Plants cannot move away from danger, so they have defences that help them resist invasion by microorganisms and attack by animals. These defences can be physical, chemical or mechanical.
Physical defences form a barrier that microorganisms find hard to get through. Plant cells have cellulose cell walls. Many leaves are covered by a tough waxy cuticle. Stems have layers of dead cells around them, such as the bark on trees, which fall off and take any microorganisms with them.
Chemical defences are substances the plant makes. Some are antibacterial chemicals that kill bacteria. Others are poisons that deter herbivores from eating the plant.
Plants also have mechanical adaptations that deter animals. Thorns and hairs make a plant hard or painful to eat. Some leaves droop or curl when touched, which can scare off or dislodge an animal. Some plants use mimicry, where they look like something else, to trick animals.