3.3 Plant Disease

These flashcards cover specification point 4.3.3 Plant Disease (Biology Only) in Topic 3 - Infection & Response for AQA GCSE Biology. This includes: 4.3.3.1 Detection & Identification of Plant Diseases and 4.3.3.2 Plant Defence Responses.

What can plant diseases be detected by? (7)

• Stunted growth

• Spots on leaves

• Areas of decay (rot)

• Growths

• Malformed stems or leaves

• Discolouration

• The presence of pests

In relation to plant diseases, what can identification be made by? (3)

• Reference to a gardening manual or website

• Taking infected plants to a laboratory to identify the pathogen

• Using testing kits that contain monoclonal antibodies

What are three ways that aphids can weaken a plant?

• They have sharp mouthparts that penetrate the phloem vessels of a plant, allowing the insect to feed on the sugar-rich phloem sap.

• They attack in such huge numbers that they may deprive the plant cells of the products of photosynthesis.

• They also act as vectors, transferring viruses, bacteria, and fungi from diseased plants into healthy plants on their mouthparts.

How can aphids be destroyed? (2)

• Chemical pesticides

• Releasing aphid-eating insects (e.g. ladybirds)

How do plants use nitrate ions?

To convert the glucose made in photosynthesis into the proteins needed for growth.

What are signs that a plant has a nitrate ion deficiency? (3)

• Photosynthesis is limited

• Growth is stunted

• Poor crop

How do plants use magnesium ions?

To make the chlorophyll needed for photosynthesis.

What are signs that a plant has a magnesium ion deficiency? (3)

• Photosynthesis is reduced

• Chlorosis

• Growth slows down

What is chlorosis?

Yellowing of plant leaves

How can missing mineral ions be replaced in a plant?

Fertilisers

What are the physical defence responses that plants use to resist invasion of microorganisms? (3)

• Cellulose cell walls

• Tough waxy cuticle on leaves

• Layers of dead cells around stems (bark on trees) which fall off

How do cellulose cell walls help plants resist invasion of microorganisms?

It acts as a barrier to the entry of pathogens.

How does the tough waxy cuticle on leaves help plants resist invasion of microorganisms?

It acts as a barrier to the entry of pathogens.

How do layers of dead cells around stems (bark on trees) which fall off help plants resist invasion of microorganisms?

• They form a protective layer that is hard for pathogens to penetrate.

• When the dead cells are lost or shed, the pathogens fall off with them.

What are the chemical defence responses for plants? (2)

• Antibacterial chemicals

• Poisons to deter herbivores

What are the mechanical adaptations of plants that protect them? (3)

• Thorns and hairs deter animals

• Leaves which droop or curl when touched

• Mimicry to trick animals

How do thorns and hairs protect plants?

Makes it difficult and painful for animals to eat them.

How do leaves that droop or curl when touched protect plants?

Allows them to move insects off their leaves.

How does mimicry protect plants?

• Some plants droop to look like unhealthy plants so that animals avoid them.

• Plants can have patterns that appear to look like butterfly eggs, so butterflies do not lay their eggs here in order to avoid competition.