Respiration in cells can take place aerobically or anaerobically. The energy released is used in a variety of ways. The human body needs to react to the increased demand for energy during exercise
The chemical reactions inside cells are controlled by enzymes. b) During aerobic respiration (respiration that uses oxygen) chemical reactions occur that: ■ use glucose (a sugar) and oxygen ■ release energy. c) Aerobic respiration takes place continuously in both plants and animals. d) Most of the reactions in aerobic respiration take place inside mitochondria. e) Aerobic respiration is summarised by the equation: glucose + oxygen ➞ carbon dioxide + water (+ energy)
f) Energy that is released during respiration is used by the organism. The energy may be used: ■ to build larger molecules from smaller ones ■ in animals, to enable muscles to contract ■ in mammals and birds, to maintain a steady body temperature in colder surroundings ■ in plants, to build up sugars, nitrates and other nutrients into amino acids which are then built up into proteins. g) During exercise a number of changes take place: ■ the heart rate increases ■ the rate and depth of breathing increases. h) These changes increase the blood flow to the muscles and so increase the supply of sugar and oxygen and increase the rate of removal of carbon dioxide. i) Muscles store glucose as glycogen, which can then be converted back to glucose for use during exercise.
a) During exercise, if insufficient oxygen is reaching the muscles they use anaerobic respiration to obtain energy. b) Anaerobic respiration is the incomplete breakdown of glucose and produces lactic acid. c) As the breakdown of glucose is incomplete, much less energy is released than during aerobic respiration. Anaerobic respirationresults in an oxygen debt that has to be repaid in order to oxidise lactic acid to carbon dioxide and water. d) If muscles are subjected to long periods of vigorous activity they become fatigued, ie they stop contracting efficiently. One cause of muscle fatigue is the build-up of lactic acid in the muscles. Blood flowing through the muscles removes the lactic acid. Suggested ideas for practical work to develop skills and understanding include the following: ■ investigating the rate of respiration in yeast using carbon dioxide sensors and dataloggers ■ investigating the effect of exercise on pulse rate, either physically or using pulse sensors and dataloggers ■ investigating the link between exercise and breathing rate with a breathing sensor ■ investigating holding masses at arm’s length and timing how long it takes the muscles to fatigue ■ designing an investigation using force meters and dataloggers to find the relationship between the amount of force exerted by a muscle and muscle fatigue.