Theory question 106
Nutrient Cycling(a) Explain briefly the importance of the following factor and organisms in the nitrogen cycle: (i) lightning; (ii) Nitrosomonas; (iii) Azotobacter. (b) Name the excretory organ in: (i) insects; (ii) earthworm. (c) Explain briefly the following diseases: (i) hepatitis; (ii) kidney stones. (d)(i) State three effects of lack of sense receptors in the skin of humans. (ii) List three layers of the epidermis in the skin of humans. (e)(i) What is metamorphosis? (ii) State the type of metamorphosis exhibited by each of the following insects listed in the table below.
Insect | Type of metamorphosis
Grasshopper |
Cockroach |
Butterfly |
Mosquito |
Housefly |
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(a)(i) Lightning: its energy makes nitrogen and oxygen in the air combine into oxides of nitrogen, which dissolve in rain and reach the soil as nitrates.
(ii) Nitrosomonas: a nitrifying bacterium that changes ammonium compounds into nitrites.
(iii) Azotobacter: a free-living nitrogen-fixing bacterium in the soil that turns atmospheric nitrogen into nitrogen compounds.
(b)(i) Insects: Malpighian tubules. (ii) Earthworm: nephridia.
(c)(i) Hepatitis: inflammation of the liver, usually caused by a virus (hepatitis A, B, C), spread through contaminated food/water or blood and body fluids; signs include jaundice, fever, tiredness; can lead to liver damage.
(ii) Kidney stones: hard deposits of salts (e.g. calcium oxalate) that form in the kidney; they can block urine flow and cause severe pain and blood in urine; linked to low water intake.
(d)(i) Any three: inability to feel pain, so injuries go unnoticed; cannot feel heat, so burns may result; cannot sense touch or pressure; cannot sense cold, so body may not respond to cold; increased risk of injury and infection.
(ii) Any three: cornified layer (stratum corneum); granular layer; Malpighian (germinative) layer.
(e)(i) Metamorphosis is the series of changes in form that an insect goes through from egg to adult.
(ii) Grasshopper: incomplete. Cockroach: incomplete. Butterfly: complete. Mosquito: complete. Housefly: complete.
Section C (candidates in Nigeria only). Incomplete metamorphosis has a nymph stage; complete metamorphosis has larva and pupa.