Plant Diseases and Defences

Question 1

Why do plants need mineral ions from the soil?

Answer 1

If there aren’t enough, plants suffer deficiency symptoms.

Question 2

What are nitrates needed for in a plant?

Answer 2

To make proteins and therefore for growth. A lack of nitrates causes stunted growth.

Question 3

What are magnesium ions needed for in a plant?

Answer 3

Making chlorophyll, which is needed for photosynthesis. Plants without enough magnesium suffer from chlorosis and have yellow leaves.

Question 4

What types of pathogen can plants be infected by?

Answer 4

Viral, bacterial and fungal.

Question 5

Give an example of an insect that a plant can be infested and damaged by?

Answer 5

Aphids are an insect that can cause huge damage to plants.

Question 6

What are the common signs that a plant has a disease?

Answer 6

1. Stunted growth.
2. Spots on the leaves.
3. Patches of decay
4. Abnormal growths, e.g. lumps
5. Malformed stems or leaves
6. Discolouration

Question 7

How are infestations of pests easy to spot?

Answer 7

You should be able to see them on the plants.

Question 8

Different plant diseases have different signs. How can they be identified?

Answer 8

By:

1. Looking up signs in a gardening manual or on a gardening website.
2. Taking the infected plant to a laboratory, where scientists can identify the pathogen.
3. Using testing kits that identify the pathogen using monoclonal antibodies.

Question 9

What are the physical defences of a plant?

Answer 9

1. Most plant leaves and stems have a waxy cuticle, which provides a barrier to stop pathogens entering.
2. Plant cells themselves are surrounded by cell walls made from cellulose. These form a physical barrier against pathogens that make it past the waxy cuticle.
3. Plants have layers of dead cells around their stems, for example, the outer part of the bark on trees. These act as a barrier to stop pathogens from entering.

Question 10

What are the chemical defences of a plant?

Answer 10

1. Some can produce antibacterial chemicals which kill bacteria - e.g. the mint plant and witch hazel.
2. Other plants produce poisons which can deter herbivores - e.g. tobacco plants, foxgloves and deadly nightshade.

Question 11

What are the mechanical defences of a plant?

Answer 11

1. Some plants have adapted to have thorns and hairs. These stop animals from touching and eating them.
2. Other plants have leaves that droop or curl when something touches them. This means that they can prevent themselves from being eaten by knocking insects off themselves and moving away from things.
3. Some can cleverly mimic other organisms. E.g. the passion flower has bright yellow spots on its leaves which look like butterfly eggs. Several species of plant in the “ice plant family” in southern Africa look like stones and pebbles. This tricks other organisms into not eating them.