Growth Factors in Flowering Plants (AQA A Level Biology): Revision Note

Plant responses to stimuli

• As in animals, the survival of plants is dependent on their ability to respond to changes in the environment

• Plants carry out growth responses to directional stimuli

  • E.g. when light falls on a plant from one direction, the plant can grow towards the light

• This type of directional growth response is known as a tropism

  • Phototropism is a growth response to light

  • Gravitropism is a growth response to gravity

• Tropisms can be positive or negative, causing the plant to grow towards or away from a stimulus

Plant growth factors

• The growth responses of plants due to the effects of chemical growth factors released by plant cells

  • These growth factors act in a similar way to hormones in animals

• Growth factors are specific; different growth factors bring about different plant responses

• Growth factors are often produced in the growing parts of plants, before moving to other tissues, where they regulate growth in response to a stimulus

  • E.g. the growth factor IAA is synthesised at the tips of roots and shoots, but it mainly affects growth in the region adjacent to the tip