Transcript Plant Growth

Plant Hormones
B3f
OBJECTIVES
Key Objective
• Describe the role of hormones in plant growth
C/D
• Use the words phototropic and geotropic to describe the
growth of roots and shoots
• Identify the chemicals responsible for growth in plants
A/B
• Interpret data from phototropism experiments in terms of
hormone action
• Explain how hormones brings about shoot curvature in
terms of cell elongation
How Does This Plant Know to Send
Its Shoots ‘Up’ and Its Roots
‘Down’?
Response in plants
•
•
Tropism – plant growth in response to a stimulus
Stimulus
Light
Tropism
Phototropism
Gravity
Geotropism
Growth towards the stimulus is a positive tropism and
growth away is a negative tropism
– e.g. shoots are positively phototropic but negatively geotropic
Some Definitions
Shoots grow towards light (positive phototropism)
and against gravity (negative geotropism).
Roots grow away from light (negative phototropism)
and in the direction of gravity (positive
geotropism).
Plant Hormones
The growth of roots and shoots is controlled by hormones:
In the shoots the hormone
auxin is “destroyed” by
light, so the shoot will bend
towards the light as the
cells on the shaded side
grow quickest.
In the roots hormones slow
down growth of the cells in
the lower region, which
makes the root bend down.
Typical Exam Question
Typical Exam Question
Auxin is made in the tip or top of plant
The tip is covered so it doesn’t receive light
Auxin levels are equal on both sides
Both sides grow at the same rate
PLENARY
Create a brainstorm/mind/concept
map on plant hormones
summarising the information
discussed in the lesson