3.3 Plant Disease

Question 1

How do aphids cause damage to plants?

Answer 1

They use their sharp mouthparts to extract sap from the plant phloem, weakening the plant. They are also vectors who can transfer pathogen from diseased plants to healthy plants.

Question 2

How can we reduce the number of aphids?

Answer 2

• Chemical pesticides
• Biological pest control - using ladybirds

Question 3

Why do plants need a good supply of nitrate ions

Answer 3

Nitrate Ions are required to convert sugars into protein which are required for the plant to grow. As a result, the growth of the plant will be a stunted if there is not an adequate supply of nitrates

Question 4

Why do plants need a good supply of magnesium ions?

Answer 4

Required to synthesise chlorophyll, which absorbs light energy during photosynthesis. As a result, the leaves cannot photosynthesise properly and turn yellow (chlorosis)

Question 5

What are the symptoms of disease in plants?

Answer 5

• Stunted growth
• Spotted leaves
• Decay/rotting
• Growths
• Malformation of stems/leaves
• Discolouration
• Presence of pests

Question 6

What are three ways in which plant disease can be identitfied?

Answer 6

• Reference to a gardening website or manual
• Laboratory testing
• Monoclonal antibody test kits

Question 7

Give examples of physical defence responses used by plants.

Answer 7

• Cellulose cell walls
• Tough waxy cuticle on leaves
• Outside layer on stem/bark on trees
• Leaf fall

Question 8

Give examples of chemical defence responses used by plants

Answer 8

• Antibacterial chemicals
• Poisons

Question 9

Give examples of mechanical defence responses used by plants

Answer 9

• Thorns and hairs to deter animals
• Leaves that droop/curl on contact
• Mimicry to trick animals