B2.6 Respiration
Summary
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.
Respiration
- Definition: The process of transferring energy from food molecules in every living cell.
- Aerobic respiration – uses oxygen
- Anaerobic respiration – uses no oxygen
- All chemical reactions inside cells are controlled by enzymes.
Aerobic respiration
- Glucose reacts with oxygen, producing carbon dioxide and water as waste products.
- This takes place continuously in animals and plants.
Word equation:
Chemical equation (do not need to learn!):
- Respiration actually involves a series of many small reactions.
- Each reaction is controlled by an enzyme.
Mitochondria
- Most of the reactions in respiration happen in the mitochondria.
- The inner surface of the mitochondria is highly folded to increase the surface area for enzymes.
Energy use
The energy that is released during respiration is used:
- To build up larger molecules using 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.
The role of respiration during exercise
- Muscles contract to move the bones in our bodies.
- Respiration releases energy, which is used to contract the muscles:
- When we exercise, our muscles contract more quickly and with more force.
- This requires more energy.
- This requires more glucose and oxygen.
- Also, more carbon dioxide is created which needs to be removed.
- The human body needs to react to the increased demand for energy during exercise.
Changes during exercise
- During exercise a number of changes take place: o The rate and depth of breathing increases.
- This increases the rate of gaseous exchange.
- More oxygen is taken into the blood.
- More carbon dioxide is removed from the blood. o The heart rate increases.
- This increases rate of blood flow to the muscles
- All of 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.
Glycogen
- Glucose is stored as glycogen is in the muscles.
- During exercise, glycogen is broken down into glucose in the muscles.
- This increases the amount of glucose that can be respired.
Anaerobic respiration
- During exercise, if insufficient oxygen is reaching the muscles they use anaerobic respiration to obtain energy.
- Anaerobic respiration is the incomplete breakdown of glucose and produces lactic acid.
- As the breakdown of glucose is incomplete, much less energy is released than during aerobic respiration.
- However, lactic acid is poisonous. We can only tolerate small amounts in our body.
- 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.
- During and after exercise, we breathe heavily to take in extra oxygen to oxidise the lactic acid:
- The extra oxygen is called the oxygen debt.
- The heart continues to pump faster.
- The breathing rate remains high.
- This delivers the extra oxygen to the muscles.
- This pays back the oxygen debt.
