Respiration in human cells can happen aerobically or anaerobically.

Both processes release energy from glucose.

Draw one line from each type of respiration in human cells to the correct information.

One type of respiration in humans is aerobic respiration.

What is the correct chemical equation for aerobic respiration?

In which cellular organelle does aerobic respiration take place?

Energy is released in respiration.

Give two uses of this energy.

A scientist investigated respiration in a species of yeast.

The scientist followed the method below.

1. Add 10 cm³ of a yeast and water mixture to 4 test tubes.
2. Add different masses (0, 2, 4 and 6g) of sugar to each tube and mix gently.
3. Place the test tubes in a water bath at 25 °C.
4. Over the next 20 minutes, record the volume of gas released in each test tube.

The table shows the student’s results.

Which two variables did the scientist control in the method?

In the investigation, the scientist recorded the volume of gas released when the yeast respires. Which gas is released?

There was no gas released in the tube with 0 g of sugar.

Suggest a reason for this result.

Which of the following is another substance produced when yeast respires anaerobically?

Anaerobic respiration in yeast is also called fermentation. 

Give one use of fermentation in the food industry.

When we breathe, our blood transports the oxygen from our lungs to cells in our body, where aerobic respiration takes place.

Balance the symbol equation for aerobic respiration.

C₆H₁₂O₆  +   O₂   →   CO₂  +   H₂O

What is the name of the substance with the formula C₆H₁₂O₆?

When oxygen is not available, our muscles can perform anaerobic respiration.

Name two differences between aerobic and anaerobic respiration in humans.

Do not refer to oxygen in your answer.

A student used the apparatus pictured below to investigate aerobic respiration in plants.

Limewater is an indicator for carbon dioxide because limewater turns cloudy in the presence of carbon dioxide.

After a few minutes the limewater in flask 1 was still colourless, but the limewater in flask 3 was cloudy.

Explain why.

Flask 1 acts as a control in this experiment.

Why do scientists use controls?

The student repeated the investigation with dead boiled peas.

Predict what will happen to the limewater in flasks 1 and 3 after 10 minutes.

Plant cells can also respire anaerobically.

What are the two products of anaerobic respiration in plants?

When an athlete goes for a run, his heart beats faster than it does when he is at home watching television.

When he is running, the athlete’s muscles need to release a lot more energy, so his muscle cells at a faster rate. 

The athlete’s heart beats faster so that the flow of increases.

This allows his muscles to receive a quick supply of glucose and , the reactants in the process of aerobic respiration.

It also allows for the products of the reaction, and water, to be transported away from his muscles.

A scientist investigated how much lactic acid the athlete produced when running at different speeds. 

• The scientist asked him to run on the treadmill at 5km/h and measured the lactic acid concentration in his blood after 5 minutes of running. 
• The scientist then allowed the athlete to rest, and when his lactic acid levels returned to normal, the scientist repeated the experiment at different speeds.

The graph below shows the scientist's results.

Calculate the percentage change in lactic acid concentration in the athlete's blood from when he was running at 6 km/h to when he was running at 16 km/h.

Why is more lactic acid made in the muscles when running at 18 km per hour than when running at lower speeds?

The equation below describes a type of respiration that happens in our muscle cells when we do vigorous exercise.

glucose ➔ lactic acid

What is the name of this type of respiration?

Explain how you know which type of respiration this is by looking at the equation above.

Why can’t we sustain exercise when this reaction happens in our muscle cells?

Micrograph 1 shows cells in muscle tissue.

Micrograph 2 shows an organelle inside a muscle cell.

Micrographs 1 and 2 were obtained using different types of microscopes.

Which type of microscope was used to obtain micrograph 2?

Explain your answer.

The sub-cellular structure shown in micrograph 2 is where aerobic respiration happens.

What is the name of this organelle?

Complete the word equation for aerobic respiration.

+ oxygen → + water (+ energy)

The organelle shown in micrograph 2 uses oxygen. 

Explain how oxygen is transported from the blood to the organelle.

A student performed an experiment to investigate anaerobic respiration in yeast cells. 

Why did the student add a layer of oil to the test tube containing the yeast and glucose solution?

Suggest how the student could modify his method to ensure his results are reproducible.

How does anaerobic respiration in yeast differ from anaerobic respiration in muscle cells?

A group of students planned an investigation to determine the effects of running on breathing rate.

The students measured their breathing rates before running and immediately after running for 5 minutes.

Write a hypothesis for their investigation.

Describe how the students could measure their breathing rates.

Suggest why running has an effect on the students' breathing rate.

A group of scientists conducted an identical experiment, but instead of measuring the volunteers' breathing rate, the scientists analysed the composition of the air exhaled before and after running for 5 minutes.

Describe how you would expect the concentration of carbon dioxide to vary. Give reasons for your prediction.

Two friends decided to go for a swim.

The graph below shows the friends' heart rates before, during and after the swim.

Compare the heart rates of the two friends.

Why do the friends' heart and breathing rates increase during exercise?

One of the friends leads a sedentary lifestyle, whilst the other exercises several times a week. 

Which friend exercises regularly?

Explain your answer.