Coordination in plants Edexcel 2020

2. ¨ Why is this plant
growing to one side?
¨ How would it benefit
from this behavior?
¨ What happens inside
the plant to produce
such a behavior?

3. ¨ Plants grow when the
tips divide producing
more cells then the
cells start to elongate.
¨ Plant cells produce a
hormone-like
chemical called
Auxins that affect cell
growth.
¨ P.S. Auxin is a greek
word which means to
increase.

4. Lets try to understand how Auxins work from these experiments.

5. 1 , 2 and 3 are diagrams of the same plant shoot but at different times during the experiment.
Use this experiment’s result to figure what causes a shoot to grow to one side.

6. ¨ Which part of the shoot causes response to light?
¨ Tip of shoot
¨ If cut the shoot grows straight.
¨ What is the nature of auxins?
¨ Chemical.
¨ It can diffuse through gelatin block, not through mica
¨ What changes do they cause to plant shoot cells?
¨ Grow faster, bent towards light.
¨ As shown by Control, shoot covered by transparent
cap and gelatin block.
¨ When are auxins most active? light or dark?
¨ In dark
¨ When tip was covered grows faster.

7. ¨ Unlike animals plants respond slower, by growing,
this is called tropism.
¨ Growing towards light is positive phototropism
while growing away is negative phototropism.
¨ Shoots grow toward light to place their leaves in
the best conditions for photosynthesis and their
flowers for pollination and seeds for dispersal.
¨ Roots grow away from light, to find soil to attach
to, and absorb minerals and water.
¨ Auxins stimulate growth of shoot cells, but inhibit
growth of root cells.

8. .