Cell — The Unit of Life — Practice

Question 1

Who proposed the fluid mosaic model and what is the structure of the cell membrane?

Accepted Answer

Singer and Nicolson (1972). The membrane is a phospholipid bilayer with hydrophilic heads facing outward and hydrophobic tails inward, with proteins embedded as integral (transmembrane) or peripheral proteins. The lipids and proteins can move laterally, giving the membrane its fluid, mosaic nature.

Question 2

Differentiate between RER and SER.

Accepted Answer

Rough ER bears ribosomes and is involved in protein synthesis and secretion. Smooth ER lacks ribosomes and functions in lipid synthesis, detoxification, and calcium storage.

Question 3

What is the 9+2 arrangement and where is it found?

Accepted Answer

It is the arrangement of 9 outer doublet microtubules surrounding 2 central singlet microtubules, found in the axoneme of cilia and flagella.

Question 4

Why are mitochondria called semi-autonomous organelles?

Accepted Answer

They have their own circular DNA and 70S ribosomes and can synthesise some of their own proteins, but they still depend on nuclear DNA for most of their proteins -- hence semi-autonomous.

Question 5

How does the nucleolus differ from the nucleus?

Accepted Answer

The nucleolus is a dense, dark-staining region inside the nucleus, rich in rRNA, where ribosomal RNA is synthesised and ribosome subunits are assembled. The nucleus is the whole membrane-bound organelle containing the chromatin and nucleolus.

Practice — Cell — The Unit of Life

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