Class 11 Biology

Chapter 8 Solutions — Cell: The Unit of Life

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Solutions

Overview

Step-by-step NCERT solutions for Cell: The Unit of Life (Chapter 8, NCERT Class 11 Biology) — every question and answer worked out in full, not just the final result. You can also read the Cell: The Unit of Life textbook chapter.

Solved

What these solutions cover

All 14 questions in Cell: The Unit of Life are solved in the PDF. Here's what's inside, exercise by exercise:

Exercises

1.
Which of the following is not correct?
- (a) Robert Brown discovered the cell.
- (b) Schleiden and Schwann formulated the cell theory.
- (c) Virchow explained that cells are formed from pre-existing cells.
- (d) A unicellular organism carries out its life activities within a single cell.
2.
New cells generate from
- (a) bacterial fermentation
- (b) regeneration of old cells
- (c) pre-existing cells
- (d) abiotic materials
3.
Match the following: Column I Column II
- (a) Cristae
- (i) Flat membranous sacs in stroma
- (b) Cisternae
- (ii) Infoldings in mitochondria
- (c) Thylakoids
- (iii) Disc-shaped sacs in Golgi apparatus
4.
Which of the following is correct:
- (a) Cells of all living organisms have a nucleus.
- (b) Both animal and plant cells have a well defined cell wall.
- (c) In prokaryotes, there are no membrane bound organelles.
- (d) Cells are formed de novo from abiotic materials.
What is a mesosome in a prokaryotic cell? Mention the functions that it performs.
How do neutral solutes move across the plasma membrane? Can the polar molecules also move across it in the same way? If not, then how are these transported across the membrane?
Name two cell-organelles that are double membrane bound. What are the characteristics of these two organelles? State their functions and draw labelled diagrams of both.
What are the characteristics of prokaryotic cells?
Multicellular organisms have division of labour. Explain.
Cell is the basic unit of life. Discuss in brief.
What are nuclear pores? State their function.
Both lysosomes and vacuoles are endomembrane structures, yet they differ in terms of their functions. Comment.
13.
Describe the structure of the following with the help of labelled diagrams.
- (i) Nucleus
- (ii) Centrosome
What is a centromere? How does the position of centromere form the basis of classification of chromosomes. Support your answer with a diagram showing the position of centromere on different types of chromosomes.

Sample

Worked examples

2 questions from Cell: The Unit of Life, solved step by step.

Exercises

What is a mesosome in a prokaryotic cell? Mention the functions that it performs.

A mesosome is a specialised membranous structure found in prokaryotic cells, particularly bacteria.

It is formed by extensions (infoldings) of the plasma membrane into the cell interior. These extensions may be in the form of vesicles, tubules, or lamellae.

Functions of the mesosome:

1. Cell wall formation — assists in the synthesis and assembly of the new cell wall during cell division.

2. DNA replication and distribution — helps in the replication of the bacterial chromosome (genomic DNA) and its distribution to daughter cells.

3. Respiration — increases the surface area of the plasma membrane, providing additional sites for respiratory enzymes, thereby facilitating aerobic respiration.

4. Secretion — involved in secretory processes of the cell.

5. Increases surface area of the plasma membrane and enzymatic content of the cell.

Answer: A mesosome is an infolding of the plasma membrane in prokaryotes (appearing as vesicles, tubules, or lamellae). It aids in cell wall formation, DNA replication and segregation to daughter cells, respiration, and secretion.

Exercises

What are nuclear pores? State their function.

Nuclear pores are minute, circular openings (passages) present in the nuclear envelope.

Structure:

- The nuclear envelope consists of two parallel membranes separated by a perinuclear space (10-50 nm).

- At certain places, the two membranes fuse together, creating gaps called nuclear pores.

- Each nuclear pore is lined by a complex protein structure called the nuclear pore complex.

Function:

- Nuclear pores are the passages through which the movement of RNA molecules (including mRNA, rRNA, tRNA) and protein molecules takes place in BOTH directions between the nucleus and the cytoplasm.

- mRNA (carrying genetic information) moves from nucleus to cytoplasm for protein synthesis.

- Ribosomal proteins and other regulatory proteins move from the cytoplasm into the nucleus.

- They thus facilitate bidirectional exchange of materials between the nucleus and cytoplasm, allowing the nucleus to control cellular activities.

Answer: Nuclear pores are openings formed by the fusion of the two membranes of the nuclear envelope. They serve as passages for bidirectional movement of RNA (mRNA, rRNA, tRNA) from nucleus to cytoplasm and proteins from cytoplasm to nucleus, enabling the nucleus to regulate cellular activities.

All 14 questions in Cell: The Unit of Life are solved step by step in the Solutions PDF above.

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Chapter 8 Solutions — Cell: The Unit of Life

Overview

What these solutions cover

Exercises

Worked examples

What is a mesosome in a prokaryotic cell? Mention the functions that it performs.

What are nuclear pores? State their function.

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