Nutrition in Plants and Animals
What this domain tests
Plant nutrition centres on photosynthesis, limiting factors and mineral requirements; animal nutrition covers diet, dentition, digestion and absorption. You must be able to interpret food tests and explain how the gut is adapted for absorption.
Core rules
- Photosynthesis: carbon dioxide + water → glucose + oxygen, in chloroplasts, using light energy trapped by chlorophyll.
- Limiting factors (light, CO₂, temperature) control the rate; raising a non-limiting factor changes nothing.
- Nitrate ions supply nitrogen for amino acids; magnesium is needed for chlorophyll.
- Enzymes work at specific sites: amylase (mouth, pancreas, small intestine), protease (stomach, pancreas), lipase (pancreas, small intestine).
- Bile, made in the liver and stored in the gall bladder, emulsifies fat but is not an enzyme.
Worked example
A variegated leaf has a white edge. After a sunny day the leaf is destarched, partly covered, and tested with iodine. Only the green areas turn blue-black. Reasoning: iodine detects starch; starch is made only where chlorophyll absorbs light, so the white edge has no starch even though light reaches it.
Traps that cost marks
- Using iodine to test for reducing sugar - that is Benedict's, and it needs heating in a water bath.
- Forgetting to destarch the leaf first, so old starch gives a false positive.
- Saying bile digests fat.
- Writing “vitamin C is a mineral” - it is a water-soluble vitamin.