The diagram shows an evolutionary tree for the whale genus Mysticetes - Edexcel - GCSE Biology - Question 1 - 2018 - Paper 1

Prebiotics play a crucial role in increasing the population of beneficial bacteria. They provide a food source that beneficial bacteria can utilize. In Flask 2, which contained prebiotics, the beneficial bacteria had access to oligosaccharides that support their growth and reproduction. As a result, the population of beneficial bacteria increases due to less competition for resources and the presence of a suitable food source.