AQA · A-Level · Biology
Course version: 7402 · Version from Sept 2016
In flowering plants, specific growth factors move from growing regions to…
Full specification wording
Survival and response (A-level only): In flowering plants, specific growth factors move from growing regions to other tissues, where they regulate growth in response to directional stimuli.
Plants have no nervous system and no glands, so coordination is chemical.
Checked against the AQA 7402 specification (opens in a new tab) on .
- Point 2 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Plants have no nervous system and no glands, so coordination is chemical. Growth factors, of which indoleacetic acid is the one the specification names, are produced in the meristems at shoot tips and root tips, the growing regions where cells are actively dividing. From there they move to the tissue just behind the tip, the zone of elongation, where they change the rate at which cells elongate. Movement is by diffusion and active transport over short distances and in the phloem over longer ones, and, crucially, it can be lateral: when light or gravity acts from one side, IAA is redistributed across the tip so that one flank of the shoot or root receives more than the other. Because a growth factor acts on the cells that receive it, an uneven distribution produces uneven elongation and therefore bending.
What earns the marks
- Growth factors being produced in the growing regions, the meristems of shoot and root tips.
- Their movement to the zone of elongation just behind the tip.
- Lateral redistribution in response to a directional stimulus such as light or gravity.
- Unequal distribution causing unequal elongation and therefore bending.
Common mistakes and how to put them right
Calling IAA a hormone produced by a gland, when plants have neither glands nor a circulatory system.
Saying the tip bends, when it is the cells in the zone of elongation behind the tip that elongate.
Claiming the growth factor is destroyed by light rather than redistributed away from it.
Assuming the same concentration has the same effect in every tissue.
Describing the response as growth towards a stimulus without naming cell elongation.
Exam tips
- Name the regions precisely: produced at the tip, acting in the zone of elongation behind it.
- For any tropism, state where IAA accumulates, then what those cells do, then the direction of bending.
- Use the term growth factor rather than hormone when writing about plants.
Try the lesson
The start of the Survival and response (A-level only): In flowering plants, specific growth factors move from growing regions to other tissues, where they regulate growth in response to directional stimuli. lesson, made from checked teaching notes for this specification point.
Have a go first
In flowering plants, specific growth factors move from growing regions to other tissues, where they regulate growth in response to directional stimuli. Which statement correctly describes a named plant growth factor and its role?
Listen
Plants have no nervous system and no glands, so coordination is chemical. Growth factors, of which indoleacetic acid is the one the specification names, are produced in the meristems at shoot tips and root tips, the growing regions where cells are actively dividing. From there they move to the tissue just behind the tip, the zone of elongation, where they change the rate at which cells elongate. Movement is by diffusion and active transport over short distances and in the phloem over longer ones, and, crucially, it can be lateral: when light or gravity acts from one side, IAA is redistributed across the tip so that one flank of the shoot or root receives more than the other. Because a growth factor acts on the cells that receive it, an uneven distribution produces uneven elongation and therefore bending. A strong answer earns marks for these points. growth factors being produced in the growing regions, the meristems of shoot and root tips. their movement to the zone of elongation just behind the tip. lateral redistribution in response to a directional stimulus such as light or gravity. unequal distribution causing unequal elongation and therefore bending. Exam tip: Name the regions precisely: produced at the tip, acting in the zone of elongation behind it.
Key words
Say what each word means before you turn the card.
plant growth factors
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IAA
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meristems
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zone of elongation
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See every definition
- plant growth factors
- Specific factors that move from growing regions to other tissues, where they regulate growth in response to directional stimuli.
- IAA
- Indoleacetic acid, the growth factor the specification names, produced in the meristems at shoot tips and root tips.
- meristems
- The growing regions at shoot tips and root tips where cells are actively dividing and growth factors are produced.
- zone of elongation
- The tissue just behind the tip where growth factors change the rate at which cells elongate.
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