Anaerobic respiration

Yeast is a fungus that can respire anaerobically.

What substance is the cell wall of a yeast cell made of?

Which row of the table shows the substances produced by yeast during anaerobic respiration?

A student uses this apparatus to investigate the effect of temperature on anaerobic respiration by yeast.

This is the student’s method.

• place yeast cells and glucose solution into a test tube

• keep the test tube at a temperature of 25 °C

• cover the yeast and glucose solution with paraffin oil

• count the number of bubbles produced each minute for 20 minutes

• repeat at a temperature of 37 °C

The student draws a graph to show the total number of bubbles that have been produced by the end of each minute for the 20‑minute period. The graph shows the student’s results.

State the function of the paraffin oil.

Describe a method the student could use to keep the temperature of the yeast and glucose mixture constant.

Calculate the rate of bubble production from 0 minutes to 8 minutes when the yeast is at 37 °C.

rate of bubble production =_........ bubbles per minute

Explain the change in the total number of bubbles produced from 0 minutes to 20 minutes at 25 °C.

Explain the difference in the rate of bubble production between 0 and 10 minutes at 37 °C compared with 25 °C.

Describe how the student could modify the experiment to give more accurate results.

Yeast can be used in experiments to investigate the effect of different concentrations of glucose solution on the rate of anaerobic respiration. The diagram shows apparatus used to measure the rate of anaerobic respiration in yeast.

Give the function of the water bath.

Liquid A can be used to identify the gas released during anaerobic respiration by the yeast. Explain which substance can be used as liquid A.

A student wants to accurately measure the rate of anaerobic respiration in yeast using this apparatus. State what additional apparatus they would require.

The process of anaerobic respiration is sometimes referred to as fermentation. Industrial fermenters are used to grow microorganisms. These microorganisms produce penicillin, an antibiotic that is used to treat bacterial infections.

Explain how named conditions in an industrial fermenter are controlled.

Some antibiotics are becoming less effective at controlling bacterial infections. Explain how bacteria have evolved so that antibiotics are less effective.

The diagram shows a yeast cell.

In which of the labelled structures in the yeast cell does aerobic respiration occur?

What substance is the yeast cell wall made of?

Which of these structures found in the yeast cell would also be present in a prokaryotic cell?

Yeast cells are often used when making bread.

A student uses this method to investigate the effect of temperature on the height that bread dough rises.

• place dough containing flour, sugar, water and yeast into a measuring cylinder

• measure the height of the dough

• place the measuring cylinder in a 25 °C water bath

• measure the height of the dough after two hours

• repeat the experiment at temperatures of 35 °C and 65 °C

The diagram shows the student’s apparatus.

The table shows the student’s results.

Calculate the percentage increase in the height of the dough after two hours at a temperature of 35 °C.

Explain why yeast causes the bread dough to increase in height.

Explain why the dough rises to a different height at 25 °C compared with the height at 35 °C.

Explain why the dough rises to a different height at 35 °C compared with the height at 65 °C.

Scientists carry out an experiment to see if reducing the availability of oxygen affects the production of yoghurt. They use increasing acidity as a measure of yoghurt production. They record the acidity of two cultures, one with a reduced oxygen level and one with a normal oxygen level, over 210 minutes. The table shows their results.

Explain why increasing acidity can be used as a measure of yoghurt production.

Give one abiotic variable that the scientists should control in their experiment.

Plot a line graph to show how the percentage acidity changes over the period of 210 minutes for the reduced oxygen level and for the normal oxygen level. Use a ruler to join the points with straight lines.

Explain why the changes in percentage acidity are different in the reduced oxygen level and in the normal oxygen level cultures.

The diagram shows a yeast cell.

Which row of the table is correct for this yeast cell?

Which type of organism is a yeast cell?

Biofuel is made from ethanol.

Scientists use genetically modified (GM) yeast to produce biofuel.

The GM yeast contains an enzyme that digests plant cell walls to produce glucose.

The yeast uses the glucose in respiration to produce ethanol.

Which of these equations shows the respiration in the yeast?

Name an enzyme used by scientists to genetically modify the yeast.

The GM yeast is a recombinant strain.

State what is meant by the term recombinant.

Suggest why biofuel produced using glucose from plants could reduce global warming.

The graph shows the mass of ethanol produced by GM yeast and by normal yeast over a period of 3 days.

Calculate the percentage increase in the mass of ethanol produced by GM yeast compared to normal yeast after 1 day.

Give two reasons why the rate of ethanol production decreases after 1 day.

The diagram shows a forest food web.

How many producers are shown in this food web?

How many secondary consumers are shown in this food web?

The coyote uses some of its senses to catch deer.

Name the sense that uses receptor cells in the retina.

A coyote runs 530 metres in 30.0 seconds trying to catch a deer.

Calculate the speed of this coyote in metres per second.

The coyote will not catch the deer if too much lactic acid builds up in its muscles.

Explain why lactic acid builds up in the coyote’s muscles when it runs.

A student investigates the effect of temperature on gas production in yeast.

The student uses this apparatus to count the number of gas bubbles produced per minute at different temperatures.

Name the process in yeast that produces the gas bubbles.

What gas is produced by the yeast?

The table shows the student’s results.

Plot a graph to show these results.

Join the points with straight lines.

Explain the result at 55C.

Describe how the student should modify the investigation to obtain a more accurate measure of the optimum temperature.