(a) List four functions of soil water to crops. (b) Enumerate five factors that could cause low soil pH. (c) Briefly discuss the life cycle of Liver Fluke.

Answer Details

(a) Four functions of soil water to crops

• It acts as a solvent, dissolving mineral nutrients in the soil so that plant roots can absorb them.
• It is the medium by which dissolved nutrients are transported into and within the plant.
• It supplies the water needed as a raw material for photosynthesis.
• It maintains the turgidity of plant cells, keeping the plant firm and erect; it also helps to regulate soil and plant temperature and is needed for seed germination.

(b) Five factors that could cause low soil pH (acidity)

• Leaching of basic cations (calcium, magnesium, potassium) by heavy rainfall.
• Continuous use of acid-forming fertilizers such as ammonium sulphate.
• Decomposition of organic matter which releases organic acids.
• Acidic parent material from which the soil is formed.
• Accumulation of acidic ions such as hydrogen, aluminium and iron; acid rain and continuous cropping that removes bases also contribute.

(c) Life cycle of the liver fluke (Fasciola)

1. The adult fluke lives in the bile ducts of the liver of a ruminant (sheep or cattle) and lays eggs.
2. The eggs pass out with the animal's faeces onto pasture.
3. In moist conditions or water, each egg hatches into a ciliated larva called a miracidium.
4. The miracidium enters the intermediate host, a mud snail (Lymnaea).
5. Inside the snail it develops in stages: sporocyst, then redia, then cercaria.
6. The cercariae leave the snail, swim and encyst on grass or vegetation as metacercariae.
7. A grazing animal swallows the metacercariae with the herbage.
8. The young flukes bore through the gut wall, migrate to the liver and bile ducts, mature into adults, and the cycle begins again.