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 pathogens from diseased plants to healthy plants.

Question 2

how can we reduce the number of aphids?

Answer 2

• chemical pesticides
• biological pest control - using ladybids

Question 3

why do plants need a good supply of nitrate ions?

Answer 3

nitrate ions are required to convert sugars into proteins which are required for the plant to grow. as a result, the growth of the plant will be stunted if there is not an adequate supply of nitrates.

Question 4

why do plants need a good supply of magnesium ions?

Answer 4

magnesium ions are required to synthesise chlorophyll, which absorbs light energy during photosynthesis. as a result, the leaves cannot photosynthesise properly and they turn yellow (chlorosis).

Question 5

what are the symptoms of disease in plants?

Answer 5

• stunted growth (lack of nitrate ions)
• spotted leaves (e.g. rose black spot fungus)
• decay/rottung
• growths
• malformation of stems/leaves
• discolouration
• presence of pests

Question 6

what are three ways in which plant disease can be identified?

Answer 6

• reference to a gardening website or manual
• labouratory 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 of stems/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