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

Exam code: 7402

Lára Marie McIvor

Written by: Lára Marie McIvor

Reviewed by: Naomi Holyoak

Updated on

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

Diagram of a potted plant with stems bending towards a light source on the left, illustrating phototropism. Plant has many green leaves.
In flowering plants, specific growth factors regulate growth in response to directional stimuli

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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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology, Psychology & Sociology Subject Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

Naomi Holyoak

Reviewer: Naomi Holyoak

Expertise: Biology Content Creator

Naomi graduated from the University of Oxford with a degree in Biological Sciences. She has 8 years of classroom experience teaching Key Stage 3 up to A-Level biology, and is currently a tutor and A-Level examiner. Naomi especially enjoys creating resources that enable students to build a solid understanding of subject content, while also connecting their knowledge with biology’s exciting, real-world applications.