Nutrition in Plants and Animals
What this domain tests
Nutrition in Plants and Animals covers photosynthesis, leaf structure, mineral nutrition, human dentition, digestion, absorption and food tests. Expect questions on limiting factors, enzyme action and diet-related disease.
Core rules
- Photosynthesis: carbon dioxide + water → glucose + oxygen, using light energy trapped by chlorophyll. Chlorophyll is not a reactant.
- Limiting factors include light intensity, carbon dioxide concentration and temperature. Increasing a non-limiting factor does not raise the rate.
- Leaves have a waxy cuticle, upper epidermis, palisade mesophyll, spongy mesophyll, veins and stomata guarded by guard cells.
- Nitrates make amino acids and proteins; magnesium is needed for chlorophyll; phosphates for DNA and membranes; potassium for enzyme action.
- Digestion breaks large insoluble molecules into small soluble ones: amylase converts starch to maltose; protease converts proteins to amino acids; lipase converts fats to fatty acids and glycerol. Bile emulsifies fats but is not an enzyme.
- Absorption occurs in the ileum through villi; surface area is increased by microvilli, rich blood supply and a thin epithelium.
Worked example
Pondweed is placed in water at different light distances. Bubbles per minute: 10 cm = 32, 20 cm = 18, 30 cm = 9. As distance increases, light intensity falls, so photosynthesis slows. The trend is inverse and roughly proportional to light intensity, but at very close distances another factor such as carbon dioxide may become limiting.
Traps
Do not write that plants respire only at night; they respire continuously. In food tests, Benedict's detects reducing sugars (brick-red), iodine detects starch (blue-black), Biuret detects protein (purple), ethanol emulsion detects fat (white emulsion). Deficiency diseases: vitamin C-scurvy; vitamin D-rickets; iron-anaemia; calcium-weak bones and teeth.