(a) What is a sense organ? (b) List four sense organs found in mammals. (c) Describe the processes that will cause a person who has been spinning to feel di...

Answer Details

(a) A sense organ is a specialised organ or structure that contains receptor cells sensitive to a particular kind of stimulus (such as light, sound, chemicals, heat or touch) and which converts the stimulus into nerve impulses sent to the brain for interpretation.

(b) Four sense organs found in mammals

• Eye (sight)
• Ear (hearing and balance)
• Nose (smell)
• Tongue (taste)
• Skin (touch, temperature, pain)

(c) Why a person who has been spinning feels dizzy

Balance is detected by the semicircular canals of the inner ear, which are filled with fluid (endolymph) and contain sensory receptors. When the person spins, the fluid in the canals is set in motion and stimulates the receptors, which send impulses to the brain telling it that the body is turning. When the person suddenly stops, the fluid keeps moving (by inertia) for a short while and continues to stimulate the receptors. The brain therefore still receives messages that the body is turning even though the eyes report that the body is now still. This conflict of information between the ear and the eyes confuses the brain, and the person feels giddy or dizzy and loses balance until the fluid comes to rest.

(d) Two functions each

(i) Cerebellum

• Controls and coordinates voluntary muscular movements so that they are smooth and accurate.
• Maintains balance and posture of the body.

(ii) Cerebrum

• Centre of intelligence, memory, reasoning, thought and will.
• Controls voluntary actions and interprets sensations (sight, hearing, smell, touch).

(iii) Medulla oblongata

• Controls involuntary vital activities such as heartbeat and breathing rate.
• Controls reflex actions such as coughing, sneezing, swallowing and vomiting, and regulates blood pressure.