Antibacterial chemicals. • Poisons to deter herbivores.

The idea

This statement separates two chemical defence strategies. Antibacterial chemicals are produced by plants to inhibit or kill bacteria, especially where tissue is wounded and vulnerable to infection. Poisons deter herbivores by making plant material toxic or unpleasant, so animals learn to avoid that plant. The two strategies differ in target: bacteria versus animals. A clear method is to ask what organism is harmed and how the plant benefits. For example, some plants release antibacterial compounds into damaged areas, reducing decay, while others store alkaloids in leaves that cause illness in grazing mammals. Both defences are inherited adaptations, not learned behaviour, and both raise survival and reproductive success. When answering, name the chemical where known, state its target, and explain the benefit to the plant.

What earns the marks

• Antibacterial chemicals inhibit or kill bacteria and reduce infection of damaged plant tissue.
• Poisons are toxins that deter herbivores by making the plant harmful or unpalatable to eat.
• The two categories differ by target organism: bacteria for antibacterials, animals for poisons.
• Defensive chemicals may be stored in leaves, bark, roots or seeds and released on damage.
• Named examples include tannins and alkaloids, each with a specific defensive role.

Common mistakes and how to put them right

• Saying antibacterial chemicals deter herbivores.

  Put it right by stating that they act on bacteria, while poisons deter animals.

• Describing poisons as killing the plant.

  Put it right by explaining that they harm or deter the herbivore, protecting the plant.

• Believing plants choose to make chemicals when attacked.

  Put it right by describing production as an inherited, automatic response.

Exam tips

• Always name the target organism when describing a chemical defence.
• Use comparative language such as whereas or in contrast to distinguish the two categories.
• Finish an explanation by linking the defence to the plant's survival or reproduction.