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Summary Control and coordination in plants
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Biology A level revision notes on Control and coordination in plants
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mollybuckwald
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Control and coordination in plantsPlants have electrochemical gradients across their surface membranes in the same way as
animal cells. The depolarisation in plants results not from the influx of positively charged
sodium ions but the outflow of negatively charged chloride ions. Repolarisation happens in
the same way by the outflow of potassium ions. The action potentials last longer and travel
slower than in animals.
Plants do not have specific nerve cells but many of their cells transmit waves of electrical
activity. The action potentials travel along the cell membranes of plant cells and from cell to
cell through the plasmadesmata that are lined by cell membrane.
The Venus fly trap obtains a supply of nitrogen compounds by trapping and digesting insects.
The specialised leaf is divided into two lobes either side of a midrib. The inside of each lobe
is normally red and has nectar secreting glands around the edge to attract insects. Each lobe
has three stiff sensory hairs that respond to being deflected. The outer edges of the lobe
have stiff cilia that interlock to trap the insect. The surface of the lobes have many glands
that secrete enzymes for digestion.
The deflection of a sensory hair activates calcium ion channels in cells at the base of the hair.
These channels open so that calcium ions flow to generate a receptor potential. If two of
the hairs are stimulated within a period of 30 seconds, or one hair is touched twice in the
same period, action potentials travel along the trap. If a hair is deflected a third time then
the trap will close and the time between stimulus and response is about 0.5s, taking 0.3s to
close the trap.
The lobes of the leap bulge upwards in a convex shape when the trap is open and change to
a concave shape when the trap closes. The trap is only completely closed if there is an
ongoing activation of the trigger hairs by the prey and further triggering action potentials.
This also stimulates the entry of calcium ions into gland cells, which stimulate the exocytosis
of vesicles containing digestive enzymes. After a week the trap is reset.
Venus fly taps have two adaptations to prevent energy waste:
The stimulation of one hair does not cause the trap to close. Prevents closure
when rain or debris falls
The gaps between the cilia allows small insects to climb out as they are not worth
digesting
Chemical communication in plants
Unlike animal hormones, plant growth regulators are not produced in specialised cells
within glands, but in a variety of tissues. They move in the plants from cell to cell, by
diffusion or active transport, or are carried in the phloem or xylem sap.
There are two types of plant growth regulators:
Auxins – influence many aspects of growth including elongation, which determines
the overall length of roots and shoots
Gibberellins – which are involved in seed germination and controlling stem
elongation
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