(a)(1) Explain briefly chemosynthesis as a mode of nutrition.
(ii) Give two examples of organism that carry out chemosynthesis.
(b) List three gases in the atmosphere with their percentage composition.
(c) (i) State four characteristics of a salt marsh habitat.
(ii) Explain briefly how plants are modified for anchorage in a salt marsh habitat.
(d) (i) List four bacterial disease associated with poor food hygiene.
(ii) State three effects of poor food hygiene.
(e) A person was involved in a car accident and became unconscious due to excessive blood loss. Explain briefly how the blood lost could be restored.
(f) State three differences between tillage and bush burning as farming practices.
(a)(i) Chemosynthesis
Chemosynthesis is a mode of nutrition in which certain autotrophic bacteria manufacture their own organic food using energy obtained from the oxidation of inorganic chemical substances, instead of using light energy as in photosynthesis.
(a)(ii) Two examples of chemosynthetic organisms: nitrifying bacteria (Nitrosomonas and Nitrobacter) and sulphur bacteria (Thiobacillus).
(b) Three atmospheric gases and their percentage composition
| Gas in the atmosphere | Percentage composition |
|---|
| Nitrogen | 78% |
| Oxygen | 21% |
| Carbon dioxide | 0.03% |
(c)(i) Four characteristics of a salt marsh habitat
- The water and soil have a high salt content (high salinity).
- The soil is soft, muddy and waterlogged with little oxygen (anaerobic).
- It is periodically flooded and drained by the tides.
- It is exposed to strong winds and wide changes in temperature.
(c)(ii) Modification of plants for anchorage
Salt marsh plants (e.g. mangroves) develop strong, widely spreading and prop / stilt roots that grow into the soft mud. These extensive roots anchor the plant firmly and prevent it from being swept away by the tides.
(d)(i) Four bacterial diseases linked to poor food hygiene: cholera, typhoid fever, bacterial food poisoning (salmonellosis) and bacillary dysentery.
(d)(ii) Three effects of poor food hygiene: contamination of food and food poisoning; spread of communicable diseases; ill-health and possible death, with economic loss.
(e) How lost blood is restored
The blood is restored by blood transfusion: blood of a compatible (matching) group is collected from a healthy donor and introduced into a vein of the accident victim. Intravenous fluids (a drip) may first be given to restore blood volume, and over time the body itself replaces the lost plasma and blood cells.
(f) Three differences between tillage and bush burning
| Tillage | Bush burning |
|---|
| Soil is loosened and turned, improving aeration | Vegetation is destroyed by fire |
| Weeds are buried and rot to form manure (humus) | Adds ash (potash) but destroys humus |
| Soil organisms are conserved | Kills useful soil organisms and exposes soil to erosion |
