plant defences

• Pathogens are disease-causing viruses, bacteria, fungi or protists which attack plants as well as animals.
• Plants have physical and chemical defences against pathogens.
• Many plants are covered with a thick bark, which is an external layer of dead cells that forms a physical barrier against infection.
• Each plant cell has a cellulose cell wall which acts as another barrier against infection.
• Herbivores are animals that feed only on plants.
• Plant defences do not defend plants from infection by pathogens.
• Bacteria are single-celled microorganisms, some of which are pathogenic in humans, animals and plants.
• Farmers can now genetically engineer crop plants to be resistant to infections.
• Chemical defences are used in antiseptics for humans.
• Some plants, such as mint and witch hazel, produce antibacterial chemicals which protect them from bacterial pathogens.
• Leaves are covered with a waxy cuticle which protects them and stops their cells from becoming infected.