Types of Plant Responses

Why is it important for plants to respond to the environment?

- To avoid abiotic stress

- To avoid herbivory

- To maximise photosynthesis

- To help ensure germination/fertilisation

Phototropism

A plant's growth response to light

Positive Phototropism

- Growth towards light

- Found in the stem tips or shoots

- It maximises light for photosynthesis

Negative Phototropism

- Growth away from light

- Found in roots

- Prevents roots from drying out

Geotropism

A plant's growth response to the Earth's gravitational field

Positive Geotropism

Plant roots grow towards the gravitational attraction (down)

Negative Geotropism

Plant stems (shoots) grow away from the gravitational attraction

Hydrotropism

A plant's growth response to the Earth's water

Thigmotropism

A plant's growth response to touch

Chemical Defences

- Alkaloids

- Pheromones

Alkaloids

- Very bitter tasting

- Nitrogenous compounds found in many plants

What does alkaloids include?

Caffeine and nicotine.

Caffeine is toxic to fungi and insects, and nicotine is a toxin produced in the roots of tobacco plants that is poisonous to insects.

Pheromones

Chemicals made by organisms that affect the behaviour of other/same species

An example of pheromones

When corn plants are being eaten by caterpillars, they can produce chemicals which attract parasitic wasps. These wasps lay their eggs on the caterpillars, which eventually causes the caterpillars death.