Read the passage below. Use the information in the passage and your own knowledge
to answer the questions that follow.
Ragwort is a plant with yellow insect-pollinated flowers.
Many insect species eat ragwort leaves. The larvae of some insects damage the
leaves when they eat into leaf mesophyll tissue to feed on the cells. This feeding
behaviour reduces the growth of the ragwort plant. The larvae of the cinnabar
5 moth, found in the UK, are very efficient at eating ragwort leaves. For this reason,
the moth has been introduced into other countries as a biological control.
Ragwort plants contain a poison that kills many insects. However, the cinnabar
moth is not killed by this poison and it builds up in its body. This makes the moth
taste unpleasant to its predators.
10 Unfortunately, if a horse eats ragwort, the poison damages its liver. The poison
also causes blindness by making the cornea cloudy. A horse that eats 11% of
its own body mass of ragwort will be poisoned and die. It is estimated that
6500 horses in the UK die every year from ragwort poisoning.
Honey bees that visit ragwort flowers may collect nectar that can also contain
15 the poison. This nectar is used to make honey. If a human consumes this honey
it may harm their liver.
It is hard to control the size of the ragwort population because the flowers of a
single plant can produce about 200 000 seeds in one season. These seeds remain
dormant in the soil until they are stimulated to germinate by light.
20 Apart from using biological control, farmers can use other methods to reduce the
size of the ragwort population in their fields. One method is to use weed killer.
Another method involves keeping farm animals out of their fields to allow the
grass to grow.