AQA GCSE Biology 4.5.4 Plant Hormones Exam Questions

About AQA GCSE Biology 4.5.4 Plant Hormones

Plant hormones is a Biology only section of AQA Homeostasis and response, examined on Paper 2. It explains how plants coordinate growth in response to light and gravity using auxin, and introduces gibberellins and ethene. The uses of plant hormones in agriculture and horticulture are Higher tier only. A required practical investigates the effect of light or gravity on the growth of newly germinated seedlings. Examiners often ask you to explain why a shoot bends towards light, interpret experiments with shoots and roots, and describe uses such as weedkillers and rooting powders.

What you need to know

• Phototropism and gravitropism Plants respond to light (phototropism) and gravity (gravitropism or geotropism). Shoots grow towards light and away from gravity; roots grow towards gravity.
• Auxin Unequal distribution of auxin causes unequal growth. In shoots, auxin moves to the shaded side and stimulates cell elongation there, so the shoot bends towards the light. In roots, auxin collects on the lower side and inhibits growth, so the root bends downwards.
• Gibberellins and ethene (Higher tier only) Gibberellins are important in initiating seed germination. Ethene controls cell division and the ripening of fruits.
• Required practical: seedlings Grow seedlings such as cress with light from one side or with dishes placed at different angles, and measure and record the direction and length of growth. Control seed type, water and temperature.
• Uses of auxins (Higher tier only) Auxins are used as weedkillers (selective weedkillers affect broad-leaved weeds), as rooting powders to help cuttings form roots, and to promote growth in tissue culture.
• Uses of ethene and gibberellins (Higher tier only) Ethene is used in the food industry to control ripening during storage and transport. Gibberellins can end seed dormancy, promote flowering and increase fruit size.

Common mistakes in 4.5.4 Plant Hormones

• Saying auxin is destroyed by light on the bright side. Auxin moves (redistributes) to the shaded side of the shoot.
• Saying auxin always speeds growth. Auxin stimulates growth in shoots but inhibits growth in roots.
• Saying plants 'want' or 'need' to grow towards light. Describe the mechanism: auxin, cell elongation and unequal growth.
• Saying the shoot bends because cells on the light side grow faster. Cells on the shaded side elongate faster.

Try three 4.5.4 Plant Hormones exam-style questions