Coordination and control in plants

HideShow resource information

Plant growth substances

Plant growth regulators include:

  • Auxins - stimulate cell elongation in zone of elongation
  • Cytokinins - promote cell division
  • Gibberellins - stimulate elongation of internodal regions
1 of 6

Auxin action

  • Auxins are produced in the shoot tip and diffuse down to the zone of elongation.
  • They stimulate the pumping of hydrogen ions into the cellulose cell wall
  • The acidification of the cell wall activates agents which loosen the linkages between cellulose microfibrils - making the wall more flexible
  • The cells absorb water by osmosis and the flexible cell walls allow the cells to expand as the extra water exerts increased hydrostatic pressure against them
2 of 6

Auxin and phototropism

  • Auxins are involved in producing the positive phototropic response in plant shoots.
  • As the auxins diffuse down from the tip, unidirectional light causes auxin to move towards the shaded side promoting greater cell elongation on the shaded side and a resultant curvature of the shoot towards the light.
3 of 6


  • Plants have phytochromes that detect the photoperiod.
  • They are interchangeable: P660 and P730.
  • P660 (Pr) maximally absorbs red light, while P730 (Pfr) maximallly absorbs far-red light.
  • During darkness, there is a slow conversion of P730 to P660 - P660 accumulates
  • During daylight, P730 accumulates
4 of 6

The control of flowering

  • P730 is a physiologically active form, and can either stimulate or inhibit flowering
  • LONG DAY PLANTS - require a critically short period of darkness, so that high levels of P730 accumulate and stimulate flowering
  • SHORT DAY PLANTS - require a critically long period of continuous (uninterrupted) darkness, so that the inhibitory effect of P730 is removed
5 of 6

Comparison of coordination in plants and animals

In both plants and animals:

  • Chemicals are used to communicate between receptors and effectors
  • Receptors receive the stimulus (e.g. phytochromes detects photoperiod in plants, while osmoreceptors detect changes in water potential and retina in eye detects light in animals).
  • Effectors bring about the response (e.g. plants may bud into a flower, and cells elongate in response to auxin, while in animals muscle contracts)
  • However, plants lack a nervous system, which animals require for rapid communication in the body and is important in coordinating movement.
6 of 6


No comments have yet been made

Similar Biology resources:

See all Biology resources »See all Human, animal and plant physiology resources »