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PhotosynthesisPhotosynthesis

Intermediate 2

How plants make food

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What is photosynthesis?What is photosynthesis?

The word The word photophoto means means light and light and synthesissynthesis means to build upmeans to build up

Photosynthesis is the Photosynthesis is the process whereby green process whereby green plants make glucoseplants make glucose

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What does the plant need ?What does the plant need ?

For photosynthesis to take For photosynthesis to take place a plant needs place a plant needs

Carbon dioxide Carbon dioxide from the airfrom the air

LightLight from the sun from the sun

Water Water from the soilfrom the soil

ChlorophyllChlorophyll from the from the leaves leaves

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Testing for photosynthesisTesting for photosynthesis

We can check for evidence of We can check for evidence of photosynthesis by testing a leaf for starch.photosynthesis by testing a leaf for starch.

1.1. Boil the leaf in water (bursts cells)Boil the leaf in water (bursts cells)

2.2. Boil the leaf in alcohol (removes chlorophyll)Boil the leaf in alcohol (removes chlorophyll)

3.3. Dip leaf in hot water (softens the leaf)Dip leaf in hot water (softens the leaf)

4.4. Put leaf in iodine solution (turns blue black if Put leaf in iodine solution (turns blue black if starch is present)starch is present)

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Test for Starch

Boil for 1 Minute Warm in Ethanol

Testing a leaf for StarchTesting a leaf for StarchWash in Water

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Testing your knowledgeTesting your knowledge A variegated leaf is covered with a strip of A variegated leaf is covered with a strip of

metal foil then the leaf is tested for starch. metal foil then the leaf is tested for starch. Which diagram shows the correct result.Which diagram shows the correct result.

Metal foil

Blue Black Starch present

Orange No Starch present

A B C D

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Word Equation for Word Equation for PhotosynthesisPhotosynthesis

CarbonDioxide

+ Water Glucose + Oxygen

CO2 H2O C6H12O6 O2

Light energy

Raw Materials Products

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Stages of PhotosynthesisStages of Photosynthesis

1st Stage - 1st Stage - PHOTOLYSISPHOTOLYSIS

Light energy

Absorbed by Chlorophyll

WATER

ADP + Pi

ATP

HYDROGEN + OXYGEN

Only HYDROGEN and ATP go on to the second stage

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22ndnd Stage Carbon Fixation Stage Carbon Fixation

HYDROGEN

ATP

ADP + Pi

GLUCOSE

Starch

Cellulose

+ CARBON DIOXIDE (from the air)

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Glucose

What happens to the glucose?What happens to the glucose?

Cellulose made up of parallel chains of glucose to form tough fibres used to make cell walls

For energyin respiration

Starch made up of coiled chains of glucose to form starch grains.

Can be converted back when glucose is needed byplant.

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Limiting FactorsLimiting Factors Carbon Dioxide Concentration - Carbon Dioxide Concentration - Less Carbon

Dioxide means less glucose can be made.

Light Intensity - More light means more energy

Temperature -Temperature - Warmth increases the rate that enzymes work, however, high temperature denatures enzymes. Low temperatures slow reactions.

If any of these are in short supply, they cut down or LIMIT the rate of photosynthesis.

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Measuring the rate of Measuring the rate of photosynthesisphotosynthesis

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Rate of PhotosynthesisRate of Photosynthesis

If we move If we move the lamp the lamp back and back and forwards we forwards we can change can change the light the light intensityintensity

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Light IntensityLight IntensityR

ate

of P

hoto

synt

hesi

s

Light Intensity

CO2 readily availableand warmth

If light is increased photosynthesis will increase up to a certain point.After this something else becomes the limiting factor e.g. CO2

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Limiting FactorsLimiting Factors

Level of CO2

What is the limiting factor at point X?

What is the limiting factor at point Y?X

Y

Rat

e of

Pho

tosy

nthe

sis

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More to do!More to do! Go to Go to http://lgfl.skoool.co.uk/keystage3.aspx?id=63http://lgfl.skoool.co.uk/keystage3.aspx?id=63

and do lesson numbersand do lesson numbers

49. Photosynthesis49. Photosynthesis50. The Role of the Leaf in Photosynthesis50. The Role of the Leaf in Photosynthesis51. Rate of Photosynthesis51. Rate of Photosynthesis52. Testing a Leaf for Starch52. Testing a Leaf for Starch53. Experiments to see if Chlorophyll and 53. Experiments to see if Chlorophyll and

Light are Needed to Make StarchLight are Needed to Make Starch54. The Uses of Glucose 54. The Uses of Glucose