Observation

 

This was a compulsory question.

In (a), candidates could not state the importance of lightning, Nitrosomonas and Azotobacter in the Nitrogen cycle.
In (b), some candidates could name the excretory organs in insects and earthworm but some carelessly spelt the terms wrongly, making them lose the marks.

In (c) (i), some candidates could explain hepatitis although, some could not state the symptoms of the disease.
In (c) (ii), the salient function of the kidney stones which is the blockage of the nephron was not emphasized but rather symptoms of the blockage was emphasized.
In (d) (i), candidates failed to mention death as the likely final effect of lack of sense receptors in the skin.
In (d) (ii), some candidates could list the layers of the epidermis in the skin of humans but could not spell them well.

In (e), some candidates could define metamorphosis although ‘involving 3 or 4 stages’ was not mentioned.
Some candidates could name the type of metamorphosis exhibited by some of the organisms listed on the table, although some lost marks because they could not spell complete or incomplete correctly.

The expected answers are:

6. (a)Importance of the following in the Nitrogen Cycle
(i) Lightning
ii Nitrosomonas
- Is a nitrifying bacterium in the soil;
- that converts ammonia to nitrites in the soil.
iii Azotobacter
- Is a nitrogen-fixing bacterium in the soil;
- that converts nitrogen in the soil;
- into ammonium compounds/amino compounds and protein in the soil;
- converts nitrites to nitrates in the soil.

(b)Excretory organs
Insects – malpighian tubules;
Earthworm – nephridium
Note: Spellings must be correct to score.

(c) Explanation of diseases
(i)Hepatitis
- Is the inflammation/destruction of liver cells;
- hepatitis can arise from bacteria/virus/an autoimmune disease;
- or from excess consumption of alcohol.
- the symptoms include fatigue;
- loss of appetite/anorexia;
- muscle aches/pains;
- flu;
- fever;
- nausea;
- jaundice;
- and dark coloured urine/stool.
(ii) Kidney stones
- Are small solids/crystals of concentrated minerals/uric acid found in the urine;
- they are formed if there is an excessive loss of water/insufficient water intake;
- so that the solubility of minerals/calcium phosphate/calcium oxalate in the urine is reduced;
- high levels of uric acids/amino acids can lead to kidney stones;
- bacteria may be trapped in the kidney tubules as the kidney stones get bigger;
- symptoms are sharp pain at the flank of back;
- frequent urination;
- nausea;
- sweating;
- kidney stones can be treated by medications;
- change in diet of food rich in calcium;
- surgery;
- drinking plenty of water.

(d) (i) Explanation of diseases
- Humans will not be able to sense/feel/perceive external stimuli in the environment;
- pain;
- touch;
- a change in temperature;
- pressure;
- danger which could lead to death.
(ii)Layers of the epidermis
- cornified layer/stratum corneum;
- granular layer/stratum granulosum;
- malpighian layer/stratum Malpighi.
Note: Spellings must be correct to score.

(d) (ii)Metamorphosis
Is the development of some/certain organisms from the egg; to an adult stage; involving three to four stages.
(ii)Type of metamorphosis of listed insects

Insect	Type of metamorphosis
Grasshopper	Incomplete
Cockroach	Incomplete
Butterfly	Complete
Mosquito	Complete
Housefly	Complete