1.1. A scientist uses this method to investigate the effect of water quality on the growth of fish.

• fill a pond with filtered water

• fill another pond with unfiltered water

• place the same mass of fish of the same species in each pond

• determine the increase in total mass of fish in each pond after 180 days

The graph shows the scientist’s results.

The mean rate of increase in total mass of the fish in the filtered water is 0.214kg per day.

Calculate the difference between the mean rate of increase in the total mass of the fish in filtered and unfiltered water.

1.2. Unfiltered water contains more bacteria.

Explain why unfiltered water containing more bacteria affects the growth of fish.

1.3. Give one biotic variable the scientist controlled in the investigation.

1.4. Give a method the scientist could use to control interspecific predation in the ponds.