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BISC 104 Principles of Biology

PHOTOSYNTHESISLAB

PS – What is it?

• Photo (use of light) – Synthesis (to synthesize sugar, related biomolecules)

• Sunlight (Energy) is required because:6 H2O + 6 CO2 C6H12O6 + 6 O2

Low energy High energy

molecules molecules

Why is PS Important?

• It produces Oxygen for all organisms• It produces Food (carbohydrates) which

is the base of all food chains

• It produces the C “backbone” for all biological molecules

• It removes CO2 from the atmosphere, off setting the greenhouse effect

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Where does PS take place?

Leaves – cells with chloroplasts (with pigments)

PS in the plant:The Raw Materials

• Water enters through roots• CO2 enters through stomata in leaves

• Air spaces surround leaf cells

Cross section of leaf(Microscope slide used by permission of Carolina

Biological Supply Co.)

Intercellular Air spaces Stomata

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Cross section of leaf(Microscope slide used by permission of Carolina

Biological Supply Co.)

Intercellular Air spaces Stomata

2�

&2�

Cross section of leaf(Microscope slide used by permission of Carolina

Biological Supply Co.)

Intercellular Air spaces Stomata

Cross section of leaf(Microscope slide used by permission of Carolina

Biological Supply Co.)

Intercellular Air spaces Stomata

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Cross section of leaf(Microscope slide used by permission of Carolina

Biological Supply Co.)

Intercellular Air spaces Stomata

Cross section of leaf(Microscope slide used by permission of Carolina

Biological Supply Co.)

Intercellular Air spaces Stomata

Two Basic Reactions in PS

Overall Reaction (abbreviated):Sunlight

CO2 + H2O �

Low energy

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Two Basic Reactions in PS

Overall Reaction (abbreviated):Sunlight

CO2 + H2O �ATP, NADPH �Glucose + O2

Low energy High energy High energyIntermediates

Light-dependent reaction

Sunlight

Pigments

Light-dependent reaction

Sunlight

Pigments

H2O + ADP + NADP

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Light-dependent reaction

Sunlight

Pigments

H2O + ADP + NADP �ATP + NADPH + ½ O2

High energyintermediates

Light-dependent reaction

Sunlight

Pigments

H2O + ADP + NADP �ATP + NADPH + ½ O2

High energyintermediates

Light-independent reaction(Calvin cycle)

The “synthesis” part of photosynthesis:

CO2 + NADPH + ATP � Glucose

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Challenge Questions

• 1. What are ways to measure photosynthesis taking place?

Challenge Questions

• 1. What are ways to measure photosynthesis taking place?

• 2. What factors affect the rate of photosynthesis?

Ways to measure photosynthesis

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Ways to measure photosynthesis

• Use of CO2 – done in BISC207 labs

Ways to measure photosynthesis

• Use of CO2 – done in BISC207 labs

• Production of Glucose

Ways to measure photosynthesis

• Use of CO2 – done in BISC207 labs

• Production of Glucose• Evolution of O2 – this is basis of

BISC104 experiment

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Ways to measure photosynthesis

• Use of CO2 – done in BISC207 labs

• Production of Glucose• Evolution of O2 – this is basis of

BISC104 experiment• Use of water

What affects rate of PS?

What affects rate of PS?

• Light intensity

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What affects rate of PS?

• Light intensity• Wavelengths of light (color)

What affects rate of PS?

• Light intensity• Wavelengths of light (color)• CO2 concentration

What affects rate of PS?

• Light intensity• Wavelengths of light (color)• CO2 concentration

• Type of leaf (plant) used

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What affects rate of PS?

• Light intensity• Wavelengths of light (color)• CO2 concentration

• Type of leaf (plant) used• Age of leaf

What affects rate of PS?

• Light intensity• Wavelengths of light (color)• CO2 concentration

• Type of leaf (plant) used• Age of leaf

• Temperature

What affects rate of PS?

• Light intensity• Wavelengths of light (color)• CO2 concentration

• Type of leaf (plant) used• Age of leaf

• Temperature• Available soil water

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Lab 4 - Photosynthesis

• Uses O2 evolution to measure rate of light reaction (dependent variable)

• At different light intensities- (independent variable)

Hypothesis

The rate of photosynthesis, as

measured by O2 evolution, will

increase at higher light intensity and

decrease at lower light intensity

Theory behind Methods

• Discs are cut from leaves• Leaf discs have air in them

• Air is pumped from air spaces in leaf, replaced with HCO3; discs sink

• As PS occurs, O2 is produced• Air spaces fill up – discs float

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Theory behind Methods

• Rate of PS = How quickly do they float?What percentage float?

• Control – do discs float in dark? (no PS)

Results & Conclusions

• Collect Data

• Do Results Support Hypothesis?

Bright (lamp)

Low (room)

None

% floating# floatingLight

Additional Questions

• Did this experiment include the light independent reaction?

• What was purpose of bicarbonate?