Transcript ap ch 10 powerpoint - Pregitzersninjascienceclasses

Phenomenal
Photosynthesis
Chapter 10 notes
Photosynthesis
 Capturing light energy from the sun and
converting it to chemical energy stored in
sugar and organic molecules
Where do you get your
Energy?
 Autotrophs – make organic molecules from
inorganic raw material (don’t need to eat) =
PRODUCERS!!
 Photoautotrophs – use light as an energy
source to make organic molecules ex. plants,
algae, some protists, some prokaryotes
 Chemoautotrophs – Use inorganic substances
(sulfur, ammonia) to make organic compounds
(no light) ex. Bacteria only
Where do you get your
Energy?
 Heterotrophs – live on compounds
produced by other organisms (must eat
to live) = CONSUMERS!!! ex. animals,
decomposers, etc
 Depend on photosynthesis for both food
and oxygen
The Perfect Setting
Leaf Structure
 Chloroplasts – contained in any green
part of a plant but photosynthesis
happens mainly in the leaves
 Chlorophyll – pigment in chloroplasts that
absorbs light from the sun
 Mesophyll – tissue on interior of leaf that
contains chloroplasts
The Perfect Setting
Leaf Structure
 Stomata – microscopic pores in leaves
that allow CO2 in and O2 out
 Veins – transport water from roots to
leaves and sugar from leaves to the rest
of the plant
An Overview of
Photosynthesis
 Easy Equations
 6CO2 + 12 H20 + Light C6H12O6 + 6O2 + 6H20
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Simplified
6CO2 + 6 H20 + Light  C6H12O6 + 6O2
REALLY SIMPLIFIED
CO2 + H20 CH2O + O2
An Overview of
Photosynthesis
 Mechanisms
 A series of experiments have been done to
determine how photosynthesis works. Read
about them in your book 
An Overview of
Photosynthesis
 The Bottom Line
 1. The oxygen that is released comes
from the splitting of WATER (not from
CO2)
 2. Photosynthesis is a redox process
(like respiration). Water is oxidized and
CO2 is reduced to sugar
An Overview of
Photosynthesis
 3. Light Reactions
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** convert solar energy to chemical energy
Inputs – H20, NADP+, Light, ADP
Outputs – O2, NADPH, ATP
ATP is made by photophosphorylation
Happens in the THYLAKOIDS of
chloroplasts
An Overview of
Photosynthesis
 4. Calvin cycle (“dark reaction”)
 Carbon fixation – incorporates CO2 from air
into organic molecules using ATP and
NADPH from the light reaction
 Inputs – CO2, ATP, NADPH
 Outputs – Glucose, NADP+, ADP
 Does not require light, but normally occurs
during the day
 Happens in the STROMA of chloroplast
The Sunlight and Color
 Sunlight – electromagnetic energy
 Visible light – The wavelengths of light
used in photosynthesis – detectable by
the human eye
 Photons – particles of light that have a
certain amount of energy
The Sunlight and Color
 Pigments – Substances that absorb visible light
 Different pigments can absorb different
wavelengths of light
 Wavelengths that are absorbed disappear
 Example – leaf appears green because
chlorophyll absorbs red and blue light but
transmits and reflects green light (red and blue
disappear and green shows up
The Sunlight and Color
 Blue and Red light are the most effective
wavelengths for photosynthesis and
green light is the least effective
Plant Pigments
 Chlorophyll A – The main pigment in
plants. Participates directly in the
photosynthesis light reaction. This is a
GREEN pigment
Plant Pigments
 Chlorophyll B – An accessory pigment. It
doesn’t participate directly in the light
reaction, but it can transfer energy to
chlorophyll a. This is a YELLOWGREEN pigment
Plant Pigments
 Carotenoids – Yellow and Orange
hydrocarbons that are found in the
thylakoid membrane of chlorophyll a and
b
Fun Photosystems
 The three plant pigments are arranged into
photosystems within the thylakoid membrane.
Each photosystem is made of 3 parts
 1. Antenna complex – made of several
hundred chlorophyll a, b and carotenoid
molecules. This complex gathers light and
absorbs photons and then passes the photons
from one molecule to the next
Fun Photosystems
 2. Reaction Center - Only ONE
chlorophyll a molecule can actually
transfer an excited electron into the light
reaction. This chlorophyll a molecule is
located in the reaction center
Fun Photosystems
 3. Primary electron acceptor – Near the
reaction center. It traps the excited
electron that comes from the reaction
center. This is the first step of the light
reaction. The energy from this trapped
electron will be used to make ATP and
NADPH to be used later
Electrifying Light Reaction
 Photosystem II (PSII)
 1. Light Strikes!!!
 2. An electron in the chlorophyll P680 is
excited to a higher level…Weeee!!!
Electrifying Light Reaction
 3. Water is split by an Enzyme.
Electrons from the water are given to
P680 to replace their long lost electron
from step 2.
 4. Oxygen is Released – Yeah – we can
breathe!!!
Electrifying Light Reaction
 5. The excited electron passes from
Photosystem II (PSII) to Photosystem I (PSI)
by an Electron Transport Chain.
 6. As the electron falls down the chain, their
fall drives the reaction
ADP + Pi  ATP (Chemiosmosis). Remember,
the energy actually pumps those H+ out. As
they come back in through ATP synthase, ADP
gets phosphorylated to make ATP.
Electrifying Light Reaction
 Photosystem I
 7. When the electron gets to the bottom
of the chain, it fills a hole in P700.
 8. More photons of sunlight come in and
excite the electron in P700 to a higher
energy level.
Electrifying Light Reaction
 9. The electrons falls down another
electron transport chain. NADP+
reductase (another enzyme) transfers the
electron from Fd to NADP+ to make
NADPH (our energy storage molecule).
 10. NADPH and ATP move on to the
Calvin Cycle!!! Let’s go make some
sugar!
Kickin’ Calvin Cycle
 Setting… Stroma of chloroplast
 ***CO2 in , Sugar Out
 ***Use ATP and NADPH (from light
reaction)
 ***Produces Glyceraldehyde-3biphosphate (G3P)
 ***Needs to go around 6 times to make a
glucose
Kickin’ Calvin Cycle
 1. Carbon Fixation
CO2 enters through stomata
 Each CO2 is combined with ribulose
bisphosphate (RuBP) by an enzyme called
Rubisco
 It produces a 6 carbon molecule. It’s not stable
so it immediately breaks in half. At the end
you’re left with 2, 3-carbon phosphoglycerates
(PGA)
Kickin’ Calvin Cycle
 2. Reduction
 ATP phosphorylates each PGA
 NADPH reduces it to G3P (by donating
electrons) – this also recycles NADP+
 1 molecule of G3P is released to form
sugar
Kickin’ Calvin Cycle
 3. Regeneration of CO2 acceptor (RuBP)
 Carbon skeletons of 5 molecules of G3P
are rearranged into RuBP in a series of
FUN chemical reactions!!
Kickin’ Calvin Cycle
 Fun facts
 In all, Calvin cycle uses 18 ATP and 12
NADPH to get just ONE glucose
The Skinny on Rubisco,
the friendly Enzyme
 Rubisco is the most common protein on
Earth because it is the enzyme that
“fixes” CO2 in plants.
 Rubisco can also “fix” oxygen because it
fits in its active site. This is called
photorespiration.
 OH NO!!! Competitive Inhibition!!
The Skinny on Rubisco,
the friendly Enzyme
 Photorespiration doesn’t produce useful
products. The products have to be
broken down by peroxisomes.
 Photorespiration slows down
photosynthesis and wastes valuable
resources. Ugh!!
Fun Photosynthesis,
Final details
 Non-cyclic Photophosphorylation
produces ATP, NADPH and O2 by using
both Photosystem I and II (like we just
learned)
 Problem – there is not enough ATP
produced to run the Calvin cycle
Cyclic
Photophosphorylation
 A simpler pathway that involved only
Photosystem I
 Makes ATP without producing NADPH or
O2
Cyclic
Photophosphorylation
 Here’s how it works
 1. Photons of light are absorbed by
Photosystem I and P700 releases the electrons
to the primary electron acceptor
 2. From here, the electrons travel to
Ferredoxin (Fd) and then to the cytochrome of
PSII and end up back at PSI again.
 3. During this electron transport chain, ATP is
made by chemiosmosis and it is called cyclic
photophosphorylation.
C4 Photosynthesis
 Used in plants that live in Hot, Arid (dry)
conditions.
 These hot dry conditions favor
photorespiration (bad) over
photosynthesis (good).
 C4 plants take in CO2 and convert it to a
4 carbon sugar BEFORE the Calvin cycle
C4 Photosynthesis
 C4 plants have a special leaf structure with two
types of photosynthetic cells
 1. Bundle sheath cells – have tightly packed
sheaths (insulators) around the veins of the
leaf. Their thylakoids are not stacked into
grana
 THE CALVIN CYCLE IS DONE ONLY IN
CHLOROPLASTS OF THE BUNDLE SHEATH
CELLS IN C4 PLANTS
C4 Photosynthesis
 2. Mesophyll cells are found between the
bundle sheath and the leaf surface (near
the stomata).
 CO2 enters the plant through the
mesophyll cells.
C4 Photosynthesis
 Here’s how it works
 1. CO2 enters through the stomata and goes
into the mesophyll cells.
 2. CO2 is add to PEP to form oxaloacetate (a 4
carbon product). This reaction is catalyzed by
PEP carboxylase (another enzyme).
 PEP carboxylase is much more efficient than
Rubisco. Oxygen does not fit in its active site,
so there is NO PHOTORESPIRATION!!
C4 Photosynthesis
 This carbon fixation is useful in hot dry
areas because the stomata on the leaves
close so that the plant doesn’t dry out.
 When the stomata are closed, CO2 from
the air can’t get in, and O2 from the light
reactions can’t get out. Levels of CO2
decrease and O2 levels increase inside
the leaf.
C4 Photosynthesis
 3. After CO2 has been fixed, Oxaloacetate is
converted to another 4 carbon compound
(malate).
 4. The malate moves into the Bundle sheath
cells (by the wonderful plasmodesmata
bridges)
 5. In the bundle sheath cells, the malate
releases CO2 which is then fixed by rubisco for
the Calvin Cycle.
C4 Photosynthesis
 Overall
 No Oxygen is allowed into the bundle sheath
cells, making rubisco fix ONLY CO2 and not
Oxygen.
 NO Photorespiration. HOORAY!!!
 This type of photosynthesis uses a
SEPARATION OF SPACE to make it more
efficient
CAM Photosynthesis
 Used in plants that open their stomata
mostly at NIGHT, because it is too hot in
the day and they would lose too much
water. (desert plants like cactus)
 Problem – by keeping stomata closed,
water is conserved, but CO2 can’t get in
for photosynthesis.
CAM Photosynthesis
 At night, when stomata are open, CO2 enters
the plant and is incorporated into organic acids.
 This carbon fixation is called Crassulacean
Acid Metabolism (CAM) photosynthesis
 Organic acids are stored in the vacuoles of the
mesophyll cells until morning when stomata
close.
CAM Photosynthesis
 During the daytime, light reactions supply
the ATP and NADPH for the Calvin cycle.
 At this time, CO2 from the organic acids
is released and made into sugar in the
chloroplasts.
 CAM photosynthesis uses a
SEPARATION OF TIME to make
photosynthesis more efficient.
End Thoughts on
Photosynthesis
 Overall, photosynthesis is the most
important chemical reaction that happens
on Earth.
 Without it, we wouldn’t be here. It
produces both Food and Oxygen.
End Thoughts on
Photosynthesis
 Plants use about 50% of the products of
photosynthesis to drive respiration (for
ATP) and for growth.
 The main sugar produced is glucose
(monomer) which combines to for
sucrose and cellulose (cell walls).
 The other 50% is stored as starch in
roots, tubers, seeds and fruits (YUM!!!)