A grower sees pale patches on the leaves of some tomato plants.
She uses a testing kit containing monoclonal antibodies to find out if three plants are infected with tobacco mosaic virus (TMV).
A coloured line appears at T if TMV is present. A coloured line should always appear at C.
The diagram shows her results.
(a) Which plant is infected with TMV? [1]
(b) Explain why the result for plant 3 cannot be used. [1]
(c) The kit cannot be used to find out if a plant is infected with the fungus that causes black spot.
Explain why. [1]
(d) Give one other way the grower could identify the disease. [1]
- (a) plant 2(1)
- (b) no line at C, so the test has not worked / is not valid; allow the sample did not move along the strip(1)
- (c) the antibodies are specific to (an antigen / protein on) TMV so will not bind to (antigens on) the fungus / black spot(1)
- (d) any one from: use a gardening manual / website; send a sample for laboratory testing; allow compare with photographs of diseased plants; ignore 'look at the leaves' unqualified(1)
- Answer: (a) plant 2 (b) control line missing — test failed (c) antibodies only bind to TMV antigens (d) gardening manual/website or lab testing
- Examiner tip: No control line means the test failed — it does NOT mean the plant is healthy.