1.3 Respiration

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)

(ii)

(iii)

(iv)

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.

(ii)

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.