Photosynthesis and respiration are two essential processes that keep life...
Biology185 views·Updated Jun 28, 2026·2 pagesComplete Guide to Bioenergetics - AQA GCSE Biology Topic 4
O
oliviaa2008@oliviaa2008
1
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Photosynthesis: How Plants Make Food
Ever wondered how plants create their own food using just sunlight, water, and carbon dioxide? Photosynthesis is an endothermic reaction that happens in the chloroplasts of plant cells. The green pigment chlorophyll acts like a solar panel, trapping light energy and converting it into chemical energy.
The equation for photosynthesis shows exactly what's happening: carbon dioxide + water → glucose + oxygen . Plants use the glucose they make in brilliant ways - for respiration to release energy, converting it to starch for storage, making cellulose to strengthen cell walls, and producing amino acids for proteins.
Limiting factors control how fast photosynthesis happens. Temperature, light intensity, carbon dioxide concentration, and chlorophyll concentration can all slow things down when they're in short supply. The inverse square law explains why moving a plant twice as far from a light source reduces light intensity by a quarter.
Top Tip: In exam questions about limiting factors, look for which one is preventing the rate from increasing further - that's your limiting factor!
Commercial greenhouses cleverly manipulate these limiting factors to maximise plant growth and profits.
2
of 2
Cellular Respiration: Releasing Energy for Life
Your cells are constantly working to release energy from food through cellular respiration - an exothermic reaction that happens in the mitochondria. Unlike photosynthesis, this process releases energy and occurs in all living things, not just plants.
Aerobic respiration uses oxygen to completely break down glucose: glucose + oxygen → carbon dioxide + water . When oxygen runs short during intense exercise, your muscles switch to anaerobic respiration, producing lactic acid instead. This causes muscle fatigue and that burning sensation you feel during hard workouts.
Fermentation is anaerobic respiration in yeast and plants, producing ethanol and carbon dioxide . This process is essential for making bread rise and producing alcoholic drinks.
Remember: Aerobic respiration releases much more energy than anaerobic respiration - that's why you can't sprint forever!
Metabolism encompasses all these chemical reactions in your body. The energy from respiration powers everything from building proteins to keeping your body temperature constant, making it absolutely vital for survival.
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Biology185 views·Updated Jun 28, 2026·2 pagesComplete Guide to Bioenergetics - AQA GCSE Biology Topic 4
O
oliviaa2008@oliviaa2008
Photosynthesis and respiration are two essential processes that keep life on Earth running. Photosynthesis lets plants capture sunlight to make food, whilst respiration helps all living things release energy from that food to power their daily activities.
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of 2
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Photosynthesis: How Plants Make Food
Ever wondered how plants create their own food using just sunlight, water, and carbon dioxide? Photosynthesis is an endothermic reaction that happens in the chloroplasts of plant cells. The green pigment chlorophyll acts like a solar panel, trapping light energy and converting it into chemical energy.
The equation for photosynthesis shows exactly what's happening: carbon dioxide + water → glucose + oxygen . Plants use the glucose they make in brilliant ways - for respiration to release energy, converting it to starch for storage, making cellulose to strengthen cell walls, and producing amino acids for proteins.
Limiting factors control how fast photosynthesis happens. Temperature, light intensity, carbon dioxide concentration, and chlorophyll concentration can all slow things down when they're in short supply. The inverse square law explains why moving a plant twice as far from a light source reduces light intensity by a quarter.
Top Tip: In exam questions about limiting factors, look for which one is preventing the rate from increasing further - that's your limiting factor!
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of 2Sign up to see the content. It's free!
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Cellular Respiration: Releasing Energy for Life
Your cells are constantly working to release energy from food through cellular respiration - an exothermic reaction that happens in the mitochondria. Unlike photosynthesis, this process releases energy and occurs in all living things, not just plants.
Aerobic respiration uses oxygen to completely break down glucose: glucose + oxygen → carbon dioxide + water . When oxygen runs short during intense exercise, your muscles switch to anaerobic respiration, producing lactic acid instead. This causes muscle fatigue and that burning sensation you feel during hard workouts.
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