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3.8 Photosynthesis (Core)

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Page 1: 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

3.8 Photosynthesis (Core)

Page 2: 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

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.

Page 3: 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

My favourite song ...soon to be yours

Page 4: 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

What is photosynthesis?

The conversion of light energy into chemical energy in plants.

Page 5: 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

The Visible Spectrum

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.

Page 6: 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

ChlorophyllChlorophyll traps sunlight.

It is the main photosynthetic pigment in plants

Page 7: 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

Why do leaves look green?

visible light

Red and blue light is absorbed by the leaf.

Green light is reflected and reaches our eyes

Page 8: 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

visible light

Green light is reflected and reaches our eyes

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

Leaf extract (chlorophyll)

Page 9: 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

Try this:

Why are plants not always green?

Page 10: 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

Go here:

Page 11: 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

Absorption Spectrum

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.

Page 12: 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

Action Spectrum

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

Page 13: 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

Comparing the Spectra

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.

Page 14: 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

chlorophyll achlorophyll b

carotenoids

Page 15: 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

Try this:

Plant pigment chromatography

Page 16: 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

Assessment Statements:

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.

Page 17: 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

What is the light used for?

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.

Page 18: 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

Assessment Statement:

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.

Page 19: 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

Measuring the rate of photosynthesis

Page 20: 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

What can we measure? How?

How quickly raw materials are used:

e.g. water and carbon dioxide

How quickly products are formed:

e.g. oxygen production and biomass

Page 21: 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

Controlling Variables

Controlling temperature is always important when enzymes are involved. The water bath keeps the temperature constant.

Water plants like Elodea are ideal as we can see the oxygen forming.

Page 22: 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

Try this - Virtual Photosynthesis Lab

Page 23: 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

Photosynthesis Design Lab

Design an experiment to investigate photosynthesis using leaf discs.

Page 24: 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

Assessment Statement:

3.8.8Outline the effects of temperature, light

intensity and carbon dioxide concentration on the rate of photosynthesis.

Page 25: 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

Effect of changing light intensity

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.

Page 26: 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

Effect of changing carbon dioxide

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.

Page 27: 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

Effect of changing temperature

Plant enzymes have an optimum of about 25oC and are denatured at 45oC

As the temperature and kinetic energy increase the rate of photosynthesis also increases. Enzymes needed for photosynthesis work better in warmer temperatures.

Maximum rate at optimum temperature