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Biology · AQA Paper 2

Plant Hormones

How plants coordinate and control their growth with hormones, how auxins cause phototropism and gravitropism, how to investigate the effect of light and gravity on the growth of newly germinated seedlings, and how auxins, gibberellins and ethene are used in agriculture, horticulture and the food industry. Matches AQA topic 4.5.4 (plant hormones) and required practical 8. The whole of 4.5.4 is marked biology only in the specification, so this chapter is for separate Biology only: Trilogy students do not need it. Auxins and tropisms, and required practical 8, are for both tiers. Gibberellins and ethene, and the use of plant hormones (4.5.4.2), are for the Higher tier only.

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Key terms in this chapter

All 36, gathered from every lesson.

Plant hormone
A chemical that is made in a plant, and coordinates and controls its growth and responses.
Auxin
A plant hormone that controls the elongation of cells in shoots and roots.
Phototropism
A growth response to the direction of light.
Gravitropism
A growth response to gravity, which is also called geotropism.
Elongation
The growth of a cell by getting longer.
Tropism
A directional growth response of a plant to a stimulus.
Stimulus
A change in the environment that an organism detects.
Positive tropism
Growth towards the stimulus.
Negative tropism
Growth away from the stimulus.
Hypothesis
A testable explanation or prediction that can be tested by an investigation.
Clinostat
A device that turns seedlings slowly, so that gravity acts on all sides equally.
Resolution
The smallest change in a quantity that an instrument can detect.
Accurate
A result is accurate if it is close to the true value.
Repeatable
The same person gets similar results when the investigation is repeated.
Reproducible
Other people, or other methods, give similar results.
Valid
A valid investigation measures what it is meant to measure.
Control variable
A variable that is kept the same.
Biological drawing
A large, accurate, labelled line drawing of a specimen.
Gibberellin
A plant hormone that is important in starting the germination of seeds.
Ethene
A plant hormone, which is a gas, that controls cell division and the ripening of fruits.
Germination
The start of growth of a seed into a seedling.
Dormant
In a resting state, and not growing.
Ripening
The changes that make fruit soft, sweet and coloured.
Embryo
The young plant inside a seed.
Cell division
A process in which one cell divides to make two.
Mechanism
The way in which something works.
Control
A test in which the factor being investigated is left out, for comparison.
Agriculture
The growing of crops and the rearing of animals on a large scale.
Horticulture
The growing of fruit, vegetables, flowers and ornamental plants.
Weed killer
A chemical that kills weeds.
Rooting powder
A powder that contains auxin, which makes cuttings grow roots.
Tissue culture
The growing of new plants from small pieces of plant tissue, in sterile conditions.
Clone
A genetically identical copy.
Biodiversity
The variety of different species in an ecosystem.
Selective
Acting on some things but not on others.
Dormancy
A resting state, in which a seed does not germinate.