(a) Process of perceiving smell in humans
- Odorous chemical substances in inhaled air enter the nasal cavity.
- The odour molecules dissolve in the mucus covering the olfactory epithelium in the upper part of the nasal cavity.
- They stimulate the olfactory receptor cells.
- Nerve impulses are generated and transmitted through the olfactory nerve to the cerebrum of the brain.
- The brain interprets the impulses, and the particular smell is perceived.
(b) Adaptive features of the egg of a domestic fowl
- The hard shell protects the embryo from mechanical injury and reduces water loss.
- The shell is porous, allowing gaseous exchange.
- The shell membranes provide additional protection and permit gaseous exchange.
- The yolk is rich in fats and proteins and provides food for the developing embryo.
- The albumen contains water and protein; it nourishes and cushions the embryo against shock.
- The air space provides a reserve of air for respiration, especially near hatching.
- The chalazae hold the yolk and embryo in position.
(c)(i) Autotrophs
Autotrophs are organisms that manufacture their own food from simple inorganic substances, using light energy or chemical energy.
(c)(ii) Two unicellular autotrophs
Chlamydomonas and Euglena.
(d) Five functions of the World Health Organisation (WHO)
- It coordinates international health programmes and sets health standards.
- It promotes the prevention, control and eradication of diseases.
- It assists countries with vaccines, drugs and medical supplies during epidemics and other emergencies.
- It provides health education and public information on disease outbreaks and health matters.
- It supports medical research and the training of health personnel.
(e) Organisms found in a freshwater pond
| Plants | Animals |
|---|
| Water lily | Tilapia fish |
| Spirogyra | Tadpole |
(f) Differences between the skin of a mammal and the epidermis of a leaf
| Skin of a mammal | Epidermis of a leaf |
|---|
| It consists of many layers of cells. | It is usually a single layer of cells. |
| It has sweat glands. | It has no sweat glands. |
| It has sebaceous glands. | It has no sebaceous glands. |
| It has hair follicles and may bear hairs. | It has no hair follicles. |
| It has no stomata with guard cells. | It has stomata surrounded by guard cells. |
(g) Type of competition
(i) Plot A: Intraspecific competition, since maize plants of the same species compete with one another.
(ii) Plot B: Interspecific competition, since maize and pepper are different species competing for resources.
