The flow chart shows steps taken in the production of yoghurt from milk. [Figure 3 (Flow chart showing steps: milk is heated to 90 °C for 15 minutes -> milk is cooled to 43 °C -> a starter culture containing two species of bacteria is added -> the mixture is kept at 43°C for several hours -> fruit may be added and the yoghurt is refrigerated)]

1. (a)Heating the milk to 90 °C for 15 minutes sterilises the milk. Suggest the importance of sterilising the milk.[2]
2. (b)Explain why the milk must be cooled to 43°C before the starter culture of bacteria is added.[3]
3. (c)(i)The two species of bacteria added to the milk are not mobile and are not pathogens. State the external structure used for movement by some species of bacteria.[1]
4. (c)(ii)Explain why it is important that the bacteria added to milk are not pathogens.[1]
5. (d)Describe, with reference to named chemicals, the role of the bacteria during the time for which the mixture is kept at 43°C.[4]
6. (e)Suggest and explain one benefit to human health of eating yoghurt to which fruit has been added rather than eating yoghurt to which no fruit has been added.[2]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.