
Ans.The physiological condition or responses in order to get accl imatised to high attitudes are:
(i) To compensate low oxygen, the production of red blood cells is increased.
(ii) High haemoglobin content and its decreased binding capacity.
(iii) Faster breathing rate (any two).

Q. Define homeostasis. [All India 2008 C]
Ans.The process to maintain the constancy of internal environment of the body, despite varying external environmental conditions is called homeostasis

Q. When and why do some animals like frogs hibernate? [Delhi 2008]
Ans.When unfavourable conditions are for a short time period and animals are unable to migrate, they hibernate to avoid the stres winter.

Q. Between amphibians and birds, which will be stable to cope with global warming? Give reason.[HOTS; All India 2008]
Ans.Birds will be stable to cope with global warming because they can tolerate a wide range of temperatures (eurythermals).

Q. How do herbs and shrubs survive under the shadow of big canopied trees in forests?   [Delhi 2008C]
Ans.The herbs and shrubs are adapted to perform photosynthesis optimally under very low light conditions due to growing in the forests under the shadow’ of big canopied trees

Q. Why many of the freshwater animals cannot live for long in seawater or vice versa?[HOTS; Delhi; All India 2008 C]
Ans.Seawater contains high quantity of salt that is not favourable for freshwater animals. They face osmotic problems, hence they cannot survive in seawater for long.

Q. Why do predators avoid eating Monarch butterfly? How does the butterfly develop this protective feature?    [Foreign 2010]
Ans.Predators avoid the monarch butterfly as it is highly distasteful to its predators (birds) because of a special chemical present in its body. It acquires this chemical during the caterpillar stage by feeding on a poisonous weed

Q. Comment on the interaction between a clown fish living among the tentacles of a sea anemone.[Delhi 2010]
Ans.The interaction between a clown fish living among the tentacles of sea anemone is called commensalism.

Q. Comment on the interaction between certain species of fig trees and Wasps. [Delhi 2010c]
Ans.The relation between fig trees and wasps is of mutualism.

Q. Name the type of interaction seen between whale and barnacles growing on its back. [Foreign 2009]
Ans.The type of interaction observed between whale and barnacles growing on its back is commensalism.

Q. How does camouflage help an insect?   [All India 2009 C]
Ans.Camouflage is a prey defence mechanism to avoid being detected easily by the predators.

Q. Mention any two significant roles predation plays in nature.[All India 2008]
Ans.Significant roles played by predators are predators keep prey population under control. They help in maintaining species diversity in a community by reducing the intensity of competition

Q. List two advantages that a mycorrhizal association provides tO the plant.  [All India 2008 C]
Ans.Mycorrhizal association helps plants in
(i) Providing resistance to root borne pathogens.
(ii) Absorbing nutrients.

Q. Give one example where population estimation of an organism is done indirectly without actually counting the organism.    [All India 2008 c]
Ans.The number of fish caught per trap is a population estimation method done indirectly without actually counting them.

Biodiversity and its Conservation

Q.Write the level of biodiversity represented by a mangrove. Give another example falling in the same level.    [Delhi 2014C]

Ans.The mangroves represents biodiversity at ecological level. Other examples of ecological diversity are deserts, rainforests, coral reefs, etc.

Q. Name the type of biodiversity represented by the followings

  • 1,000 varieties of mangoes in India.
  • Variations in terms of potency and concentration of reserpine in Rauwolfia vomitoria growing in different regions of Himalayas.   [All India 2013]

Ans. (i) Genetic diversity

(ii) Genetic diversity

Q. Why is tropical environment able to support greater species diversity? [Delhi 2011C]

Ans. Tropical latitudes have remained undisturbed for millions of years and had a long evolutionary time for species diversification. Thus, it supports greater species diversity.

Q. Eichhornia crassipes is an alien hydrophyte introduced in India. Mention the problem posed by this plant.[All India 2010C]

Ans. Water hyacinth (Eichhornia) introduced in India is threatening the existing aquatic life in ponds and lakes, etc., as it clogs the stagnant water bodies very fast, thus, the native species are endangered.

Q. The Amazon rainforest is referred to as the lungs of planet. Mention any one human activity which causes loss of biodiversity in this region. [All India 2010C]

Ans. Human activity causing loss of biodiversity are:

(i) Many plants are cut in Amazon rainforest

(ii) Forests are converted   to grasslands for raising beef cattle.

Q. Name the unlabelled areas A and B of the pie chart representing biodiversity of vertebrates showing the proportionate number of species of major taxa. [Foreign 2009]
Important Questions for Class 12 Biology Term 2 with Answers_40.1

Ans.  A- Fishes

B  Amphibians
Q.Name the unlabelled areas A and B of the pie chart representing the global biodiversity of invertebrates showing their proportionate number of species of major taxa. [Delhi 2009]
Important Questions for Class 12 Biology Term 2 with Answers_50.1

Ans. A- Insects

B Molluscs
Q.Name the unlabelled areas A and B of the pie chart representing the biodiversity of plants showing their proportionate number of species of major taxa. [All India 2009]
Important Questions for Class 12 Biology Term 2 with Answers_60.1

Ans. A- Fungi

B  Angiosperms
Q. About 200 species of cichlid fish became extinct when a particular fish was introduced in Lake Victoria of Africa. Name the invasive fish. [Foreign 2008] 

Ans. Nile perch is the invasive fish introduced in Lake Victoria.

Q. Write the importance of cryopreservation in conservation of biodiversity.    [Delhi 2011]

Ans.  Gametes of threatened species can be preserved in viable and fertile conditions for long periods by cryopreservation

Important Questions for Class 12 Biology Term 2 with Answers: 3 marks

Here we have given the chapter wise questions of Class 12 Term 2 Biology. The questions given here are based on the Term 2 syllabus of Biology. The candidates must refer to all the questions:

Human Health and Diseases

Q. What is ‘withdrawal syndrome’? List any two symptoms it is characterised by.            [Foreign 2014]
Ans.If the regular does of drug or alcohol in an addicted person is discontinued abruptly, the body exhibits a characteristic and unpleasant symptoms called ‘withdrawal syndrome’, The ‘withdrawal syndrome’ is characterised by symptoms like anxiety, nausea and sweating

Q. How are morphine and heroin related? Mention the effect each one of them has on the human body?[All India 2014 C]
Ans.Both morphine and heroin are extracted from the latex of plant Papaver somniferum.Heroin is actually obtained from acidulation of morphine. Thus, both are related.  Morphine acts as an effective sedative and pain killer while heroin acts as depressant and slows down body functions.

Q. Why is using tobacco in any form injurious to the health? Explain.[Delhi 2008]
Ans.Tobacco is injurious to health because it, contains alkaloid nicotine which releases adrenaline and noradrenaline. It also,
(i) causes cancer of lungs, urinary bladder and throat, emphysema, bronchitis, coronary heart disease, etc
(ii)increases CO content in blood and reduces concentration of haem-bound oxygen, thus causing oxygen deficiency in the body when smoked.
(iii) causes cancer of oral cavity due to chewing.
(iv) increases blood pressure and heart rate.

Q. Why do sportsperson often fall a victim to cocaine addiction? [HOTS; All India 2008]
Ans.Cocaine exerts stimulating action on central nervous system, producing a sense of euphoria and increased energy .This is the reason some sports person misuse it to enhance their performance and with repeated use, gets addicted

Q. Due to undue peer pressure, a group of adolescents started using opioids intra- venously. What are the serious problems they might face in future?[Foreign 2008]
Ans.Serious problems due to opioids taken intravenously are:
(i) AIDS and hepatitis-B may occur. Because the viruses of these diseases are spread through sharing the infected needles and syringes.
(ii) Due to regular use, tolerance of the receptors increases, so they respond only to higher doses of drugs leading to greater intake and addiction.

Q. Name the blank spaces A, B,C and D in the table given below: [Foreign 2008]
Important Questions for Class 12 Biology Term 2 with Answers_70.1
Ans.A – Morphine
B – Central nervous system
C – Cannabis sativa
D – Cardiovascular system

Q. List four reasons to justify ban on intake of cannabinoids by sportsperson.       [All India 2008]
Ans.Cannabinoids intake by sportsperson leads to increased muscular strength, promote aggressiveness and increases the atheletic performance. It also affect cardiovascular system. So, it is justified to ban cannabinoids for sportsperson as it is an injustice on the part of other participants

Q. Write the scientific name of the source plant of the drugs-marijuana and hashish and mention their effect on human body.        [Delhi 2014 C]
Ans.The scientific names of source plant of drugs Marijuana and Hashish is Cannabis sativa. (l) They usually effect the cardiovascular system of human body.

Q. Name the plant source of the drug popularly called smack. How does it affect the body of the abuser?
[Delhi 2012]
or
Name the opioid drug and its source plant. How does the drug aff the human body?[All India 2010]
Ans.Smack is obtained from Papaver somniferum (poppy plant).
(i) It binds to specific opioid receptor present in our central nervous system and gastrointestinal tract.
(ii) It is a depressant and slows down the body functions.

Q. Why is tobacco smoking associated with rise in blood pressure and emphysema (oxygen deficiency in the body) ? Explain. [All India 2011]
Ans.The nicotine present in tobacco stimulates adrenal glands to secrete adrenaline and noradrenaline. Both these hormones increase blood pressure and heart rates. Smoking increases carbon monoxide level of the blood, which competes with oxygen for transport. As the concentration of haem-bound oxygen decreases, there is oxygen deficiency in the body.

Q. Name one plant and the addictive drug extracted from its latex. How does this drug affect the human body?[All India 2009]
Ans.Both morphine and heroin are extracted from the latex of plant Papaver somniferum.Heroin is actually obtained from acidulation of morphine. Thus, both are related.  Morphine acts as an effective sedative and pain killer while heroin acts as depressant and slows down body functions.

Q. How do macrophages in the human body act as HIV factory?[All India 2010]
Ans.After entering the macrophage, the RNA of the virus replicates to form viral DNA by enzyme reverse transcriptase.
This viral DNA gets into the DNA of host cell and directs it to produce viral particles. The macrophages continues to produce virus and in this way acts as HIV factory

Q. (i) What does the below diagram illustrate?
(ii)Name the parts labelled A and B
(iii)Name the type of cells that produce this molecule. [Delhi 2009]
Important Questions for Class 12 Biology Term 2 with Answers_80.1
Ans.(i)It shows antibody molecule.
(ii) A – Antigen-binding site B – Heavy chain
(iii) B-lymphocytes (B-cells) produce antibodies

Q. State the effect of carcinogens on human body. Name the carcinogenic ionising and non-ionising radiations. Mention their carcinogenic effect. [All India 2010 C]
Ans.Carcinogens can transform normal cell into cancerous neoplastic cell. Carcinogenic ionising radiations are X-rays and gamma rays. Carcinogenic non-ionising radiations are UV-rays.These radiations cause damage to DNA, i.e. mutations that leads to transformation of normal cells into cancerous cell

Q. list the specific symptoms of typhoid. Name its causative agent.[All India 2009]
Ans.Symptoms of typhoid are:
(i) Constant high fever (39-40°C)
(ii) Weakness and headache
(iii) Stomach pain
(iv) Loss of appetite
Intestinal (small intestine) perforation in severe cases which may cause death. Causative agent – Salmonella typhi

Q. (i) Explain the property that prevents normal cells from becoming cancerous.
(ii)All normal cells have inherent characteristic of becoming cancerous. Explain.[HOTS; Foreign 2009]
Ans.(i)Contact inhibition is the property shown by normal cells. Due to contact with other cells, they inhibit their uncontrolled proliferation and growth.
(ii) All normal cells have oncogenes (c-onc) or protooncogenes. When activated under certain conditions, such genes could lead to oncogenic transformation of cells, i.e. they become cancerous,

Q. What is colostrum? Why is it important to be given to the newborn infants?[Foreign 2009, Delhi 2009]
Ans.
Colostrum is the milk produced by mother during initial days of lactation.Colostrum contains antibody IgA that provides protection against disease, thus protecting the newborn infants

Q. How does spleen act as lymphoid organ? Explain. [Foreign 2009]
Ans.Spleen is a large, bean-shaped organ, which contain lymphocytes and phagocytes. It act as a filter to trap blood-borne microbes and contain large pool of erythrocytes, thus acts as secondary lymphoid organs.

Q. Explain the response initiated when a dose of vaccine is introduced into the human body.    [Delhi 2009]
Ans.When a dose of vaccine is administered in the human body, antibodies are produced in the body against these antigens. They would neutralise the pathogenic agents during actual infection.The vaccines also generate memory-B and T-cells, that recognise the pathogen quickly on subsequent exposure

Q. How do normal cells get transformed into cancerous neoplastic cells? Mention the difference between viral oncogenes and cellular oncogenes. [Foreign 2008]
Ans.Normal cells are transformed into cancerous neoplastic cells due to physical, chemical or biological agents, which are known as carcinogens.
(i) Viral oncogenes Genes of viruses, which cause cancer.
(ii) Cellular oncogenes Genes present in normal cells, which become activated under certain conditions and cause oncogenic transformation of the cell.

Q. Name the two special types of lymphocytes in humans. How do they differ in their roles in immune response?   [All India 2012]
Ans.Two types of lymphocytes are:
(i) B-lymphocytes or B-cells (ii) T-lymphocytes or T-cells
B-lymphocytes and T-lymphocytes are

Q. (i) Name the group of virus responsible for causing AIDS in humans. Why are these virus so named?
(ii)List any two ways of transmission of HIV infection in humans other than sexual contact? [All India 2012]
Ans.(i)Retrovirus is the group of virus causing AIDS in humans. They contain RNA as genetic material and with the help of enzyme reverse transcriptase they make DNA on RNA template. Thus, they are called retrovirus.
(ii) (a) By sharing infected needles.
(b) By transfusion of blood contaminated with HIV

Q. Why is an antibody represented H2L2 ?[Foreign 2012]
Ans.Antibody is represented as H2L2 because each antibody molecule has four peptide chains, i.e. two small light (L) chains and two longer heavy (H) chains.

Q. Name the different types of cell providing cellular barrier responsible for innate immunity in humans.[Foreign 2012]
Ans.Cellular barriers are provided by:
(i) Certain types of WBC like polymorphonuclear leukocytes and monocytes in blood.
(ii) Macrophages in tissue

Q. List any two emergent circumstances, when a medical doctor would recommend injection of a pre-formed antibody into the body of a patient and why?   [HOTS; Delhi 2011C]
Ans.(i) In case of snake bite, quick immune response is required and we cannot wait for the body to produce antibodies.
(ii) In tetanus, it is infected with some deadly microbes to which quick immune  response is required

41.How is an allergic reaction caused by an allergen? Name the drug that can reduce the symptoms of allergy? [All India 2011 C]
Ans.Allergens can produce IgE type of antibodies. There is release of histamine and serotonin like chemicals from mast cells, which cause allergic reactions.The use of drug anti-histamine, adrenalin and steroids quickly reduce the symptoms of allergy.

Q. Name the two types of immunity in a human body. Why are cell mediated and humoral immunities so called?[Delhi 2011]
Ans.Types of immunity system in human are:
(i) Innate immunity, acquired immunity or humoral immunity system and cell mediated immunity system.
(ii) Cells mediated immunity is so called as it involves specialised cells, the T-lymphocytes.  Humoral immunity is so called because it includes antibodies, which are found circulating in body fluid, the blood (humors-body fluids).

Q. Write the scientific names of the causal organisms of elephantiasis and ringworm in humans. Mention the body parts affected by them.     [Delhi 2011]
Ans.(i)Elephantiasis is caused by Wuchereria bancrofti and W. malayi. These affect lower limbs and genital organs.
(ii) Ringworm is caused by Microsporum, Trychophyton and Epidermophyton. They affect the skin, nails and scalp.

Q. Name the host and the site, where the following occur in the life cycle of a malarial parasite
(i)Formation of gametocytes
(ii)Fusion of gametocytes [Delhi 2010]
Ans.(i)Formation of gametocytes occurs in erythrocytes (RBC) of human beings.
(ii) Fusion of gametocytes occurs in the intestine of mosquito

Q. Define the term health. Mention any two ways of maintaining it.[All India 2010]
Ans.Health can be defined as a state of complete physical, mental and social well-being. It can be maintained by taking balanced diet, maintaining personal hygiene, regular exercise/yoga, vaccination against infectious diseases, etc

Q. Why does a doctor administer tetanus antitoxin and not a tetanus vaccine to a child injured in a roadside accident with a bleeding wound?[HOTS; All India 2010]
Ans.In case of injury, tetanus antitoxin, i.e. preformed antibodies for tetanus are injected, as the child is infected with deadly microbes (tetanus-bacteria) to which fast immunisation is required.
If tetanus vaccine is injected, it will take sometime for the body to develop immunity and that will be too late and may prove fatal.

Q. Identify A, B,C and D in the following table
Ans.A – Small intestine B – Rhinovirus
C – Nose, respiratory passage D – Alveoli of lungs.

Q. The barriers in the innate immunity are given in the following table. Identify A, B, C and D. [Delhi 2010 c]
Important Questions for Class 12 Biology Term 2 with Answers_90.1
Ans.A-Lining of epithelium B-Tears C-Cytokine
D-Polymorphonuclear leukocytes

Q. (i) How does a vaccine affect immunity?
(ii) How can we get immunisation against tetanus?    [All India 2010]
Ans.(i) In vaccination, a preparation of antigenic proteins of pathogen or inactivated/ weakened pathogen (vaccine) are introduced into the body. The antibodies produced in the body against these antigens would neutralise the pathogenic agents during actual infection. The vaccines also generate memory B and T-cells.
(ii) Preformed antibodies for tetanus are directly injected to acquire quick immune response. This is called passive immunisation.

Microbes in Human Welfare

Q. How do methanogens help in producing biogas?   [Delhi   2012]
Ans. Methanogens grow anaerobically on cellulosic material and produce large amount of methane along with C02 and H2. Since, biogas is a mixture of methane and C02, methanogens helps in its production

Q. Why is Rhizobium categorised as a symbiotic bacterium? How does it act as biofertilisers?            [Delhi  2012]
Ans. The nodules on the roots of leguminous plants are formed by Rhizobium bacteria for their survival. These bacteria fix atmospheric nitrogen into organic form, which is used by the plant as nutrients. Since, Rhizobium forms symbiotic association with leguminous plants these are considered as symbiotic bacteria, (l) Rhizobium fixes the atmospheric nitrogen into organic form, i.e. nitrates which can be utilised by the plant as nutrient. So, it is used as biofertilisers.

Q. How do plant benefit from having mycorrhizal symbiotic association?
[Foreign 2010]
Ans. The plants get benefits from mycorrhizal symbiotic association in the following two ways:
(i) The fungal symbiont in mycorrhizal associations absorb phosphorus from soil and passes it to the plant.
(ii) It also provides resistance to root borne pathogens and increases plant growth and development

Q. How do mycorrhizae act as biofertilisers? Explain. Name a genus of fungi that forms a mycorrhizal association with plants. [Delhi 2012]
Ans. Fungi form symbiotic association with plants, which is called mycorrhiza. The fungal symbiont in these associations absorbs phosphorus from soil and passes itto the plant. Thus, acts as a biofertiliser. The fungi belonging to the genus Glomus form mycorrhizal associations with plants.

Q. What are methanogens? Name the animals in which methanogens occur and the role they play there.[Delhi 2014]
Ans. Methanogens are groups of anaerobic bacteria, that produces large amount of methane.
Methanogens are found in rumen of cattle and intestine of humans.
The methanogens present in intestine of animals and humans act on cellulosic part of food and digests them, thereby releasing methane along with C02 and H2.

Q. How are baculoviruses and Bacillus thuringiensis used as biocontrol agents? Why are they preferred over readily available chemical pesticides?  [2014c]
Ans. Bacillus thuringiensis as biocontrol agent
(i) Through genetic engineering, the gene coding for the toxic protein is introduced into crop plants, which make them resistant to insect pests.
(ii) When they are eaten by the larvae, the toxin becomes active in the gut of larvae and kills the larvae.
(iii) They are available in sachets as dried spores, which have to be mixed with water and sprayed onto vulnerable plants.
Baculovirus (Nucleopolyhedrovirus) as biocontrol agents:
(i) These are excellent candidates for species-specific, narrow spectrum insecticidal application.
(ii) They show no negative impact on plants, mammals, birds, fish or even non-target insects.
(iii) These are especially desirable when beneficial insects are being conserved to aid in an overall Integrated Pest Management (IPM) programme.

Q. Draw a labelled sketch of a typical biogas plant. [2014c]
Ans. Biological control of pests and pathogens must be preferred over conventional use of chemical pesticides because
(i) the chemicals cause pollution to soil, ground water and agricultural products.
(ii) the chemicals are toxic and harmful to both human being and animals.
(iii) overuse of chemical fertilisers make soil infertile.
(iv) kills harmful as well as useful organisms indiscriminately.
Important Questions for Class 12 Biology Term 2 with Answers_100.1

 

Q. Why is ‘starter’ added to set the milk into curd? Explain. [All India 2014c]
Ans. When a small amount of curd as starter is added to fresh milk, millions of Lactic Acid Bacteria (LAB) present in the starter grow in milk and convert it to curd. During this process, acids are produced by LAB that coagulate and partially digest the milk proteins (casein). LAB increases vitamin-B12 content along with other vitamins in the curd

Q. Name the bacterium responsible for the large holes seen in swiss cheese. What are these holes due to?
[All India 2013, Delhi 2008C]
Ans. Swiss cheese is produced by the bacterium Propionibacterium shermanii. The large holes in swiss cheese are due to the large amount of C02 production

Q. Name the source of streptokinase. How does this bioactive molecule function in our body. [Delhi 2012]
or
Name the enzyme produced by Streptococcus bacterium. Explain its importance in medical sciences.
[All India 2011]
Ans. Streptokinase enzyme is produced by the bacterium Streptococcus. It is modified by genetic engineering and is used as a clot buster for removing clots from the blood vessels of patients who have suffered from myocardial infarction.

Biotechnology – Principles and Processes

Q. How does a restriction nuclease function? Explain. [All India 2014]
Ans. Restriction nucleases function by inspecting the length of DNA sequence, and then binding to specific recognition sequences and cutting the strands at sugar phosphate backbones.
These nucleases are of two types depending on their mode of action.
(i) Restriction exonucleases cut sequences at terminal ends of DNA.
(ii) Restriction endonucleases cut between the two bases of recognition sequence.

Q. Write the role of Ori and restriction site in a cloning vector pBR322.
[Delhi 2014]
or
How do Ori and cloning sites facilitate cloning into a vector? 
[All India 2008C]
Ans.Ori is a sequence of DNA from where replication starts. Any piece of DNA that needs to replicate in the host cell has to be linked to it.
Cloning sites refers to the site/sequence of DNA where the alien DNA is linked.

Q. Explain with the help of a suitable example the naming of a restriction endonuclease.  [Delhi 2014]
Ans. Naming of restriction endonuclease are:
(i) The first letter of the name comes from the genus and next two letters from species of the prokaryotic cell from where enzymes are extracted.
(ii) The Roman numbers following the name show the order in which the enzymes, were isolated from the bacterial strain. For example, Eco Rl is derived from Escherichia coli RY 13, Hind II from Haemophilus influenzae Rd, etc.

Q. How are sticky ends formed on a DNA strand? Why are they so called? [Delhi 2014]
Ans.Sticky ends on DNA are formed by action of enzymes restriction endonucleases. These enzymes cut the strand of DNA a little away from the centre of the palindrome sequence between the same two bases on both the strands. This results in single stranded stretches on both the complementary strands at their ends.
These overhanging stretches are called sticky ends as they form hydrogen bonds with the complementary base pair sequences.

Q.How is insertional inactivation of an enzyme used as a selectable marker to differentiate recombinants from non-recombinants?
[Foreign 2014]
Ans. The insertional activation of J3-galactosidase enzyme, i.e. by inserting the desired gene in the coding region of enzyme, results in inactivation of (3-galactosidase gene in recombinants. The recombinant on transformed hosts are unable to produce any colour when grown on chromogenic substrate, thus acting as a selectable marker to differentiate recombinants from non-recombinants.

Q. Explain palindromic nucleotide sequence with the help of a suitable example.         [Foreign   2014]
Ans.The palindromic nucleotide sequence is the sequence of base pairs in DNA that reads the same on both the complementary strands of DNA, with same orientation of reading.
For example
5′-GAATTC-3′
3′-CTTAAG-5′

Q. Why are molecular scissors so called? Write their use in biotechnology?   [Foreign   2014]
Ans. Molecular scissors are so called because they cut DNA at specific sequences between base pairs.
Since, molecular scissors on restriction enzymes cut DNA at desired sequences and generate sticky ends that facilitate to join with host genome or vector DNA, they play an important role in genetic engineering or biotechnology. It is because with the help of these enzymes we can cut the desired gene and introduce into vectors for expression.

Q. Why is making cells competent essential for biotechnology experiments? List any two ways by which this can be achieved.
 [Delhi 2014C]
Ans. Since, DNA molecules are hydrophillic, they cannot pass through cell membranes. For recombinant DNA to be integrated into vector or host genome it is necessary for the DNA to be inserted in the cell. Therefore, making the host cells competent is necessary in biotechnology experiments.
The two ways by which cells can be made competent to take up DNA are:
(i) Chemical action By increasing concentration of divalent cation, calcium, thereby increasing the efficiency of DNA entering through pores in cell, wall.
(ii) Heat shock treatment Incubating the cells with recombinant DNA on ice, followed by brief treatment of heat at 42 °C and again putting them back on ice.

Q. How is an exonuclease functionally different from an endonuclease? Give an example of any two endonucleases other than Sal I. [Delhi 2013C]
Ans. Exonucleases are the enzymes which cleaves base pairs of DNA at their terminal ends and act on single strand of DNA or gaps in double stranded DNA. While, endonucleases cleaves DNA at any point except the terminal ends and can make cut on one strand or on both strands of double stranded DNA, e.g. Eco Rl and Hind II.

Q. Explain the contribution of Thermus aquaticus in the amplification of a gene of interest.       [Delhi  2009]
Ans. Thermus aquaticus provides thermostable DNA polymerase. It can withstand the high temperature used in denaturation and separation of DNA strands during Polymerase Chain Reaction (PCR). Hence, can be used for repeated amplification of DNA.

Q. What are recombinant proteins? How do bioreactors help in their production?    [All India 2009]
Ans. Recombinant proteins are produced by the expression of recombinant DNA in the transgenic organism. Bioreactors help in producing these proteins on a large scale as
(i) Large volumes of culture can be processed in bioreactors to produce desired quantity of product.
(ii) These provide optimum conditions of pH, oxygen, salts, substrates, etc., to get the desired product.

Q. Mention the three steps involved in each cycle of Polymerase Chain Reaction (PCR). How is repeated amplification of DNA made possible using PCR? [All India 2008C]
Ans. (i) A-Denaturation of the double stranded DNA.
(ii) B-Primers
(iii) C-DNA polymerase or Taq polymerase.
Importance in PCR    
It extends the primers using the nucleotides provided in the reaction medium and the genomic DNA as the template. Taq polymerase is thermostable and withstands the high temperature used in denaturation process.
Repeated amplification of DNA in PCR is made possible by using thermostable DNA polymerase, which remain active during high temperature.

Biotechnology and its Application

Q. State how was Agrobacterium tumefaciens been made as a useful cloning vector to transfer DNA to plant Cells.   [Delhi       2014]
Ans. The bacterium Agrobacterium tumefaciens is known to be natural vector capable of passing its DNA to plants and induce tumour by integrating its DNA with host genome. The tumour causing gene in the plasmid of this bacteria is replaced by gene of interest and is now used as a cloning vector to transfer the DNA into plant cells.

Q. What is gene therapy? Name the first clinical case in which it was used.  [Delhi       2014]
Ans. Gene therapy is a corrective therapy or technique of genetic engineering to replace a faulty or non-functional gene with a normal healthy functional gene,
The first clinical gene therapy was given to a 4 years old girl with ADA (Adenosine Deaminase) deficiency in 1900, due to the deletion of the gene coding for ADA

Q. Human insulin when synthesised in the body needs to be processed before it can act. Explain giving reasons.   [Delhi 2014c]
Ans. Human insulin when initially synthesised in human body consists of three peptide chains- A, B and C. The C-peptide is an extra stretch of amino acids joining the A and B-chains. This is called proinsulin or prohormone. It undergoes processing or splicing to release the functional mature insulin that can carry out its normal functions. During processing, the C-peptide is removed. Only A and B-chains contribute to form the functional insulin.

Q. Write any two ways how genetically modified plants are found to be useful?  [All India 2014C]
Ans. Then genetically modified plants are found to be useful as, they :
(i) reduce or minimise the use of chemicals,fertilisers, insecticides, herbicides, etc.
(ii) reduce post-harvest losses and enhance nutritional value of crop.

Q. Name the disease that was first to get the gene therapy treatment. Write the cause of the disease and the effect it has on the patient. [Delhi 2014C]
Ans. The ADA (Adenosine Deaminase) deficiency disease was the first to get the gene therapy treatment.
The disease is caused due to the deletion of gene that codes for Adenine Deaminase (ADA) enzyme. The deficiency of the ADA enzyme effects the functioning of immune system.

Q. Why is proinsulin so called? How is insulin different from it? [All India 2013]
Ans. Proinsulin contains an extra stretch called C-peptide that needs to be removed to become fully mature insulin, therefore it is called proinsulin (prohormone). The mature functional insulin contains only A and B-peptide chain

Q. (i) State the role of DNA ligase in biotechnology.
(ii) What happens when Meloidogyne incognita consumes cells with RNAi gene? [Delhi 2012]
Ans. (i) DNA ligase enzyme is used to join two DNA fragments from their ends.
(ii) When Meloidogyne incognita (parasite) consumes cells with RNAi gene, parasite cannot survive and this prevents infection. The introduced DNA forms both sense and anti-sense RNA. These two strands being complementary to each other form ofsRNA, leading to RNAi. Thus, the mRNA of nematode is silenced and the parasite cannot survive there. This produces Meloidogyne incognita resistant tobacco plants.

Q. (i) Mention the cause and the body system affected by ADA deficiency in humans.
(ii) Name the vector used for transferring ADA-DNA into the recipient cells in humans. Name the recipient cells. [All India 2012]
Ans. (i) ADA is caused due to deletion of gene for adenosine deaminase. Immune system of body is affected due to this.
(ii) Retroviral vector is used to transfer ADA-DNA into the recipient cells of human.
Recipient cells-Lymphocytes.

Q. Explain how a hereditary disease can be corrected. Give an example of the first successful attempt made towards correction of such disease?     [Delhi 2011]    
or         
How is gene therapy being used in  treating ADA deficiency patients?    [All India 2008C]
Ans. Hereditary disease can be corrected by gene therapy. It is a collection of methods that allows correction or replacement of defective gene. The first gene therapy was given in 1990 to a 4 years old girl with Adenosine Deaminase (ADA) deficiency. It is caused due to the deletion of gene for adenosine deaminase.
The treatment involves following steps:
(i) Lymphocytes from the blood of patient are grown on culture outside the body.
(ii) A functional ADA, cDNA (using a Retro viral vector) is then introduced into these lymphocytes.
(iii) Such genetically engineered lymphocytes are returned to the blood of patient.
(iv) Periodic infusion of such genetically engineered lymphocyte is required by the patient.

Q. How is recombinant DNA technology help in detecting the presence of mutant gene in cancer patients?   [All India 2011c]
Ans. A single stranded DNA or RNA, tagged with a radioactive molecule (probe) is allowed to hybridise with its complementary DNA in a clone of cells followed by detection using autoradiography.
The clone having the mutated gene will not appear on photographic film, because probe will not be complementary with mutated gene thus, helpful in detecting the presence of mutated gene in cancer patients.

Q. What is biopiracy? State the initiative taken by the Indian Parliament against it. [Delhi 2014]
Ans. Biopiracy refers to the use of bio-resources by multinational companies and other organisations without proper authorisation from the concerned countries and people.
The Indian Parliament has cleared a second Amendment of Indian Patents Bill as a initiative step against biopiracy. This bill consider issues including patent terms, emergency provisions as well as research and development initiative.

Q.  How have transgenic animals proved to be beneficial in
(i) production of biological products?
(ii) chemical safety testing?  [Delhi 2014]
Ans. (i) The transgenic animals are proved to be beneficial in production of biological products like human protein a-1 antitrypsin (by coding genes for that protein only) in treatment of emphysema, and human protein (a-lactalbumin) enriched milk by transgenic cow, i.e. Rosie. This milk was more nutritionally balanced for human babies than natural cow milk.
Transgenic animals are studied for testing toxicity of drugs and other chemicals, as they carry genes that makes them more sensitive to toxic substances.

Q. How is ‘Rosie’ considered different from a normal cow? Explain.
[All India 2011; Foreign 2010]
Ans. The transgenic cow, Rosie, produced human protein-enriched milk (2.4 gm/L). It contained the human a-l actalbumin and was nutritionally more balanced product for human babies than natural cow’s milk.

Q. Biopiracy should be prevented. State why and how? [All India 2011]
Ans. Biopiracy should be prevented because
(i) The countries and people concerned are not given adequate compensatory payment.
(ii) The countries/people also lose their right to grow and use     breeding experiments to improve the other varieties of the same species.

Q. Describe the responsibility of GEAC, set-up by the Indian Government. [Delhi 2009]
Ans. GEAC (Genetic Engineering Approval Committee) is an organisation set-up by the Indian Government to make decisions regarding the validity of GM research and the safety of introducing GM organisms for public services.

Organisms and Populations

Q.Some organisms suspend their metabolic activities to survive in unfavourable condition. Explain with the help of any four examples.[Delhi 2012]
Ans.Examples of organisms that suspend their metabolic activities in unfavourable condition.
(i) Bacteria, fungi and lower plants They form thick-walled spores, which help them to survive in unfavourable conditions. Spores germinate on  return of favourable conditions.
(ii) Higher plants Seeds and some other vegetative reproductive structures serve as means to tide over periods of stress. They reduce their metabolic activity and undergo dormancy.
(iii) Animals They undergo hibernation or aestivation, if unable to migrate. For example, some snails and fishes.
(iv) Zooplanktons They enter diapause (suspended development) under unfavourable conditions.

Q.Explain the response of all communities to environment over time.  [All India 2011]
Ans.Response of communities to environment:
(i) Some organisms maintain homeostasis by physiological or behavioural means (regulate).
(ii)The internal environment in majority of animals and nearly all plants change with the change of external environment (conform).
(iii)Some organisms leave their habitats temporarily during unfavourable conditions and return back when conditions become favourable (migrate).
(iv)Some organisms suspend their metabolic activities to avoid stress by timely escaping, e.g. hibernation and aestivation.

Q.Bear hibernates, whereas some species of zooplanktons enter diapause to avoid stressful external conditions. How are these two ways different from each other?[Foreign 2011]
Ans.Difference between diapause and hibernation:
Important Questions for Class 12 Biology Term 2 with Answers_110.1

Q.How does our body adapt to low oxygen availability at high altitudes?[Foreign 2011]
Ans.Body adaptations at high altitudes are:
The physiological condition or responses in order to get accl imatised to high attitudes are:
(i) To compensate low oxygen, the production of red blood cells is increased.
(ii) High haemoglobin content and its decreased binding capacity.
(iii) Faster breathing rate (any two).

Q.Why are small animals rarely found in the polar regions? Explain.[HOTS; Foreign 2010]
Ans.Small animals have a large surface area relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this smaller animals are rarely found in polar regions.

Q.How do seals adapt to their natural habitat? Explain.  [Foreign 2010]
Ans.Seals adapt to the natural habitat (cold climate) by developing a thick layer of fat (blubber) below their skin that acts as an insulator and reduce excess loss of body heat.

Q.Humming birds v live among the bushes in tropics, while penguins live on icebergs. They cannot survive if their habitats are reversed. Justify.    [HOTS; Delhi 2010 C]
Ans.Humming birds are natural habitats of tropics. They have large surface area relative to their volume. So, they tend to lose heat very fast, even when it is cold outside.Penguins live on icebergs (natural habitat). They have less surface area to volume ratio. The lesser the ratio, more effective will be the thermoregulation. Also, they hide in group to escape from cold conditions. Therefore, both of them will not survive if their habitats are reversed

Q.How does human body maintain constant temperature both in summers and winters? Explain.[Delhi 2009 C]
Ans.Human body maintains constant body temperature (37°C) as follows:
In summers, the outside temperature is very high than our body temperature. Due to this, profuse sweating occurs. This causes evaporation and cooling effect on the body.
In winters, the outside temperature is much lower than our body temperature. This causes shivering, a kind of exercise that produces heat and raises the body temperature.

Q.Differentiate between commensalism arid mutualism by taking one example each from plants Only.   [All India 2014]
Ans.Commensalism is the kind of interaction between species in which one is benefitted and other is neither benefitted nor-harmed. Example of such association is orchid growing as an epiphyte on a mango tree, which remains unaffected by its growth.
Whereas mutualism is the type of interaction in which both the species involved are benefitted. e.g. lichen representing mutual ‘ association between algae and fungi, in which algae is protected by fungi, which also provides nutrients for synthesis of food, while algae provides food to fungi, as they are incapable of synthesising their own food.

Q.Explain Verhulst-Pearl Logistic Growth of a population. [All India 2014]
Ans.The population growing in a habitat with limited resources initially shows a lag phase, followed by exponential phase and finally a declining or stationary phase, when the growth or density of population reaches carrying capacity is called Verhulst-Pearl logistic growth.
It can be explained by following equation
Important Questions for Class 12 Biology Term 2 with Answers_120.1
­Where, N – Population density at time t.
r – Intrinsic rate of natural increase K – Carrying capacity

Q.Explain mutualism with the help of an example. [All India 2014]
Ans.The type of interaction where both the species involved are benefitted is called mutualism. For the relationship between fig and wasp is mutualism. The wasp while in search of egg laying sites pollinate the fig’s inflorescence, while the fig offers fruit or ovary for oviposition (egg laying). It also offers its seeds to the developing larva

Q.Provide two reasons that make the count of prokaryotic species difficult. [All India  2014]
Ans.The two reasons that make the count of prokaryotic species difficult is
(i) they are microscopic not visible by naked eyes.
(ii)they form dense colonies, i.e. population size is so, huge that counting is time taking and almost possible.
(iii) the rate of growth is very fast in prokaryotic species, which may almost double itself while counting

Q.How does Monarch butterfly defend itself from predators? Explain.[Delhi 2013 C]
Ans.Predators avoid the monarch butterfly as it is highly distasteful to its predators (birds) because of a special chemical present in its body. It acquires this chemical during the caterpillar stage by feeding on a poisonous weed

Q.Why do clown fish and sea anemone pair up? What is this relationship called ?  [Delhi 2012; All India 2008]
Ans.Clown fish maintains commensalism with the sea anemone. In this interaction, one species is benefitted and the other is neither harmed nor-benefitted. Sea anemone has stinging tentacles that provide protection to clown fish from predators. The anemone does not appear to derive any benefit from the clown fish

Q.Explain brood parasitism with the help of an example. [All India 2012]
Ans.The phenomenon in which one organism(parasite) lays its eggs in the nest of another organism is called brood parasitism. e.g. cuckoo (parasite) lay eggs which resemble the host’s (crow) egg in size and colour in crow’s nest and let it incubate them.

Q.How does the floral pattern of mediterranean orchid Ophrys guarantee cross-pollination?[Delhi 2010; Foreign 2009]
Ans.In the flowers of Ophrys
(i) One petal resembles the female of a bee species in size, colour, markings, etc.
(ii) Male bee perceives it as a female and pseudocopulates with it.
(iii)During the process, the pollen grains from the anthers become dusted on the body of the bee.
(iv)When the bee is attracted to another flower of this orchid species, the process is repeated and the pollen grains from the body of the bee get dusted on the stigma thus, pollination is achieved.

Q.How do plants benefit from having mycorrhizal symbiotic association?[Foreign 2010]
Ans.Benefits to plants having mycorrhizal association are:
(i) The fungus absorbs nutrients from the soil and passes it to the plant.
(ii) Mycorrhiza provide resistance to root-borne pathogens.
(iii) They show increased tolerance to salinity and drought.
(iv) An overall increase occurs in plant growth and development.

Biodiversity and its Conservation

Q.List four causes of biodiversity loss. [Delhi 2014C]

Ans.  (i) Habitat loss and fragmentation (ii) Over-exploitation (iii) Alien species invasions

Q.What is meant by alien species invasion? Name one plant and one animal alien species that are a threat to our Indian native species. [All India 2013]

Ans. Intentional or chance introduction of exotic species into new islands or countries by man is called alien species invasion. For example, Nile perch introduced into Lake Victoria in East Africa caused loss of more than 200 species of cichlid fish. Plant alien species-Lantana camara and animal alien species – Clarius gariepinus are a threat to our Indian native species.

Q. Justify with the help of an example where a deliberate attempt by humans has led to the extinction of a particular species.            [Delhi 2011]

Ans. Over-exploitation of natural resources or over hunting of animals has led to extinction of particular species,

e.g. Steller’s sea cow and passenger pigeon.

Q. The given graph shows species-area relationship. Write the equation of the Curve A and Explain. [All India 2011]
Important Questions for Class 12 Biology Term 2 with Answers_130.1

Ans. The equation for the curve A is

S – CAZ

where, S-Species richness,

A- Area C-Y-interecept,

Z- Slope of line

(regression coefficient)

(i) Alexander Von Humboldt observed that within a region, species richness increased with increasing explored area, but only up to a limit.

(ii) The relation between species richness and area for a wide variety of taxa like angiosperms, birds, fishes, etc., turns out to be a rectangular hyperbola.

Q.With the help of an example, explain how alien species invasion causes biodiversity loss? [Delhi 2011]

or

Alien species are a threat to native species. Justify taking examples of an animal and a plant alien species. [All India 2010]

or

Sometimes alien species affect the indigenous organisms leading to their extinction. Substantiate this statement with the help of any two examples. [Delhi 2010 C]

Ans. Alien species become invasive, compete with the native species and cause extinction of indigenous species.

(i) Introduction of Nile perch into Lake Victoria lead to extinction of more than 200 species of cichlid fish in that lake.

(ii) Carrot grass (Parthenium and Lantana) introduced in our country have become invasive and cause environmental damage. They pose a threat to the native species of plants in our forests.

Q.Giving two reasons explain why there is more species biodiversity in tropical latitudes than in temperate ones.           [All India 2010]

Ans. Biodiversity is more in tropical latitudes than in temperate ones. The reasons are:

(i) Speciation is a function of time. The temperate regions were subjected to frequent glaciation in the past, while the tropics have remained undisturbed and so had longer time to evolve more species diversity.

(ii) More solar radiation is available in tropical region. This leads directly to more productivity and indirectly to greater species diversity.

(iii) The environment of tropics is less seasonal and relatively more constant and predictable, which encourages niche specialisation and species diversity.

Q. State the uses of biodiversity in modern agriculture.       [All India 2011]

Ans. Uses of biodiversity in modern agriculture are:

(i) Humans obtain food, fibres, medicines and many industrial products from plants.

(ii) Wild varieties of plants are used for breeding to obtain disease and pest resistant crops with many desirable traits.

(iii) By exploring molecular, genetic and species level diversity for economically important products, rich biodiversity can be obtained.

Important Questions for Class 12 Biology Term 2 with Answers: 5 marks 

Here we have given the case-based questions of all the chapters of Term 2 Biology. The students must go through all the questions to boost their preparation.

Human Health and Diseases

Q. Do you support ‘Dope’ test being conducted on sports persons participating in a prestigious athletic meet? Give three reasons in support of your answer.    [All India 2014 c]
Ans.Yes, the ‘dope test’ should be conducted on sportspersons participating in a prestigious athletic meet. This is done to find out whether any participant had taken any kind of performance enhancing drugs.The use of drugs in sports should be banned as:
(i) they increase muscle strength.
(ii) promote aggressiveness.
(iii) increase athletic performance.
Because of above reasons, use of such drugs, e.g. steroids, analgesics, diuretics should be banned for participants as it would be unfair on the part of other participants (not consuming such drugs).

Q. An active member of an awareness group conducts regular programmes to sensitise public against alcoholism amongst youth as a serious health hazard in his locality.
Identify the values this member of the group is trying to propagate amongst the people in his locality.
[Value Based Question, Delhi 2013 C]
Ans.Member of an awar+eness group is trying to aware public commonly youth about the harmful impacts of alcohol. He wants to tell people that alcohol has several ill effects which affects the body of the individual in many ways.
(i) Alcohol affect the foetus in case of pregnancy.
(ii) It leads to reckless behaviour, vandilism and violence.
(iii) It also cause aggressiveness, rebellious behaviour and depression.
(iv)Fatigue, isolation, fluctuations in weight are the other ill effects.
(v)Change in sleeping pattern, loss of appetite and lack of personal hygiene is also seen in addicts.

Q. Write the source and the effect on the human body of the following drugs.
(i)Morphine
(ii)Cocaine
(iii)Marijuana [Delhi 2011]
Ans.(i)Morphine is obtained from the latex of  Papaver somniferum. It is a depressant,
which slows down the body functions.
(ii)Cocaine is obtained from Erythroxylum coca. It is a stimulant and produces a sense of euphoria and increased energy.
(iii) Marijuana is obtained from the inflorescence of Cannabis sativa. It affects cardiovascular system of the body.

Q. (i) Name the drug used (a) as an effective sedative and pain killer (b) for helping patients to cope with mental illness like depression but often misused, (ii) How does moderate and high dosage of cocaine affect the human body? [Foreign 2011]
Ans.(i) (a) Morphine is an effective sedativeand pain killer.
(b) Lysergic acid diethylamides (LSD)
or barbiturates are often misused.
(ii) Moderate dose of cocaine have a stimulating action on central nervous system. It produces a sense of euphoria and increased energy.High dosage of cocaine causes hallucinations

Q. (i) All human beings have cellular oncogenes but only few suffer from cancer disease.Give reasons.
(ii)How is a malignant tumour different from a benign tumour?[Foreign 2010]
Ans.(i) All cells have cellular oncogenes or proto-oncogene, which code for certain growth factors. Under certain conditions, they get activated and lead to oncogenic transformation causing cancer.
This transformation is induced by physical, chemical and biological factors called carcinogens.
(ii) Differences between benign and malignant tumour are:
Important Questions for Class 12 Biology Term 2 with Answers_140.1

Q. Trace the life cycle of Plasmodium in humans from the stage of entry until it is picked up by the female Anopheles. [All India 2010; Delhi 2008]
Ans. Life cycle of Plasmodium (malarial parasite)
(i) The infected female Anopheles mosquito transfers the infectious form of Plasmodium, i.e. sporozoites to the human body by biting.
(ii) Sporozoites reach the liver cells, where they multiply.
(iii) This is followed by their attack on red blood cells resulting in the rupture of RBCs.
(iv) Ruptured RBCs release a toxin called haemozoin, responsible for recurring fever, chills and shivering.
(v)The parasite enter female Anopheleswhen they bite an infected person.
(vi)In the body of mosquito, they fertilise and multiply in stomach wall.
(vii)Sporozoites are then again transferred to the human body by mosquito bite.

Q. Give the scientific name of the parasite that causes malignant malaria in humans.At what stage does this parasite enter the human body? Trace its life cycle in human body. [Delhi 2009]
Ans.Plasmodium falciparumcauses malignant malaria. It enters into human body in sporozoites form.
Plasmodium  Life Cycle of Malarial Parasite (Plasmodium) in Human Body
Important Questions for Class 12 Biology Term 2 with Answers_150.1
Important Questions for Class 12 Biology Term 2 with Answers_160.1

Q. (i) Name the respective forms in which the malarial parasite gains entry into.
(a)Human body
(b)Body of female
(ii)Name the hosts where the sexual and asexual reproduction occur respectively.
(iii)Name the toxin responsible for the appearance of symptoms of malaria in human. Why do these symptoms occur periodically?[Delhi 2003]
Ans.(i) (a) Sporozoite
(b) Gametocytes
(ii) Sexual reproduction occurs iri mosquito and asexual reproduction takes place in human body.
(iii)Haemozoin is the toxin. The parasites after entering the fresh RBCs take 48-72 hours to complete the erythrocytic cycle. Then they burst to release toxic substance called haemozoin. So, the symptoms like chill and high fever occur periodically

Q. (i) Why do the symptoms of malaria not appear immediately after the entry of sporozoites into the human body when bitten by female Anopheles? Explain.
(ii) Give the scientific name of the malarial parasite that causes malignant malaria in humans.[HOTS; All India 2009]
Ans.(i)Malarial parasite completes its asexual cycle in liver cells and then it attacks the Red Blood Cells (RBCs) resulting in their rupture. The ruptured RBCs release toxic substance called haemozoin that is responsible for the symptoms of malaria like chill and high fever. Thus, no symptoms appear in the infected person between the period, the parasite enters the body and till RBCs release haemozoin,
(ii) Plasmodium falciparumcauses malignant malaria. It enters into human body in sporozoites form.
Plasmodium  Life Cycle of Malarial Parasite (Plasmodium) in Human Body
Important Questions for Class 12 Biology Term 2 with Answers_150.1
Important Questions for Class 12 Biology Term 2 with Answers_160.1

Q. Community service department of your school plans a visit to a slum near the school with an objective educate the slum dwellers with respect to health and hygiene.
(i)Why is there a need to organise such visits?
(ii)Write the steps you will highlight, as a member of this department, in your interactions with them to enable them to lead a healthy life.[All India 2014]
Ans.(i)Slums are generally unauthorised and encroached colonies with no public facilities and organisation. Due to lack of education, cleanliness and other facilities and the poor living standard in terms of health, hygiene and nutrition such people are always at risk of acquiring infections. Therefore, there is a need to organise visits to slums so as to educate and crate awareness among them regarding the importance of hygiene.
(ii) The points to be highlighted while interacting with the slum people may be.

  • Importance of cleanliness and hygiene of body as well as surroundings.
  • Awareness and prevention of infectious diseases.
  • Use of public facilities, i.e. toiletries.
  • Consumption of properly cooked and hygienic food and water.
  • Administration of vaccines to newborn children so as to prevent diseases.

Q. (i) Name and explain going reason, the type of immunity provided to the newborn by the colostrum and vaccinations
(ii)Name the type of antibody:

  • present in colostrum
  • produced in response to allergens in human body.[Foreign 2014]

Ans.(i) The immunity provided to the newborn by colostrum and vaccinations is called passive immunity. This is because both in colostrum and vaccines the antibodies conferred are not produced by own body but are rather transferred passively to recipient’s body. Such as IgA antibodies pass across the placenta or through milk (colostrum) to infants and provides passive immunity against infection.
(ii) The type of antibody present in

  • colostrum is IgA.
  • response to allergens in human body is IgE

Q. (i)Name the causative organisms for the following diseases.
(a)Elephantiases
(b)Ringworm
(c)Amoebiasis
(ii)How can public hygiene help control such diseases? [Delhi 2014C]
Ans.(i)The causative agent or organism forfollowing diseases are:
(a)Elephantiasis is caused by Wuchereria bancrofti and W. malayi. These affect lower limbs and genital organs.
(b) Ringworm is caused by Microsporum, Trychophyton and Epidermophyton. They affect the skin, nails and scalp.
(c)Entamoeba histolytica is a protozoan parasite in the large intestine of human, which causes amoebiasis (amoebic dysentery).
(ii) Maintenance of public hygiene such as:

  • keeping body and surroundings clean.
  • consumption of clean drinking water, fruits and vegetables, etc.
  • regular cleaning and disinfection of tanks and other water reservoirs, etc.
  • All the above measures help controlproper disposal of waste and excreta.the increase in vectors of infectious diseases and their breeding places. Thus, there would be reduced chances of transmission of infectious diseases.

Q. Name the cells HIV attacks first when it gains entry into a human body. How does this vims replicate further to cause immunodeficiency in the body?[Delhi 2013 C, 2010; All India 2010 C]
or
Trace the events occur in human body to cause immunodeficiency, when HIV gains entry into the body.[Delhi 2011; Foreign 2009]
Ans.The HIV virus attacks the macrophages cells in human body.
(i) RNA is replicated to form viral DNA by the enzyme reverse transcriptase.
(ii) Viral DNA now gets incorporated into the host cell’s DNA and directs the infected cells to produce viruses.
(iii) Macrophages continue to produce virus particles and function as HIV factories.
(iv) The virus particles enter helper T-lymphocytes in the blood, where they continue to replicate and produce viral progenies.
(v)The number of helper T-lymphocytes progressively decreases in the body of the infected person.
(vi) With the decrease in number of T-cells, the immunity also decreases. The person is unable to produce any immune response even against common bacteria like Mycobacterium, parasites like Toxoplasma, viruses and fungi.

Q. Trace the life cycle of malarial parasite in human body, when bitten by infected female [All India 2012]
Ans.Life Cycle of Malarial Parasite (Plasmodium) in Human Body
Important Questions for Class 12 Biology Term 2 with Answers_150.1
Important Questions for Class 12 Biology Term 2 with Answers_160.1

66.Study a part of the life cycle of malarial parasite given below.
Important Questions for Class 12 Biology Term 2 with Answers_210.1
(i)Mention the roles of A in the life cycle of the malarial parasite.
(ii)Name the event C and the organ where this event occurs.
(iii)Identify the organ B and name the cells being released from it.[Delhi 2012]
Ans.(i)A is female Anopheles mosquito, these mosquito act as vectors and transmit the disease from patients to healthy individuals.
(ii) The event C is fertilisation. It occurs in the intestinal wall of mosquito.
(iii) B is salivary glands, sporozoites cells are released from it.

Q. (i) Name the causative agent of typhoid in humans.
(ii) Name the test administered to confirm the disease.
(iii)How does the pathogen gain entry into the human body? Write the diagnostic symptoms and mention the body organ that gets affected in severe cases?[All India 2011]
Ans.(i) Salmonella typhi.
(ii) Widal test.
(iii) Pathogens enter the human body through contaminated food and water.
Symptoms of typhoid are:
(a) Constant high fever (39-40°C)
(b) Weakness and headache
(c) Stomach pain
(d) Loss of appetite
Intestinal (small intestine) perforation in severe cases which may cause death. Causative agent – Salmonella typhi

Microbes in Human Welfare

Q. (i) Why do farmers prefer biofertilisers to chemical fertilisers these days? Explain, (ii) How do Anabaena and mycorrhiza act as biofertilisers? [Delhi 2011]
Ans. (i) A farmer relies on biofertilisers then chemical fertilisers because
(a) Chemical fertilisers significantly increase the soil pollution and reduce quality of soil, as well as water pollution, when it drains into nearby water bodies, after rain.
(b) Overuse of chemical fertiliser makes the soil infertile.
(ii) Anabaena fix atmospheric nitrogen, thus enriching the nitrogen content of the soil, as well as the organic matter.
In mycorrhiza, the fungal symbiont absorbs phosphorus from the soil and passes it to the plant and provides resistance to root borne diseases. Since, they fulfil the nitrogen and phosphorus requirement they act as biofertilisers.

Q. (i) Why do organic farmers not recommend eradication of insect pests? Explain giving reasons.
(ii) How do ladybird beetles and dragonflies act as biocontrol agents?           [Delhi 2009C]
Ans. (i) The organic farmers do not recommend eradication of insect pests as without them, the beneficial predatory and parasitic insects which depend upon pests as food or hosts would not be able to survive.
(ii) The ladybird beetles and dragonflies feed upon aphids and mosquitoes respectively. Hence, they act as biocontrol agents by helping to get rid of them.

Q. Name the genus to which baculoviruses belong. Describe their role in the integrated pest management programme. [Delhi 2011; Foreign 2011]
Ans. Baculoviruses belongs to the genus Nucleopolyhedrovirus.
Baculovirus (Nucleopolyhedrovirus) as biocontrol agents:
(i) These are excellent candidates for species-specific, narrow spectrum insecticidal application.
(ii) They show no negative impact on plants, mammals, birds, fish or even non-target insects.
(iii) These are especially desirable when beneficial insects are being conserved to aid in an overall Integrated Pest Management (IPM) programme.

Q. An organic farmer relies on natural predation for controlling pests and diseases. Justify giving reasons, why this is considered to be a holistic approach? [Foreign 2010]
Ans. Organic farming is a holistic approach that seeks to develop an understanding of the webs of interaction among the myriads of organisms that form the flora and fauna of the field.
(i) An organic farmer works to create a system, where the insects are not eradicated, but kept at manageable level by a complex system of checks and balance within a living and vibrant ecosystem.
(ii) Organic farmer states that the eradication of pests is not only possible but also undesirable, because many beneficial predatory and parasitic insects cannot survive without them.
(iii) This use of bicontrol methods reduces the use of chemical pesticides and thereby pollution.

Q. (i) Baculoviruses are excellent candidates for integrated pest management in an ecologically sensitive area. Explain giving reasons.
(ii) What is organic farming? Why is it suggested to switch over to organic farming?           [Foreign 2008]
Ans.(I) Baculoviruses belongs to the genus Nucleopolyhedrovirus.
Baculovirus (Nucleopolyhedrovirus) as biocontrol agents:
(i) These are excellent candidates for species-specific, narrow spectrum insecticidal application.
(ii) They show no negative impact on plants, mammals, birds, fish or even non-target insects.
(iii) These are especially desirable when beneficial insects are being conserved to aid in an overall Integrated Pest Management (IPM) programme.
(II) The use of biofertilisers and biopesticides to improve the crop yield is called organic farming.
It is advised to switch over organic farming due to the following reasons:
(a) Use of excess chemical fertilisers make the soil unsuitable for cultivation.)
(b) Natural resources get depleted due to the manufacturing of chemical fertilisers.
(c) Avoids killing harmful as well as useful life forms or organisms indiscriminately, thus maintains ecological balance.

Q. Why should biological control of pests and pathogens be preferred
to the conventional use of chemical pesticides? Explain how the following microbes act as biocontrol agents?
(i) Bacillus thuringiensis (ii) Nucleopolyhedrovirus. [Delhi 2008]
Ans. Bacillus thuringiensis as biocontrol agent
(i) Through genetic engineering, the gene coding for the toxic protein is introduced into crop plants, which make them resistant to insect pests.
(ii) When they are eaten by the larvae, the toxin becomes active in the gut of larvae and kills the larvae.
(iii) They are available in sachets as dried spores, which have to be mixed with water and sprayed onto vulnerable plants.
Baculovirus (Nucleopolyhedrovirus) as biocontrol agents:
(i) These are excellent candidates for species-specific, narrow spectrum insecticidal application.
(ii) They show no negative impact on plants, mammals, birds, fish or even non-target insects.
(iii) These are especially desirable when beneficial insects are being conserved to aid in an overall Integrated Pest Management (IPM) programme.

Q. Identify A, B, C, D, E and F in the table given below: [Foreign 2014]
Important Questions for Class 12 Biology Term 2 with Answers_220.1
Ans.The codes are identified as
A- Clot buster in patents who underwent myocardial infarction.
B- Trichoderma polysporum
C- Immunosuppressive agent in organ transplantation
D- Statins
E – Blood cholesterol lowering agents
F – Lactic acid

Q. Name the two different categories of microbes naturally occurring in sewage water. Explain their role in cleaning sewage water into usable water. [Delhi 2012]
Ans. Bacteria and fungi are the two categories of naturally occurring microbes in sewage. The bacteria along with the fungal mycelia form the floes. These floes are utilised during the secondary treatment of sewage. The primary effluent after separation of the grit and debris is taken to the secondary treatment.
Here, the effluent is passed to an aeration tank, where it is constantly agitated and air is pumped into it. This leads to vigorous growth of bacteria and floe formation. The bacteria in these floes consume organic matter, thus decreasing the BOD of the sewage.

Q. Explain the different steps involved in sewage treatment before it can be released into natural water bodies. [Foreign 2011]
Ans.Sewage treatment includes following steps:
(i) Primary Treatment

  • It is a physical process of removal of small and large particles through filtration and sedimentation.
  • The first step is to remove the floating objects (like polythene bags) by letting the sewage to pass through wire mesh screens of sequential smaller pore sizes.
  • Sewage is then passed into the grit chamber, where grit is sedimented.
  • Sewage is then allowed to pass into the settling tank, where the suspended materials settle down to form primary sludge.
  • Effluent is then taken for the secondary treatment.
  • (ii)Secondary Treatment
  • It is a biological process in which bacteria naturally occurring in sewage are used.
  • Effluent obtained from the primary treatment is passed into large aeration tank. Here, it is constantly agitated and air is pumped into it.
  • Due to this, rapid growth of aerobic bacteria occur into floes. These consume the organic matter of the sewage and reduce the BOD.
  • Effluent is passed into settling tank, where the floes are allowed to settle forming the activated sludge.
  • A small amount of activated sludge is pumped back into aeration tank as inoculum.
  • The remaining major part of the activated sludge is pumped into anaerobic sludge digesters, where the anaerobic bacteria digest the organic matter and produce methane, hydrogen sulphide and carbon dioxide.
  • Effluent is then allowed to pass into the water body.

Q. Identify A, B, C, D, E and F in the table given below:
Ans.A-Statins, B-They are used as blood cholesterol lowering agent, C-Penicillium notatum, D-Penicillin, E-Trichoderma polysporum, F-Used as an immunosuppressive agent in organ transplant patients.

Q. Mention the product and its use produced by each of the microbes listed below:

  • Streptococcus
  • Lactobacillus
  • Saccharomyces cerevisiae  [All India 20101]

Ans.(i) Streptococcus Product is streptokinase. It is used as a clot-buster for removing the clots from the blood vessels of patients suffering from myocardial infarction.
(ii) Lactobacillus Product is lactic acid. It is used to convert milk into curd and improves nutrient quality of curd by enriching it with vitamin-B12.
(iii) Saccharomyces cerevisiae Product is ethanol and also used for bread making and beverages.31. Describe how biogas is obtained from the activated sludge?  
[Foreign 2010]
Ans. Biogas formation from activated sludge:
(i) A small part of activated sludge is pumped into the aeration tank to serve as inoculum. It grows into floes and consume organic matter to reduce BOD.
(ii) The remaining major part of sludge is pumped into large tanks called anaerobic sludge digesters.
(iii) Here, anaerobic bacteria digest the organic material of the sludge.
(iv) During this digestion, the bacteria produces a mixture of gases like carbon dioxide, methane and hydrogen sulphide which form the biogas.

Q. (i) How does activated sludge get produced during sewage treatment?
(ii) Explain how this sludge is used in biogas production? [All India 2009]
Ans.(i)  (a) The primary effluent is passed into large aeration tanks. Due to the constant agitation floes formation occur, which are masses of bacteria associated with fungal hyphae.
(b) These microbes consumes sufficient quantity of organic matter and there by reduce BOD.
(c) Once, the BOD of sewage water gets reduced significantly, the effluent is passed into a settling tank, where the bacterial floes undergo sedimentation and the sediment is called activated sludge.
(ii) Biogas formation from activated sludge:
(i) A small part of activated sludge is pumped into the aeration tank to serve as inoculum. It grows into floes and consume organic matter to reduce BOD.
(ii) The remaining major part of sludge is pumped into large tanks called anaerobic sludge digesters.
(iii) Here, anaerobic bacteria digest the organic material of the sludge.
(iv) During this digestion, the bacteria produces a mixture of gases like carbon dioxide, methane and hydrogen sulphide which form the biogas.

Q. How are floes produced in the secondary treatment plant of the sewage? Explain their role. [All India 2009C]
Ans. The effluent obtained from primary treatment is passed into large aeration tanks, where it is constantly agitated and air is pumped into it. This allows rapid growth of aerobic microbes into floes.

Floes consume organic matter of the sewage and reduce the Biochemical Oxygen Demand (BOD). When BOD of sewage is reduced, the effluent is passed into a settling tank, where the floes are allowed to form the activated sludge.

Q. (i)Expand BOD.
(ii) At a particular segment of a river near a sugar factory, the BOD is much higher than the normal level. What is it indicative of? What will happen to the living organism in this part of the river?
(iii) Under what conditions will the BOD be lowered in the river? How will it affect the aquatic life?  [HOTS; Foreign 2008]
Ans. (i) Biochemical Oxygen Demand.
(ii) The higher BOD indicates high organic matter in river. Microbes involved in the biodegradation of organic matter in water body consume a lot of oxygen.
Due to this, a sharp decline occur in the amount of dissolved oxygen. This leads to killing of fish and othe microorganisms in that part of river.
(iii) BOD of water body decreases when the amount of organic matter decreases. Thus, microbes do not need oxygen for its decomposition.
Due to the decreased BOD, aquatic life will start flourishing.

Biotechnology – Principles and Processes

Q. What is a bioreactor used for? Name a- commonly used bioreactor and any two of its components?            [All India 2014C]
Ans. A bioreactor is used for converting the raw materials into specific products biologically such as proteins, enzymes, etc., through the use of microbial, plant or animals cells.
The most commonly used bioreactors are of stirred type.
The two components of a stirred tank bioreactor are:
(i) In let for sterile air or oxygen
(ii) Agitator system
(iii) Temperature control system
(iv) pH control system
(v) Foam control system
(vii) Sampling ports (choose any two)

Q. How is the amplification of a gene sample of interest carried out using Polymerase Chain Reaction (PCR)? [All India 2012]
or
Describe the process of gene amplification for rDNA technology experiments.         [All India 201 ic]
Ans. Amplification of gene is done using polymerase Chain Reaction (PCR). it is carried out in the following steps:
(i) Denaturation The double stranded DNA is denatured by applying high temperature of 95°C for 15 seconds. Each separated strand acts as a template.
(ii) Annealing Two sets of primers are added, which anneal to the 3′ end of each separated strand.
(iii) Extension DNA polymerase extends the primers by adding nucleotides complementary to the template provided in the reaction. Taq polymerase is used in the reaction, which can tolerate heat. All these steps are repeated many times to get several copies of the desired DNA.
Q. How is the bacterium Thermus aquaticus employed in recombinant DNA technology?        [All India 2008]
Ans. Thermus aquaticus, a bacterium yields DNA polymerase used in PCR in recombinant DNA technology.
(i) This enzyme remains active during the high temperature applied in the denaturation of double stranded DNA.
(ii) It extends the primers using the nucleotides provided in the reaction and the genomic DNA as template.
(iii) Repeated amplification is achieved by this enzyme. The amplified fragments, if desired can be used to ligate with a vector for further cloning.

Q. What are bioreactors? List five growth conditions that a bioreactor provides for obtaining the desired product. [Delhi 2008C]
Ans. (i) Bioreactors are large vessels in which raw materials are biologically converted into specific products by microbes, plant and animal cells or human cells.
The bioreactors work by providing optimal conditions to process the culture as well as the production of desired product by maintaining optimum pH, temperature, oxygen and other growth conditions required.
Growth conditions that a bioreactor provides for obtaining desired product are:
(i) Optimum temperature
(ii) Suitable pH
(iii) Salt
(iv) Vitamins
(v) Oxygen
Q. If a desired gene is identified in an organism for some experiments, explain the process of the following
(i) Cutting this desired gene at specific location.
(ii) Synthesis of multiple copies of this desired gene.   [All India 2011]
Ans. (i) Cutting of desired gene at specific location is done by incubating the DNA with specific restriction endonuclease.  Restriction
enzymes recognise a particular palindromic nucleotide sequence and cuts the DNA at that site.
(ii) Synthesis of multiple copies of desired gene is carried out by Polymerase Chain Reaction (PCR).
Amplification of gene is done using polymerase Chain Reaction (PCR). it is carried out in the following steps:
(i) Denaturation The double stranded DNA is denatured by applying high temperature of 95°C for 15 seconds. Each separated strand acts as a template.
(ii) Annealing Two sets of primers are added, which anneal to the 3′ end of each separated strand.
(iii) Extension DNA polymerase extends the primers by adding nucleotides complementary to the template provided in the reaction. Taq polymerase is used in the reaction, which can tolerate heat. All these steps are repeated many times to get several copies of the desired DNA.

Q. Name the source of taq polymerase.
Explain the advantage of its use in biotechnology.  [All India 2009]
Ans. Taq polymerase is Pbtained from the bacterium Thermus aquaticus.
The enzyme is thermostable and can withstand the high temperature used for denaturation and separation of the two strands of DNA in PCR. Desired gene can be amplified to produce even a billion copy of DNA.
Thermus aquaticus, a bacterium yields DNA polymerase used in PCR in recombinant DNA technology.
(i) This enzyme remains active during the high temperature applied in the denaturation of double stranded DNA.
(ii) It extends the primers using the nucleotides provided in the reaction and the genomic DNA as template.
(iii) Repeated amplification is achieved by this enzyme. The amplified fragments, if desired can be used to ligate with a vector for further cloning.

Q.Explain the basis on which the gel electrophoresis technique works. Write any two ways the products obtained through this technique can be utilised. [Delhi 2013C]
Ans. Gel electrophoresis technique works on the principle of separation of DNA fragment on the basis of electric charge.
Since, DNA is negatively charged molecule so, they can be forced to separate out according to their size towards anode under an electric field through a medium or matrix (commonly used is agarose). Shorter molecule moves faster and migrate further than the lohger one.
The products obtained through this technique can be utilised as follows:
(i) Construction of recombinant DNA by joining with cloning vectors.
(ii) Used in making multiple copies of same DNA by using PCR (Polymerase Chain Reaction).

Q. How can the following be made possible for biotechnology experiments?
(i) Isolation of DNA from bacterial cell.
(ii) Reintroduction of the recombinant DNA into a bacterial cell.
[Foreign 2012]
Ans. (i) Isolation of DNA from bacterial cell can be done by:
(a) treating the bacterial cells with enzymes such as lysozyme to remove cell wall.
(b) the RNA associated with DNA can be removed by treatment with ribonuclease, whereas protein can be removed by treatment with protease. Similarly other molecules (if any) are removed by appropriate treatment.
(ii) Reintroduction of the recombinant DNA into bacterial cell can be done by the following methods:
(a) The recipient bacterial cell is made ‘competent’ to take up the recombinant DNA by treatment with a specific increase in concentration of calcium ions.
(b) the recombinant DNA is forced into the cells by heat shock treatment, i.e. by incubating the cells with rDNA followed by placing them at 42°C (heat shock) and then putting them back on ice. This enables bacteria to take up rDNA.

Q. (i) Identify A and B illustrations in the following:
Important Questions for Class 12 Biology Term 2 with Answers_230.1(ii) Write the term given to A and C and why?
(iii) Expand PCR. Mention its importance in biotechnology. [Delhi 2011]
Ans. (i) (a) A is recognition or restriction site (AATTC), which is recognised by restriction enzyme Eco
(b) B is rop gene protein involved in the replication of plasmid coded by this gene.
(ii) A and C are called palindromes. These are sequence of base pairs that reads same on the two strands of DNA, when orientation of reading is kept same.
(iii) PCR is polymerase chain reaction, multiple copies of the gene of interest can be synthesised in vitro by this technique. Thus, PCR can be utilised to amplify a single gene or fragment into thousands of copies to be used in cloning experiments.

Biotechnology and its Application

Q.How did the process of RNA  interference help to control the nematode from infecting the roots of  tobacco plants.
Ans. When the nematode infects the roots of tobacco plants and feeds upon cells containing RNAi gene. This DNA produced both sense and anti-sense RNA in the host cells (tobacco plant) and is complementary to the functional mRNA of the nematode. This complementarity between both RNA makes it double stranded and, hence silenced by not being translated into protein. Interference with RNA expression and protein synthesis makes it difficult for the pathogen to survive in tobacco plants and hence killed. In this way RNA interference protects and control the nematode infection.

Q. Name the host plant and its part that  Meloidogyne incognita infects. Explain the role of Agrobacterium in  the production of dsRNA in the host plant.   [Delhi 2014C]
Ans. The nematode Meloidogyne incognita infects the roots of tobacco plants.
The Agrobacterium are used as vectors carrying nematode specific genes to be introduced in host plant. These genes when expressed inside host plant produces sense and anti-sense RNA strands, complementary to nematode’s functional mRNA. This binding results in formation of double stranded RNA and inhibiting or silencing the translation of RNA specified. This process is called RNA interference.

Q. Name the pest that destroys the cotton bolls. Explain the role of Bacillus thuringiensis in protecting  the cotton crop against the pest to increase the yield.          [All India 2013]
   or
How is the Btcotton plant created as a GM plant? How is it protected against bollworm infestation? [Delhi 2013C]
Ans. The pest that destroys the cotton balls are cotton boll worms and cotton borer. Bt cotton is created by using some strains of a bacterium, Bacillus thuringiensis (Btis short form).
(i) This bacterium produces protein that kill certain insects such as lepidopterans (tobacco budworm and armyworm), coleopterans (beetles) and dipterans (flies and mosquitoes).
(ii) Bacillus thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein.
(iii) Bt toxin protein exist as inactive protoxins, but once an insect ingests the inactive toxin, it is converted into an active form due to the alkaline pH of the gut which solubilise the crystals.
(iv) The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis leading to death of insect.
(v) Specific Bttoxin genes were isolatedfrom Bacillus thuringiensis and incorporated into several crop plants.
(vi) Most Bttoxins are insect-group specific.Hence, the toxin is coded by a gene named  cry.  For  example,  the proteins encoded by the genes cry I Ac and cry lAb control the cotton boll worms and cry lAb controls corn borer.

Q. Name the genes responsible for making Bt cotton plants resistant to bollworm attack How do such plants attain resistance against bollworm attacks. Explain. [Delhi 2012]
Ans. Genes cry IAc and cryIIAb control cotton bollworm.
‘cry genes’ in Bacillus thuringiensiscodes for toxic insecticidal proteins that exist as inactive prototoxins.
These proteins when expressed in cotton crops through genetic engineering confers pest resistance against cotton bollworms and prevents damage. As the larva of these insects when feed upon cotton plant parts, the toxin gets activated in their gut, lysing their cells and leads to death thus, making them pest resistant.

Q. (i) Tobacco plants are damaged severely when infested with Meloidogyne incognita. Name and explain the strategy that is adopted to stop this infestation,
(ii) Name the vector used for introducing the nematode specific gene in tobacco plant. [All India 2012]
or
How does RNA interference help in developing resistance in tobacco plant agamst nematode infection?   [Delhi 2010]
Ans. (i)Infestation of tobacco plant can be stopped by using  RNA interference
(RNAi) process.
Process of RNAi
Process of RNA interference (RNAi) is related with silencing of a specific mRNA. It is a method of cellular defence in all eukaryotes.
(i) A complementary RNA binds to the mRNA making it double stranded and prevent its translation.
(ii) This complementary RNA could be from an infection by viruses having RNA genomes or mobile genetic elements (transposons) that replicate via an RNA intermediate.
(iii) Using Agrobacterium vectors, nematode specific genes were introduced into the host plants.
(iv) It produces both sense and anti-sense RNA in the host cells.
(v) These two RNAs being complementary to each other form a double stranded RNA (dsRNA) that initiated RNAi, silencing the specific mRNA of the nematode.
(vii) Due to this, parasite could not survive in a transgenic host expressing interfering RNA. So, transgenic plant is protected.
(ii) Vector        used  for       introducing    the nematode specific gene in tobacco plant
is Agrobacterium.

Q. One of the main objectives of biotechnology is to minimise the use of insecticides on cultivated crops. Explain with the help of a suitable example, how insect resistant crops have been developed using techniques of biotechnology. [Delhi 2009; Foreign 2008]
Ans. The pest that destroys the cotton balls are cotton boll worms and cotton borer. Bt cotton is created by using some strains of a bacterium, Bacillus thuringiensis (Btis short form).
(i) This bacterium produces protein that kill certain insects such as lepidopterans (tobacco budworm and armyworm), coleopterans (beetles) and dipterans (flies and mosquitoes).
(ii) Bacillus thuringiensis forms protein crystals during a particular phase of their growth. These crystals contain a toxic insecticidal protein.
(iii) Bt toxin protein exist as inactive protoxins, but once an insect ingests the inactive toxin, it is converted into an active form due to the alkaline pH of the gut which solubilise the crystals.
(iv) The activated toxin binds to the surface of midgut epithelial cells and create pores that cause cell swelling and lysis leading to death of insect.
(v) Specific Bttoxin genes were isolatedfrom Bacillus thuringiensis and incorporated into several crop plants.
(vi) Most Bttoxins are insect-group specific.Hence, the toxin is coded by a gene named  cry.  For  example,  the proteins encoded by the genes cry I Ac and cry lAb control the cotton boll worms and cry lAb controls corn borer.

Q. Expand the name of the enzyme ADA. Why is the enzyme essential in the human body? Suggest a gene therapy for its deficiency.    [All India 2009]
Ans. ADA-Adenosine Deaminase. It is required for the proper functioning of immune system.
Gene therapy for ADA deficiency are:
Gene therapy is helpful in case of ADA deficiency.
Hereditary disease can be corrected by gene therapy. It is a collection of methods that allows correction or replacement of defective gene. The first gene therapy was given in 1990 to a 4 years old girl with Adenosine Deaminase (ADA) deficiency. It is caused due to the deletion of gene for adenosine deaminase.
The treatment involves following steps:

(i) Lymphocytes from the blood of patient are grown on culture outside the body.
(ii) A functional ADA, cDNA (using a Retro viral vector) is then introduced into these lymphocytes.
(iii) Such genetically engineered lymphocytes are returned to the blood of patient.
(iv) Periodic infusion of such genetically engineered lymphocyte is required by the patient.

Q. What is ADA deficiency? Describe three methods to cure it. [All India 2009]
Ans. ADA deficiency is   caused  due  to   the deletion of gene for adenosine deaminase.
Methods to cure ADA deficiency are:
(i) 1st method In some cases, it can be cured by bone marrow transplantation and enzyme replacement therapy but it is not fully curative.
(ii) 2nd method Lymphocytes from patient’s blood were grown in a culture and functional ADA, cDNA was intr* iuced in these lymphocytes using a retroviral vector. The lymphocytes were then transferred into the patient’s body. Periodic infusion of sucH genetically engineered lymphocytes is done because these cells are mortal.
(iii) 3rd method This is a permanent method. Genes isolated from the bone marrow cells producing ADA is introduced into cells at early embryonic stage.

Q. What are transgenic animals? Explain any four ways in which such animals can be beneficial for humans. [Foreign 2008]
Ans. Animals that have had their DNA manipulated to possess and express an extra (foreign) gene are called transgenic animals. Transgenic rats, rabbits, pigs and cows have been produced.
Uses of transgenic animals for humans are:
(i) To study gene regulation, their effect on the normal functions of the body and its development,
(ii) Study of genes, which are responsible for diseases in human and their treatment, e.g. cancer,
(iii) Useful biological products can be produced by introducing the portion of DNA, which codes for a particular product into transgenic animals.
(iv) Transgenic mice are developed to test the safety of vaccines before being used in humans.

Organisms and Populations

Q.(i)State how the constant internal environment is beneficial to organisms.
(ii)Explain any two alternatives by which orgnaisms can overcome stressful external conditions.[All India 2014]
Ans.(i)Constant internal environment is beneficial to organisms as it permits all biochemical reactions and physiological functions to proceed with maximal efficiency, thereby enhancing the overall efficiency of organism.
(ii) The two alternatives by which organisms can overcome stressful external conditions are

  • Migration-organisms move temporarily to a favourable area under stressful conditions and return back when the period is over.
  • Hibernation and aestivation are ways to escape the stress during winters and summers respectively.

Q.Water is very essential for life. Write any three features both for plants and animals which enable them to survive in water scarce environment,
or
How do organisms cope with stressful external environmental conditions which are localised or of short duration?   [ah India 2011]
Ans.Adaptation in plants
(i) Thick cuticle on their leaf surface.
(ii) Stomata are arranged in deep pits (sunken) to minimise water loss through transpiration.
(iii) Leaves are reduced to spines. The photosynthetic function is carried out by thick, fleshy flattened stems.
Adaptation in animals
(i) Kangaroo rat meets the water requirement through internal oxidation of fat. They concentrate their urine, so that minimum volume of water is excreted.
(ii) Snails undergo aestivation during summers.
Organisms either migrate or suspend their metabolic activities when conditions are stressful for short duration.In such conditions, organisms are as follow:
(i) Moving away from stressful habitat to more favourable area and return to their habitat when stressful period is over. For example, birds from Siberia and other cold countries migrate to Bharatpur Sanctuary of Rajasthan.
(ii) Hibernating (frogs) or aestivating (snails) or undergo diapause (zooplanktons).
(iii) Thick-walled spores are formed in stressful conditions and germinate under suitable conditions, e.g. bacteria, fungi and lower groups of plants.

Q.How do organisms like fungi, zooplanktons and bears overcome the temporary short-lived climatic stressful conditions? Explain.[All India 2010; Delhi 2008]
Ans.(i)Fungi They produce various kinds of thick-walled spores to survive under unfavourable conditions, which germinate on return of favourable conditions.
(ii) Zooplanktons They enter diapause, a stage of suspended development under unfavourable conditions.
(iii)Bears They hibernate during winter to escape the time of unfavourable conditions.

Q.The following graph represents the organismic response to certain environmental condition (e.g. temperature)
Important Questions for Class 12 Biology Term 2 with Answers_240.1
(i)Which one of these A or B depicts conformers?
(ii)What does the other line graph depict?
(iii)How do these organisms differ from each other with reference to homeostasis?
(iv)Mention the category to which human belong.   [All India 2009]
Ans.(i)A depicts conformers.
(ii) The other line B depicts regulators.
(iii) Differences between conformer and regulator are:
Important Questions for Class 12 Biology Term 2 with Answers_250.1
(iv) Humans are regulators.

Q.(i) Explain giving reasons why the tourists visiting Rohtang Pass or Mansarovar are advised to resume normal active life only after a few days of reaching there.
(ii) It is impossible to find small animals in the polar regions. Give reasons.   [All India 2012]
Ans.(i)Tourists visiting to Rohtang Pass near Manali (> 3500 m) may suffer from altitude sickness. They resume normal active life only after a week because in low atmospheric pressure at high altitudes, the body does not get enough oxygen. Gradually, the body compensates low oxygen availability by
(a)Increasing red blood cell production.
(b)Decreasing the binding affinity of  haemoglobin.
(c)Increasing the breathing rate.
(ii)Small animals have a large surface area relative to their volume. So, they tend to lose body heat very fast during cold conditions. They need to spend more energy to generate body heat. Due to this smaller animals are rarely found in polar regions.

Q.list the different ways by which organisms cope or manage with abiotic stresses in nature. Explain any three ways.     [All India 2009c]
Ans.Organisms cope up with abiotic stress by:
(i)Regulating Some organisms maintain homeostasis by physiological and behavioural means. They are called regulators, e.g.

  • In summers, when outside temperature is more, we sweat profusely that results in evaporative cooling to bring down the body temperature.
  • In winters, when temperature is low, we shiver (a kind of exercise) that produces heat and raise the body temperature.

(ii) Conformating Organisms that cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. Such animals are called conformers. For example, small animals have larger surface area relative to their volume. They lose body heat very fast in low temperature. So, they expend energy to generate body heat through metabolism for adjusting.
(iii) Migrating The temporary movement of organisms from the stressful habitat to a more hospitable area and return when favourable conditions reappear is called migration. The long distance migration is very common in birds.

Q.(i) Write the importance of measuring the size of a population in a habitat or an ecosystem.
(ii) Explain with the help of an example, how the percentage  cover is a more meaningful measure of population size than mere numbers?     [All India 2013]
Ans.(i) Measurement of population in a habitat determines the relative abundance of a particular species and its effect on the available resources of that particular habitat.
(ii) The percentage cover is more meaningful measure of population size than mere numbers because the relative abundance of a species is not only determined by number of individuals but by both the relative abundance in biomass and number.
e.g. in a unit area the number of grass species or relative abundance in number is high but not the relative biomass, if the same area has one or two Ficus bengalensis tree, it is very low in relative abundance but high in relative abundance of biomass

Q.(i)Explain death rate in a population by taking a suitable example.
(ii) Write the other two characteristics, which only a population shows but an individual cannot. [All India 2013]
Ans.Death or mortality rate is expressed as the number of deaths of individual of a population per year.
Example If 80 individuals in a laboratory population of 800 fruit fly died in a week then death rate is 80/800=0.1/fruityfly/week
(ii)Characteristics of population, not exhibited by individual are:

  • Population size or density
  • Population interactions

Q.(i) Explain birth rate in a population by taking a suitable example.
(ii) Write the other two characteristics, which only a population shows but an individual cannot. [All India 2013]
Ans.(i) Due to natality or birth rate, population increases continuously. It is covering the production of new individual by birth, hatching, by asexual mode, etc. It is expressed as the number of birth per 1000 individual of a population per year.
(ii) The characteristic, which are unique to the group (population) and not shown by an individual are.

  • Population dynamics theories to explain population growth. Size of population for any species is not a static parameter.Population growth change during time and depend upon food availability, predation, pressure, weather and also depend upon natality and mortality, immigration, emigration.
  • Regulation of population Govern population density or population size. It is the number of individual of a species per unit area or volume

Q.(i) List any three ways of measuring population density of a habitat.
(ii) Mention the essential information that can be obtained by studying the population density of an organism.[All India 2013]
Ans.(i)Three ways of measuring population density of a habitat
A- Per cent cover for trees with larger canopy.
B- Number of fishes caught per trap.
C- Pug marks or faecal pellets for tiger census.
(ii) The population density tells us about the status of a species, i.e. the outcome of competition, impact of predation or effect of pesticides, etc.

Q.Name the type of interaction seen in each of the following examples
(i)Ascaris worm living in the intestine of human.
(ii)Wasp pollinating fig’s inflorescence.
(iii)Clown fish living among the tentacles of sea anemone.
(iv)Mycorrhizae living on the roots of higher plants.
(v)Orchid growing on a branch of mango tree.
(vi)Disappearance of smaller barnacles when Balanus dominated in the coast of Scotland.  [Delhi 2011]
Ans.(i) Parasitism        (ii)  Mutualism
(iii) Commensalism      (iv) Mutualism
(v)Commensalism         (vi) Competition

Q.Study the three different age pyramids, for human population given below and answer the questions that follow
Important Questions for Class 12 Biology Term 2 with Answers_260.1
(i)Write the names given to each of these age pyramids.
(ii)Mention the one which is ideal for human population and why?[Foreign 2011]
Ans.(i) A – Expanding, B – Stable,C -Declining
(ii) Stable population is preferred.It is beneficial for survival and better living of the human population. It is helpful for planning welfare activities.

Q.Why is predation required in a community of different organisms?[Foreign 2009]
Ans.Requirement of predation:
(i) Acts as a conduit for energy transfer across trophic levels.
(ii) Keep the prey population under control.
(iii) Helps in maintaining species diversity in a community by reducing the intensity of competition.
(iv) Biological control of pests is based on predation.

Q.Study the population growth curves in the graph given below and answer the questions which follow
Important Questions for Class 12 Biology Term 2 with Answers_270.1
(i) Identify the growth curves A and B
(ii)Which one of them is considered a more realistic one and why?
(iii)If
Important Questions for Class 12 Biology Term 2 with Answers_280.1
equation of the logistic growth curve, what does K stand for?
(iv)What is symbolised by N?[Delhi 2008]
Ans.(i)A – Exponential growth curve B – Logistic growth curve
(ii) Logistic growth curve B is considered more realistic one because the resources are finite and become limiting sooner or later.
(iii) K-stands for carrying capacity. It is the maximum number of individuals of a population, that the given environment can sustain.
(iv) N-symbolises population density. It is the number of individuals in a given population per unit area

Q.Study the population growth curves shown below
Important Questions for Class 12 Biology Term 2 with Answers_290.1
(i)Identity curves A and B,
(ii)Mention the conditions responsible for the curves A and B respectively,
(iii)Give the necessary equation for the curve B. [All India 2008]
Ans.(i)A-Exponential growth curve B-Logistic growth curve.
(ii) A- Any species growing exponentially under unlimited resource conditions, shows this growth curve.
B- A population growing in a habitat with limited resources shows an initial lag phase, an accelerated log phase and a decelerated steady phase.
(iii)
Important Questions for Class 12 Biology Term 2 with Answers_280.1

Q.Study the graph below and answer the questions which follow
Important Questions for Class 12 Biology Term 2 with Answers_310.1
(i)The curve A is represented by the equation
dN /dt=rN  represent in the equation and what is its importance?
(ii)Which one of the two curves is considered a more realistic one for  most of the animal population?
(iii)Which curve would depict the population of a species of deer if there are no predators in the habitat? Why is it SO? [Foreign 2008]
Ans.(i) r is intrinsic rate of natural increase. It is an important parameter for assessing the impact of any abiotic or biotic factors on the population growth.
(ii) Curve-B is more realistic for animal population
(iii) Curve-B. When the predators are absent, there will be competition among large prey population for resources.

Biodiversity and its Conservation

Q. The following graph shows the species-area relationship. Answer the following questions as directed.
Important Questions for Class 12 Biology Term 2 with Answers_320.1
(i) Name the naturalist who studied the kind of relationship shown in the graph. Write the observations made by him.

(ii) Write the situations as discovered by the ecologists when the value of Z (slope of the line) lies between

  • 1 and 0.2
  • 6 and 1.2

What does Z stand for?

(iii) When would the slope of the line ‘b’ become steeper? [All India 2014] 

Ans.  (i) Alexander Von Humboldt studied the relationship shown in above graph. He observed that the species richness in an area increased with an increase in exploring area, up to a certain limit only.

(ii) (a) Ecologists have observed that when the value of Z lies between 0.1 – 0.2 when the species are considered for a small or average area.

(b) When the value of Z lies between 0.6-1.2, the area considered is very large. Z represents the slope of the line, i.e. regression coefficient.

(iii) The slope of the line ‘b’ will become steeper when very large areas such as continents are considered for species area relationship.

Q. Explain giving three reasons, why tropics show greatest levels of species diversity? [All India 2014]

or

List the reasons that account for the greater biological diversity in tropics.   [Foreign 2012]

Ans. Levels of biodiversity in biosphere

(i) Genetic diversity It refers to the diversity of genes within a species.

For example, there are more than 50,000 genetically different strains of rice in India.

(ii) Species diversity It refers to the number of different species within a given region. For example, Western Ghats have a greater amphibian species diversity than Eastern Ghats.

Q. Alien species are highly invasive and are a threat to indigenous species. Substantiate this statement with any three examples. [All India 2012]

Ans. Alien species become invasive, compete with the native species and cause extinction of indigenous species.

(i) Introduction of Nile perch into Lake Victoria lead to extinction of more than 200 species of cichlid fish in that lake.

(ii) Carrot grass (Parthenium and Lantana) introduced in our country have become invasive and cause environmental damage. They pose a threat to the native species of plants in our forests.

(iii) Introduction of African cat fish Clarius  gariepinus for aquaculture posses a threat to indigenous cat fishes in Indian rivers.

Q. Explain by giving example, how co-extinction is one of the causes of loss of biodiversity? List the three causes also (without description). [Foreign 2011]

Ans.  Co-extinction is one of the cause of loss of biodiversity as when a species become extinct, the plant and animal species associated with it in an obligatory manner, also become extinct.

For example,

(i) In plant pollinator mutualism, extinction of one results in the extinction of other.                ‘

(ii) If a host fish become extinct, the unique , parasites depending on it would also become extinct.

The other causes of loss of biodiversity are:

  • Habitat loss fragmentation
  • Over-exploitation
  • Invasion of alien species.

Q. Explain rivet popper hypothesis. Name the ecologist who proposed it. [Foreign 2011]

Ans. Rivet popper hypothesis

(1) The hypothesis was proposed by Paul Ehrlich.

(ii) In an airplane (ecosystem), all parts are joined together using thousands of rivets (species).

(iii) If every passenger travelling in it, starts popping a rivet to take home (causing a species to become extinct), it may not affect the flight safety (proper functioning of ecosystem) initially, but as more and more rivets are removed, the plane becomes dangerously weak after some time.

(iv) Further, which rivet is removed may also be critical loss of rivets on the wings. (Key species that drive major ecosystem function) is obviously a more serious threat to flight safety than loss of a few rivets on the seats or windows inside the plane.

Q. (i) Why is there a need to conserve biodiversity?

(ii) Name and explain any two ways that are responsible for the loss of biodiversity.  [All India 2014]

Ans.(i) The biodiversity needs to be conserved because of three categories:                     .

  • Narrow utilarian includes most of the resources required for our day-io-day life, e.g. food, oil, clothes, firewood, drugs and medicines, industrial products all are derived from nature, thus needs to be conserved to reap more benefits.
  • Broadly utilarian includes most of the ecosystem services provided to us by nature. Such as release of oxygen and fixation of C02 by photosynthesis in plants, pollination and dispersal of seeds, etc. Therefore, for the continuation of these services biodiversity needs to be conserved.
  • Ethical reasons as it becomes our moral duty to take care of all living species in our surroundings irrespective of their economic importance and pass this biological legacy to our future generations.

(ii)  The two ways that are responsible for the loss of biodiversity are:

  • Habitat loss and fragmentation of natural habitats due to the natural reasons or human activities and pollution results in degradation of habitats, thereby threatening the survival of many species concerned.
  • Co-extinction also leads to loss of biodiversity as when a species becomes extinct, the plant and animal species associated with it in obligatory way also become extinct, e.g. when a host organism (fish) becomes extinct, the parasites exclusive to it also becomes extinct

Q. (i) Why is there a need to conserve biodiversity?

(ii) Name and explain any two ways that are responsible for the loss of biodiversity.  [All India 2014]

Ans.(i) The biodiversity needs to be conserved because of three categories:                     .

  • Narrow utilarian includes most of the resources required for our day-io-day life, e.g. food, oil, clothes, firewood, drugs and medicines, industrial products all are derived from nature, thus needs to be conserved to reap more benefits.
  • Broadly utilarian includes most of the ecosystem services provided to us by nature. Such as release of oxygen and fixation of C02 by photosynthesis in plants, pollination and dispersal of seeds, etc. Therefore, for the continuation of these services biodiversity needs to be conserved.
  • Ethical reasons as it becomes our moral duty to take care of all living species in our surroundings irrespective of their economic importance and pass this biological legacy to our future generations.

(ii)  Hot spots are regions exhibiting high degree of endemism and great species richness, therefore designating these areas as ‘biodiversity hot spots’ allows their maximum protection and reduce the ongoing extinction by  about 30%.

Such hot spot regions in India are Western Ghats and Himalayas.

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Important Questions for CBSE Class 12 Biology Term 2 with Answers: FAQs

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