B2.2 Respiration and photosynthesis · KS3 Science

Aerobic respiration

Respiration releases energy from glucose. It happens in every living cell, all the time.
Aerobic respiration uses oxygen and happens in the mitochondria: glucose + oxygen → carbon dioxide + water (energy is released).
The energy is used for movement, growth, repair and keeping warm.
During exercise, breathing rate and heart rate rise to bring more oxygen and glucose to the muscles and remove carbon dioxide.

Anaerobic respiration happens without oxygen and releases much less energy.
In human muscles during hard exercise: glucose → lactic acid. Lactic acid causes muscle fatigue and cramp. Afterwards, you keep breathing hard to repay the oxygen debt.
In yeast (fermentation): glucose → ethanol + carbon dioxide. The carbon dioxide makes bread rise, and the ethanol is the alcohol in beer and wine.
A healthy lifestyle (exercise, a good diet and not smoking) keeps the heart and lungs working well.

Plants make their own food by photosynthesis: carbon dioxide + water → glucose + oxygen. Light energy is absorbed by chlorophyll in the chloroplasts.
Plants use the glucose for respiration, store it as starch, and use it to make cellulose for cell walls and proteins for growth.
Test a leaf for starch with iodine: it turns blue-black if starch is present.
Pondweed gives off bubbles of oxygen. Moving a lamp closer (more light) increases the number of bubbles, until something else, such as carbon dioxide or temperature, limits the rate.

Leaves are broad and flat (large surface area to absorb light), thin (so gases don't have far to travel), full of chlorophyll, and have stomata (tiny holes) to let carbon dioxide in and oxygen out.
Plants are adapted to their habitats: cacti have spines instead of leaves and thick stems that store water.
A few plants, such as dodder, can't photosynthesise and take their food from other plants.
Biodomes create controlled environments so plants from different climates can grow.

Aerobic respiration: Respiration using oxygen, releasing lots of energy.
Anaerobic respiration: Respiration without oxygen, releasing less energy.
Glucose: A sugar that is broken down in respiration.
Mitochondria: Where aerobic respiration happens in a cell.
Lactic acid: Made in muscles during anaerobic respiration.
Oxygen debt: The extra oxygen needed after exercise to break down lactic acid.
Fermentation: Anaerobic respiration in yeast, making ethanol and carbon dioxide.
Photosynthesis: Plants making glucose from carbon dioxide and water, using light energy.
Chlorophyll: The green pigment that absorbs light for photosynthesis.
Chloroplast: The part of a plant cell where photosynthesis happens.
Stomata: Tiny holes in a leaf that let gases in and out.
Limiting factor: Something that stops the rate of photosynthesis increasing any more.