Respiration (OCR GCSE Biology A (Gateway))

Fermentation involves enzymes breaking down sugar and releasing carbon dioxide gas.

The volume of carbon dioxide released can be used to measure how fast these enzymes are working.

A student investigates if fermentation works faster at 25°C or 30°C.
She measures the volume of carbon dioxide released in 10 minutes.
The diagram shows the apparatus she uses.

Using a Bunsen burner to heat a water bath is one way the student could keep the flask at a constant temperature.

(i) What other way could be used to keep the flask at a constant temperature?

[1]

(ii) She chooses to use a Bunsen burner and water bath. Give one safety precaution she should take.

[1]

(iii) Explain why using a Bunsen burner and water bath may introduce errors into her results.

[2]

The table shows the student’s results.

(i) Calculate the mean for the results at 30°C and complete the table.

[2]

(ii) The student repeated the experiment at two more temperatures, 20°C and 35°C, to get enough readings to plot a line graph.

Which measurement should the student plot on the x-axis?

[1]

(iii) Describe one way that the range would improve any conclusions made from the graph.

[1]

(iv) The mean volume at a temperature of 20°C was 15cm³ and for a temperature of 35°C it was 27cm³.

Describe what the student’s results show about the effect of temperature on enzyme activity.

[2]

Yeast cells can respire anaerobically.

Complete the word equation for anaerobic respiration in yeast.

glucose ⟶ ...................................... + ......................................

Write down two ways in which anaerobic respiration in yeast cells is different from anaerobic respiration in human muscle cells.

1 ..................................................................
2 ...................................................................

Date fruits contain three different sugars, fructose, glucose and sucrose.

Different strains of yeast can ferment different sugars to produce a fermented product.

Scientists investigate how two different strains of yeast, A and B, ferment sugars inside date fruits.

Look at their results.

(i) Which sugar is not fermented by either strain of yeast?

Tick (✓) one box.

[1]

(ii) After 24 hours, how many times higher is the fermented product yield of yeast A compared to yeast B?

Number of times higher = .................................................. [2]

(iii) Which sugar would increase fermentation the most if added to either yeast A or yeast B?

Tick (✓) one box.

[1]
(iv) Fermented dates are used to supply both fructose and fermented product.

Explain why it would be best to use yeast B to ferment dates to supply both fructose and fermented product.

 [2]

A chemical in stevia leaves makes them taste sweet. This chemical is not a sugar.
People with diabetes need to know if the food they eat contains sugar.

(i) Describe how you could test some stevia leaves to prove that they do not contain sugar.

Reagent used .................................
Method ..........................
Expected result ................................

[3]

(ii) Will using stevia in foods help people with type 2 diabetes?

Explain your answer.

[2]