Transcript Photosynthesis - Mr Lewis Biology

Photosynthesis
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Learning objectives
• By the end of the lesson you should be able
to:
• State the word and symbol equations for
photosynthesis.
• Describe the process of photosynthesis and
understand its importance in conversion of
light energy to chemical energy
• Explain how the structure of the leaf is
adapted for photosynthesis
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How do plants get the food they need?
All living organisms need food to grow and survive.
This is because food provides raw materials for growth
and energy for chemical reactions.
Plants are known as producers
because they provide food for
many other organisms.
Without plants, other
organisms would have no raw
materials for growth or energy.
Unlike animals, plants cannot
move very much, so how do they
get the food that they need?
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Do plants eat soil?
It used to be thought that plants
got their food from the soil.
Greek scientists believed that
plants increased in mass by
taking in minerals from the soil.
A scientist called Van Helmont
performed an experiment to test
this idea. He grew a willow tree and
measured the mass of the soil, the
tree and the water he added.
After five years the plant had gained about 74 kilos but the
mass of the soil was the same. He concluded that the
tree's weight gain had come from water. Was he right?
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Oxygen from plants
Joseph Priestley discovered oxygen, and later showed that
it was made by plants.
He placed a mint plant and a candle in an enclosed
space, and soon discovered that the candle went out
when all of the oxygen was used up in combustion.
He kept the container closed and
relit the candle 27 days later.
The candle was able to burn again.
Priestley concluded that
something must have been made
by the plant that changed the air.
The gaseous product was oxygen.
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What is photosynthesis?
Plants make their own food by photosynthesis. A few
micro-organisms can do this too.
Photosynthesis is a chemical reaction that uses light energy.
light energy
The word photosynthesis comes from the Greek language:
 ‘photo’ means ‘light’
 ‘synthesis’ means ‘putting together’.
Photosynthesis just means ‘putting together with light’.
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Photosynthesis
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Photosynthesis: summary
How can the process of photosynthesis be summarized in
one sentence?
Photosynthesis is a chemical reaction that takes
place in the chloroplasts of green plant cells, where
light energy is used to convert carbon dioxide and
water into glucose and oxygen.
What is the word equation for this chemical reaction?
carbon
dioxide
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light energy
+
water
 glucose
+
oxygen
chlorophyll
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Photosynthesis: word equation
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Symbol equation for photosynthesis
The reaction of photosynthesis can be represented by
the following equation:
carbon
dioxide
light energy
+
water
 glucose
+
oxygen
chlorophyll
What is the symbol equation for this reaction?
light energy
6 CO2
+
6 H2O

C6H12O2
+
6 O2
chlorophyll
Is this a balanced symbol equation?
How would you balance the equation?
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Word equation to symbol equation
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Why do plants
photosynthesize?
• Plants do several things with the sugar
made from photosynthesis:
1. Use it for energy;
2. Make cellulose for cell walls;
3. Make proteins needed for growth and
repair;
4. Store as starch, fats and oils.
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Why do plants store glucose as
starch?
•What is glucose?
•What important process uses glucose?
•Does glucose dissolve in water?
•How might this affect a plant?
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Answer these questions in
your book - you have 10
1.How does a plant make proteins for growth
minutes!
and repair?
2.Why does a plant store starch?
3.When does photosynthesis happen?
•Now get someone sitting near you to check
them. Do you agree with the answer? If not,
why?
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Photosynthesis equation quiz
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How can you test for photosynthesis?
The presence of starch in a leaf can be used to show that
photosynthesis has taken place. After photosynthesis
occurs, the glucose is often converted to starch for storage.
Iodine is used to test for starch.
It reacts with starch and changes
colour from brown to blue-black.
The starch test can be used to
prove that photosynthesis
needs light, carbon dioxide and
chlorophyll to take place.
How would you set up an experiment to test the conditions
needed for photosynthesis?
How would you make the experiment fair and reliable?
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Testing leaves for starch
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Is chlorophyll needed for photosynthesis?
Chlorophyll cannot be removed from a plant without killing
the plant. Instead, variegated leaves can be used to show
chlorophyll is essential for photosynthesis.
Variegated leaves have pale parts,
which do not contain chlorophyll.
The green parts of the leaf contain
chlorophyll and are the control.
Which areas will react with iodine?
Only the green areas of the leaf
react with the iodine and turn
blue-black. Without chlorophyll,
the pale areas have been unable
to produce starch and do not turn
blue-black.
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Testing leaves for starch – activity
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Where does the oxygen come from?
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What is the rate of photosynthesis?
Photosynthesis is a chemical reaction and so has a rate.
Like many reactions, photosynthesis requires enzymes.
Is the rate of photosynthesis always the same?
Which factors do you think affect the rate of photosynthesis?
light
carbon dioxide
temperature
How do these factors affect the rate of photosynthesis?
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How does light affect photosynthesis?
Light energy has to be absorbed by
chlorophyll for photosynthesis to take place.
carbon
dioxide
light energy
+ water
 glucose
+ oxygen
chlorophyll
The brighter the light, the more light energy there is,
so will photosynthesis be faster or slower?
More light energy means that photosynthesis will be faster.
If light intensity is too high plant cells can be damaged.
How is photosynthesis affected if this happens?
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Investigating photosynthesis
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Investigation photosynthesis – results
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Carbon dioxide and the rate of photosynthesis
Carbon dioxide is one of the raw materials
used by plants to make their food.
carbon
dioxide
light energy
+
water
 glucose
+
oxygen
chlorophyll
The concentration of carbon dioxide in the air is actually
quite low (0.03%).
Why is the concentration of carbon dioxide in commercial
greenhouses often raised to about 0.1%?
More carbon dioxide means more photosynthesis, so plants
make more food and grow more quickly.
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Does temperature affect photosynthesis?
Photosynthesis is controlled by
enzymes, which usually work
best at warmer temperatures.
Does increasing the
temperature always increase
the rate of photosynthesis?
If it gets too hot (above 40 °C),
the enzymes needed for
photosynthesis begin to break
down and are destroyed or
denatured. The rate of
photosynthesis decreases or
even stops completely.
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What is a limiting factor?
What is the ideal combination of factors for the maximum
rate of photosynthesis?
 enough light
 enough carbon dioxide
 ideal temperature (not too hot or cold).
How does restricting one of these facts affect the rate?
If one of the factors is restricted, the rate of photosynthesis
will be below the maximum possible rate.
The restricted factor controls how quickly photosynthesis
occurs and so limits the rate. It is called the limiting factor.
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Light intensity and photosynthesis
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Carbon dioxide and photosynthesis
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Temperature and photosynthesis
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Limiting factors – activity
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Limiting factors in a greenhouse
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Glossary
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Multiple-choice quiz
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