(a) Name three main parts of the human brain (b) State the functions of the following: (i) Cerebrum (ii) Hypothalamus (iii) Medulla Oblongata. (c)(i) List t...

(a) Three main parts of the human brain are:

1. Forebrain (cerebrum)
2. Midbrain
3. Hindbrain, which includes the cerebellum and medulla oblongata

(b) Functions of parts of the brain

(i) Cerebrum

• It is the seat of consciousness and sensory perception.
• It controls voluntary actions of the body.
• It is responsible for intelligence, memory, reasoning, learning, judgement and imagination.
• It receives, interprets and stores information from the sense organs.

(ii) Hypothalamus

• It regulates body temperature.
• It regulates water balance and osmoregulation.
• It controls hunger, appetite, thirst and feeding.
• It controls sleep and wakefulness.
• It controls the pituitary gland.
• It is associated with emotions such as anger and aggression.

(iii) Medulla oblongata

• It controls involuntary activities such as breathing and heartbeat.
• It controls the diameter of blood vessels and blood pressure.
• It controls swallowing, coughing, sneezing, yawning and vomiting.
• It helps control digestive activities, including peristalsis and salivation.

(c)(i) Three organs of a higher plant that can respond to stimuli are:

• Root
• Stem
• Leaf

Other examples include flowers and tendrils.

(c)(ii) Tactic movement

Tactic movement, or taxis, is the directional movement of the whole body of a free-living organism from one place to another in response to an external stimulus. The movement may be positive, towards the stimulus, or negative, away from the stimulus.

(d) Explanation of terms with examples

(i) Phototaxis

Phototaxis is the directional movement of a whole organism in response to light. Example: Euglena moves towards light; this is positive phototaxis.

(ii) Hydrotaxis

Hydrotaxis is the directional movement of a whole organism in response to water or moisture. Example: A woodlouse moves towards a region of high humidity.

(iii) Chemotaxis

Chemotaxis is the directional movement of a whole organism in response to a chemical substance. Example: Antherozoids of moss or fern swim towards chemicals secreted by the archegonium.