Question 2
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(a) State four functions of soil water to crops. (4 marks)
(b) Outline five factors that could cause low soil pH. (5 marks)
(c) Explain the life cycle of liver fluke. (9 marks)
Observation
- This question was fairly popular among the candidates but some candidates could not state the function of soil water as it relates to crops but were giving general uses of water.
- Many candidates were able to outline the factors that could cause low soil pH.
- However, majority of candidates shied away from question (2)(c) and could not explain the life cycle of liver fluke in sequential order.
The expected answers include:
2. (a) Functions of soil water to crops
- Cooling of plants through transpiration
- Needed for all metabolic reactions in plants
- Used in photosynthesis
- Needed for germination of seeds
- Helps in transportation of manufactured food
- Dissolves nutrients in the soil for plant use
- Responsible for plant cell turgidity
(b) Factors that could cause low soil pH
- Acid rains in industrial areas
- Use of sulphur-based agro-chemicals/fertilizers
- Leaching
- Erosion
- Acidic parent materials
- Absorption of basic cations from the soil/Preferential nutrient uptake by plants
- Hydrolysis of aluminium
(c) Explanation of life cycle of Liver fluke
- Eggs pass from the uterus of the adult liver fluke into the bile duct of the host
(livestock)
- The eggs move from the bile duct into the intestine
- They are passed out with the faeces of host on to pastures
- Eggs hatch into miracidiae
- The miracidiae penetrate the water snail (secondary host)
- The miracidiae develop into sporocysts in the snail
- By cell division, the sporocysts develop into rediae
- The rediae develop into cercariae
- The cercariae pass out of the water snail, remain in the pasture and become
encysted (metacercaria)
- Encysted cercaria is eaten by livestock (host) along with the pasture
- Metacercaria develops into young liver fluke
- Young liver fluke swims through the intestine into the blood stream to the liver and