Transcript Photosynthesis Limiting Factors

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Photosynthesis Limiting
Factors
Noadswood Science, 2012
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Thursday, July 16, 2015
Photosynthesis Limiting Factors
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To know and understand the limiting factors of
photosynthesis
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Vocal Plants
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Is it the case that talking to your plants can help them grow?!
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Photosynthesis can be reduced by a variety of factors, including
 Temperature
 Carbon dioxide concentration
 Light intensity
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Plants also need water, however if a plant is so short of water that
it becomes the limiting factor the plant will be in serious trouble
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If the environmental conditions are such that CO2 is a limiting
factor then talking to the plant may well help it grow (as you are
supplying it with CO2, a by-product of respiration)!
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Experiment
1.
Take 2 similar pieces of elodea
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Place 1 piece of elodea in a test tube and submerge with
hydrogen carbonate indicator
3.
Place 1 piece of black paper around the test tube, ensuring
the top is sealed (use the rubber band)
4.
Repeat this experiment, this time placing 1 piece of tracing
paper around the test tube
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Finally set up a control – a test tube with only hydrogen
carbonate indicator and no elodea in it or paper around it!
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Leave test tubes in a rack, by the window for >20 mins…
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Test
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Hydrogen carbonate indicator reacts when carbon dioxide is
present:  In normal atmospheric conditions, the indicator is orange/red
 When there is lots of carbon dioxide the indicator is yellow
 When there is not much carbon dioxide the indicator is purple
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So we can set up an experiment, changing the light intensity, and
then measure the hydrogen carbonate indicator to see how the
CO2 levels vary…
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Graph
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Using the secondary data, produce a graph for the time
taken to fill the container, when the distance the light source
was from the plant changed
Distance apart between lamp &
beaker (cm)
Time taken for end of funnel to fill
with oxygen (seconds)
0
50
10
80
20
130
30
160
40
163
50
162
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Graph
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Green Plants
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Green plants absorb light energy using chlorophyll in their
leaves – they use it to react carbon dioxide with water to
make glucose (used for respiration, or converted into starch
and stored)
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Plants also need mineral ions, including
nitrate and magnesium, for healthy
growth – they suffer from poor growth in
conditions where mineral ions are
deficient
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Photosynthesis
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Photosynthesis is the chemical change which happens in the
leaves of green plants
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It is the first step towards making food - not just for plants but
ultimately every animal on the planet
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Photosynthesis takes place in
leaf cells – these contain
chloroplasts, which are tiny
organelles containing
chlorophyll which absorbs
light energy for the reaction to
take place
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Photosynthesis
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What is photosynthesis?
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Plants make their own food via photosynthesis (chlorophyll
in the leaves) with the energy coming from the Sun
chlorophyll
light energy
carbon dioxide + water  glucose + oxygen
6CO2 + 6H2O  C6H12O6 + 6O2
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Limiting Factors
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What limiting factors affect photosynthesis?
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Photosynthesis can be reduced by a variety of factors,
including
 Temperature
 Carbon dioxide concentration
 Light intensity
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Limiting Factors
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Plants also need water, however if a plant is so short of water
that it becomes the limiting factor the plant will be in serious
trouble
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Environmental conditions influence which factor(s) limit the
rate of photosynthesis (light limits it at night; temperature
often limits it in winter; and when it is warm and bright CO2
usually limits it)
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Limiting Factors
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Light intensity – without enough light, a plant cannot
photosynthesise very quickly, even if there is plenty of water
and CO2
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Increasing the light intensity will boost the speed of
photosynthesis
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Draw a sketch graph of light intensity against photosynthesis
rate…
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Limiting Factors
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CO2 – sometimes photosynthesis is limited by the
concentration of CO2 in the air
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Even if there is plenty of light, a plant cannot photosynthesise
if there is insufficient CO2
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Draw a sketch graph of CO2 against photosynthesis rate…
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Limiting Factors
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Temperature – if it gets too cold, the rate of photosynthesis
will decrease
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Plants cannot photosynthesise if it gets too hot and enzymes
within the chlorophyll begin to denature above 45oC
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Draw a sketch graph of temperature against photosynthesis
rate…
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Greenhouse
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Farmers can use their knowledge of these limiting factors to
increase crop growth in greenhouses
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They may use artificial light so that photosynthesis can
continue beyond daylight hours, or in a higher-than-normal
light intensity
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The use of paraffin lamps
inside a greenhouse increases
the rate of photosynthesis
because the burning paraffin
produces carbon dioxide, and
heat too
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Limiting