Exam questions · Biology
Plant Disease
- 14 exam questions
- 37 marks
- 16 quick checks
Detecting and Identifying Plant Diseases
Just this lesson-
1 State [1 mark]
Name one insect pest that harms plants.
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Model answer
Aphids.
Mark scheme
- Aphid — 1 mark
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2 Name [3 marks]
Figure 1 shows three plants. Plant A is healthy. State which ion plant B and plant C are short of, and name the symptom of plant C.
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Model answer
Plant B is short of nitrate ions. Plant C is short of magnesium ions. The symptom of plant C is chlorosis (yellow leaves).
Mark scheme
- B: nitrate — 1 mark
- C: magnesium — 1 mark
- Chlorosis / yellow leaves — 1 mark
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3 Explain [2 marks]
Explain why a plant that is short of nitrate ions shows stunted growth.
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Model answer
Nitrate ions are needed to make amino acids, which are used to make proteins. Without enough protein the plant cannot make new cells, so it cannot grow properly.
Mark scheme
- Nitrate needed for protein — 1 mark
- Cannot grow / stunted — 1 mark
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4 Explain [3 marks]
Explain why the leaves of a plant that is short of magnesium ions turn yellow.
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Model answer
Magnesium ions are needed to make chlorophyll. Without enough magnesium, less chlorophyll is made, so the leaves are yellow (chlorosis). The plant also photosynthesises less.
Mark scheme
- Magnesium needed for chlorophyll — 1 mark
- Less chlorophyll so yellow leaves — 1 mark
- Less photosynthesis — 1 mark
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5 Describe [3 marks]
Describe three signs that could show a plant has a disease.
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Model answer
Spots on leaves, such as those of rose black spot. Stunted growth, where the plant is smaller than it should be. Discolouration, such as the mosaic pattern on the leaves in tobacco mosaic virus. (Also accept: areas of decay, growths, malformed stems or leaves, the presence of pests.)
Mark scheme
- A first correct sign — 1 mark
- A second correct sign — 1 mark
- A third correct sign — 1 mark
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6 Describe [3 marks]
Describe three ways in which a plant disease can be identified.
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Model answer
By comparing the symptoms with a gardening manual or website. By taking an infected plant to a laboratory to identify the pathogen. By using a testing kit that contains monoclonal antibodies.
Mark scheme
- Manual or website — 1 mark
- Laboratory — 1 mark
- Monoclonal antibody testing kit — 1 mark
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7 Explain [3 marks]
Explain how a testing kit containing monoclonal antibodies can identify a plant pathogen.
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Model answer
The monoclonal antibody is specific to one antigen on the pathogen. If the pathogen is present in a sample from the plant, the antibody binds to it. The kit then shows a colour change, which shows the pathogen is present.
Mark scheme
- Antibody specific to the pathogen's antigen — 1 mark
- Binds if the pathogen is present — 1 mark
- Colour change shows it — 1 mark
Quick check
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1
Which ion is needed to make chlorophyll?
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B: Magnesium
Magnesium ions are needed to make chlorophyll.
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2
Which ion is needed to make proteins?
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A: Nitrate
Nitrate ions provide the nitrogen needed for amino acids and proteins.
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3
What is chlorosis?
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D: Yellowing of the leaves
Chlorosis is the yellowing of leaves, which happens when a plant lacks magnesium.
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4
Which symptom is caused by a lack of nitrate?
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C: Stunted growth
A shortage of nitrate causes stunted growth, because the plant cannot make enough protein.
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5
Which of these is an insect pest of plants?
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B: An aphid
Aphids are insects that feed on the sap of plants.
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6
How can a testing kit identify a plant pathogen?
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A: It uses monoclonal antibodies
The monoclonal antibodies in it bind to the pathogen and give a colour change.
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7
Which would a horticulturist add to treat stunted growth caused by a lack of nitrate?
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D: A nitrate fertiliser
A fertiliser containing nitrate provides the missing ions.
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8
Which disease would give a leaf a mosaic pattern?
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C: Tobacco mosaic virus
Tobacco mosaic virus causes a mosaic pattern of discolouration.
Plant Defence Responses
Just this lesson-
1 State [1 mark]
Name the material that makes up the cell walls of plant cells.
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Model answer
Cellulose.
Mark scheme
- Cellulose — 1 mark
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2 Describe [2 marks]
Describe how the bark of a tree helps to protect it against pathogens.
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Model answer
The bark is made of layers of dead cells, which form a barrier that pathogens cannot easily pass. The layers fall off, which carries away microorganisms on the surface.
Mark scheme
- Layers of dead cells form a barrier — 1 mark
- Fall off and take pathogens with them — 1 mark
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3 Name [3 marks]
Figure 1 shows some defences of plants. Name the type of defence shown at A, B and C (physical, chemical or mechanical).
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Model answer
A is a physical defence. B is a chemical defence. C is a mechanical adaptation.
Mark scheme
- A: physical — 1 mark
- B: chemical — 1 mark
- C: mechanical — 1 mark
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4 Explain [3 marks]
Explain how a poison made by a plant can protect the plant from being eaten.
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Model answer
Animals that eat the plant take in the poison, which makes them ill or kills them. They learn not to eat that plant, and other animals avoid it, so the plant survives with less damage.
Mark scheme
- Poison harms animals that eat it — 1 mark
- Animals learn to avoid it — 1 mark
- Plant is damaged less / survives — 1 mark
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5 Describe [3 marks]
Describe three mechanical adaptations that deter animals from eating a plant.
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Model answer
Thorns that are sharp and hurt the animal. Hairs on the leaves or stem that deter animals. Leaves that curl or droop when touched. (Also accept mimicry, for example looking like something unpleasant.)
Mark scheme
- Thorns — 1 mark
- Hairs — 1 mark
- Drooping or curling leaves / mimicry — 1 mark
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6 Explain [3 marks]
Explain why the cellulose cell wall and the waxy cuticle are both useful defences against the invasion of microorganisms.
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Model answer
The cellulose cell wall is a strong barrier around each cell, which most microorganisms cannot easily break through. The waxy cuticle is a tough layer on the leaf surface that microorganisms cannot easily get through, and water runs off it so they do not collect there. Together they make it harder for microorganisms to get in.
Mark scheme
- Cell wall is a strong barrier — 1 mark
- Waxy cuticle is a tough barrier on the surface — 1 mark
- Together they make entry harder — 1 mark
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7 Evaluate [4 marks]
A plant has thorns, poisonous leaves and bark. Explain how each of these features protects the plant, and say which type of defence each one is.
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Model answer
The thorns are a mechanical adaptation, which deter animals from eating the plant. The poison is a chemical defence, which makes animals that eat the leaves ill. The bark is a physical defence, made of dead cells, which resists the invasion of microorganisms. Together, they protect the plant from both animals and pathogens.
Mark scheme
- Thorns: mechanical, deter animals — 1 mark
- Poison: chemical, harms animals — 1 mark
- Bark: physical, resists microorganisms — 1 mark
- Together they defend against animals and pathogens — 1 mark
Quick check
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1
What is the bark of a tree made of?
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B: Dead cells
The bark is made of layers of dead cells, which form a barrier against microorganisms.
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2
Which of these is a chemical defence of a plant?
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C: A poison
Antibacterial chemicals and poisons are chemical defences.
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3
Which of these is a mechanical adaptation?
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A: Thorns
Thorns are a mechanical adaptation that deters animals.
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4
What is a herbivore?
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D: An animal that eats plants
A herbivore is an animal that eats plants.
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5
What does the waxy cuticle do?
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B: It is a barrier on the leaf surface
The cuticle is a tough barrier on the surface of the leaf.
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6
What is mimicry in plants?
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C: Looking like something else
In mimicry, a plant looks like something else to trick animals.
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7
Why do leaves that curl when touched help a plant?
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A: They are harder for animals to eat
They are harder to eat and may scare animals away.
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8
Which defence is made of cellulose?
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D: The cell wall
Plant cell walls are made of cellulose and form a barrier to microorganisms.