Plant Defenses

Plants use both chemical and physical defenses in order to help protect the plants.

Plants are always having to defend themselves from attacks from fungi, bacteria, insects and animals.

The plants are at risk because of their bright colors and the nutrients and water that they have. Animals and insects are always looking to have some of these nutrients.

Surface Defense

A plants defense starts on the surface. A tree for example, has hard bark that contains lignin, which is hard for animals to chew.

Some leaves are covered in a waxy like material that that helps to keep insects from eating them and other leaves have trichomes, which is a hair like material that is sharp, but some trichomes release a chemical that stings their predators.

Other plants have thorns or spines to help keep them save. Other plants release a chemical that cause animals pain when they eat them.

Some plants do not hurt their predator until after they are eaten.

Some plants make raphides that are needle shaped crystals that cause small holes in the mouth of animals and then release toxins.

Some plants can tell when they are about to be eaten and these plants release charged particles that can shock their attacker and the leaves roll in, scaring away their predator.


Some plants grow where they blend into their environment. One example of a hidden plant is the living stone plant.

This plant grows in a dry, rocky area where there are stones and pebbles. This plant looks and feels like a stone and this helps to protect the plant from being eaten.

Plants Immune System

When a plants defense is triggered, it triggers the immune system to act as a healing and defending system.

The plants have different receptors that alert the cells to recognize molecules that bring danger such as microbes or insects.

The cells prevent more threat by the cell wall getting thicker and stronger, and guard cells seal the pores so that more organisms cannot enter into the plant.

If a plant is invaded by an insect or a microbe, the plant can shut that part of the leaf off to make sure that the rest of the plant is safe.

Compounds that are poisonous to microbes and insects are produced and the plant sometimes makes these specifically for what is attacking them.

Plant Sensors

Plants that are being attacked can alert other plants that this is happening. They do this by using hormones, electric signals and air born compounds.

When the other plants detect this, they put up defenses to protect themselves.

Some plants, such as cotton plants, tell other cotton plants that they are being attacked and these plants let off an odor that attracts wasps that lay eggs that kill caterpillars.

Facts about Plant Defenses

  • The kidney bean plant has small hooks that keep away bedbugs and other insects by stabbing them.
  • Plants that are made for human medicines are oftentimes taken from a plants immune system because they are anti-microbial and
  • Spinach release raphides that can cause small holes inside the animal’s mouth which then allows the plant to release toxins.
  • Plants or trees that have spikes can help keep animals from eating them.
  • Most prickles grow out of a plants stem and these are normally found on small shrubs or flowering plants.
  • Thorns mostly grow on large shrubs.
  • Some plants, like cactus’ have spines to defend themselves, spines look like thorns, but they are different because they do not dry out and they are actually leaves.
  • Stinging plants have a small tube that is filled with stinging liquid.

What Did You Learn?

  • What kind of defense does a tree have? A tree has bark that is hard to chew, and this helps to make the animals not want to eat them.
  • What do some plants release that can cause small holes to get in an animal’s mouth? Some plants release raphides which cause small holes to go into the animal’s mouth and then the plant can release toxins.
  • How can a plant alert other plants when it is being attacked? A plant can alert other plants through hormones, electric signals and air born compounds.
  • What is the difference between a thorn and a spine? A spine is actually a leaf and a thorn is a pointy piece that grow out of the plants branches.
  • How can plants use insects to their advantage when they are being attacked? Some plants send out a special smell that attracts the enemy of their attacker.