Uses of energy from respiration

Respiration releases energy in living cells. Cells use this energy to carry out processes that keep the organism alive, including building substances, moving materials and producing movement.

Energy from respiration is used for:

• Muscle contraction: muscle cells contract to produce movement.
• Protein synthesis: cells join amino acids together to make proteins.
• Cell division: cells copy and separate their contents to form new cells.
• Active transport: cells move substances across membranes from a lower concentration to a higher concentration.
• Growth: organisms make new cell material and, in many cases, produce new cells.
• Nerve impulses: nerve cells use energy to maintain the conditions needed for impulses to pass along them.

In animals that maintain a constant body temperature, energy released as heat helps replace heat lost to the surroundings.

Effect of temperature on respiration in yeast

Yeast respires using sugar and produces carbon dioxide. The amount of carbon dioxide produced in a fixed time gives an indication of the rate of respiration: more carbon dioxide in the same time indicates a faster rate.

Comparing respiration at different temperatures

Prepare yeast and sugar mixtures at different temperatures. For each mixture, collect the carbon dioxide produced over the same fixed time and measure its volume. The mixtures can be kept at their chosen temperatures using water baths.

Keep other conditions the same, including the amounts of yeast and sugar and the measurement time. This makes temperature the main difference between the mixtures, so differences in carbon dioxide production can be attributed to temperature more confidently.

Why respiration rate changes with temperature

Respiration consists of enzyme-controlled reactions. At low temperatures, these reactions proceed slowly, so yeast produces carbon dioxide slowly. As temperature rises, the reactions speed up and the respiration rate increases.

At sufficiently high temperatures, the enzymes involved are disrupted: their shapes change, so they no longer work effectively. The respiration rate then falls, and less carbon dioxide is produced in the fixed time.