Form 1:
Cell physiology Kcse questions

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1. The table below shows the concentration of some ions in pond water and in the cells sap of an aquatic plant growing in the pond.

Ions Concentration in pond water (parts per million) Concentration in cell sap (parts per million)
Sodium 50 30
Potassium 2 150
Calcium 1.5 1
Chloride 180 200

a) Name the processes by which the following ions could have been taken up by this plant. (2mks)

i) Sodium ions


ii) Potassium ions

Active transport

b) For each processes named in (a) (i) and (ii) above, state one condition necessary for the process to take place. (2mks)

Diffusion-A concentration gradient between sodium ions in sap and those in the pond.

Active transport-energy in form of ATP must be available/Oxygen and food in the living tissue for respiration provide energy.

2. Explain how water in the soil enters the root hairs of a plant. (4mks)

A film of water surrounds the soil particle. Root hairs of the plants penetrate between the soils particles/are close to the soil particles; cell sap of the root hair cells is more concentrated in solutes/has less water than the soil solution. Thus water moves into root hair cell by osmosis i.e across the cell a wall and the semi permeable membrane.

3. Explain how drooping of leaves on a hot sunny day is advantageous to a plant.

The leaves expose a smaller surface area to the sun. Thus reducing transpiration/excessive water loss.

4. a) What is diffusion? (2mks)

Diffusion is defined as the net movement of a substance from aregion where its concentration is high to a region where its concentration is low.

b) How do the following factors affect the rate of diffusion?

i) Diffusion gradient (1mk)

Diffusion gradient-the greater the diffusion gradient, the greater the rate of diffusion.

ii) Surface area to volume ratio (1mk)

Surface area to volume ratio-the greater the S.A to V.R the greater the rate of diffusion.

iii) Temperature (1mk)

Temperature - The higher the temperature the greater the rate of diffusion

c) Outline 3 roles of active transport in the human body (2mks)

i) Absorption of mineral salts from the soil by root hairs.
ii) Re-absorption of glucose molecules in the kidney tubule.
iii) Absorption of digested food in the ileum e.g glucose,amino acids.

5. State the importance of osmosis in plants (3mks)

i) Uptake of water from the soil into root hairs of plant roots
ii) Movement of water from the veins of leaves through the leaf cells to the atmosphere during transpiration.

6. An experiment was set up as shown in the diagram below.

The set up was left for 30 minutes.

a) State the expected results. (1mk)

The visking tubing was fully filled with solution. Level of water in beaker decreased .

b) Explain your answer in (a) above. (3mks)

Sucrose solution in visking tubing created high concentration gradient.
Water molecules moved from distilled water to the visking tubing by osmosis.

7. Explain why plant cells do not burst when immersed in distilled water. (2mks)

Plant cells have cells membrane and cell wall. When the cell is placed or immersed in distilled water, the water is absorbed by osmosis. As cell becomes turgid, the cell creats an inward force, wall pressure that prevents the cell from bursting.

8. Distinguish between diffusion and osmosis. (2mks)

Diffusion Osmosis
Involves movement of particles of molecules of liquid or gas. Involves movement of solvent.
It may be through a membrane or in air. It takes place through a semi-permeable.
Not affected by PH changes. Rate affected by pH changes.

9. Define the following terms in relation to a cell

a) Isotonic solution

Isotonic solution- a solution which has the same concentration as the cell sap.

b) Hypotonic solution

Hypotonic solution- a solution which is less concentrated than the cell sap.

c) Hypertonic solution (3mks)

Hypertonic solution- A solution which is more concentrated than the cell sap.

10. Addition of large amounts of salt to soil in which plants are growing kills the plants. Explain (6mks)

Plants normally grow in soils whose solute concentration is lower than that of the cell sap. This enables the plants to take up water by osmosis. Addition of large amounts of salt to the soil increases the solute concentration of soil water beyond that of the cell sap. The result is that the plants lose water to the soil by osmosis. Since water is very important for maintaining the structural and metabolic activities of plants, its deficiency leads to death of the plants.

11. Explain why

a) Red blood cells burst when placed in distilled water while plant cells remain intact.

The red blood cells take in water by osmosis. They swell and exert pressure on the fragile plasma membrane which then breaks. Plant cells take in water and swell but do not burst. This is because their tough cell wall can only stretch to a limited extent. Once fully stretched, the cell wall resists further expansion of the cell and no more water is taken up.

b) Fresh water protozoa like amoeba do not burst when placed in distilled water. (2mks)

Fresh water protozoa take in water by osmosis. The excess wateris then actively pumped into the contractile vacuole which discharges the water to the outside.
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