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Higher Biology
Effects of Chemicals and Light
on Growth in Plants
Effects of chemicals and light on
plants
By the end of this lesson you should be
able to:
 Know the symptoms of deficiency of nitrogen,
potassium, phosphorus and magnesium in plants.
 Describe the effect of light on shoot growth
and development.
 Understand what is meant by phototropism
and etiolation.
 Describe the effect of light on flowering in
long day and short day plants.
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Introduction
Elements play an important role in the
growth and development of organisms.
 If an element is missing then this can lead
to nutrient deficiency.
 In addition to carbon, oxygen and hydrogen
for photosynthesis plants also need other
elements.
How do plants take up these minerals?
 Through the root hairs in the soil(remember?)

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Macro-elements in plants


Macro-elements are required by plants in
small but significant quantities for normal
growth to occur.
Four of these elements are:

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

Nitrogen (N)
Phosphorus (P)
Potassium (K)
Magnesium (Mg)
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Macro-elements in plants
Element
Function
Deficiency
Phosphorus
ATP & nucleic acid
formation
Growth reduced,
leaf bases red
Potassium
Role in transport
Growth reduced,
of molecules
death of older leaves
across membranes
Nitrogen
Magnesium
Chlorotic leaves,
Amino acids, proteins
& nucleic acids formation
leaf base red
Required for
chlorophyll
formation
Growth reduced,
chlorotic leaves
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Macro-elements in plants


Water culture experiments
Complete your “Macro-element Deficiency”
Sheet from your diagram pack.
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Effect of Light on Shoot Growth
1.
2.
3.
Read page 273 of Torrance and then
answer the following questions:
Name the term used to describe a plant
which has grown in the dark.
Describe the appearance of such a plant in
terms of:
a)
b)
c)
d)
4.
Colour
Size of leaves
Internodes
Stem
Briefly describe the role of light in
phototropism.
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Effect of Light on Flowering



Many plants stop producing leaves and
instead start to produce flowers at certain
times of the year.
This occurs in response to changing periods
of light and darkness.
Photoperiodism is a response (e.g.
flowering) to changing daylength.
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Long day plants






Also called short night plants.
Usually flower in spring.
Only flower when the numbers of hours of
light is more than a critical level.
Critical length of light varies from species
to species.
Normally 11-13 hours of light
E.g. spinach only flowers when there is
more than 13 hours light.
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Short day plants






Also called long night plants.
Usually flower in autumn or winter
Only flower when the numbers of hours of
light is less than a critical level.
Critical length of light varies from species
to species.
Can be less than 12 hours of light.
E.g. strawberry only flowers when there is
less than 10 hours light. (i.e. must have at
least 14 hours of darkness).
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Practice Questions

1.
Torrance
TYK page 270 Q1, p277 Q1-3
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Effects of chemicals and light on
plants
Can you do it?
 Know the symptoms of deficiency of nitrogen,
potassium, phosphorus and magnesium in plants.
 Describe the effect of light on shoot growth
and development.
 Understand what is meant by phototropism
and etiolation.
 Describe the effect of light on flowering in
long day and short day plants.
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