4.4.2 Respiration

4.4.2.1 Aerobic and anaerobic respiration

Respiration

• Respiration is a reaction where energy is released from living cells
• Respiration is an exothermic reaction
• Breathing in and out supplies oxygen
• Respiration uses food or photosynthesis to release energy

Body Processes Requiring Energy

• Building larger molecules: e.g. synthesising proteins from amino acids
• Contraction of muscles to help us move
• Maintaining a constant body temperature uses energy
• Digesting food uses muscle contraction
• Breathing uses intercostal muscles and diaphragm

1. Building larger molecules

2. Contraction of muscles to help us move

3. Maintaining a Constant Body Temperature

4. Digesting Food

5. Breathing

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Aerobic Respiration

• Aerobic respiration requires oxygen for energy
• Aerobic respiration also requires glucose for energy

• Anaerobic respiration occurs in the absence of oxygen

• Anaerobic respiration transfers less energy than aerobic respiration
• Glucose is oxidised in respiration (electrons are lost by glucose)

Aerobic Respiration

• CO2 represents carbon dioxide
• H2O represents water
• C6H12O6 represents glucose
• O2 represents oxygen

Plants and Yeast

• Anaerobic respiration in plants and yeast is different, as there are different circumstances in the different cell types

Fermentation

• In yeast cells, anaerobic respiration is called fermentation
• Fermentation of yeast is used to make bread rise
• Fermentation of yeast is used to make alcoholic drinks, using ethanol

4.4.2.2 Response to exercise

Normal Changes During Exercise

• When you exercise, the rate of respiration increases to supply the increased amount of energy the muscles need to contract.
• Oxygen is a requirement for aerobic respiration, so if cells are respiring more they need more oxygen.

• To increase the amount of oxygen in the blood, breath volume and breathing rate rise.
• Heart rate increases to take oxygen to the respiring cells and remove the waste product, CO2.

Anaerobic Respiration in Exercise

• Intense exercise can mean that the body cannot deliver oxygen to the muscles fast enough, leading to anaerobic respiration.
• Anaerobic respiration during exercise leads to a build up of lactic acid.
• This can cause pain and explains what happens when we have a ‘stitch’.
• The build up of lactic acid causes an oxygen debt.

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Oxygen Debt

• Oxygen debt is the additional oxygen you need to remove the build up of lactic acid.
• Even after stopping exercising, there will be lactic acid in the cells which will need to be reacted with oxygen to form CO2 and water.
• Therefore BR and HR stay high after exercise in order to deliver the oxygen to the cells.

• When lactic acid levels fall, there is no longer an oxygen debt and so the heart rate and breathing rate falls.
• The blood transports lactic acid from the muscle cells to the liver where it is made back into glucose.

Muscle Fatigue

• Exercising for a long period can cause muscle fatigue.
• This reduces their effectiveness and reduces the strength of contractions.

Measuring Heart and Breathing Rates

• Heart rate – measured by your pulse at your wrist which allows you to find the beats per minute.
• Breathing rate – by looking at how many times your chest rises, you can count the number of breaths per minute.

Investigating Effect of Exercise

1. Measure HR and BR at rest

In pairs, you could take your pulse and breathing rate without exercise. You can later compare this with the values during exercise.

2. Do 10 star jumps, and measure again

You could then do 10 star jumps and measure it again.

3. Do 50 start jumps, and measure again

You could then do 50 star jumps and measure it once more. Measuring values after more intense exercise will show the effect of this increased effort on heart rate.

4. Measure again after 3 minutes of rest

Measuring after 3 minutes will enable you to consider the oxygen debt, and see if the heart rate has fallen back to its normal level.

5.  Repeat the experiment more individuals

You can take all the results from the whole class and find the average heart and breathing rate each time. By taking a mean, it reduces the chance of random errors in your results.

6. Plot the mean values on a bar chart

The average values could be plotted on a bar chart to show the trend. Plotting the chart

will show that increasing the intensity of exercise increases the breathing rate and pulse.

7. Analyse the oxygen debt

Consider the values recorded after 3 minutes of rest. If the heart and breathing rate are still above the rate at rest, it shows that the cells are still breaking down lactic acid – which is the idea of oxygen debt.

Summary

1. Measure HR and BR at rest
2. Do 10 star jumps, and measure again
3. Do 50 start jumps, and measure again
4. Measure again after 3 minutes of rest
5. Repeat the experiment with more individuals
6. Plot the mean values on a bar chart
7. Analyse the oxygen debt

4.4.2.3 Metabolism

Making Large Molecules

• Large molecules in cells are made up of lots of smaller molecules, called monomers.
• Together, these monomers join together to form polymers.

Starch

• A starch molecule is made up of lots of glucose molecules joined together.
• When we eat bread, starch in the bread is broken down by the digestive system to give glucose molecules, which can be absorbed into the blood.

Lipids

• A lipid (fat) molecule has one glycerol molecule bonded to three fatty acids.
• Again, when we eat ice cream, lipids are broken down by the digestive system into glycerol and fatty acids.

Proteins

• A protein molecule is made up of many amino acids joined together in a chain.
• Amino acids are themselves made up of glucose and nitrate ions.
• Each protein has a different chain or order of amino acids.
• For example, an enzyme (a protein) has a specific chain of amino acids which ensures that it’s the correct shape to catalyse a reaction.

Breaking Down Large Molecules

In the body, these large molecules often need to be broken down:

• Respiration – in respiration, glucose is broken down to produce energy for cell processes.
• Digestion – digestion involves breaking down large insoluble molecules in food (e.g. starch), into small soluble molecules (e.g. glucose) that can be absorbed into the bloodstream.
• Protein breakdown – additional excess proteins in the body are broken down into urea, which is removed from the body in urine.

Metabolism

• The metabolism of a cell or body is the combination of all the reaction occurring in them.
• The reactions which occur in cells to synthesise new molecules or break them down are often controlled by specialised proteins called enzymes.