Triple Science Only - Plant Disease
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of plant structure and function, including tissues and organs, and how pathogens cause disease.
What are the four main types of pathogen?
Viruses, bacteria, protists and fungi.
What is a monoclonal antibody?
A monoclonal antibody is an identical antibody produced from a single clone of white blood cells that binds to one specific antigen.
Name a virus that infects plants.
Tobacco mosaic virus (TMV).
Topic Explainer Video
Check out this @JoeDoesBiology video that explains plant disease, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
Detection and Identification of Plant Diseases
Plant deficiencies
Not all plant problems are caused by pathogens. Ion deficiencies can produce similar symptoms:
|
Deficiency |
Symptoms |
Cause |
|
Nitrate deficiency |
Stunted growth |
Nitrates are needed to make amino acids for protein synthesis and growth. |
|
Magnesium deficiency |
Yellow leaves (chlorosis) |
Magnesium ions needed to make chlorophyll. |
Higher Tier only
How Plant Diseases Are Detected
Plant diseases can affect crop yield and food security. Scientists and horticulturists need accurate methods to detect and identify plant diseases early.
Symptoms of Plant Disease:
Common signs that a plant might be infected include:
- Stunted growth
- Spots on leaves
- Areas of decay (rot)
- Abnormal growths
- Malformed stems or leaves
- Discolouration
- Presence of pests (e.g. aphids)
These symptoms may suggest a disease caused by a pathogen (virus, bacterium, or fungus) or a mineral ion deficiency.
Many diseases link to reducing the rate of photosynthesis and therefore how much glucose is produced.
Example:
A lack of magnesium ions means a plant cannot produce as much chlorophyll. This means less light can be absorbed which reduces the rate of photosynthesis. This means the plant produces less glucose. With less glucose for respiration, they have less energy for growth.
Higher Tier only
How Plant Diseases Are Identified
When a plant shows signs of disease, identification of the exact cause is important so the correct treatment can be given. There are three main methods of identification:
1. Gardening Manual or Website
- Compare symptoms with pictures and descriptions.
2. Laboratory Testing
- Pathogens can be grown or analysed in a lab to confirm infection.
3. Testing Kits Using Monoclonal Antibodies
- Monoclonal antibodies are highly specific and will only bind to one antigen, such as a protein found on a pathogen. This makes them useful in plant disease testing kits.
- These kits are highly accurate and use monoclonal antibodies to detect the presence of specific plant pathogens or molecules linked to infection.
Key Terms and Definition
Term |
Definition |
|
Monoclonal antibody |
Identical antibodies produced from a single clone of white blood cells that bind to one specific antigen. |
|
Pathogen |
A microorganism that causes disease. |
|
Aphid |
Insect pests that can damage plants and spread diseases. |
No answer provided.
Exam Tips
In questions asking how a plant disease could be diagnosed, always include symptom observation, lab testing, and monoclonal antibody kits.
Be prepared to think about how the symptoms of a disease affect the plant, such as a reduction in photosynthesis.
No answer provided.
Practice Question
Describe how a plant disease can be detected and identified. (4 marks)
Model Answer:
- A diseased plant may show symptoms such as stunted growth, spots on leaves, or discolouration.
- Identification can be made by comparing symptoms with a gardening manual or website.
- In a laboratory, scientists can analyse the plant for pathogens.
- Alternatively, testing kits that use monoclonal antibodies can detect specific pathogens quickly and accurately.
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!