a. Explain briefly the importance of the following factors and organisms in the nitrogen cycle
(i) lightning; [3 marks]
(ii) Nitrosomonas; [2 marks]
(iii) Azotobacter. [2 marks]
b. Name the excretory organ in:
(i) insects: [1 mark]
(ii) earthworm.
c. Define
(i) hepatitis; [4 marks]
(ii) kidney stones [4marks]
d. (i) State three effects of lack of sense receptors in the skin to humans. [3 marks]
(ii) List three layers of the epidermis in the skin of humans. [3 marks]
e. (i) What is metamorphosis? [2 marks]
(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 |
|
(a)(i) Lightning: The high electrical energy of lightning supplies enough energy to make atmospheric nitrogen combine directly with oxygen to form oxides of nitrogen (nitric oxide and nitrogen dioxide). These oxides dissolve in rain water to form dilute nitric acid, which reaches the soil and forms nitrates that plants absorb. Lightning therefore fixes free nitrogen into a usable form.
(a)(ii) Nitrosomonas: It is a nitrifying bacterium that oxidises (converts) ammonia or ammonium compounds in the soil to nitrites.
(a)(iii) Azotobacter: It is a free-living, nitrogen-fixing soil bacterium that fixes atmospheric nitrogen into nitrogenous compounds, enriching the soil with usable nitrogen.
(b) Excretory organs:
- (i) Insects: Malpighian tubules.
- (ii) Earthworm: Nephridia.
(c) Definitions:
- (i) Hepatitis is the inflammation of the liver, usually caused by a viral infection, which damages liver cells and may lead to jaundice.
- (ii) Kidney stones are hard, solid crystalline deposits of mineral salts (such as calcium oxalate and urates) that form inside the kidney from substances concentrated in the urine.
(d)(i) Three effects of lack of sense receptors in the skin:
- Inability to feel pain, so injuries occur without the person being aware.
- Inability to detect temperature changes, leading to burns or excessive cold exposure.
- Inability to detect touch and pressure, so harmful contact is not sensed.
(d)(ii) Three layers of the epidermis of human skin: the cornified (horny) layer, the granular layer, and the Malpighian (germinative) layer.
(e)(i) Metamorphosis is the series of distinct changes in body form and structure that an insect undergoes during its development from the egg to the adult stage.
(e)(ii) Type of metamorphosis in each insect:
| Insect | Type of metamorphosis |
|---|
| Grasshopper | Incomplete metamorphosis |
| Cockroach | Incomplete metamorphosis |
| Butterfly | Complete metamorphosis |
| Mosquito | Complete metamorphosis |
| Housefly | Complete metamorphosis |
(a)(i) Lightning: The high electrical energy of lightning supplies enough energy to make atmospheric nitrogen combine directly with oxygen to form oxides of nitrogen (nitric oxide and nitrogen dioxide). These oxides dissolve in rain water to form dilute nitric acid, which reaches the soil and forms nitrates that plants absorb. Lightning therefore fixes free nitrogen into a usable form.
(a)(ii) Nitrosomonas: It is a nitrifying bacterium that oxidises (converts) ammonia or ammonium compounds in the soil to nitrites.
(a)(iii) Azotobacter: It is a free-living, nitrogen-fixing soil bacterium that fixes atmospheric nitrogen into nitrogenous compounds, enriching the soil with usable nitrogen.
(b) Excretory organs:
- (i) Insects: Malpighian tubules.
- (ii) Earthworm: Nephridia.
(c) Definitions:
- (i) Hepatitis is the inflammation of the liver, usually caused by a viral infection, which damages liver cells and may lead to jaundice.
- (ii) Kidney stones are hard, solid crystalline deposits of mineral salts (such as calcium oxalate and urates) that form inside the kidney from substances concentrated in the urine.
(d)(i) Three effects of lack of sense receptors in the skin:
- Inability to feel pain, so injuries occur without the person being aware.
- Inability to detect temperature changes, leading to burns or excessive cold exposure.
- Inability to detect touch and pressure, so harmful contact is not sensed.
(d)(ii) Three layers of the epidermis of human skin: the cornified (horny) layer, the granular layer, and the Malpighian (germinative) layer.
(e)(i) Metamorphosis is the series of distinct changes in body form and structure that an insect undergoes during its development from the egg to the adult stage.
(e)(ii) Type of metamorphosis in each insect:
| Insect | Type of metamorphosis |
|---|
| Grasshopper | Incomplete metamorphosis |
| Cockroach | Incomplete metamorphosis |
| Butterfly | Complete metamorphosis |
| Mosquito | Complete metamorphosis |
| Housefly | Complete metamorphosis |
