Form 4:
Reception,Response and co-ordination

Home|Table of content

1. State one structural and one functional differences between motor and sensory neurons(2 marks)

Structural difference- the cell body in motor neurone is terminal (at the end) and inside the central is nervous system. While the cell body in sensory neuron is not terminal but has axon on both end i.e. bipolar.

Functional differences – motor neurone carries impulses from CNS to the effectors i.e. muscles, while sensory neurons carry impulse for receptor to CNS.

2. The table below shows two mammalian hormones. For each hormone, state the site of production and its function in the body.


(i) With an arrow, indicate on the diagram the direction of the impulse through the neurone ( 1 mark)

(ii) State the functions of parts labeled P and Q ( 2 marks)

P- Protection/ insulation

Q- Impulses transmitted/depolarization is faster.

4. (a) How are structures of the human eye adapted to their functions ( 14 marks)

(b) State three defects of the eye and how each can be corrected ( 6 marks)

5. State the changes that occur in a nerve axon to produce an action potential

( 3 marks)

When an impulse passes along the axon, the membrane of the axon becomes depolarized to sodium ions to diffuse into the axon; the inside of the axon becomes positively charged relative to the outside, an action potential is generated.

6. In an accident a victim suffered brain injury. Consequently he had loss of memory. Which part of the brain was damaged? ( 1 mark)

Cerebrum/ cerebral hemisphere/ cerebral cortex

7. The diagram below shows surface view of a human brain

(a) Name the parts labeled B and C ( 2 marks)

B- Cerebellum

C- Medulla oblongata

(b) State three functions of the part labeled A ( 3 marks)

- Control locomotion

- Control voluntary movement

- Vision/ hearing/ smell/ taste

- Intelligence/ memory

 - Personality speech

- Mediates cranial co-ordination

(c) State what would happen if the part labeled B was damaged. ( 1 mark)

Loss of muscle coordination/ balance

8. What is the function of the following cells in the retina of the human eye?

(2 marks)

(a) Cones

Cones- Discrimination of colour/ sensitive to high light intensity / bright light.

(b) Rods

Rods- Dim light vision/ low light intensity

9. (a) State the functions of the following parts of the mammalian ear  

 (i) Tympanic membrane ( 3 marks)

-Receive sound waves

-Transforms sound waves into vibrations

-Transmit vibration to the ear ossicles

(ii) Eustachian tube ( 1 mark)

Equalizes the air pressure in the middle ear to that in the outer ear.

(iii) Ear ossicles ( 2 marks)

Amplify/ transmit vibrations from the lympanic membrane in the

inner ear.

(b) Describe how semi- circular canals perform their functions ( 2 marks)

There are three semi- circular canals arranged in a plane at right angles to each other. At the end of each canal is a swelling called ampulla which contains receptors.

Movement of the beat cause movement of the fluid in at least one canal/ the fluid movement deflect the coperta and stimulate the receptors/sensory hairs. Nerve impulses are transmitted to the brain by the auditory nerve.

10. State the importance of tactic response among some members of Kingdom Protista? ( 1 mark)

The organisms move towards light so as to absorb it for photosynthesis.

(a) What name is given to response to contact with surface exhibited by tendrils and climbing stems in plants? ( 1 mark)


(b) State three biological importances of tropisms to plants (3 marks)

-That part of plants is offered support

-The leaves become more exposed to sunlight increasing photosynthesis.

-Flowers become exposed to pollinating agents.

11. The diagram below represents a reflex arc in human

(a) Name the parts labeled X and Y ( 2 marks)

X- Motor neurone

Y- Receptor

(b) Name the substance that is responsible for the transmission of an impulse across the synapse ( 1 mark)


12. (a) State the function of the ciliary muscles in the human eye. (1 mark)

Alter the shape of the lens during accommodation

(b) State two functional differences between the rods and cones in the human eye ( 2 marks)

- Rods- sensitive to dim light

Cannot distinguish colour

- Cones- Sensitive to colour

Enhance high clarity of vision

13. State the function of each of the following parts of human ear ( 4 marks)

(a) Ear ossicles

Magnify sound wave vibrations from the ear drum

(b) Cochlea

Receives sound vibrations from the oval window and transmits into the auditory nerve.

(c) Semi- circular canals

Structures that help maintain body balance

(d) Eustachian tube

Enhance equalizing of pressure between outer and

the middle ear.

14. (a) Where in the human body are relay neurons found? ( 1 mark)

In the central nervous system (spinal cord)

(b) The diagram below represents a neurone

(i) Name the neurone ( 1 mark)

Motor neurone

(ii) Name the parts labeled P and Q ( 2 marks)

P – Dendrites

Q- Axoplasm (Axon)

15. (a) Name the hormone that is responsible for apical dominance ( 1 mark)


(b) What is thigmotropism? ( 1 mark)

Growth response due to touch of a part of a plant e.g. tendrils

16. Describe the structure and functions of the various parts of the human ear

( 20 marks)

The ear is an organ involved in perceiving sound and maintaining body  balance and posture. It is made of the following sections.

 - Pinna- That is funnel shaped structures made of skin and cartilage. It receives sound waves and directs them to the ear tube.

- External /auditory meatus- That is a canal lined with hair and wax. It allows passage of sound waves to the middle ear. The hairs and wax trap dust particles that enter the ear.

- Tympanic membrane that is a thin flexible sheet-like structure receives sound waves and passes the vibration to the ossicles.

- Middle ear that is composed of:

Tiny bones known as ossicle. They are stapes, anvil and incus. They amplify vibration from the tympanic membrane.

- Eustachian tube that connects the ear to the nasal cavity. It balances pressure on both sides of the tympanic membrane.

- Oral window that is a thin flexible membrane that opens into the inner ear. it receives vibrations from the ossicles and passes them to the inner ear.

Inner ear that is composed of:

- Vestibular apparatus that are the semi circular canals, utricles and the saccules. They help in maintenance of body balance and posture.

- Cochlea that is a coiled structure that has sensory cells for hearing. It is connected to the auditory nerve that is involved in transmission of sounds to the brain.

17. (a)Nocturnal animals such as the owl are capable of seeing fairly well at night

Presence of rods having rhodopsin pigment that is sensitive to dim light.

(b)What two retinal adaptations have made this possible? ( 2 marks)

- Rods are more sensitive to motion and easily notes movement from the cornea of the eye.

- More than 120 million rods present on the retina.

18. State two functions of the human ear? ( 2 marks)

Perceive sound waves.

Maintain body balance and posture.

19. State four differences between co- ordination of the human eye’s internal response to light and that of tropic movement of the flowering plant in response to light. ( 4 marks)

20. The figure below shows a stem of a plant growing round a tree trunk

(i) What is the name of the response, which causes the twisted growth?

( 1 mark)


(ii) Explain how the twisting process is accomplished ( 2 marks)

Auxins on the stem are sensitive to touch. They migrate to opposite side.

Growth is more on the touched side. This causes bending.

(iii) Identify the state of leaves if the plant is autotrophic ( 2 marks)

Have more chlorophyll to trap sunlight

- Have stomata for entry of carbon dioxide.

- Thin and transparent cuticle to allow entry of light into the photosynthetic cells

- Presence of veins for transportation of raw materials to the leaf or food for the leaf.

21. Euglena is positively phototactic. Of what biological significance is this characteristics? ( 1 mark)

Euglena have chlorophyll and are autotropic. They move towards light source (positive phototactic) to absorb sunlight for photosynthesis.

22. State the function of acetylcholine ( 2 marks)

Acetylcholine is a chemical substance present at the synaptic knob. When a nerve impulse reaches the synapsis, acetylcholine forms in vesicles moving to the membrane.

23. Where in the human body is the relay neurone located? ( 1 mark)

In the spinal chord.

24. State three effects of nicotine to human health ( 3 marks)

- Tar is deposited on parts of the respiratory tract causing cancer.

- Hardening the blood vessels and can cause heart attack.

- Irritation of the respiratory tract resulting to frequent coughing.

- Smoke can cause air pollution.

25. state the part of the eye involved in

(i) Colour vision

Cones on retina.

(ii) Maintaining shape of the eyeball

Vitreous humour.

(iii) Change in diameter of the lens

Suspensory ligaments.