Aerobic respiration and investigating it

Last time

Before we start: last time, in The breathing system and ventilation, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Energy from food

Every cell in your body, every second, is releasing energy from glucose. That is respiration. It happens in plants, animals and bacteria, day and night. Today: aerobic respiration, its equation, what the energy is used for, and how to measure it.

Respiration

Respiration is the chemical reactions in cells that break down nutrient molecules and release energy for metabolism. It is NOT breathing. Breathing just moves air. Aerobic respiration uses oxygen.

The equation

Here is the word equation. Glucose plus oxygen gives carbon dioxide plus water. And the balanced symbol equation: C six H twelve O six plus six O two gives six C O two plus six H two O. It is photosynthesis in reverse.

Where it happens

Aerobic respiration happens in the mitochondria. Cells that need a lot of energy, such as muscle cells and sperm cells, have many mitochondria. It releases a large amount of energy from each glucose molecule.

Uses of the energy

Muscle contraction, and protein synthesis to make new proteins. Cell division for growth and repair, and active transport. The passage of nerve impulses, and keeping a constant body temperature.

Respiration is controlled by enzymes

Respiration is a series of enzyme-controlled reactions. So it speeds up as temperature rises, up to the optimum. Above the optimum the enzymes denature and the rate falls.

Investigating respiration

Germinating seeds respire quickly. Put them in a flask with a thermometer: the temperature rises, because respiration releases heat. Boiled, dead seeds are the control: their temperature does not rise. Using disinfected seeds stops bacteria respiring and affecting the result.

A respirometer

A respirometer measures how fast organisms take in oxygen. Soda lime absorbs the carbon dioxide they give out. As oxygen is used, the gas volume falls, so a drop of coloured liquid moves towards the organisms.