Theory question 102
Photosynthesis and Plant Nutrition(a) What is photosynthesis?
(b) List: (i) four external factors; (ii) two internal factors; that affect the rate of photosynthesis.
(c)(i) List the major products of the light dependent stage of photosynthesis. (ii) State the importance of each of the products listed in 2(c)(i) above.
(d)(i) Explain why there are no green plants at the lower depths of some lakes. (ii) State why decomposers are important to flowering plants.
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(a) Photosynthesis is the process by which green plants make glucose from carbon dioxide and water using light energy trapped by chlorophyll, releasing oxygen.
(b)(i) External (any four): light intensity; carbon dioxide concentration; temperature; water supply; mineral salts (e.g. Mg). (ii) Internal (any two): amount of chlorophyll; number/structure of stomata; enzymes; leaf structure/thickness; accumulation of end products.
(c)(i) ATP; NADPH2 (reduced NADP/hydrogen); oxygen.
(ii) ATP supplies energy for the dark (light-independent) stage; NADPH2 supplies hydrogen to reduce CO2 to carbohydrate; oxygen is released for respiration (by-product).
(d)(i) Light does not reach the deep water, so plants there cannot photosynthesise and cannot survive.
(ii) Decomposers break down dead matter and release mineral salts (e.g. nitrates) into the soil, which plants absorb for growth.
Light-stage products power the dark stage.