Theory question 102
Photosynthesis and Plant Nutrition(a) Explain how the leaf of a flowering plant is adapted for photosynthesis. (b) Describe briefly the mode of feeding in tapeworms. (c) Name one mineral element each needed for the proper functioning of (i) bones; (ii) red blood cells; (iii) thyroid gland. (d)(i) State three benefits of including roughage in the diet of humans. (ii) State three reasons why proteins are important to humans.
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(a) Broad, flat lamina gives a large surface to trap light.
Thin lamina lets light and gases reach all cells quickly.
Palisade cells packed with chloroplasts lie just under the upper epidermis, at right angles to it.
Spongy mesophyll has large air spaces for gaseous exchange.
Many stomata (controlled by guard cells) let CO2 in and O2 out.
Transparent epidermis lets light through.
Network of veins: xylem brings water, phloem carries away sugar.
Leaf arrangement (mosaic) reduces shading.
(b) The tapeworm is a parasite in the host's intestine. It has no mouth or gut. It holds on with hooks and suckers on the scolex and absorbs already digested food through its whole body surface; its body is protected from the host's enzymes by a thick cuticle and anti-enzymes.
(c)(i) Calcium (or phosphorus). (ii) Iron. (iii) Iodine.
(d)(i) Any three: adds bulk to food; helps peristalsis; prevents constipation; helps remove waste; may reduce risk of bowel disease.
(ii) Any three: growth; repair of worn-out tissues; making enzymes and hormones; making antibodies; source of energy when carbohydrate and fat run short; forming haemoglobin.
Link each leaf feature to the job it does in photosynthesis.