Do Now
What does a chloroplast look like?
How do plants obtain energy?
What is the formula for glucose?
How do autotrophs obtain energy?
How do heterotrophs obtain energy?
Chapter 6
Photosynthesis: Capturing
and Converting Energy
Energy – the ability to do work
Photosynthesis
• Plants use the energy of sunlight to produce
carbohydrates
• Energy is now in the chemical bonds
Jan Van Helmont
• Where does a tree’s increased mass come from?
• Seedling – 5 years – soil same mass – tree gained
75 kg
• Conclusion  water “hydrate”
Priestly
• Candle and a jar  candle goes out – no oxygen
• Candle + jar + plant  candle does not go out
Ingenhousz
Oxygen produced in light
Equation for Photosynthesis
Requirements for
Photosynthesis
1. Sunlight
• Autotrophs – can use sunlight to make food
– Ex. Plants obtain energy
• Heterotrophs – obtain energy by eating other
organisms
–
Ex. Animals
• All organisms on earth depend on the sun for
energy
• Sunlight is “white” light
• Many wavelengths of light
• ROYGBIV – visible spectrum
2. Pigments
• Colored substances that absorb or reflect light
• Photosynthesis begins when light is absorbed by
pigments
• Chlorophyll – principle pigment of green plants
• Absorbs red and blue and reflects green light
Chromatography
Paper chromatography is a way to separate chemical
components of a solution.
How it Works
1.A drop of solution is placed at the bottom of a
paper.
2.The paper is put in a solvent (tip only).
3.The solvent rises through the paper.
4.As it rises it carries the solution with it.
5.The parts of the solution move at different
speeds depending on their mass. Lighter
molecules move faster.
3. Energy Storing Compounds
•
•
•
Like solar cells
Electrons are raised to higher energy levels – then
trapped in bonds
Two ways that energy from the sun is trapped in
chemical bonds
1. High energy e- are passed to an electron carrier
(NADP +)  NADPH
– Electron carrier – a molecule that can accept a
pair of high energy electrons and later transfer
them with most of their energy to another
compound
– Conversion of NADP+ to NADPH – one way that
energy from the sun can be trapped in a
chemical form
2. Second way light energy is trapped  ATP
(Adenosine Triphosphate) – 3 phosphates
Fig 6-6
Green plants produce ATP in photosynthesis
ATP energy storage compound used by every cell
Producing ATP
1. AMP (mono) – one phosphate
2. AMP + P  ADP (two – di)
3. ADP + P  ATP
• Energy is stored in the P bonds
• Energy is released when P bonds are broken
Forming and Breaking Down ATP
Adenosine
P
P
P
Adenosine triphosphate (ATP)
P
P
Adenosine diphosphate (ADP)
Adenosine
P
P
6-2 Photosynthesis: The Light and Dark
Reactions
• Light Reaction – energy of sunlight captured to
make energy storing compounds
• ATP and NADPH
• Short term energy storage
Sun
Light-Dependent
Reactions
At each step along the
transport chain, the
electrons lose energy.
Light energy transfers to chlorophyll.
Chlorophyll passes energy down through the
electron transport chain.
Energized electrons provide energy that
splits
H2 O
H+
NADP+
bonds P to ADP
forming
oxygen
ATP
released
NADPH
for the use in
light-independent reactions
• Dark Reaction – energy from ATP and NADPH to
make glucose (100 x the energy)
• Long term energy storage
The Light Reactions
Chloroplast
Parts of a chloroplast
Stroma – “cytoplasm”
Grana – pancake
Thylakoid – stacks of pancakes (grana)
Thylakoid = photosynthetic membrane
4 Parts of the Light Reaction
1.
2.
3.
4.
Light absorption
Electron transport
Oxygen production
ATP formation
Photosystems
• Clusters of pigment molecules that capture energy
from the sun
• Two in plants – Photosystems I and II
Photosynthesis – plants - autotrophs
• Occurs in the chloroplast
• Absorbs light
• Light reaction occurs in the thylakoid
(photosynthetic environment) – needs sun to
occur
Light Absorption
• Photosystem I & II – absorb sunlight
• Pigment molecules pass the energy to other
pigment molecules
• Reach a special pair of chlorophyll molecules in the
reaction center
• High energy electrons released and passed to
many electron carriers
Electron Transport
• Electron transport – electron transport chain
• e- passed from one carrier to another (bucket
brigade)
• Passed to electron carrier NADP+
• NADPH
Electron Transport Chain
NADPH – restoring electrons
• Water is split (photolysis)
• 2 H O  4 H+ + O + 4 e• Oxygen is released
• 4 e- go to the chloroplast
• 4 H+ are used to make ATP
2
2
ATP Formation
• 4 H+ released inside the membrane
• H+ build up
• Inside positive – outside is negative (charge
difference is a source of energy)
• Enzymes use this energy to
attach P to ADP  ATP
The Dark Reaction
or Calvin Cycle
The Dark Reaction or Calvin Cycle
• Does not need sunlight to happen
• Often happens with sunlight
• Uses products of the light reaction (ATP + NADPH)
• This series of reactions is particularly critical to
living things
• Carbon dioxide is used to build complex organic
molecules  glucose
Dark Reaction or Calvin Cycle
Occurs in the stroma
5 C sugar (RuBP) + CO2
This reaction is slow and is catalyzed by rubisco
Next two 3 C sugars are produced (PGA)
ATP and NADPH from the light reaction are used to
convert PGA eventually into PGAL (3 C) – products
P + ADP and NADP+
PGAL can use some ATP and become RuBP (5 C)
After several turns of the cycle 2 PGAL can leave and
form glucose
6-3 Glycolysis and Respiration
• Enables organisms to release energy in glucose
• Breaks down food molecules
• C H O + 6O  6CO + 6H O + energy (ATP)
• 1 g of glucose  3811 calories
• 1 cal = amount of heat energy to raise
6
12
6
2
2
O
1 g of water 1 C
2
Glycolysis
occurs in the cytoplasm
Changes a molecule of glucose into many different
molecules step by step
• Glucose (6 C)
• 2 ATP are used to make 2-3-C PGAL
• PGAL is converted into pyruvic acid and 4 ATP and
2 NADH are produced
• Pyruvic acid can enter aerobic or anaerobic
respiration based on whether there is oxygen
available or not
Presence of Oxygen – Cellular Respiration
• Aerobic oxygen needed
• Takes place in the mitochondria
• Krebs cycle (Citric Acid Cycle)
• Starts with Pyruvic acid
• Carbon dioxide is removed
• Acetyl CoA is produced
• Citric acid is then produced
• 9 reactions
• 9 intermediate
• citric acid is produced and the cycle begins again
• Carbon dioxide is released
• Make FADH2 and NADH
• FADH2 and NADH go to the inner membrane of the
mitochondria
• Electrons passed to enzymes
• Electron transport chain
• At the end – enzyme combines
• H+ + O2  H2O
• Therefore Oxygen is the final electron acceptor
• Mitochondrial membrane is charged (H+ ions
pumped to one side)
• Provides energy to convert ADP  ATP
• 36 ATP are produced
6-4 Alcoholic Fermentation
• Glycolysis – net 2 ATP
NAD+  NADH
• If you remove an electron from NADH glycolysis
can continue
Fermentation – Anaerobic (no Oxygen)
• NADH converted to NAD+ (acceptor molecule take
the H)
• Allows cells to carry out energy production in the
absence of oxygen
• 1 glucose  2 ATP
• Prokaryotes use many different acceptors
• Eukaryotes use two different acceptors
1. Lactic acid fermentation
2. Alcoholic fermentation
Alcoholic Fermentation
Occurs in yeast and a few other organisms
Pyruvic acid is broken down to produce 2-C alcohol
and carbon dioxide
Pyruvic acid + NADH  alcohol + CO2 + NAD+
Brewers and bakers
Carbon dioxide produced causes bread to rise
Bubbles in beer
Yeast dies at 12% alcohol content
Lactic Acid Fermentation
Pyruvic acid created in glycolysis can be converted to
lactic acid
The conversion regenerates NAD+
Pyruvic acid + NADH  lactic acid + NAD+
Lactic acid produced in muscles during rapid exercise
when the body does not supply enough oxygen
Lactic acid – produced burning sensation in muscles
Comparing Photosynthesis and
Cellular Respiration
Table 9.1 Comparison of Photosynthesis and Cellular Respiration
Photosynthesis
Cellular Respiration
Food synthesized
Energy from sun stored in glucose
Food broken down
Energy of glucose released
Carbon dioxide taken in
Carbon dioxide given off
Oxygen given off
Oxygen taken in
Produces sugars from PGAL
Produces CO2 and H2O
Requires light
Does not require light
Occurs only in presence of
chlorophyll
Occurs in all living cells
The End