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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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3.8.1 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.

3.8.4 Outline the differences in absorption of red, blue and green light by chlorophyll.


My favourite song soon to be yours
My favourite song ...soon to be yours light energy into chemical energy.


What is photosynthesis
What is photosynthesis? light energy into chemical energy.

The conversion of light energy into chemical energy in plants.


The visible spectrum
The Visible Spectrum light energy into chemical energy.

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
Chlorophyll light energy into chemical energy.

Chlorophyll traps sunlight.

It is the main photosynthetic pigment in plants


Why do leaves look green
Why do leaves look green? light energy into chemical energy.

visible light

Red and blue light is absorbed by the leaf.

Green light is reflected and reaches our eyes


Green light energy into chemical energy. light is reflected and reaches our eyes

visible light

Leaf extract (chlorophyll)

The amount of red and blue,light absorbed can be measured using a spectrophotometer


Try this
Try this: light energy into chemical energy.

Why are plants not always green?


Go here
Go here: light energy into chemical energy.


Absorption spectrum
Absorption Spectrum light energy into chemical energy.

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.


Action spectrum
Action Spectrum light energy into chemical energy.

If we pass different wavelengths of light through a leaf extract and measure the rate of photosynthesis we get an action spectrum.


Comparing the spectra
Comparing the Spectra light energy into chemical energy.

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.


chlorophyll a light energy into chemical energy.

chlorophyll b

carotenoids


Try this1
Try this: light energy into chemical energy.

Plant pigment chromatography


Assessment statements
Assessment Statements: light energy into chemical energy.

3.8.5

State that light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen.

3.8.6

State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.


What is the light used for
What is the light used for? light energy into chemical energy.

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.


Assessment statement
Assessment Statement: light energy into chemical energy.

3.8.7

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.


Measuring the rate of photosynthesis
Measuring the rate of photosynthesis light energy into chemical energy.


What can we measure? How? light energy into chemical energy.

How quickly raw materials are used:

e.g. water and carbon dioxide

How quickly products are formed:

e.g. oxygen production and biomass


Controlling variables
Controlling Variables light energy into chemical energy.

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.


Try this virtual photosynthesis lab
Try this - Virtual Photosynthesis Lab light energy into chemical energy.


Photosynthesis design lab
Photosynthesis Design Lab light energy into chemical energy.

Design an experiment to investigate photosynthesis using leaf discs.


Assessment statement1
Assessment Statement: light energy into chemical energy.

3.8.8

Outline the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis.


Effect of changing light intensity
Effect of changing light intensity light energy into chemical energy.

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.


Effect of changing carbon dioxide
Effect of changing carbon dioxide light energy into chemical energy.

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.


Effect of changing temperature
Effect of changing temperature light energy into chemical energy.

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


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