(a) Describe an experiment to show that green plants require sunlight for photosynthesis. (Details of test for starch not required)
(b) What other conditions are necessary for photosynthesis?
(c) Name the part of a dicotyledonous leaf where most food is manufactured, giving reasons.
(d) What happens to the manufactured food?
Explanation
(a) Experiment to show that green plants require sunlight for photosynthesis;
(i) Take two potted plants and get them well watered
(ii) De-starch the leaves by keeping plants in a dark cupboard ‘at least for 24 hours/overnight
(iii) Then test leaf samples of both plants for starch
(iv) The result is negative/yellowish-brown colour which shows absence of starch
(v) Leave one potted plant in the dark cupboard as a control and put the other plant in sunlight for 4-6 hours
(vi) Re-test leaves from both plants for starch. You will discover that
(vii) leaves from plant exposed to sunlight show presence of starch, while those from the control plant/kept in dark cupboard shows absence of starch
(viii) This indicates that sunlight is necessary for photosynthesis.
(b) Other conditions necessary for photosynthesis include the following:
(i) Presence of water
(ii) carbon dioxide
(iii) chlorophyll/chloroplast
(vi) suitable temperature
(c) Site or part of dicotyledonous leaf where photosynthesis occurs is the palisade layer; because it contains more chloroplasts/chlorophyll; than the spongy layer/other parts. Palisade cells are located just beneath the upper epidermis; where the chlorophyll could absorb more sunlight
(d) Fate of food manufactured by green plants:
(i) Manufactured food/glucose; is trans-located to various parts of the plant through the phloem
(ii) This can be combined with other elements such as nitrogen and sulphur to form proteins; for growth. It can also be converted to starch and stored. It is needed/used in respiration/metabolic activities. It is broken down into carbon dioxide and water to produce energy. Other products like lipids and cellulose can also be manufactured from glucose.