A plant infected with Rhizobium:
1. has necrotic tissues.
2. dies.
3. gets flaccid.
4. probably will grow faster.

Identify the correct statement regarding biological nitrogen fixation:
1. The plant contributes the nitrogenase enzyme.
2. The process does not require much energy.
3. Leghemoglobin keeps ${\mathrm{O}}_2$ concentration low within the nodule.
4. The bacteria of the nodule are autotrophic.

Leghemoglobin in a root nodule:
1. regulates the supply of oxygen to Rhizobium.
2. promotes ion uptake by root hairs.
3. retards the activity of nitrogenase.
4. supplies the legume with fixed nitrogen.

Rhizobacteria do not:
1. produce hormones that stimulate plant growth
2. absorb toxic metals
3. carry out nitrogen fixation
4. supply growing roots with glucose

Identify the correct statement regarding the primary difference between endomycorrhizae andectomycorrhizae?
1. The former have thicker, shorter hyphae than ectomycorrhizae.
2. The former, but not the latter, form a dense sheath over the surface of the root.
3. The latter do not penetrate root cells, whereas the former grow into invaginations of the root cell membranes.
4. The former is a symbiont while the latter is not.

With respect to symbiotic relationships of plants, consider the following two statements:
I. Plants acquire most of their nitrogen in the form of N₂ that they obtain from rhizobacteria.
II. The fungal hyphae of both ectomycorrhizae and arbuscular mycorrhizae absorb water and minerals, which they supply to their plant hosts.

Protein malnutrition is a serious problem in developing countries. If the essential amino acids in crop plants for human consumption can be increased, it can help to overcome this problem. The best method to produce such crop plants is by:
1. breeding for higher yield of deficient amino acids.
2. increasing the amount of NPK fertilizer used on fields.
3. creating mutants that do not form symbiotic relationship with microbes.
4. transferring nitrogen fixing genes to plants through genetic engineering.

Nitrogen is unique amongst the essential mineral nutrients needed by the plant as it:
1. can be lost from the soil.
2. requires the action of bacteria to be made available to plants.
3. is part of nucleic acids.
4. is absorbed by the leaves through stomata.

The importance of nitrogen fixation can be judged by the fact that:
1. it can only be done by certain prokaryotes.
2. it is most often the limiting factor in plant growth.
3. it is very expensive in terms of metabolic energy.
4. its availability replaces requirement of some other essential nutrients.

Nitrogen fixation means:
1. releasing nitrogen from dead and decaying materials.
2. conversion of nitrite to nitrate.
3. conversion of nitrate to nitrite.
4. conversion of nitrogen gas into ammonia.