Photosynthesis

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Photosynthesis

• All Energy originates from the Sun
• Some chemosynthetic bacteria can use sulforus
  compounds from deep ocean vents

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8-1 Energy Life

• Energy is ability to do work
• All living things need energy
• Without energy, life would cease to exist
• Energy can be light, heat, electricity, stored
  in chemicals

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Chemical Energy

• Living things must release ATP from compounds
• Adenosine triphosphate (ATP)

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The Generation of ATP

• ATP is generated by the phosphorylation of ADP
  (adding a PO4)

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Storing Energy

• In the form of ADP (adenosine diphosphate)
• Only has 2 phosphate groups
• When your cells need energy, they add a phosphate
  group to ADP a little energy to make more ATP
  molecules
• Use glucose to store long term energy

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Releasing Energy

• ATP molecules have bonds between the phosphate
  groups
• ATP is the basic energy source for cells
• Your cell breaks the bond to release energy
• One breaking bond is enough energy to power
  active transport, protein synthesis,
  cytoskeleton movement in a cell

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Biochemical Energy

• Na-K pump in the membrane pumps Na ions out K
  ions in
• ATP provides the energy to do this
• ATP even provides the energy for fireflies to
  light up!
• Glucose is the primary source for ATP

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Autotrophs

• Organisms that make their own food.
• Example plants, cyanobacteria, blue-green
  bacteria, algae make chemical energy from sunlight

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Heterotrophs

• Organisms must consume food (plants or animals)
  to obtain energy
• Example animals, fungi, bacteria

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8-2 Overview of Photosynthesis

• Process of converting water carbon dioxide into
  high-energy carbohydrates (sugars starches)

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How plants grow--Van Helmonts experiment

• Mass of dry soil a seedling
• Watered plant for 5 years
• Seedling grew to 75 kg mass
• Mass of soil was almost unchanged
• He concluded most of the mass had come from the
  water
• Actually, the seedling received carbon dioxide
  from the air to make sugars to grow

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Joseph Priestly

• Glass jar over a candle saw flame go out
• He reasoned there was something in the air that
  the flame needed
• He took a sprig of mint leaf put it in the jar,
  after a few days he put the candle in the flame
  stayed lit for a while
• He believed that the plant had made something
  (oxygen) that the flame needed

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Jan Ingenhousz

• Showed that the plant could only keep the flame
  lit if the plant was exposed to sunlight
• Proved sunlight was necessary for the plant to
  make oxygen
• These experiments proved that plants, in the
  presence of sunlight will transform carbon
  dioxide water into carbohydrates oxygen

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Equation
sunlight

• 6 CO2 6 H 2 O C6 H12 O6 6O2

Know this equation
Plants can use the sugars produced by
photosynthesis to make complex carbohydrates like
starch
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Light Pigments

• In addition to water carbon dioxide,
  photosynthesis requires light chlorophyll, a
  molecule in chloroplasts
• Sunlight is actually a mixture of different
  wavelengths
• Plants gather the suns energy with light
  absorbing molecules called pigments

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Photosynthesis Movie
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Chlorophyll

• 2 types of chlorophyll absorbs different light
  wavelengths

Red
Violet
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Green leaves

• Green light is reflected by leaves, so thats why
  they look green
• Plants also contain red orange pigments such as
  carotene (in carrots) that absorb other light
  wavelengths
• When chlorophyll absorbs light, much of this
  energy is transferred to the electrons raises
  the energy

What colors would be absorbed by a red rose?
All colors except red
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Pigments

• When carotene and chlorophyll occur in the same
  leaf, together they remove red and violet light
  from sunlight that falls on the leaf.

Chlorophyll is not a very stable compound bright
sunlight causes it to decompose.
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Why do leaves change colors in the Fall?
Carotene is a much more stable compound than
chlorophyll. Carotene persists in leaves even
when chlorophyll has disappeared. When
chlorophyll disappears from a leaf, the remaining
carotene causes the leaf to appear yellow.  
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Photosynthesis

• Take place inside the chloroplasts
• Thylakoids are saclike membranes arranged in
  stacks called grana
• Proteins in thylakoid organize chlorophyll
  other pigments into clusters known as
  photosystems
• Photosystems collect light
• The Stroma is the fluid
• portion outside the thylakoids

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Light movie
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8.3 Process of Photosynthesis

• Light-dependent take place in the thylakoid
• Light-independent (the Calvin cycle) take place
  in the Stroma, which is outside of the thylakoid
  membranes

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Electron Carriers

• Sunlight excites electrons in chlorophyll
• Electron Transport electron carriers transport
  the electrons to other molecules
• NADP (nicotinamide adenine dinucleotide
  phosphate) can hold 2 high-energy electrons along
  with a H ion
• This forms NADPH (energy in chemical form)

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Light-dependent Reactions

• Require light to take place
• Produce Oxygen gas , ATP, NADPH
• Step 1. Photosystem II absorbs light
• Enzymes on the thylakoid break up water molecules
  into 2 e - s, 2 Hs, and 1 O2
• The plant uses the e-s releases O2 into the
  atmosphere

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• Step 2. Electron Transport Chain
• High-energy e-s move from photosystem II to
  photosystem I through the electron transport
  chain
• Hs are transported from stroma into inner
  thylakoid space

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• Step 3. Photosystem I pigments use light energy
  to reenergize the e-s
• NADP transports the e-s Hs to make NADPH

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• Step 4 Hs pumped across membrane
• Inside becomes positively charged
• This provides energy to make ATP

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• Step 5 ATP synthase allows Hs to pass through
  membrane
• ATP synthase is a protein that rotates like a
  turbine
• As it rotates, ADP is bond to a PO4 to make ATP

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Overall Light dependent

• Water, ADP, NADP are used to produce
  Oxygen, 2 ATPs, NADPH
• This gives energy to make sugars in a later
  process

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Light Dependent

• Needs light energy with chlorophyll to make the
  products ATP, NADPH, oxygen in Thylakoid

1. Starts in Photosystem II
Photons break apart water into Hydrogen oxygen
2. Electrons from photosystem II are used to make
NADPH in Photosystem I
3. ATP synthase turns to make ATP molecules
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Light Dependent Movie
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Calvin Cycle

• Light-independent phase
• Uses ATP NADPH from the light- dependent
  reactions to produce high-energy sugars
• Named after Melvin Calvin who received the Noble
  prize for his work

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Calvin Cycle Steps

• 3 CO2 molecules join to a 3 carbon molecule
• ATP NADPH join the 3 carbon molecules to form
  the G3P molecules
• The cycle must repeat 6 times to form 1 glucose
  molecule
• The G3P molecules are joined to form glucose in
  the cytoplasm

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Calvin Cycle Summary

• Major molecules coming In Out
• 6 Turns of the cycle produces 1 glucose molecule

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Calvin Cycle

• Light Independent stage in Stroma
• Uses ATP NADPH that was produced in light
  dependent stage plus the CO2 to make the products
  high-energy sugars
• It take 6 cycles to convert 6 Carbon dioxides
  into 1 6-carbon sugar
• Glucose stores gt90 times the energy stored by ATP

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Calvin Cycle Movie
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Photosynthesis Summary

• Definition of Photosynthesis

Use of sunlight energy to convert water carbon
dioxide into high energy sugars oxygen

• ATP is adenosine triphosphate
• Its Sugar is ribose it stores energy

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Factors Affecting Photosynthesis

• Water -- shortage slows it down
• Temperature-- best 0-35C, temps above or
  below, slows it down
• Light Intensity will increase the rate until the
  limit is reached (for that particular plant),
  then it plateaus

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Animated photosynthesis
The Big Picture Photosynthesis Video
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Extreme Conditions

• Tropics Desert
• extreme heat plants close the openings in their
  leaves to keep from drying out
• This also reduces the absorption of CO2
• Some plants have adapted to these bright hot
  conditions

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Special Plants

• C4 plants specialized chemical pathway to
  capture more CO2 (requires more ATP) EX corn,
  sugar cane, sorghum
• CAM plants Crassulacean Acid Metabolism allows
  air in only at night that combines to CO2 to
  form acids to trap the CO2 in their leaves
• Carbohydrates are then formed during the day
• The leaves are sealed with a waxy coating to
  prevent water loss during the day

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Putting it all together

• Animation

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Review

• The light dependent reactions occur in the
• Thylakoid membrane
• The Reactants of the light-dependent reactions
  are
• 6 H2O, sunlight, chlorophyll
• The products of the light-dependent reactions in
  photosynthesis are
• 6 O2, ATP, NADPH

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Review

• The Calvin Cycle occurs in the
• Stroma
• The Reactants in the Calvin Cycle are
• 9 ATP, 6 NADPH, 6 CO2
• The Products in the Calvin Cycle are
• 9 ADP, 6 NADP, G3P
• 2 G3Ps are joined in a glucose molecule in the
  cytoplasm

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Standardized Prep pg 219

• The principal pigment in plants is
• 2. Which of the following is NOT produced in the
  light-dependent reactions of photosynthesis?

A. chlorophyll
B. sugars
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Standardized Prep pg 219

• 3. Which equation best summarizes the process of
  photosynthesis?
• 4. The color of light that is LEAST useful to a
  plant during photosynthesis is

light
A. Water CO2 sugars O2
C. green
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Standardized Prep pg 219

• 5. The first step in photosynthesis is the
• 6. In a typical plant, all of the following
  factors are necessary for photosynthesis EXCEPT

E. Absorption of light energy
C. oxygen
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Standardized Prep pg 219

• 7. Which pigment traveled the shortest distance?
• 8. A valid conclusion that can be drawn from
  this information is that spinach leaves

D. yellow-green
B. Contain several pigments
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Standardized Prep pg 219

• 9. In which organelles would most of these
  pigments be found?

D. chloroplasts