Plant Disease (AQA GCSE Biology)

Exam Questions

2 hours13 questions
1a2 marks

Plants require certain minerals in order to grow.

If the plant does not get enough minerals it can exhibit symptoms of a deficiency, such as those listed below in Figure 1.

Draw one line from each type of mineral in Figure 1 to the symptom the plant shows when it is deficient in that mineral.

Figure 1

network-of-capillariesto-maximise-oxygen-absorptionfunctionfeaturethin-liningmoist-surfaceallows-oxygen-to-readily-dissolvefor-efficient-gas-exchange-with-red-blood-cellsto-minimise-diffusion-distancelarge-surface-area-1
1b1 mark

One of the symptoms listed in Figure 1 is chlorosis. 

What is chlorosis?

1c1 mark

If a crop plant growing in a farmer's field experiences a mineral deficiency it might have a reduced yield. 

This would result in the farmer losing money when they go to sell their crops after harvest. 

What could the farmer do to their fields to prevent their plants experiencing a mineral deficiency? 

1d3 marks

Minerals enter the plants through the roots. 

Describe the process that allows plants to absorb mineral ions into their roots.

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2a1 mark

Figure 2 shows a food chain. 

Figure 2

food-chain-for-plant-disease-q-1

What is the trophic level of the aphid in Figure 2

2b2 marks

Using Figure 2, describe what would happen to the number of aphids if a disease caused the number of ladybirds to decrease. 

2c4 marks

A gardener is growing tomatoes in their garden. 

They have identified that the tomato plants have been infested with a large number of aphids which are reducing the growth of the tomatoes. 

The gardener would like to remove the aphids and is considering two different options for treatment:

  • Option 1: Chemical pesticides, which are poisons that the gardener can spray in the garden which will kill all insects

  • Option 2: Biological control, which involves releasing large numbers of ladybirds into the garden

Evaluate the use of chemical pesticides and biological control in the garden to remove the aphids. 

2d2 marks

Higher Tier Only

As well as causing reduced growth, aphids can also act as vectors for disease. 

The gardener notices that some of his plants have a slight yellowing of some of the leaves after being infested with aphids. 

How could the gardener find out what disease the tomato plants are infected with?

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3a3 marks

This question is about how plants defend themselves against pathogens. 

Complete the sentences by picking one of the words in bold in each set of [ ] brackets. 

  1. Plant cells have physical barriers to defend themselves against the entry of pathogens. An example is the cell wall made of [starch / chitin / cellulose]  that acts as a barrier.

  2. A physical barrier around the outside of the leaf is called the [waxy cuticle / guard cells / palisade mesophyll].

  3. The outside of trees have a thick protective layer of dead cells around the stems called [cork / xylem / bark].

3b1 mark

The passion flower (Passiflora) is a genus of plant that produces leaves with small yellow spots, as shown in Figure 3. 

Figure 3

passion-flower-leaf-1

The spots on the leaves have evolved to mimic the eggs of butterflies.

What category of adaptation does this feature fall into?

Pick one option:

  • Physical

    • Mechanical

    • Chemical

3c2 marks

Suggest why having a mimicry of butterfly eggs on the leaves might benefit the plant.

3d1 mark

Methods to avoid herbivory are widespread in many different species of plants. 

Whilst these adaptations help to protect plant tissues from damage, they also protect from the entry of pathogens.

Suggest why does a defence against herbivores also defend against pathogens?

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4a2 marks

Many plants have varied strategies to avoid being eaten by herbivores, such as insects and animals. 

One adaptation is to produce poisonous chemicals. 

Name two other adaptations that plants can possess to defend themselves against herbivores. 

4b2 marks

Coffee plants produce a poisonous chemical called caffeine that acts as a pesticide, meaning that it kills insects that eat the plant.

The highest concentration of caffeine can be found in growing coffee seedlings.

Suggest why this stage of the plant lifecycle benefits from having such a high concentration of caffeine.

4c2 marks

Another place that caffeine can be found is in the soil surrounding the coffee plant. 

When found in the soil, caffeine prevents seeds from germinating in that region.

Why does this benefit the plant?

4d1 mark

One of the places that caffeine is stored in the plant cell is the vacuole.

The vacuole is useful for storage, but it also has another important role in the plant cell. 

What is the other important role of the vacuole in the plant cell? 

  • To carry out protein synthesis

  • To support the plant cells by making them turgid

  • It contains chlorophyll to carry out photosynthesis

  • To produce energy for the cell through the process of respiration

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5a1 mark

Higher Tier Only

Which of the following options is not a method used to detect disease in plants?

  • Variegated leaves

  • Spots on leaves

  • The presence of pests

  • Tumour growth

5b2 marks

Describe the symptoms a plant will show if it is infected with Tobacco Mosaic Virus (TMV).

5c
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2 marks

A farmer surveyed their plants for symptoms of TMV. 

During the survey the farmer identified that 24 of his 359 plants showed signs of having the disease. 

What percentage of his crop had symptoms of TMV? 

5d1 mark

Once the diseased plants have been identified, they then need to be treated. 

TMV has no cure.

What can the farmer do to prevent the spread of the pathogen to other plants? 

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1a2 marks

Plants can be infected by a range of pathogens.

Aphids are small insects that feed on plant sugars and carry pathogens.

Figure 1 shows an aphid feeding on a plant

Figure 1

aphid

Plants infested with aphids show signs of reduced growth.

Suggest and explain one reason why.

1b2 marks

Newly-hatched aphids do not have wings.

After a number of generations, a number of aphids hatch with wings.

A mutation in one population of aphids results in the wings failing to develop.

Suggest the impact of this on the aphid and other organisms. 

1c4 marks

It is common for plants infested with aphids to show signs of magnesium deficiency.

Describe and explain the symptoms displayed by a plant with a magnesium deficiency.

1d1 mark

Plants have methods of protecting themselves from attack.

One such method is the production of oils by cells on the surface of leaves. 

Suggest how the production of oil might protect a plant from being attacked. 

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2a1 mark

Higher Tier Only

A gardener notices that the leaves of one of his rose plants are covered in black and purple spots.

Name the disease affecting the gardener's rose plant.

2b4 marks

Higher Tier Only

Describe the cause of this disease and explain how the plant is affected by it.

2c4 marks

Higher Tier Only

Figure 3 shows the arrangement of rose plants in the gardener's garden.

Figure 3

rose-plants-garden

The infected plant is labelled I.

The gardener decides to move the plants labelled A and B to the other side of the garden (the area labelled X) to try and prevent the infection from spreading.

He decides not to use a fungicide.

Evaluate the effectiveness of the gardener's decisions in controlling the spread of the infection amongst the plants. 

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3a3 marks

Witch hazel is a plant that produces oil as part of its defence against pathogens.

Many skincare companies extract the oil to use in consumer products. 

The oil prevents bacteria from attacking the plant but is safe to use in skincare products. 

Suggest and explain a reason why.

3b4 marks

Scientists working for a skincare company investigated how effective three different plant oils were at preventing the growth of one strain of E. coli bacteria.

Figure 4 shows their results.

Figure 4

antimicrobial

Evaluate the effectiveness of the three plant oils.

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4a2 marks

Higher Tier Only

A number of plants in a garden are infected with a pathogen.

Give two ways of identifying the pathogen that is infecting the plants in the garden. 

4b2 marks

A number of mineral ions are needed by plants.

Plants that are deficient in mineral ions will not be healthy.

Name two essential mineral ions and describe the appearance of plants with deficiencies in these ions.

4c4 marks

Other minerals are essential for optimum plant growth.

NPK fertilisers are three-part fertilisers containing nitrogen (N), phosphate (P) and potassium (K) in varying proportions. 

Plants deficient in potassium have stunted roots.

Plants deficient in phosphate ions cannot form flowers and fruits.

The percentages (%) of minerals in three commercially-available NPK fertilisers were compared. The gardener used this data to decide which fertiliser to buy. 

The data are shown in Table 1.

Table 1

fertilisers

The gardener decided to buy Fertiliser 2.

Explain why he chose Fertiliser 2.

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5a1 mark

A common plant disease is caused by the tobacco mosaic virus (TMV).

Describe how a gardener would be able to recognise that their plants were infected with TMV.

5b3 marks

Suggest how monoclonal antibodies could be used to confirm that TMV was the cause of the disease in the gardener's plants.

5c1 mark

Suggest why the gardener washes all of their tools in disinfectant after using them on TMV-infected plants.

5d4 marks

TMV can cause plants to produce less chlorophyll.

Explain why plants with TMV exhibit stunted growth. 

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1a1 mark

Black Sigatoka is a type of plant disease caused by the fungal pathogen Mycosphaerella fijiensis.

It mainly infects banana plants and one of the main symptoms is that the leaves appear to have black streaks across them.

The fungal spores spread in the wind and in water droplets from plant to plant. They enter via the leaves.

Using Figure 1, identify the area of the leaf that allows the entry of pathogens. 

Figure 1

leaf-structure-1
1b2 marks

The black streaks on the leaves of plants infected by Black Sigatoka, appear as a result of the cells inside the leaf being digested by enzymes from the pathogen. 

The fungi release the enzymes extracellularly (outside of their cells) and then absorb the nutrients from the digested plant cells. 

Why is it possible for fungi to digest their food extracellularly instead of having an internal digestive system? 

1c3 marks

List some methods that can be taken by people that own banana plantations in order to prevent the spread of Black Sigatoka amongst their plants. 

Name three methods.

1d2 marks

When plants are infected with Black Sigatoka they have stunted growth and 50% lower fruit yield. 

Explain why this occurs. 

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2a2 marks

A student is planning an experiment to investigate the effect of mineral deficiency on the growth of plants.

This is the method used.

  1. Nine broad bean plants were grown for two weeks from seeds. 

  2. Each of the nine plants were grown in different types of soil, three in soil high in nitrates, three in medium levels of nitrate, and three in low levels of nitrate. 

  3. After the two week growth time the height of each of the plants was measured using a rule. 

Suggest two ways the student could improve their experiment.

2b
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2 marks

The results of the investigation are shown in Table 1. 

Table 1

nitrate-investigation-table_li-1

Using Table 1, calculate the mean height of the plants in the high soil nitrate concentration after two weeks. 

2c6 marks

The student made the following conclusion:

"The higher the nitrate concentration in soil, the taller plants will grow."

Using evidence from Table 1 and your own knowledge, evaluate this student's conclusion.

2d2 marks

Suggest why it is not always the best option for growers to increase the amount of nitrate in the soil if their plants aren't growing as tall as expected. 

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3a5 marks

A farmer identified that a number of his plants were showing signs of disease. 

The farmer researched the symptoms of one of his plants and the research suggested that a possible cause of the symptoms was a magnesium deficiency. 

Magnesium deficiency symptoms include:

  • Yellow leaves

  • Stunted growth

Explain how a deficiency of magnesium could cause these symptoms.

3b4 marks

Higher Tier Only

The farmer also thinks their strawberry crop is infected with a fungal pathogen Botrytis cinerea.

The farmer obtains a monoclonal antibody test kit for Botrytis cinerea.

To make the monoclonal antibodies a scientist first isolates the Botrytis cinerea protein from the fungi.

Describe how the scientist would use the protein to produce the Botrytis cinerea monoclonal antibody.

3c4 marks

After the farmer lost a large number of his plants to disease they decided to try breeding some resistant strains on the farm. 

The farmer will selectively breed some of the surviving plants in order to achieve this. 

Describe how the farmer would do this. 

3d3 marks

Another strategy that the farmer could use would be to take cuttings from resistant plants and clone them. 

Evaluate whether cloning is a better strategy for the farmer to use to get resistant crops than selective breeding. 

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