1.1. Gut flora, or the gut microbiome, is the name given to the huge number of microorganisms that live inside the digestive system of animals, such as humans. 

Most of these microorganisms are bacteria.  

(i) State how the presence of the gut flora demonstrates that not all bacteria are pathogens.

(2)

(ii) Explain how human gut bacteria get their nutrition. 

(2)

1.2. If a patient is unwell with a bacterial infection they may take a type of medication called an antibiotic. 

Different types of antibiotics affect bacteria in different ways, for example some damage the cell walls of the bacteria, and some prevent bacteria from reproducing. 

Use the information provided to explain how taking an antibiotic would affect the bacteria that live in the gut.

1.3. To increase the number of bacteria living in the gut, people are encouraged to consume probiotics, such as health yogurts. 

These contain cultures of gut bacteria that can start to grow in number inside the intestines. This helps to keep the gut flora healthy. 

Name one example of a species of bacteria that is used in the production of yogurt from milk. 

1.4. When manufacturers are producing probiotics they must grow cultures of bacteria in a factory. They can put a small number of bacteria in a large vat called a fermenter and provide them with nutrients such as amino acids and glucose.

The graph below shows how the number of bacteria in the fermenter changes over time when no additional nutrients are added during the growth process. 

(i) Explain the shape of the curve between point A and point B.

(2)

(ii) Use your knowledge of the characteristics of living organisms to explain the shape of the curve after point C in the graph above.

(2)