Metabolism: building up and breaking down
Metabolism is the sum of all the chemical reactions in a living thing. It has two sides. Anabolism builds big molecules from small ones and uses energy: examples are making proteins from amino acids, photosynthesis, and healing a wound. Catabolism breaks big molecules down and releases energy: examples are breaking down glucose in cellular respiration and digesting fats. Photosynthesis is anabolic and cellular respiration is catabolic. Why does breaking down glucose give out energy overall? Breaking bonds needs energy and forming new bonds releases energy. When glucose is broken down, more energy is released in forming the new bonds in carbon dioxide and water than is used in breaking the old bonds, so the extra is available to the cell. Questions about metabolism and special diets belong to a doctor; we only learn the idea here.
| Anabolism | Catabolism | |
|---|---|---|
| energy | used | released |
| molecules | small → big | big → small |
| examples | photosynthesis, healing | respiration, digesting fats |
Sort the processes. Write six processes on cards: photosynthesis, digesting a meal, a cut healing, glucose broken down in a muscle, building a protein from amino acids, a plant growing a new leaf. Sort them into anabolic and catabolic. Give a one-sentence reason for each. Then draw a simple loop showing how photosynthesis and respiration are linked through glucose, oxygen and carbon dioxide.