Growth Factors in Flowering Plants (AQA A Level Biology): Revision Note
Exam code: 7402
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

Examiner Tips and Tricks
While you may have learned about "plant hormones" at GCSE, it is important to use A-level terminology here, so you should always use the term growth factors.
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