Respiration (OCR GCSE Combined Science A (Gateway): Biology)

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]