Ctet Biology Questions with Detailed Solutions

The correct answer is (c).
Explanation
Animals can be classified using a combination of observable and biological characteristics rather than relying on a single feature.
Animal P has feathers, breathes through lungs, and lays eggs—features characteristic of birds.
Animal Q has moist skin and lays eggs in water. Adult amphibians such as frogs can exchange gases through their moist skin as well as breathe through lungs. Therefore, Q represents an amphibian.
Animal R possesses fins and scales and breathes through gills, identifying it as a fish.
Animal S has hair, breathes through lungs, and gives birth to young ones—characteristics commonly associated with mammals.
Additional Information
· {a} Classification helps scientists organise organisms according to shared and distinguishing characteristics.
· {b} Using a single characteristic may sometimes lead to incorrect classification; for example, both birds and mammals breathe through lungs but belong to different groups.
· {c} Amphibians generally spend parts of their life cycle in water and on land; their larvae commonly breathe through gills.
· {d} Mammals characteristically possess mammary glands, and most give birth to young ones, although egg-laying mammals such as the platypus and echidna are exceptions.

The correct answer is (b).
Explanation
Earthworms obtain oxygen through their moist skin. Normally, they respire while living in soil because the air spaces between soil particles contain sufficient oxygen. During heavy rainfall, these air spaces become filled with water, reducing the amount of oxygen available for respiration. As a result, earthworms move to the soil surface, where atmospheric oxygen is more readily available. Thus, Statement II correctly explains the observation described in Statement I.
Additional Information
· {a} Option {a} is incorrect because both statements are scientifically correct.
· {b} Option {b} is correct because excess water reduces oxygen availability in the soil, forcing earthworms to come to the surface.
· {c} Option {c} is incorrect because Statement II correctly explains the biological reason behind the observation.
· {d} Option {d} is incorrect because earthworms are indeed commonly observed on the soil surface after heavy rainfall.

The correct answer is (a).
Explanation
Breathing is brought about by changes in the volume and pressure of the chest cavity. During inhalation, the diaphragm contracts and flattens downward while the ribs move upward and outward. This increases the volume of the thoracic cavity. According to the relationship between pressure and volume, an increase in the volume of the lungs lowers the air pressure inside them below atmospheric pressure. Consequently, air flows from the atmosphere into the lungs until the pressures become equal. Thus, Statement II not only is scientifically correct but also provides the correct explanation for Statement I.
Additional Information
· {a} Option {a} is correct because both statements are scientifically accurate, and the second statement explains the physiological basis of the first.
· {b} Option {b} is incorrect because Statement II directly explains why contraction of the diaphragm results in inhalation.
· {c} Option {c} is incorrect because Statement II is scientifically correct. A reduction in pressure inside the lungs is the reason atmospheric air enters during inhalation.
· {d} Option {d} is incorrect because the diaphragm does contract and move downward during inhalation, making Statement I correct.

The correct answer is (a).
Explanation
Fungi are microorganisms that thrive under warm, moist, and nutrient-rich conditions. Bread provides an abundant food source, and when it is kept in a warm, closed environment with sufficient moisture, fungal spores germinate rapidly and form visible mould colonies. Refrigeration slows down microbial growth because low temperatures reduce metabolic activity. Direct sunlight inhibits fungal growth by increasing temperature beyond favourable limits and exposing microorganisms to ultraviolet radiation. Similarly, a completely dry environment deprives fungi of the moisture necessary for growth and reproduction. This question requires students to interpret experimental conditions and apply their understanding of factors affecting microbial growth rather than recalling isolated facts.
Additional Information
· {a} Option {a} is correct because fungi require warmth, moisture, and nutrients for rapid growth. Bread stored in a warm, moist environment provides ideal conditions for mould development.
· {b} Option {b} is incorrect because refrigeration slows the growth and reproduction of most microorganisms. This is why food is commonly stored in refrigerators to delay spoilage.
· {c} Option {c} is incorrect because fungi do not perform photosynthesis. Sunlight generally inhibits fungal growth and may even destroy many microorganisms through ultraviolet radiation.
· {d} Option {d} is incorrect because moisture is essential for fungal growth. Dry bread greatly reduces the chances of mould formation, even if fungal spores are present.

Correct Answer: (a)
Explanation
Germinating seeds are metabolically very active because they require considerable energy for growth and development.
For active respiration, seeds need suitable conditions, including moisture, oxygen and an appropriate temperature.
· P: Moist + oxygen available + suitable conditions → favourable for active aerobic respiration.
· Q: Dry seeds → metabolic activity is greatly reduced because water is necessary for germination and cellular reactions.
· R: Restricted oxygen → aerobic respiration is limited.
· S: Very low temperature → enzymatic reactions and metabolic activity generally slow down.
Therefore, P is expected to show the highest respiratory activity.
Additional Information
· {a} Germination begins when a viable seed absorbs water and metabolic activity increases.
· {b} Aerobic respiration releases energy from stored food using oxygen and produces carbon dioxide and water.
· {c} Enzymes regulate many biochemical reactions involved in germination and respiration.
· {d} Seeds can remain dormant for long periods under suitable conditions, but germination requires appropriate environmental factors such as water, oxygen and suitable temperature.

Correct Answer: (a)
Explanation
The heart's ventricles pump blood into the arteries under relatively high pressure. Therefore, arteries have thick, muscular and elastic walls that can withstand and accommodate this pressure.
Veins generally carry blood back towards the heart at lower pressure, so their walls are thinner. Many veins, especially in the limbs, contain valves that help prevent the backward flow of blood.
The thickness of an artery's wall is therefore primarily related to the pressure and nature of blood flow, not simply to whether the blood is oxygenated.
Additional Information
· {a} The pulmonary artery carries deoxygenated blood from the right ventricle to the lungs, showing that arteries are defined by the direction of blood flow rather than oxygen content.
· {b} The pulmonary veins carry oxygenated blood from the lungs to the left atrium.
· {c} Arteries branch into smaller arterioles and eventually into capillaries.
· {d} Capillaries have extremely thin walls, generally only about one cell thick, facilitating exchange of gases, nutrients and wastes between blood and tissues.

Correct Answer: (b)
Explanation
Statement I is correct. Xylem conducts water and mineral salts absorbed by the roots towards the stem and leaves.
Statement II is correct. Phloem transports sugars and other organic substances produced in leaves to regions where they are needed or stored. This movement is commonly called translocation.
Statement III is correct. Loss of water vapour from leaves through transpiration contributes to the upward movement of water through the xylem, particularly through the transpiration-pull mechanism.
Statement IV is incorrect. Transport through plant vascular tissues is not restricted to periods of active photosynthesis. Phloem can transport stored or redistributed organic substances, while xylem transport of water and minerals is also not simply dependent on photosynthesis occurring at that moment.
Therefore, Statements I, II and III only are correct.
Additional Information
· {a} Xylem consists mainly of specialised conducting tissues that transport water and minerals and also provide mechanical support.
· {b} Phloem transports organic nutrients from source regions to sink regions; movement can occur in different directions depending on the source–sink relationship.
· {c} Stomata regulate gas exchange and also influence the rate of transpiration.
· {d} Root hairs increase the surface area available for absorption of water and mineral ions from the soil.

Correct Answer: (a)
Explanation
Variety P is produced through sexual reproduction, in which male and female gametes contribute genetic material to the offspring. The combination and reshuffling of genetic material can produce variation among offspring.
Variety Q is produced through vegetative propagation, a form of asexual reproduction. A new plant develops from a vegetative part of a single parent without fusion of gametes. Consequently, the new plants are generally genetically very similar to the parent, although mutations can still introduce occasional variation.
This difference explains why seed-produced plants generally show more genetic variation than plants produced through stem cuttings.
Additional Information
· {a} Sexual reproduction contributes to genetic variation, which is important for populations facing changing environmental conditions.
· {b} Vegetative propagation is widely used when farmers want to preserve desirable characteristics of a parent plant.
· {c} Examples include sugarcane through stem cuttings, potato through tubers and ginger through rhizomes.
· {d} Variation can arise through several mechanisms, including mutation and genetic recombination.

Correct Answer: (a)
Explanation
The observations correspond to different nutritional deficiencies:
· P → Vitamin C deficiency: Vitamin C is important for maintaining healthy connective tissues and blood vessels. Severe deficiency can cause bleeding gums and scurvy.
· Q → Vitamin D deficiency: Vitamin D is important for calcium absorption and bone health. Inadequate vitamin D can contribute to weak or poorly mineralised bones.
· R → Iodine deficiency: Iodine is required for the synthesis of thyroid hormones. Prolonged deficiency can cause goitre, characterised by enlargement of the thyroid gland.
· S → Iron deficiency: Iron is required for haemoglobin formation. Deficiency can lead to iron-deficiency anaemia, commonly associated with fatigue and pallor.
Thus, option (a} provides the correct matching.
Additional Information
· {a} Vitamin A deficiency can affect normal vision, particularly in dim light.
· {b} Iodine is needed for the production of thyroid hormones, which regulate several aspects of metabolism and development.
· {c} Calcium and vitamin D work together in maintaining healthy bones and teeth.
· {d} Nutritional deficiencies are best prevented through a varied and balanced diet rather than relying on a single food group.

Correct Answer: (b)
Explanation
Grass is the producer and forms the first trophic level in this food chain. A prolonged drought reduces grass availability, decreasing the food supply for grasshoppers, which are primary consumers.
With fewer grasshoppers available, frogs may experience reduced food availability. A decline in frogs can then affect snakes, which depend partly on frogs for food. These changes can propagate through successive trophic levels.
This demonstrates that organisms within an ecosystem are interdependent. A change affecting one trophic level can influence populations at several other levels.
Additional Information
· {a} Producers convert solar energy into chemical energy through photosynthesis and form the foundation of most terrestrial food chains.
· {b} Energy available generally decreases as it passes from one trophic level to the next because much of it is used in life processes and dissipated as heat.
· {c} Food webs provide a more realistic representation of ecosystems because most organisms have more than one food source or predator.
· {d} Environmental factors such as rainfall, temperature, habitat availability and human activities can alter population sizes and ecological relationships.

Correct Answer: (a)
Explanation
During vigorous exercise, muscles require considerably more energy. To meet this demand, the rate of cellular respiration increases. This results in greater oxygen consumption and increased production of carbon dioxide.
Even immediately after exercise stops, the body does not instantly return to its resting metabolic state. Breathing may therefore remain faster for some time so that the body can restore normal oxygen and carbon dioxide levels and meet the continuing physiological demands associated with recovery.
Hence, both the Assertion and Reason are correct, and the Reason directly explains the Assertion.
Additional Information
· {a} During exercise, both breathing rate and depth of breathing may increase.
· {b} Oxygen is transported mainly by haemoglobin in red blood cells.
· {c} Carbon dioxide produced by cellular respiration is transported through the blood to the lungs and removed during exhalation.
· {d} The respiratory and circulatory systems work together to deliver oxygen to tissues and remove carbon dioxide efficiently.

Correct Answer: (c)
Explanation
Situation P involves the fusion of male and female gametes, which is the defining feature of sexual reproduction. The genetic material contributed by the two gametes is combined, producing variation among offspring.
Situation Q involves the development of a new plant from a stem cutting, without gamete fusion. This is vegetative propagation, a form of asexual reproduction. Since the new plant originates from a single parent, it is generally genetically very similar to the parent, apart from variations such as those arising from mutations.
Thus, the two processes differ fundamentally in whether gamete fusion occurs.
Additional Information
· {a} Sexual reproduction generally generates greater genetic variation, which can contribute to the ability of populations to adapt to changing environments.
· {b} Asexual reproduction is often rapid and does not require the production or fusion of specialised gametes.
· {c} In flowering plants, sexual reproduction involves pollination followed by fertilisation and ultimately seed formation.
· {d} Examples of vegetative propagation include potato through tubers, ginger through rhizomes, and sugarcane through stem cuttings.

Correct Answer: (a)
Explanation
Children inherit genetic material from both parents, but the particular combination of genes received by each child can differ. During the formation of gametes and their subsequent fusion during sexual reproduction, genetic material is rearranged into new combinations.
Therefore, siblings can share many characteristics while still showing differences in traits such as height, facial appearance, susceptibility to certain conditions, and other inherited characteristics.
The environment also influences many characteristics. For example, nutrition, physical activity and living conditions can influence growth and development. Thus, observable characteristics are often the result of interactions between heredity and environment.
Additional Information
· {a} Genes are functional units of heredity located on chromosomes.
· {b} DNA carries genetic information that influences the development and functioning of organisms.
· {c} Variation is important for populations because it provides the raw material upon which natural selection can act.
· {d} Identical twins generally originate from the same fertilised egg and therefore have highly similar genetic material, although environmental effects can still lead to differences.

Correct Answer: (b)
Explanation
Different soils differ in particle size, pore spaces, drainage and water-holding capacity.
Sandy soil contains relatively large particles and larger spaces between them. Water therefore passes through it quickly, giving it high drainage but relatively low water-holding capacity. Hence, P is most likely sandy soil.
Loamy soil contains a balanced mixture of sand, silt and clay along with organic matter. It generally provides a useful balance between water retention, drainage and aeration, making Q consistent with loamy soil.
Clayey soil contains very fine particles with very small pore spaces. Water moves through it slowly and may remain on the surface when drainage is poor. Hence, R is most likely clayey soil.
Additional Information
· {a} Sandy soil is generally well aerated because of its larger pore spaces but tends to lose water rapidly.
· {b} Clayey soil has high water-holding capacity but can become poorly aerated when waterlogged.
· {c} Loamy soil is generally considered suitable for many crops because it provides a favourable balance of drainage, aeration, nutrients and moisture retention.
· {d} Organic matter such as humus improves several soil properties, including structure, nutrient availability and water-holding capacity.