Lessons 30–31 · 2 lessons · A. Zikiryayev, A. To‘xtayev, I. Azimov, N. Sonin. Biology. Basics of Cytology and Genetics, Grade 9, revised and expanded 5th edition. “Yangiyul Poligraph Service”, Tashkent, 2019
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Metabolism
Textbook: pp. 77–78
GoalExplain the essence and interdependence of metabolism, plastic and energy exchange (anabolism and catabolism).
The sum of all chemical reactions in the cell and organism is called metabolism. It consists of two opposite but interconnected processes: assimilation (anabolism, plastic metabolism) and dissimilation (catabolism, energy metabolism). In plastic metabolism complex substances are synthesised from simple ones (protein from amino acids, polysaccharide from monosaccharides, nucleic acid from nucleotides); these reactions proceed with absorption of energy and, under the control of enzymes and the information in DNA, produce substances specific to each species. In energy metabolism substances are broken down (starch to glucose, proteins to amino acids, fats to glycerol and fatty acids, then to still simpler substances) and energy is released. The two processes depend on each other: breakdown supplies the energy for synthesis, while synthesis supplies the enzymes and raw material for breakdown. The cell is an open system: it exchanges matter and energy with its surroundings.
Worked examples
A muscle cell makes muscle proteins from amino acids (anabolism) using ATP; the ATP is formed when glucose is broken down (catabolism).
In a growing young organism anabolism predominates; in an old organism catabolism is often relatively stronger.
Class activity
“Build and break”. Groups put the cards (protein synthesis, digestion of starch, photosynthesis, respiration, DNA doubling, fat breakdown) in the anabolism or catabolism column and mark energy absorbed or released.
Practice
1
What is metabolism? Name its two sides.
The sum of all chemical reactions in the cell and organism; plastic (anabolism) and energy (catabolism) metabolism.
2
Classify as anabolism or catabolism: a) protein synthesis, b) breakdown of glucose, c) photosynthesis.
a) anabolism; b) catabolism; c) anabolism.
3
Why is the cell called an “open system”?
Because the cell takes in matter and energy from the environment and releases them to the outside.
4
Why does a growing child need both protein-rich food and enough energy?
Making protein (anabolism) needs both amino acids and ATP energy; the ATP comes from breaking down food.