AQA GCSE Biology
AQA GCSE Biology 4.3.3 Plant Disease Exam Questions
Free AQA GCSE Biology exam questions for 4.3.3 Plant Disease, with a mark scheme for every pack. Covers signs and identification of plant disease, pests, nitrate and magnesium deficiency, and physical, chemical and mechanical plant defences.
4.3.3 Plant Disease exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Biology 4.3.3 Plant Disease
Plant disease is a Biology only section of AQA Infection and response, examined on Paper 1. It explains how gardeners and scientists recognise plant disease, what causes it, and how plants defend themselves. It links to tobacco mosaic virus and rose black spot in 4.3.1, to mineral ion uptake in 4.1.3 and to protein synthesis. Examiners ask you to list signs of disease, explain the effects of nitrate and magnesium deficiency, and classify plant defences as physical, chemical or mechanical with clear reasons.
What you need to know
- Signs of plant disease Stunted growth, spots on leaves, areas of decay (rot), growths, malformed stems or leaves, discolouration and the presence of pests can all indicate disease.
- Identifying disease Diseases can be identified by using a gardening manual or website, taking infected plants to a laboratory, or using testing kits that contain monoclonal antibodies.
- Causes of disease Plants can be infected by viral (tobacco mosaic virus), bacterial and fungal (rose black spot) pathogens, and damaged by insects such as aphids, which feed on phloem sap.
- Ion deficiency Nitrate ions are needed for protein synthesis, so deficiency causes stunted growth. Magnesium ions are needed to make chlorophyll, so deficiency causes chlorosis (yellowing leaves).
- Physical defences Cellulose cell walls, a tough waxy cuticle on leaves, and layers of dead cells such as bark that fall off, all resist invasion by microorganisms.
- Chemical and mechanical defences Chemical defences include antibacterial chemicals and poisons that deter herbivores. Mechanical defences include thorns and hairs, leaves that droop or curl when touched, and mimicry to trick animals.
Common mistakes in 4.3.3 Plant Disease
- Saying magnesium is part of protein. Magnesium is needed for chlorophyll; nitrate is needed for protein.
- Calling thorns a physical defence. AQA classifies thorns and hairs as mechanical adaptations; physical defences are barriers such as cell walls, cuticle and bark.
- Saying chlorosis means the leaves die. Chlorosis is yellowing due to lack of chlorophyll, which reduces photosynthesis.
- Describing aphids as pathogens. Aphids are insect pests, although they can carry pathogens.
Try three 4.3.3 Plant Disease exam-style questions
1. Explain why a plant lacking nitrate ions shows stunted growth. (2 marks)
Show the mark scheme answer
Nitrate ions are needed to make amino acids and proteins; proteins are needed for growth
2. Explain why magnesium deficiency reduces plant growth. (3 marks)
Show the mark scheme answer
Magnesium is needed to make chlorophyll; leaves become yellow (chlorosis); less light absorbed so less photosynthesis and less glucose for growth
3. Describe two ways a gardener could identify the disease affecting a rose plant. (2 marks)
Show the mark scheme answer
Look up the symptoms in a gardening manual or website; send a sample to a laboratory; use a testing kit containing monoclonal antibodies (any two)
4.3.3 Plant Disease FAQs
What does AQA GCSE Biology 4.3.3 Plant disease cover?
It covers signs and identification of plant disease, pathogens and insect pests, nitrate and magnesium deficiency, and physical, chemical and mechanical plant defences.
Which paper is 4.3.3 Plant disease examined on?
It is Biology only content in Infection and response, assessed on Paper 1.
How do I remember the types of plant defence?
Physical defences are barriers (cell walls, cuticle, bark), chemical defences are substances (antibacterial chemicals, poisons), and mechanical defences change how animals interact with the plant (thorns, hairs, drooping leaves, mimicry).
