BBC Bitesize- Respiration and Transpiration in plants

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Aerobic and anaerobic respiration

Respiration releases energy for cells from glucose. This can be aerobic respiration, which needs oxygen, or anaerobic respiration, which does not. During exercise, the breathing rate and heart rate increase. During hard exercise an oxygen debt may build up.

What is aerobic respiration?

Respiration is a series of reactions in which energy is released from glucoseglucoseA simple sugar made by the body from food, which is used by cells to make energy in respiration.Aerobic respiration is the form of respiration which uses oxygen. It can be summarised by this equation:

glucose + oxygen → carbon dioxide + water (+ energy)

Energy is shown in brackets because it is not a substance. Notice that:

  • Glucose and oxygen are used up
  • Carbon dioxide and water are produced as waste products

Aerobic respiration happens all the time in the cells of animals and plants. Most of the reactions involved happen insidemitochondria, tiny objects inside the cytoplasm of the cell. The reactions are controlled by enzymes [enzymeA protein which speeds up chemical reactions. ].

Using energy

Energy released during respiration is used by the organism in several ways. It may be used to build up larger molecules[moleculeA molecule is a collection of two or more atoms held together by chemical bonds. It is the smallest part of a substance that displays the properties of the substance. ] from smaller ones. For example:

  • Plants make amino acidsamino acidComplex molecules, which form the building-blocks of proteins. from sugars,nitrates [nitrateA negative complex ion with the formula NO3-. ] and other nutrients
  • These amino acids are then built up into larger molecules -proteins [proteinOrganic compound made up of amino acid molecules. One of the three main food groups, proteins are needed by the body for cell growth and repair. ]

Energy is used by animals to enable the muscles to contract so that the animals can move. Mammals and birds keep their body temperature steady. Energy from respiration is used to do this when their surroundings are colder than they are.


During exercise, the muscle cells respire more than they do at rest. This means that:

  • Oxygen and glucose must be delivered to them more quickly
  • Waste carbon dioxide must be removed more quickly

This is achieved by increasing the heart raterate of breathingand the depth of breathing.

The increased heart rate increases the rate of blood flow around the body. The increased rate and depth of breathing increases the rate of gaseous exchangegaseous exchangetransfer of oxygen from the air into our blood and carbon dioxide out of our blood into the air in the lungs.

The muscles store glucose as glycogen. This can then be converted back to glucose for use during exercise.

Take care not to get confused: plants store glucose as starch and animals store it…


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