Observation

This was a compulsory question.

In (a), candidates could not define chemosynthesis while some defined it as the process whereby plants synthesize food, which is wrong and made them lose marks. Examples of organisms that carry out chemosynthesis were wrongly spelt. Some candidates also just limited themselves to bacteria instead of organisms.

In (b), this was a very well treated question but some candidates that wrote noble gases as a gas in the atmosphere could not mention the percentage composition. Some candidates even wrote hydrogen among the gases.

In (c) (i) the characteristics of a Salt Marsh Habitat were poorly answered. Some candidates wrote high oxygen concentration instead of low oxygen concentration. Candidates could not write flat lowlands; presence of changing water levels; low light penetration.

In (c) (ii), some candidates could hardly state the modifications of salt marsh plants to anchorage, instead were writing the functions of the roots.

In (d) (i), some candidates could list the bacterial diseases associated with poor food hygiene but some could not spell them correctly;

In (d) (ii), the effects of poor food hygiene were stated well.

In (e), the candidates answered this question poorly. Most candidates were writing on the process of blood clot, some even wrote the type of food that should be given to an unconscious accident victim, instead of taking the victim to the hospital.

In (f) most candidates answered this question poorly as they could not correspond their answers. Instead of writing under tillage that it loosens the soil, and under burning that it makes the soil compact, they stated under tillage that increases soil nutrient while under burning it is a good farming method. The points neither correspond nor were factual.

The expected answers are: 

6.  (a) (i) Chemosynthesis    

• The process by which some organisms manufacture their food;
• By converting carbon molecules into organic substances;
• Using the oxidation of inorganic substances/hydrogen sulphide/ammonia/methane;
• As a source of energy without the use of sunlight/solar energy.             

(ii) Examples of organisms that carry out chemosynthesis

• Sulphur bacteria;
• Nitrosomonas;
• Nitrobacter;
• Blue-green algae;
• Nitrococcus.                                                                                             

Note: Spelling must be correct to score.

(b) Percentage composition of gases in the atmosphere
           

S/No.	Gases in the atmosphere	Percentage composition
1.	Oxygen	20.5 - 21.5
2.	Nitrogen	78 -79
3.	Noble gases/Argon	0.9 - 1.0
4.	Carbon dioxide	0.03 - 0.05

Note: Spelling must be correct to score.                                   

    (c)    (i) Characteristics of salt marsh habitat

• Presence of low oxygen levels;
• High salinity;
• Soft muddy environment;
• Presence of changing water levels;
• Flat lowland;
• Swampy/water-logged;
• Low light penetration.                                                                 

(ii) Modification of plants to salt marsh habitat

Plants grow long/have numerous roots; to hold to the substratum; possess stilt roots; for anchorage.     

    (d) (i) Bacterial diseases associated with poor food hygiene

• (Staphylococcal) Food poisoning;
• Dysentery;
• Cholera;
• Hepatitis;
• Typhoid;
• Gastritis;
• Botulism;
• Tuberculosis;
• Any correctly named disease.                                                      

Note: Spelling must be correct to score.

(ii) Effects of bad food hygiene

• May lead to intestinal ulcer;
• May lead to serious food poisoning;
• Sickness/discomfort;
• Frequent stooling/running stomach/diarrhoea;
• Loss in economic value/loss in food value;
• Death.                                                                                          

(e) Restoring blood loss of an accident victim after a car accident

• The victim must first be rushed to the hospital;
• Where the blood sample will be taken;
• For agglutination test;
• To know the blood group;
• Then the compatible blood is transfused to the victim.

(f) Differences between tillage and burning

Tillage	Burning
Loosens the soil	compacts the soil;
Aerates the soil	leads to poor aeration of the soil;
Mixes organic matter with soil/improves soil nutrient	depletes/destroys soil nutrients/leaching;
Enhances the activities of microorganisms	microfauna/soil organisms are killed;
Does not lead to air/soil pollution	leads to air/soil pollution.

Note: Points must correspond to score.