Theory question 108
Photosynthesis and Plant Nutrition(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 8(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.
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(a)(i) Autotrophic: the organism makes its own organic food from simple inorganic substances (carbon(IV) oxide and water) using light energy trapped by chlorophyll (photosynthesis).
(ii) Chemosynthetic: the organism makes its own food using energy from oxidising inorganic chemicals (e.g. ammonia, nitrites, iron or sulphur compounds) instead of light.
(iii) Carnivorous: green plants that photosynthesise but also trap and digest insects to obtain nitrogen, usually because they grow in nitrogen-poor soil.
(b) Autotrophic – any green plant, e.g. maize, hibiscus; chemosynthetic – nitrifying bacteria such as Nitrosomonas or Nitrobacter (sulphur bacteria); carnivorous – sundew (Drosera), pitcher plant (Nepenthes), bladderwort (Utricularia), Venus flytrap.
(c)(i) Any three: Rhizobium in root nodules of legumes fixes atmospheric nitrogen; free-living bacteria (Azotobacter, Clostridium) and blue-green algae fix nitrogen; lightning makes nitrogen oxides that dissolve in rain to form nitrates; decay of dead organisms and wastes releases ammonia, which nitrifying bacteria change to nitrates; adding fertilizers and manure.
(ii) Any two: denitrification by bacteria; leaching of nitrates by rain; uptake by crops that are then harvested; soil erosion; burning of vegetation.
Chemosynthesis uses chemical energy, not light.