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Chapter 8
Photosynthesis
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8-1 Energy and Life
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Energy – the ability to do work
Organisms and their cells need a steady supply of energy in order to function
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Chemical energy and ATP
Adenosine Triphosphate
ATP
Energy storing molecules
Made up of…
1 adenine
1 ribose
3 phosphates
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Adenine
3 Phosphates
Ribose
ATP is used by all types of cells as their basic energy source.
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Adenosine Diphosphate
ADP
Cells store energy by bonding a third phosphate group to ADP to make ATP
Made up of…
1 adenine
1 ribose
2 phosphates
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Using Biochemical Energy
Cells use energy to….
Maintain homeostasis
Maintain body warmth
Move cells
Transmit nerve impulses
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9. 8-2 Photosynthesis: An Overview
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Van Helmont’s Experiment
In the 1600s, Jan van Helmont wanted to find out if plants grew by taking material out of the soil
He determined the mass of a pot of dry soil and a small seedling
Planted the seedling in the pot, and watered it regularly.
After 5 years the seedling was a small tree and had gained 75kg, but the soil’s mass was almost unchanged
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Van Helmont concluded that the gain in mass came from water because water was the only thing he had added
Although van Helmont did not realize it, carbon dioxide in the air made a major contribution to the mass of his tree
In photosynthesis, the carbon in carbon dioxide is used to make glucose
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Priestley Experiment – 100 Years Later…
He took a candle, placed a glass jar over it and watched as the flame gradually died
He reasoned that the flame needed something in the air to keep burning
He placed a sprig of mint into the jar for a few days
He found that the candle could be relighted and would remain lighted for a while
The plant produced the substance required for burning
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The Photosynthesis Equation
Photosynthesis – plants trap the sun’s energy and make glucose
The equation for photosynthesis is:
6CO2 + 6H2O C6H12O6 + 6O2
carbon dioxide + water glucose + oxygen
Light
Light
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Light and Pigments
How do plants capture the energy of sunlight?
Pigments – light absorbing molecules in plants
Two main types of chlorophyll
Chlorophyll a
Chlorophyll b
Chlorophyll does not absorb green light waves
Green light is reflected by leaves which is why plants look green
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15. 8-3 The Reactions of Photosynthesis
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Inside a Chloroplast
In plants, photosynthesis takes place inside chloroplasts
Parts of a chloroplast
Thylakoid – disk-like membranes that contain chlorophyll
Grana – a stack of thylakoids
Stroma – liquid surrounding the thylakoids
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Thylakoid
Stroma
Granum
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Photosynthesis occurs in 2 Phases
Light Dependent Reaction
Light Independent Reaction
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Light Dependent Reaction
First phase of photosynthesis
Takes place in thylakoid
Sunlight strikes chlorophyll molecules in the thylakoid
Energy in the light is transferred to electrons
Highly energized electrons pass from chlorophyll to electron transport chain
Electron Transport Chain – a series of proteins embedded in the thylakoid membrane
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ADP → ATP
H2O → H + H + O
Oxygen leaves the plant and goes out into the atmosphere
Hydrogen combines with NADP
NADP → NADPH
NADPH – an electron carrier (carries energy)
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H2O
ATP
NADPH
Light
Dependent
Reaction O2
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Light Independent Reactions
Second phase of photosynthesis
Does not require light
Occurs in the stroma
Also called the Calvin Cycle
Each glucose molecule made contains 6 carbon atoms
Only one molecule of CO2 is added to the cycle each time, it takes a total of 6 rounds of the cycle to form 1 glucose
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6CO2 combines with RUBP and makes 12 PGA
12 PGA combines with ATP and NADPH and makes 12 PGAL
2 PGAL are used to make 1 glucose (C6H12O6)
10 PGAL are used to make more RUBP to keep the reaction going
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24. H2O 6CO2 ATP 12 PGA RuBP NADPH Light Light Independent Dependent
Reaction
Light
Dependent
Reaction
12 PGAL
10 PGAL
ADP
2 PGAL
NADP
C6H12O6 O2