Exercise Page: 67

1. Make a comparison and write down ways in which plant cells are different from animal cells.

Solution:

The following table depicts the differences between plant cells and animal cells.

CharacteristicPlant CellAnimal Cell
Cell wallPresentAbsent
Shape of cellDistinct edges, shape is either rectangular or square shaped.Round and irregular shape
NucleusPresent. Lies on one side of the cellPresent. Lies in the center of the cell
LysosomesRarely presentAlways present
PlastidsPresentAbsent
Structure of VacuolesSingle or a few large vacuole that is centrally locatedPresence of numerous and small vacuoles

2. How is prokaryotic cell different from a eukaryotic cell?

Solution:

The following are the differences between prokaryotic and eukaryotic cells.

Prokaryotic CellEukaryotic Cell
1.  Size: Generally small (1-10 μm)1 μm = 10-6m2.  The nuclear region is not well defined as the nuclear membrane is absent and is referred to as the nucleoid.3. There is a single chromosome.4. Membrane-bound cell organelles absent.1. Size: Generally large (5-100 μm)2. Nuclear region: well defined and girdled by a nuclear membrane.3. There are more than one chromosomes.4. Membrane-bound cell organelles present.

3. What would happen if the plasma membrane ruptures or breaks down?

Solution:

If plasma membrane ruptures or breaks down then molecules of some substances will freely move in and out of the cells. As plasma membrane acts as a mechanical barrier, exchange of material from its surroundings through osmosis or diffusion in a cell won’t take place. Consequently, the cell would die due to the disappearance of the protoplasmic material.

4. What would happen to the life of a cell if there was no Golgi apparatus?

Solution:

The Golgi apparatus consists of stacks of membrane-bound vesicles whose functions are as follows:

  • storage of substances
  • packaging of substances
  • manufacture of substances

Without the golgi apparatus, the cells will be disabled from packing and dispatching materials that were produced by the cells. The golgi apparatus is also involved in the formation of cells. Hence, in the absence of golgi apparatus, cells will not be produced.

5. Which organelle is known as the powerhouse of the cell? Why?

Solution:

Mitochondria are known as the powerhouse of the cell. It is because it releases the energy required for different activities of life. Mitochondria releases energy in the form of ATP(Adenosine triphosphate) molecules, essential for numerous chemical activities of life. Hence ATP is often referred to as ‘energy currency of the cell’.

6. Where do the lipids and proteins constituting the cell membrane get synthesised?

Solution:

Lipids and proteins are synthesised in the ER [Endoplasmic Reticulum].

How does an Amoeba obtain its food?

Solution:

Through the process of endocytosis, an Amoeba obtains its food. As its cell membrane is flexible enough, food particles are engulfed forming a food vacuole girdling it which is assisted by the pseudopodia. Amoeba secretes digestive enzymes to bring about digestion of the engulfed particle once food is trapped.

the fundamental unit of life

What is osmosis?

Solution:

The process of movement of a water molecule from a region of higher concentration to a region of lower concentration through a semipermeable membrane is known as osmosis.

9. Carry out the following osmosis experiment:

Take four peeled potato halves and scoop each one out to make potato cups. One of these potato cups should be made from a boiled potato. Put each potato cup in a trough containing water. Now,

(a) Keep cup A empty

(b) Put one teaspoon sugar in cup B

(c) Put one teaspoon salt in cup C

(d) Put one teaspoon sugar in the boiled potato cup D.

Keep these for two hours. Then observe the four potato cups and answer the following:

(i) Explain why water gathers in the hollowed portion of B and C.

(ii) Why is potato A necessary for this experiment?

(iii) Explain why water does not gather in the hollowed out portions of A and D.

Solution:

(i) Water accumulates in the hollowed portions of B and C as a difference in the water concentration

is observed. Thereby, endosmosis occurs as the cells act as a semipermeable membrane.

(ii) Potato A is essential in this experiment as it is significant to compare different scenarios seen in

potato cups B, C and D. The potato A in this experiment clearly shows that the potato cavity on its

own cannot bring about water movement.

(iii) Cup in A does not show any change in the water flow concentration for osmosis to occur, which

requires the concentration to be higher than the other. Cells in cup D are dead, thus there is no

existence of a semipermeable membrane for water flow. Consequently, osmosis does not occur.

10. Which type of cell division is required for growth and repair of body and which type is involved in formation of gametes?

Solution:

There are two ways in which a cell divides:

  • Mitosis
  • Meiosis

Mitosis is the type of cell division that is involved in the growth and repair of body whereas meiosis is a type of cell division which results in the formation of gametes.

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