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B4 The Processes of Life Bicester Community College Science Department B4 Key Questions How do chemical reactions take place in living things? How do plants make food? How do living organisms obtain energy? Bicester Community College Science Department How do chemical reactions take place in living things? The basic processes of life carried out by all living things depend on chemical reactions within cells. Photosynthesis makes food molecules and energy available to living organisms through food chains Respiration is a series of chemical reactions that release energy by breaking down large food molecules in all living cells. Bicester Community College Science Department How do chemical reactions take place in living things? Enzymes are proteins that speed up chemical reactions. Cells make enzymes according to the instructions carried in genes. Molecules have to be the correct shape to fit into the active site of the enzyme (the lock and key model) Bicester Community College Science Department How do chemical reactions take place in living things? Enzymes need a specific constant temperature to work at their optimum, and permanently stop working (denature) if the temperature is too high. Enzyme activity at different temperatures is a balance between: increased rates of reaction as temperature increases changes to the active site at higher temperatures, including denaturing An enzyme works at its optimum at a specific pH. The effect of pH on enzyme activity is due to changes to the shape of the active site. Bicester Community College Science Department How do plants make food? Bicester Community College Science Department How do plants make food? Bicester Community College Science Department How do plants make food? Light energy is absorbed by the green chemical chlorophyll. This energy is used to bring about the reaction between carbon dioxide and water to produce glucose (a sugar). Oxygen is produced as a waste product. Glucose may be: converted into chemicals needed for growth, for example cellulose, protein and chlorophyll. converted into starch for storage. used in respiration to release energy. Bicester Community College Science Department How do plants make food? The rate of photosynthesis may be limited by: temperature carbon dioxide light intensity Bicester Community College Science Department How do plants make food? Diffusion is the passive overall movement of molecules from a region of their higher concentration to a region of their lower concentration. The movement of oxygen and carbon dioxide in and out of leaves during photosynthesis occurs by diffusion. Bicester Community College Science Department How do plants make food? Active transport is the overall movement of chemicals across a cell membrane from low concentration to high concentration. Active transport requires energy from respiration. Some minerals taken up by plant roots are used to make chemicals needed by cells, including nitrogen from nitrates to make proteins Active transport is used in the absorption of nitrates by plant roots. Bicester Community College Science Department How do plants make food? Osmosis (a specific case of diffusion) is the overall movement of water from a dilute to a more concentrated solution through a partially permeable membrane. The movement of water into plant roots occurs by osmosis. Bicester Community College Science Department How do living organisms obtain energy? All living organisms require energy released by respiration for some chemical reactions in cells, including : movement synthesis of large molecules active transport The synthesis of large molecules includes: polymers required by plant cells such as starch and cellulose synthesis of amino acids from glucose and nitrates, and then proteins from amino acids in plant, animal and microbial cells Bicester Community College Science Department How do living organisms obtain energy? Bicester Community College Science Department How do living organisms obtain energy? Aerobic respiration takes place in animal and plant cells and some microorganisms, and requires oxygen. Bicester Community College Science Department How do living organisms obtain energy? Bicester Community College Science Department How do living organisms obtain energy? Anaerobic respiration takes place in animal, plant and some microbial cells in conditions of low oxygen or absence of oxygen. These conditions include: plant roots in waterlogged soil bacteria in wounds human cells during vigorous exercise glucose → lactic acid (+ energy released) glucose → ethanol + carbon dioxide (+ energy released) The reaction for anaerobic respiration in animal cells and some bacteria is: The reaction for anaerobic respiration in plant cells and some microorganisms (including yeast) is: Aerobic respiration releases more energy per glucose molecule than anaerobic respiration Bicester Community College Science Department How do living organisms obtain energy? The anaerobic respiration of microorganisms can be used by humans in many ways: the production of biogas fermentation in bread making alcohol production Bicester Community College Science Department Common B4 mistakes… make sure you don’t do these! Students often: refer to organisms working best at a particular temperature rather than optimal for enzyme activity think that bile is an enzyme think that muscle cells will produce lactic acid and CO2 in anaerobic respiration may not be able to explain that plant cells become larger by absorbing water. confuse chlorophyll with chloroplast may not understand the limiting factors in photosynthesis may not realise that photosynthesis is a chemical reaction (and cannot specify which are the reactants and which are the products) think that enzymes are a living thing (e.g. a bacterium) even though they know that they are biological catalysts may not realise that respiration occurs all the time in plants with photosynthesis only in the light may confuse cytoplasm with chloroplast or membrane may not realise that cellulose is made by plants from glucose. Bicester Community College Science Department Links from B4 to other topics B1 - genes, proteins, and enzymes B3 - the uptake of nitrates by plants B3 - photosynthesis and food chains B3. - biodiversity B5 - cells, tissues, and organs B7 - growth of microbes to produce antibiotics, medicines, single-cell protein and enzymes Bicester Community College Science Department
