What is Plant Defenses? | Types, Definition, Structure, Function & Facts

What is Plant Defenses?

From the smallest insect to the largest mammal, most animals eat plants. These animals are called herbivores. At first, you might think that plants are just sitting there and being eaten. They certainly can’t get up and run away! However, plants have many defenses to help them survive.

Two Types of Defenses

There are two main types of plant defenses: constitutive and induced.

  • Constitutive – The basic defense mechanism is one that is always present in the tree. Most plant defenses are constitutive.
  • Induced – A inflicted defense is a temporary defense that aims to defend against an area of ​​the plant where it has been attacked or injured.

Cell Walls and Cuticle

Just like us, plants can contract diseases that make them sick and die. To prevent pathogens and small bacteria from getting inside, plants have rigid cell walls. They also have a waxy cuticle on the outside of their leaves to protect them.


Plants also have to protect themselves from insects. Many trees and bushes have thick bark on their branches and trunks to deter insects. The bark is multi-layered and the outer bark is dead and hard. This prevents all but the most determined insects from burrowing into the tree trunk.


Some plants use spines to protect themselves from being eaten by larger animals. The spikes can sting and annoy an animal enough to move it to another plant. Some examples of thorns include thorns on the stems of rose bushes and thorns on cactus plants. Certain types of cactus spines can be especially dangerous because they have spines that stick to the skin and are not easy to remove.

Chemical Defenses

Plants often develop chemicals that act like poisons to make an animal sick or even kill it. Over time, animals learn not to eat poisonous plants. Some common poisonous plants include daffodils, poison ivy, wisteria, fenugreek, and chrysanthemums.

Sometimes plants can detect when they are attacked by certain insects. They will emit chemicals that attract predators to animals that attack them.

Bad Taste

One way to avoid being eaten is to taste it. Many plants use chemicals to create a bitter taste. If a plant with the best flavor is nearby, the animal will move on.

Carnivorous Plants

Some plants are actually resistant to insects and not only fight them but also eat them. An example is the Venus flytrap which has a trap that looks like leaves. If a fly or other insect lands on its leaf, it quickly closes the trap and then releases enzymes to digest the insect.

Interesting Facts about Plant Defenses

Many of the drugs we use today are made from chemicals that plants use to protect themselves.

Some plants are home to herbivores that may eat plants.

Plants can wait to produce defensive chemicals until they are attacked due to the high energy and nutritional costs of producing chemicals.

Cotton produces chemicals that fight fungi and bacteria.

Plants can sometimes use chemicals to defend themselves against other plants invading their area.

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