Form 2:
Gaseous Exchange kcse questions

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1. Discuss how gaseous exchange occurs in

a) Terrestrial Insects (9mks)

- Air enter into tracheal system through spiracles

- It moves onto the tracheoles then moves on to the tips of tracheoles.

- Air rich in oxygen dissolves in a fluid at the tip of the tracheoles. There is low concentration of oxygen in tissues as compared to the fluid.

- Oxygen diffuses into the tissues due to concentration gradient. It is used in metabolic activities. - In tissues there is high carbon dioxide concentration than in the fluid in tracheoles.

- Carbon dioxide diffuses from tissues into tracheole due to concentration gradient. It moves into trachea then out of the body through spiracles.

b) Bony fish (11mks)

- Water enters through the mouth when it opens its mouth. When it closes the floor is raised and water flows over the gills.

- Oxygen diffuses into the gills blood capillaries while carbon dioxide diffuses from the blood capillaries along concentration gradient.

- Flow of water and blood in gill filaments is by counter current flow.

2. a) Explain how mammalian lungs are adapted for gaseous exchange. (8mks)

- Large number of alveoli-increase surface area.

- Alveoli moist-dissolve diffusing gases.

- This walls- allow quick diffusion of gases

- Rich blood supply

- transport oxygen and carbon dioxide.

b) Describe how carbon dioxide is produced by

i) Respiring muscle cells reaches the alveolar cavities in  mammalian lungs.

-Carbon dioxide diffuses into the cells. It moves in the plasma or red blood cells.

- Carbonic acid in plasma or carbamino haemoglobin in red blood cells or hydrogen carbonate.

- At the lungs hydrogen carbonate, carbonic acid and carbomino haemoglobin dissociates releasing cavity due to concentration gradient.

ii) Respiring mesophyll cells of flowering plants reaches the  atmosphere. (12 mks)

Due to metabolic activities carbon dioxide is released from mesophyll cell. It diffuses into the intercellular spaces.

- Due to concentration gradient the gas diffuses into the substomatal air spaces.

- When stomata open carbon dioxide is released into the atmosphere.

3. a) Describe the path taken by carbon dioxide released from the tissues  of an insect to the atmosphere.

Carbon dioxide diffuses into the tracheoles then into the trachea and out into the atmosphere through spiracles.

b) Name two structures used for gaseous exchange in plants. (2mks)

- Stomata.

- Lenticels

- Cuticle

4. Why are gills in fish highly vascularized? (1mk)

- To facilitate transportation of gases/exchange of gases i.e. oxygen and carbon dioxide.

- Create high concentration gradient.

5. Describe the

a) Process of inhalation in mammals. (10 mks)

- External intercostals muscle contract while internal intercostals muscles relax.

- Diaphragm contract flattening.

Volume in thoracic cavity

- Air rushes into the lungs.

b) Mechanism of opening and closing of stomata (10 mks)


During the day photosynthesis takes place and sugar is formed in guard cells - Osmotic pressure increases and water is drawn from neighbouring cells by Osmosis. - The guard cells become turgid, bulge outward causing opening of stomata.


During the night there is no photosynthesis and sugar is converted to starch. - Osmotic pressure decrease and water is lost to the neighbouring cell osmosis. - Guard cells become flaccid, closing the stomata.

6. Name three sites where gaseous exchange takes place in terrestrial plants. (3mks)

- Stomata

- Lenticels

- Cuticle

7. How is aerenchyma tissue adapted to its function? (2mks)

- High number of stomata on the upper surface of the leaf.

- Absence of cuticle to allow diffusion of carbon dioxide and oxygen.

8. The diagram below represents a part of the rib cage.

a) Name parts labeled W, Y and Z.

- spinal column/vertebral column

- sternum

- intercostals muscles

b) How does the part labeled Z facilitates breathing in? (1mk)

The external intercostals muscles contract while the internal intercostals muscles relax .The movement pulls the ribs upwards and outwards.The diaphragm muscles contract hence flattens.The thoracic volume increases while pressure reduces,leading to atmospheric air rushing into the lungs through the nose and trachea hence inflating the lungs.

9. State two ways in which floating leaves of aquatic plants are adapted to gaseous exchange. (2mks)

-Stomata are found on upper epidermis to allow efficient gaseous exchange

-Presence of large air spaces/Aerenchyma tissues to enable it float or for buoyancy and also for storage of air

10. a) Name two structures for gaseous exchange in aquatic plants.



- Aerenchyma tissues

- Cuticle

b) What is the effect of contraction of the diaphragm muscles during breathing in mammals? (3mks)

- The diaphragm flattens.

- Volume in thoracic cavity increase.

- Pressure decreases compared to atmospheric pressure. Air rushes into the lungs through the nostrils.

11. The diagram below represents some gaseous exchange structures in humans.

a) Name the structure labeled K, L and M (3mks)

K- Pleaural membranes

L - Alveolus

M- Intercostals muscles

b) How is the structure labeled J suited to its functions? (3mks)

- Has c-shaped cartilage rings that support it, preventing it from collapsing and allow free flow of air.

- Inner lining has mucus secreting cells that trap fine dust particles and micro-organisms.

- Inner lining has hair like structures called cilia that enhance upward movement of the mucus to the larynx.

c) Name the process by which inhaled air moves from the structure labeled L into blood capillaries. (1mk)


d) Give the scientific name of the organism that causes tuberculosis in  humans. (1mk)

Mycobacterium tuberculosis

12 State three factors that make alveolus adapted to its function. (3mks)

- Highly folded to increase surface area.

- High network of blood capillaries

- Thin walled

- Moist

13. Name the causative agent of Tuberculosis

Mycobacterium tuberclulosis

14. Explain why water logging of the soil may lead to death in plants. (2mks)

- When soil is water logged oxygen cannot diffuse into the root tissues hence no respiration. Metabolic activities stop leading to death.

15. Write three advantages of breathing through nose than through mouth. (3mks)

- Air is cleaned by the cilia in nostrils

- Controlled amount of air is taken in through nose

- Individual is able to detect the smell of air breathed in.

16. State and explain ways the leaves are adapted for gaseous exchange (4mks)

- Spongy mesophyll cells are loosely packed allowing diffusion of gases.

- Spongy mesophyll cells have a film of moisture on the surface to dissolve diffusing gases.

- Large sub-stomatal air space in order to create high concentration gradient of diffusing gases.

- Presence of stomata where gases enter or leave the leaf

17. Name three gaseous constituents involved in gaseous exchange in plants. (3mks)

- Carbon dioxide

- Water vapour

- Oxygen

18. Name three sites of gaseous exchange in frogs. (3mks)

- Skin

- Mouth

19. Name the main site of gaseous exchange in

a) Mammals - alveoli

b) Fish - gill filaments

c) Leaves - spongy mesophyll cells

d) Amoeba - cells membrane (4mks)

20. Name the physiological process by which gas exchange takes place at the respiratory surface in animals and plants (1mk)