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

• Presence of pests

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

• Gardening manual or website

• Taking infected plants to lab to identify pathogen

• Monoclonal antibodies testing kits

What are three ways that aphids can weaken a plant?

• Sharp mouthparts— penetrate phloem vessels of plant → allowing insect to feed on sugar-rich phloem sap

• Attack in huge numbers — deprives the plant cells of products of photosynthesis

• Vectors — transferring viruses, bacteria, and fungi from diseased plants → healthy plants on mouthparts

How can aphids be destroyed? (2)

• Chemical pesticides

• Releasing aphid-eating insects — e.g. ladybirds

How do plants use nitrate ions?

Convert the glucose (made in photosynthesis) →proteins (for growth)

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

• Limited photosynthesis

• Stunted growth

• 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.