An agricultural research facility used a closed-loop liquid hydroponic system to investigate the effects of specific mineral deficiencies on the growth of lettuce seedlings (Lactuca sativa).
One group of lettuce seedlings was grown in a complete control solution containing all essential mineral ions. A second group of seedlings was grown in a modified solution containing all essential mineral ions except nitrogen (supplied as nitrates).
In this hydroponic system, a pump continuously aerates the nutrient solution. Explain why a constant supply of oxygen is essential for the active uptake of mineral ions by root hair cells.
The nutrient reservoirs are constructed from thick, opaque black plastic. Suggest why it is important to prevent light from entering the nutrient reservoirs.
Nitrogen is an essential element for plant growth. State the name of the major green pigment in plants that contains nitrogen, and describe the physical appearance of the leaves of the lettuce plants grown in the nitrogen-deficient solution.
Apart from parameters related to the nutrient solution itself, suggest two abiotic factors that must be kept constant across both seedling groups to ensure a valid comparison.
Explain how the leaching of highly soluble nitrate-containing fertilisers from agricultural soils into a nearby slow-flowing river can lead to the death of fish and other aquatic organisms.
