4.3.3 Plant disease (biology only)
4.3.3.1 Detection and identification of plant diseases
Identifying Plant Disease
- Stunted growth: it can be caused by many factors such as Mealybugs and other pets. It is often caused by a reduction in photosynthesis.
- Spots on leaves: infection can lead to black spots on leaves
- Areas of decay: leaves can often decay and rot in certain areas
- Growths: there may be unusual bumps and growths from the plant
- Malformed stems or leaves: infection can lead to poor development of stems and leaves
- Presence of pests: near a plant crop are an indicator that infection has occurred
Identifying Disease by Naked Eye
- Stunted growth: it can be caused by many factors such as Mealybugs and other pests
- It is often caused by a reduction in photosynthesis
- Spots on leaves: infection can lead to black spots on leaves
- Areas of decay: leaves can often decay and rot in certain areas
- Growths: there may be unusual bumps and growths from the plant
- Malformed stems or leaves: infection can lead to poor development of stems and leaves
- Presence of pests: near a plant crop are an indicator that infection has occurred
Further Investigation
Gardening manuals: to look up specific symptoms and check common diseases
Laboratory tests: professionals will identify the ailment or use specific testing kits
Monoclonal antibodies: testing kits often contain monoclonal antibodies
Specific Case Studies
- Tobacco mosaic virus: this virus can cause a viral disease
- Black spot: this is a fungal disease which can be identified by presence of black spots on leaves
- Aphids: these are examples of insects which can cause infection
Nitrate Deficiency
- Nitrates are the most important element in the formation of protein
- They are taken in from the soil in order to allow proper growth
- A deficiency of nitrates will lead to stunted growth
Magnesium Deficiency
- Magnesium ions are taken in to synthesise chlorophyll
- A deficiency of magnesium = chlorosis (the discolouration of the plant)
- Magnesium deficiency may be present if plants have yellow leaves
4.3.3.2 Plant defence responses
Plant Defences
- Plants have developed natural defence systems to fight against infection
- The adaptations may develop over many generations through natural selection
Physical Defences
- Cellulose Cell Wall – form a physical barrier between the cells and pathogens, thus protect against infection
- Waxy Cuticles – prevent entry of pathogens into the leaf and prevent water loss
- Bark – protects the stems, to protect against infection as it stops the passage of pathogens
Chemical Defences
- Antibacterial chemicals: some plants secrete antibacterial chemicals to kill bacterial pathogens. Different plant species may secrete different types of chemical
- Poisons: some plants produce poisons to protect against herbivores
Mechanical Defences
- Thorns and hairs: some plants protect themselves with thorns and hairs. For example. cacti have thorns which deters herbivores
- Drooping leaves: some plants have leaves that droop or curl when touched, which can push insects off the plant
- Mimicry: a plant may scare predators by mimicking the features of a dangerous species
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