Theory question 106
Homeostasis(a) Explain briefly the process of perceiving smell in humans. (b) State the adaptive features of the egg of a domestic fowl. (c)(i) What are autotrophs? (ii) Name two unicellular organisms that are autotrophs. (d) State five functions of the World Health Organization. (e) Name two examples each of plants and animals that live in a freshwater pond. (i) Plants (ii) Animals (f) State five differences between the skin of a mammal and the epidermis of a leaf. (g) A farmer has two plots of land; plots A and B. On plot A, the farmer planted several seeds of maize. On plot B, the farmer planted several seeds of maize and pepper in a small area. What type of competition would be observed on: (i) plot A; (ii) plot B?
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(a) Chemicals (odours) in the air enter the nasal cavity and dissolve in the moist mucus lining it; they stimulate the olfactory (smell) receptor cells; impulses pass along the olfactory nerve to the olfactory lobe/cerebrum of the brain, which interprets the smell.
(b) Any: hard calcium carbonate shell protects the embryo; shell is porous for gaseous exchange; shell membranes keep out germs and reduce water loss; albumen (egg white) supplies water and protein and cushions the embryo; yolk is a store of food; chalazae hold the yolk in place so the embryo stays on top; air space provides oxygen at hatching.
(c)(i) Autotrophs are organisms that make their own food from simple inorganic substances using energy from light (or chemical reactions).
(ii) Any two: Chlamydomonas; Euglena; diatoms; Chlorella; photosynthetic bacteria.
(d) Any five: fights the spread of diseases worldwide (e.g. immunisation campaigns); sets health standards; gives health advice and education; supports research into diseases and drugs; helps countries in health emergencies and epidemics; collects and shares health statistics; helps train health workers; improves nutrition, sanitation and water supply.
(e)(i) Plants, any two: water lettuce (Pistia), water lily, Spirogyra, duckweed, water hyacinth, algae.
(ii) Animals, any two: tilapia, tadpole/frog, water snail, mosquito larva, water boatman, Hydra.
(f) Any five: skin is many cells thick / leaf epidermis is usually one cell thick; skin has hairs, sweat glands and sebaceous glands / epidermis has none (may have simple hairs); skin has sense receptors and nerves / epidermis has none; skin has blood vessels / epidermis has none; skin cells have no cell walls / epidermal cells have cellulose walls; skin has a dead keratinised outer layer / epidermis is covered by a waxy cuticle; epidermis has stomata with guard cells / skin has pores of sweat glands; skin helps control body temperature / epidermis does not; skin has pigment (melanin) / epidermis is mostly colourless.
(g)(i) Plot A: intraspecific competition (between members of the same species, maize and maize).
(ii) Plot B: interspecific competition (between different species, maize and pepper) as well as intraspecific.
Section C (candidates in Nigeria only). Read each part carefully and give only the number of points asked.