Human Biology: Nutrition, Transport, Coordination and Health
Nutrition and Digestion
A balanced diet supplies carbohydrates (energy), proteins (growth and repair), fats (energy and insulation), vitamins, minerals, fibre (prevents constipation) and water. Digestion breaks large insoluble molecules into small soluble ones: starch to glucose by amylase, protein to amino acids by protease, fat to fatty acids and glycerol by lipase. Villi in the small intestine increase surface area for absorption; bile emulsifies fats and neutralises stomach acid.
Transport
Blood carries oxygen, nutrients, carbon dioxide, hormones and heat. Red blood cells contain haemoglobin, which binds oxygen in the lungs and releases it in tissues. The heart has four chambers; the left ventricle has the thickest wall because it pumps blood around the whole body. Arteries carry blood away from the heart at high pressure; veins return it with valves; capillaries are one cell thick for exchange.
Coordination and Health
Nervous control is fast and electrical along neurones, with synapses between them; reflexes protect the body without conscious thought. Hormones such as insulin (lowers blood glucose) act more slowly through the blood. Health risks include smoking (lung cancer, heart disease), excess alcohol (liver damage), obesity and lack of exercise.
Traps to Watch
- Reversing artery and vein definitions.
- Saying the right side of the heart pumps to the body.
- Forgetting that enzymes are specific to their substrate.
Worked Example
If a person's blood glucose rises after a meal, insulin is secreted, glucose is taken into cells and stored as glycogen in the liver, and the level falls back to normal.