AQA GCSE Responding to Exercise (Biology)
Responding to Exercise
In order for us to move during exercise, muscles need to contract. For muscle contraction to occur energy is needed.
Muscle cells carry out respiration to release energy from glucose.
Therefore, exercise will increase the demand for energy.
During exercise the human body reacts to the increased demand for energy.
Changes in the body during exercise
There are several changes that occur in the body during exercise.
| Body change during exercise | What changes | Why this helps muscles |
|---|---|---|
| Heart rate | Increase in beats per minute, so more blood is pumped per minute | More oxygen and glucose delivered to muscle cells. More carbon dioxide removed from muscle cells and then from body via lungs. |
| Breathing rate | More breaths per minute | Increases oxygen uptake, removes carbon dioxide faster |
| Breath volume (tidal volume) | Larger volume of air taken in per breath | Increases oxygen supply to blood. |
Aerobic vs anaerobic respiration in muscles
Muscle cells will normally use aerobic respiration if plenty of oxygen is available. Equation is below.
During exercise if oxygen cannot be delivered quickly enough to muscle cells they will switch from aerobic respiration to anaerobic respiration.
The equation for anaerobic respiration in animals is listed below.
Anaerobic respiration is the incomplete oxidation of glucose.
During anaerobic respiration in muscle cells, lactic acid builds up which has several effects:
Effects of lactic acid:
1.Lowers pH in muscle cells
2.Interferes with enzyme activity (remember each enzyme has an optimum pH)
3. Causes muscle fatigue.
As a result the fatigued muscles will contract less efficiently and may stop contracting altogether.
Lactic Acid and the oxygen debt.
The lactic acid that is formed during anaerobic respiration in muscles needs to be broken down.
Deep and rapid breathing will continue to occur after exercise to take in additional oxygen to oxidise the lactic acid to carbon dioxide and water.
(overall lactic acid is converted to carbon dioxide and water, but the steps involved in this are explained below).
The amount of extra oxygen needed after exercise to oxidise the lactic acid is known as the oxygen debt.
Mechanism of breakdown of lactic acid.
The heart pumps the blood, which flows through the muscles, transporting the lactic acid produced during anaerobic respiration within the muscle cells back to the liver.
In the liver, lactic acid is converted back to glucose using oxygen, remember that the person will continue to breathe deeply and rapidly to take in additional oxygen.
This glucose can either be:
1.Converted to glycogen and stored in liver cells as an energy storage molecule.
2. Used in aerobic respiration to produce carbon dioxide and water, releasing energy.
Practice Questions
1.During exercise both heart rate and breathing rate increase.Explain why
2.Describe two changes in breathing during exercise.
3. Explain why muscles become fatigued during long periods of vigorous exercise.
Factors affecting the rate of photosynthesis
Measuring & calculating rates of photosynthesis
Inverse square law and photosynthesis
Economics of enhancing the conditions in greenhouses
Investigating the effect of light intensity on the rate of photosynthesis