Food production using micro-organisms

Yeast is a fungus used in the production of beer.

Name the part of a yeast cell that is made of chitin.

Name the carbohydrate stored in the cytoplasm of a yeast cell.

In beer production, yeast releases carbon dioxide as a waste product. A student uses this apparatus to investigate the effect of temperature on carbon dioxide production in yeast.

The student counts the number of carbon dioxide bubbles released per minute at different temperatures. The table shows the student’s results.

Describe how the student could change the temperature of the water during the investigation.

Describe how the student makes sure that the yeast cells respire anaerobically.

Give the independent variable in this investigation.

Give three ways in which the student could improve this investigation.

Two different varieties of yeast, A and B, are used to produce beers that contain different concentrations of alcohol. Design an investigation to determine which variety of yeast is best for producing low alcohol beer. Your answer should include experimental details and be written in full sentences.

Every effort has been made to contact copyright holders to obtain their permission for the use of copyright material. Pearson Education Ltd. will, if notified, be happy to rectify any errors or omissions and include any such rectifications in future editions.

Yeast is an organism used in the production of beer. The diagram shows a yeast cell.

Give the letter of the part made of chitin.

Give the letter of the part that contains glycogen.

Yeast releases carbon dioxide when beer is made. A student uses this apparatus to measure the rate of carbon dioxide production by yeast.

The solution contains yeast cells. Name two substances in the solution.

Every three minutes, the student records the position of the drop of ink using the scale. The table shows the student’s results.

Calculate the difference between the rate of carbon dioxide production in the first three minutes and the rate in the final three minutes. Show your working.

difference in rate =_........ mm per minute

The student then investigates the effect of temperature on the rate of carbon dioxide production by yeast. He measures the volume of carbon dioxide produced rather than the distance moved by the drop of ink. The graph shows his results.

Give the optimum temperature for the production of carbon dioxide.

Explain why the rate of carbon dioxide production is slow at low temperatures.

Suggest how the student could modify the apparatus to vary the temperature.

Yeast is a single-celled fungus. The diagram shows a yeast cell with parts labelled A to F.

The table lists functions of different parts of the yeast cell. Complete the table by giving the letter of the part that carries out the function.

The table lists statements. Put a tick () in the boxes next to the statements that are correct for yeast.

A student wants to make yoghurt. The diagram shows what she did.

Which two stages help to improve the production of yoghurt by killing bacteria that compete with Lactobacillus ?

Explain why the milk needed to be cooled to 45 °C in stage 3.

Explain what could happen to the production of yoghurt if the jars used in stage 5 had not been sterilised in stage 2.

Explain what would happen to the production of yoghurt if the water cooled below 35 °C in stage 6.

The student added fruit to her yoghurt to improve the taste. Suggest how adding fruit to yoghurt also helps to maintain healthy skin.

Some food products are made using microorganisms. The table gives information about the production of two of these food products.

Complete the table by giving the missing information.

Explain one precaution that should be taken when making yoghurt so that it is safe for humans to eat.

Yeast can respire anaerobically and is used to produce beer.

Write the word equation for anaerobic respiration in yeast.

Describe a test you could use to identify the gas produced when yeast respires anaerobically.

The diagram shows a model of an industrial fermenter used to study how changes in conditions can affect the yield of products.

An acid or alkali can flow through the acid/alkali inlet to maintain a constant pH within the fermenter. Explain why the pH needs to be kept within a narrow range.

Parts of the fermenter responsible for regulating the temperature are not shown in the diagram. Name two of these parts.

This fermenter uses a sparger to introduce air into the fermenter. Suggest why it is important to introduce air into the fermenter.

Before being used the empty fermenter is cleaned using steam. Suggest why.

A student found the following instructions for making yoghurt on the internet.

put milk in a saucepan and heat the milk to 80 °C pour the hot milk into a bowl and leave to cool to 46 °C add the organisms needed to change the milk into yoghurt pour the yoghurt into glass jars and put them into a warm place for 8 hours pour the yoghurt into a sterile, airtight container and put it in the fridge

Name an organism added to change the milk into yoghurt.

Explain why the milk is heated to 80 °C.

Explain why the milk must be cooled to 46 °C.

Explain why the yoghurt is kept in a warm place for 8 hours.

Changes take place to the pH of the yoghurt when it is kept warm for 8 hours. Describe and explain how the change in pH helps to preserve the yoghurt.