Practise Detection and identification of plant diseases. 11 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
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What name is given to the yellowing of leaves caused by a lack of chlorophyll?
Chlorosis
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
A gardener noticed that some plants were not growing well.
(a) Which two of these are signs that a plant may be diseased? Tick (✓) two boxes.[2]
Areas of decay (rot)
Flowers that open in the morning
Leaves that face the light
Roots that grow downwards
Spots on the leaves
(b) Give one way the gardener could identify the disease.[1]
(c) The leaves of some of the plants were yellow. This can be caused by a lack of one type of mineral ion. Which ion is needed to make chlorophyll? Tick (✓) one box.[1]
Calcium
Magnesium
Nitrate
Sodium
(d) What name is given to the yellowing of leaves caused by a lack of chlorophyll?[1]
Show the answer and mark scheme
(a)Answer: Areas of decay (rot); Spots on the leaves
(b)
look it up in a gardening manual / on a website
take the plant to a laboratory to identify the pathogen
use a testing kit (containing monoclonal antibodies)
(c)Answer: Magnesium
(d)Answer: Chlorosis
chlorosis
Question 2Medium7 marks
Plants need mineral ions from the soil to grow well.
(a) Explain why a plant growing in soil that lacks nitrate ions has stunted growth.[3]
(b) Explain why a plant growing in soil that lacks magnesium ions grows slowly.[3]
(c) Suggest how a gardener could treat plants that lack nitrate ions.[1]
Show the answer and mark scheme
(a)
nitrate ions are needed to make amino acids / proteins
proteins are needed for growth / to make new cells / enzymes
(so) less protein is made and the plant grows less
(b)
magnesium ions are needed to make chlorophyll
(so) less chlorophyll / leaves turn yellow (chlorosis)
(so) less light is absorbed / less photosynthesis, so less glucose for growth
(c)
add a fertiliser containing nitrates (to the soil)
Question 3Hard9 marks
A grower noticed yellow areas on the leaves of some tomato plants in a greenhouse. The grower thought the cause could be either tobacco mosaic virus (TMV) or a magnesium deficiency.
(a) Describe how the pattern of yellowing on the leaves could help the grower decide which cause is more likely.[2]
(b) Give two methods the grower could use to identify the cause.[2]
(c) Explain how a testing kit containing monoclonal antibodies can show whether TMV is present.[2]
(d) The grower added a fertiliser containing magnesium ions to half of the plants. Three weeks later, new leaves on these plants were green. New leaves on the other plants were still yellow. What do these results suggest? Explain your answer.[2]
(e) Explain why it is important to identify the cause correctly before treating the plants.[1]
Show the answer and mark scheme
(a)
TMV causes a mosaic pattern of (patchy) discolouration
magnesium deficiency causes chlorosis: yellowing of the leaves (often between the veins) without a mosaic pattern
(b)
use a testing kit containing monoclonal antibodies (against TMV)
send samples of leaves to a laboratory to identify the pathogen
compare the leaves with pictures in a gardening manual / on a website
test the compost / soil for magnesium ions
(c)
the antibodies are specific: they bind only to (an antigen / protein on) TMV
if TMV is present the antibodies bind to it and a coloured line / colour change is seen
(d)
the plants had a magnesium deficiency (not TMV)
the magnesium allowed the plants to make chlorophyll in new leaves; adding magnesium would not cure a viral infection
(e)
the treatments are different, e.g. fertiliser will not cure TMV / infected plants must be removed to stop the virus spreading