GCSE Biology · AQA 8461 · Topic 4.2.2
Animal tissues, organs and organ systems
Key points
- Enzymes are biological catalysts with an active site that fits one substrate (lock and key). High temperature or the wrong pH denatures them.
- Carbohydrases (e.g. amylase) make sugars, proteases make amino acids, lipases make fatty acids and glycerol. Bile from the liver neutralises stomach acid and emulsifies fats.
- Food tests: Benedict's (sugars, blue → brick red when heated), iodine (starch, blue-black), biuret (protein, purple), ethanol (lipids, cloudy white).
- The heart is a double pump. Arteries have thick walls for high pressure, veins have valves, capillaries are one cell thick. The natural pacemaker is in the right atrium.
- Blood: red blood cells carry oxygen (haemoglobin, no nucleus), white blood cells fight disease, platelets help clotting, plasma carries everything.
- Coronary heart disease: fatty deposits narrow coronary arteries; treat with stents, statins or transplants. Faulty valves can be replaced.
- Health depends on many factors. Risk factors (smoking, obesity, alcohol) raise the chance of diseases such as cancer; benign tumours stay in one place, malignant ones spread.
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The human body depends on several organ systems working together: the digestive system supplies small molecules, the circulatory system carries them, and the lungs exchange gases. This sub-topic also covers how these systems go wrong in…
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