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Copyright Pearson Prentice Hall

• 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
Ribose
3 Phosphates
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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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Copyright Pearson Prentice Hall

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 relit and would remain lit for a while
• The plant produced the substance required for burning
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•Photosynthesis – plants trap the sun’s energy and make glucose
•The equation for photosynthesis is:
6CO
2
+ 6H
2
Light
O C
6
H
12
O
6
+ 6O
2
Light carbon dioxide + water glucose + oxygen
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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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Copyright Pearson Prentice Hall

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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Granum
Thylakoid Stroma
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• Photosynthesis occurs in 2 Phases
1. Light Dependent Reaction
2. 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
• H
2
O → 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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H
2
O
Light
Dependent
Reaction
ATP
NADPH
O
2
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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 CO
2 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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• 6CO
2 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 (C
6
H
12
O
6
)
• 10 PGAL are used to make more RUBP to keep the reaction going
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H
2
O
6CO
2
Light
Dependent
Reaction
ADP
NADP
ATP
NADPH
Light
Independent
Reaction
O
2
C
6
H
12
O
6