Which of the following pairs is INCORRECT regarding the grade of organisation and its example?

Correct option is D

​· The pair Tissue-organ grade organisation – Euplectella is incorrect. Euplectella, also known as the glass sponge, exhibits a cellular grade of organisation rather than a tissue-organ grade.

·  It is a type of sponge, and sponges typically have a simple body structure with cells performing specialized functions but lack true tissues and organs.

Grade of Organisation:

1. Protoplasmic Grade: This is the simplest level of organisation, where all life processes occur within a single cell, as seen in organisms like Paramecium.
2. Cellular Grade: In this grade, the body is composed of cells performing different functions but without forming true tissues. Sycon (a type of sponge) is an example of cellular grade organisation.
3. Cell-Tissue Grade: Here, groups of similar cells perform a specific function, but there is no real organ formation. Jellyfish (Cnidarians) exhibit this grade, where cells form tissues but not organs.
4. Tissue-Organ Grade: In this grade, tissues are organised into organs, and organisms have a more complex structure. Euplectella, however, does not fit into this category because it is a simple sponge with a cellular level of organisation.

Additional Information:

• Sycon: A simple sponge with a cellular level of organisation. Its body is made up of cells that work together but not in the form of organs or true tissues.
• Paramecium: A single-celled organism, exhibiting protoplasmic grade organisation, where all life functions occur within the single cell.
• Jellyfish: They belong to the phylum Cnidaria and have a cell-tissue grade of organisation, where cells form tissues but do not develop into complex organs.
• Euplectella: A glass sponge that, despite being a more complex organism than simpler sponges, still lacks true tissues and organs and thus falls under cellular grade organisation.

Other Options:

• Cellular grade organisation - Sycon: This is correct. Sycon (a type of sponge) is a classic example of cellular grade organisation.
• Protoplasmic grade organisation - Paramecium: This is correct. Paramecium is a unicellular organism that functions as a single cell, representing the protoplasmic grade of organisation.
• Cell-tissue grade organisation - Jellyfish: This is correct. Jellyfish have a relatively simple body structure with cells grouped into tissues but no true organs, representing the cell-tissue grade.