Edexcel IGCSE Biology Experimental Skills

A student uses this method to investigate the effect of fertiliser on the growth of plant seedlings.
- set up two trays with an equal mass of compost in each tray
- plant 100 seeds, equally spaced, in each tray
- place the trays under the same lamp until the seeds start to germinate
- water each tray every day with the same volume of water
- add fertiliser to one of the trays every day
- remove five seedlings from each tray every four days for a period of 20 days
- dry these seedlings in an oven and find their mass

The table shows the student's results.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Badgers and bovine tuberculosis

The bacterium Mycobacterium bovis causes the lung disease bovine tuberculosis (TB) in cattle. Infected cattle have damaged lungs, which causes gas exchange problems and makes them cough into the air. The pathogen spreads to humans if they inhale air containing the bacterium. Humans also become infected if they drink unpasteurised milk from infected cattle. Milk is usually pasteurised by heating it for a period of time at a high temperature.

Bovine TB can kill humans. In one year, 13400 people died from a total of 149000 reported cases of TB. Some of these cases were from Europe, where 103 people died from 1290 reported cases. The rest of the cases were from outside Europe.

Some farmers in the United Kingdom are concerned that badgers spread the TB pathogen to cattle.

The photograph shows a badger.

Badgers act as a reservoir for the TB pathogen and can live for several years without showing any signs of TB. Some farmers want badgers to be culled (killed) to stop the spread of bovine TB to cattle.

However, some scientists claim that only a fraction of cattle catch TB from badgers, and that culling badgers could spread the disease to new areas. This is because badger culling changes the behaviour of the badgers that survive. Normally, badgers live in social groups and will defend their territory from other badgers by being aggressive. This territorial behaviour reduces the spread of disease between groups. If badgers are culled, then their territories cannot be defended. Surviving badgers could move in to occupy the undefended territory, bringing TB with them. This could spread TB to new animals and new areas.

Some people believe that badgers should be vaccinated to stop the spread of TB. However, there is some concern that vaccination may increase the spread of TB because it might also change badger behaviour.

An investigation is needed to find out if badger vaccination can reduce TB both in badgers and in cattle.

Describe how scientists could find out if badger vaccination reduces TB in cattle (lines 27 to 28).

Micropropagation is used to produce plant clones.
The process involves growing explants in vitro.

The explants grow new roots and shoots.

A student investigates the effect of pH on the growth of new shoots.
The table shows the student's results.

Explain the relationship between pH and the mean number of shoots per explant.