Biology - Bioenergetics: Energy in Living Things

Photosynthesis is basically how plants make their own food using sunlight. The simple equation is: carbon dioxide + water → glucose + oxygen $CO2 + H2O → C6H12O6 + O2$. This process needs energy from light, making it an endothermic reaction. Chlorophyll, the green pigment in plants, is what makes this whole process possible.

Aerobic respiration is the opposite of photosynthesis - it breaks down glucose using oxygen to release energy. The equation flips: glucose + oxygen → carbon dioxide + water. This happens in every living thing, from tiny bacteria to massive elephants.

Your body uses the energy from respiration for three main things: building larger molecules from smaller ones, making your muscles contract, and keeping your body temperature steady when it's cold. Pretty much everything you do depends on this energy transfer.

When you exercise hard, your muscles need loads of energy quickly. Aerobic respiration happens in the mitochondria and is the most efficient way to get energy from glucose. However, when there's not enough oxygen available, your body switches to anaerobic respiration - which doesn't need oxygen but produces less energy.

Quick Tip: Remember that anaerobic respiration in animals produces lactic acid (that burning feeling in your muscles!), whilst in plants and yeast it produces ethanol and carbon dioxide - which is why bread rises during baking.