English National Curriculum - Science

Plant hormones

Mission Objectives

Describe what tropisms are and distinguish between positive and negative responses in plants

Explain the role of auxins in controlling plant growth, including their different effects on roots and shoots

Apply knowledge of auxin distribution to explain phototropism and gravitropism in plants

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Keywords

Words and meanings to learn

tropism

growth response of a plant in a particular direction due to a stimulus (e.g. light or gravity).

meristem

the region in plants where cells actively divide (growth tissue found in root and shoot tips)

gravitropism

a plant’s growth response to gravity.

phototropism

a plant’s growth response to light.

auxin

a plant hormone that controls growth by regulating cell elongation in roots and shoots.

Required Resources

  • Seeds (e.g., cress seeds, mustard seeds and bean seeds)
  • Petri dishes or small containers
  • Cotton wool or filter paper
  • Water
  • Pipette or dropping bottle
  • Light source (e.g., lamp or access to sunlight)
  • Materials to block or vary light (e.g., foil, box, cupboard)
  • Containers that can be positioned at different angles (for gravity investigation)
  • Ruler (marked in millimetres)
  • Thread (for measuring curved seedlings)
  • Paper (for recording observations and drawings)
  • Pencils (for scientific line drawings)
  • Labels or marker pens
  • Clock or stopwatch

Technical information 
It should be emphasised that this investigation is about the responses of germinated seeds and not about factors affecting germination. Therefore, students could be supplied with dishes already prepared with germinated seeds such as white mustard (Brassica alba). Cotton wool should be damp but not excessively wet. The amount of cotton wool and water needed should be determined before the students' experiment. Cotton wool pads for make-up removal are suitable and are all the same size and thickness. 

Seeds will require a day or so to germinate (depending on how warm it is). Alternative seeds, such as cress or Brassica rapa, could be used instead of white mustard seeds. However, white mustard seeds are bigger and easier to handle. You can purchase pots of cress and split them into smaller units. Partial light can be achieved by alternating a day on the windowsill with a day in the dark cupboard. 

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