3.8 Photosynthesis (Core). 3.8.1 State that photosynthesis involves the conversion of light energy into chemical energy. 3.8.2 State that light from the Sun is composed of a range of wavelengths (colours). 3.8.3 State that chlorophyll is the main photosynthetic pigment.
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3.8.2 State that light from the Sun is composed of a range of wavelengths (colours).
3.8.3 State that chlorophyll is the main photosynthetic pigment.
3.8.4 Outline the differences in absorption of red, blue and green light by chlorophyll.
The conversion of light energy into chemical energy in plants.
Light from the sun is made of a range of colours.
This is a result of the different wavelengths of light.
Blue light has a shorter wavelength and more energy.
Red light has a longer wavelength and less energy.
Chlorophyll traps sunlight.
It is the main photosynthetic pigment in plants
Red and blue light is absorbed by the leaf.
Green light is reflected and reaches our eyes
Leaf extract (chlorophyll)
The amount of red and blue,light absorbed can be measured using a spectrophotometer
Why are plants not always green?
If we pass light through a leaf extract and measure how much of each wavelength of light is absorbed we produce an absorption spectrum.
The main colours of light absorbed are red and blue. The main colour reflected is green.
If we pass different wavelengths of light through a leaf extract and measure the rate of photosynthesis we get an action spectrum.
Both show peaks in the red and blue areas of the visible spectrum.
However, there is activity in wavelengths where there is no absorption.
This is evidence for the presence of other pigments, e.g. carotenoids.
Plant pigment chromatography
State that light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen.
State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.
To produce ATP and to split water molecules to form oxygen (released as a waste product) and hydrogen. The ATP and hydrogen are used to fix carbon dioxide into glucose.
Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass.
How quickly raw materials are used:
e.g. water and carbon dioxide
How quickly products are formed:
e.g. oxygen production and biomass
Water plants like Elodea are ideal as we can see the oxygen forming.
Controlling temperature is always important when enzymes are involved.
The water bath keeps the temperature constant.
Design an experiment to investigate photosynthesis using leaf discs.
Outline the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis.
Increasing the light intensity has no effect on the rate. Other factors are limiting (carbon dioxide or temperature).
As the light intensity increases the rate of photosynthesis also increases.
At low light intensity the plant is respiring.
Increasing the carbon dioxide has no effect on the rate. Leaves are saturated with carbon dioxide. Other factors are limiting.
As the carbon dioxide increases the rate of photosynthesis also increases. The limiting factor is the carbon dioxide concentration.
As the temperature and kinetic energy increase the rate of photosynthesis also increases. Enzymes needed for photosynthesis work better in warmer temperatures.
Plant enzymes have an optimum of about 25oC and are denatured at 45oC
Maximum rate at optimum temperature