Identify and describe Why Plants Need Defence Systems, Physical Defence: Cell Walls and Physical Defence: Waxy Cuticles in the context of plant defence responses.
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GCSE Biology Revision
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GCSE Biology revision
Plant defence responses
Plant disease (biology only)
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Explain the relationships between Why Plants Need Defence Systems, Physical Defence: Cell Walls and Physical Defence: Waxy Cuticles and how they contribute to plant defence responses.
Apply and analyse knowledge of Why Plants Need Defence Systems, Physical Defence: Cell Walls and Physical Defence: Waxy Cuticles to interpret unfamiliar information about plant defence responses.
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Why Plants Need Defence Systems
- Just like humans, plants have evolved natural defence systems to protect themselves against infection and attack.
- These defences have developed over many generations through natural selection, where plants with the best defences are more likely to survive, reproduce, and pass on their genes.
Physical Defence: Cell Walls
- Cellulose cell walls form a physical barrier between plant cells and pathogens, protecting against infection.
- Unlike animal cells, which only have a cell membrane, plant cells have this extra layer of protection provided by the cell wall.
Physical Defence: Waxy Cuticles
- Leaves are covered by a waxy cuticle that acts as a physical barrier, preventing pathogens from entering the leaf.
- The waxy cuticle also serves a second function by reducing water loss from the leaf, demonstrating how plant adaptations can have multiple benefits.
Physical Defence: Bark
- Plants have layers of dead cells forming bark around their stems, which acts as a physical barrier against infection.
- Bark can be thought of as the plant equivalent of human skin — both are physical barriers that prevent pathogens from entering the internal environment.
- Different parts of the plant have different physical defences, as each structure is adapted to protect a specific region, such as bark protecting stems rather than leaves.
Chemical Plant Defences
- Some plants secrete antibacterial chemicals from glands to kill bacterial pathogens, with different plant species producing different types of these chemicals.
- This is similar to humans, who have antimicrobial chemicals in their tears to protect against infection.
- Some plants produce poisons that are toxic to herbivores (animals that eat plants), deterring them from feeding on the plant.
Mechanical Defences: Thorns and Hairs
- Some plants, such as cacti, have thorns that physically deter herbivores from eating them.
- Certain plants have hairs on their surfaces that can also act as a mechanical barrier against insects and other animals.
Mechanical Defences: Drooping and Curling Leaves
- Some plants have leaves that droop or curl when touched, which can physically dislodge insects from the plant's surface.
- This response is a mechanical adaptation that helps protect the plant from insect attack without the need for chemical defences.
Mechanical Defences: Mimicry
- Some plants use mimicry to mimic the appearance of dangerous species, which scares away potential predators.
- Certain flowers mimic the appearance of a female pollinating insect, attracting male insects and increasing the chances of pollination.
- Mimicry therefore serves a dual purpose: it can both deter predators and attract pollinators, directly benefiting the plant's survival and reproduction.
Applying Plant Defences to Unfamiliar Species
- In exam questions, you may be presented with a plant species you have never studied before, but the same physical, chemical, and mechanical defences apply across the plant kingdom.
- You do not need prior knowledge of a specific species — instead, apply your understanding of the three categories of plant defence to any example given.
Summary of Plant Defence Categories
- Physical defences include cellulose cell walls, waxy cuticles, and bark, all of which act as barriers to prevent pathogen entry.
- Chemical defences include antibacterial secretions and poisons that target pathogens or herbivores.
- Mechanical defences include thorns, hairs, drooping or curling leaves, and mimicry, all of which physically deter or manipulate other organisms.