(a) Explain the following modes of nutrition which occur in plants:
(i)Autotrophic
(ii) Chemosynthetic
(iii) Carnivorous
(b) Give one example each of a plant which undergoes the modes of nutrition listed in (a) above.
(c) (i) Describe three ways by which nitrogen is added to the soil for plant use.
(ii) State two ways by which nitrogen is lost from the soil.
Explanation
(a) Modes of nutrition in plants: Autotrophic: Plants manufacture their food; using water from the soil; and carbon dioxide from the atmosphere in the presence of sunlight.
Chemosynthetic: These plants manufacture their food; using atmospheric carbon dioxide; and energy from the breakdown of inorganic compounds.
Carnivorous: These plants in addition to photosynthesizing have special devices; for trapping and digesting insects and other small organism; to balance a deficiency in nitrogen.
(b)(i) Autotrophic: Flowering plant
(ii) Chemosynthetic: Nitorsomonas, Nitrobacter, fungi, Nitrococcus.
(iii) carnivorous: Pitcher plants, bladderwort; sundew, venus flytrap, butterwort.
(c)(i) Addition of nitrogen to soil. Decomposition of dead organic matter:
- Dead organic matter, are decomposed by putrifying bacteria; into ammonium compounds
- ammonium compounds are converted to nitrites by nitrifying bacteria, in the soil
- nitrites are converted into nitrates by nitrifying bacteria in the soil.
- Nitrogen fixation in root nodules:
- Nitrogen fixing bacteria; living in the root nodules of leguminous plants
- Convert gaseous nitrogen in the soil/atmosphere/air-spaces; into nitrates.
- During thunder storms; the energy from electrical discharge/action of lightning
- enables atmospheric nitrogen to react with oxygen to form oxides of nitrogen/nitric oxides; which dissolves in rain water to form weak nitric acid; which is washed in the soil and converted into nitrites and nitrates.
(ii) Loss of nitrogen from the soil: -
- Absorption by plant roots.
- Action of denitrifying bacteria.
- By action of leaching.