Biology Class 11 NCERT Solutions: Chapter 8 Cell the Unit of Life Part 1

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Q: 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.

Answer:

(A) Robert Brown did not discover the cell. The cell was discovered by Robert Hook.

Q: 2. New cells generate from

(A) Bacterial fermentation

(B) Regeneration of old cells

(C) Pre-existing cells

(D) Abiotic materials

Answer:

(C) According to the biogenic theory, new cells can only arise from pre-existing cells. Only complete cells, in favourable conditions, can give rise to new cells.

Q: 3. Match the following

Q_3_Table of Match the Column I and Column II
Q_3_Table of Match the Column I and Column II

Column I

Column II

(A)

Cristae

(i)

Flat membranous sacs in stroma

(B)

Cisternae

(ii)

Infoldings in mitochondria

(C)

Thylakoids

(iii)

Dis-shaped sacs in Golgi Apparatus

Answer:

Q_3_1_Table of Match the Column I and Column II
Q_3_1_Table of Match the Column I and Column II

Column I

Column II

(A)

Cristae

(ii)

Infoldings in mitochondria

(B)

Cisternae

(iii)

Dis-shaped sacs in Golgi Apparatus

(C)

Thylakoids

(i)

Flat membranous sacs in stroma

Q: 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.

Answer:

(C) Membrane-bound organelles are organelles surrounded by a double membrane. Nucleus, mitochondria, chloroplasts, etc., are examples of such organelles. These cell organelles are absent from prokaryotes.

(A) Only eukaryotic cells have nuclei. They are absent from prokaryotes.

(B) Cell walls are only present in plant cells. They are absent from all animal cells.

(D) All cells arise from pre-existing cells.

Q: 5. What is a Mesosome in a prokaryotic cell? Mention the functions that it performs.

Answer

Mesosome is a convoluted membranous structure formed in a prokaryotic cell by the invagination of the plasma membrane. Its functions are as follows:

Mesosome in a prokaryotic cell

Mesosome in a Prokaryotic Cell

Mesosome in a prokaryotic cell

(1) These extensions help in the synthesis of the cell wall, replication of DNA. They also help in the equal distribution of chromosomes into the daughter cells.

(2) It also increases the surface area of the plasma membrane to carry out various enzymatic activities.

(3) It helps in secretion processes as well as in bacterial respiration.

Q: 6. 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?

Answer:

Image shows the plasma membrane

Image Shows the Plasma Membrane

Image shows the plasma membrane

Plasma membrane is the outermost covering of the cell that separates it from the environment. It regulates the movement of substances into the cell and out from it. It allows the entry of only some substances and prevents the movement of other materials. Hence, the membrane is selectively permeable.

Movement of neutral solutes across the cell membrane – Neutral molecules move across the plasma membrane by simple passive diffusion. Diffusion is the movement of molecules from a region of higher concentration to a region of lower concentration.

Movement of polar molecules across the cell membrane – The cell membrane is made up of a phospholipid bilayer and proteins. The movement of polar molecules across the non-polar lipid bilayer requires carrier-proteins. Carrier-proteins are integral protein particles having certain affinity for specific solutes. As a result, they facilitate the transport of molecules across the membrane.