NCERT Solutions for Class 9 Science Chapter 2 The Building Blocks of Life
Page No. 8
Think It Over
Question 1:
Where does a cell come from?
Question 2:
How have technological interventions facilitated the creation of new knowledge in understanding the world beyond the naked eye?
Question 3:
How is the cell structural and functional unit of life?
Question 4:
How does a cell multiply?
Page No. 14
Pause and Ponder
Question 1:
What argument would you give for the necessity of a cell wall in plants usually fixed in one place versus in animals usually moving from one place to the other?
Question 2:
Why is it important to cut the two potato pieces in roughly equal size and measure their initial weight before placing them in different liquids?
Question 3:
What consequences would you predict for a plant cell if its cell wall were to become as flexible as a cell membrane?
Page No. 19
Pause and Ponder
Question 4:
Do white flowers contain any pigment? Give reasons.
Question 5:
Draw a well-labelled schematic diagram of a plant or an animal cell using these clues —
(i) Nucleus appears as a dark and round body inside the cell.
(ii) ER spreads like a network of extended nuclear envelope.
(iii) Mitochondria and chloroplasts are rod shaped.
Page No. 22
Pause and Ponder
Question 6:
Instead of many small ones, why does a cell not have a single giant mitochondrion? How does this relate to the concept of surface area?
Question 7:
If the skin cells start dividing by meiosis instead of mitosis, what do you think will happen to a cut on the skin?
Page No, 24
Revise, Reflect, Refine
Question 1:
Differentiate between the following pairs of terms based on the clues given in parentheses:
(i) Cell membrane and cell wall (permeability)
(ii) RER and SER (structure)
(iii) Chloroplasts and chromoplasts (pigments)
Question 2:
Two similar animal cells are placed in two different solutions:
(i) Cell X is placed in pure water.
(ii) Cell Y is placed in a concentrated salt solution
Cells are observed after some time. Cell X swells, and Cell Y shrinks.
Which statement provides the correct explanation for the above observations?
(i) Salt molecules moved into Cell Y, causing it to shrink.
(ii) Water moved into Cell X and more water moved out of Cell Y than the salt solution entered in it.
(iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.
(iv) Solute movement caused osmosis in both cells.
Question 3:
Look at the diagram of a cell in Fig. 2.20. Identify the parts labelled from (a) to (g) and correctly match them with their functions given below:
(i) Controlling all the activities of a cell.
(ii) Site of cellular respiration.
(iii) Storage organelle that also provides rigidity to the cell.
(iv) Separates the cell contents from surroundings.
(v) Provides structural rigidity to the cell.
(vi) Packs and stores materials received from ER.
(vii) Helps in manufacturing food.
