This definitions covers Key Definitions within Plant Hormones for GCSE Biology. Topic 11: Plant Hormones It is section 6 of 12 in this topic. Make sure you can use the exact wording confidently, because definition marks are often lost through vague language.
Key Definitions
Auxin: A plant hormone produced in shoot and root tips that controls cell elongation; causes shoots to grow towards light and roots to grow downwards.
Phototropism: The growth of a plant in response to light; shoots show positive phototropism (grow towards light), roots show negative phototropism.
Gravitropism (geotropism): The growth of a plant in response to gravity; roots show positive gravitropism (grow downward), shoots show negative gravitropism (grow upward).
Cell elongation: The process by which plant cells increase in length; controlled by auxin through changes in cell wall flexibility.
Gibberellin: A plant hormone that promotes seed germination, stem elongation, and fruit development; used commercially to increase fruit size and improve crop yields.
Ethylene (ethene): A plant hormone in the form of a gas that promotes fruit ripening; used commercially to ripen fruit after harvesting during transport.
Plant hormone: A chemical substance produced in small amounts that regulates growth and development in plants; transported to target cells where it causes a response.
Practice questions for Plant Hormones
When a plant shoot is lit from one side, where does auxin accumulate?
Explain how auxin causes gravitropism (geotropism) in plant roots.
Quick recall flashcards
What is gravitropism?
Gravitropism is the growth response of a plant to gravity. Roots show positive gravitropism (grow downward, towards gravity). Shoots show negative gravitropism (grow upward, away from gravity).
What is phototropism?
Phototropism is the growth response of a plant to light. Shoots show positive phototropism — they grow towards the light source.