Transcript Photosynthesis

Photosynthesis
and
Cellular Respiration
Matter is recycled; energy is not.
Energy from the sun arrives on earth in the
form of visible light, a type of
electromagnetic radiation
How objects appear different colors
White light is a mixture of all
wavelengths (and colors) of light
White
light
Green light
Is reflected and transmitted
Red and blue light
Is absorbed
We see the
Plant as green
Figure 10.6 Why leaves are green: interaction of light with chloroplasts
The wavelength of light a compound absorbs can be
determined by a spectrophotometer
Energy Pathway: The Big Picture
cellular
Chemical
photosynthesis
respiration energy for
Chemical
Light
energy stored in
energy from
use in the
glucose, fats, or
the sun
form of ATP
carbohydrates
Anabolism
Catabolism
Overview of Cellular Respiration
C6 H1 2 O6
+
6 O2
Glucose oxygen
6 CO2
carbon
dioxide
+
6H 2 O
+
energy
water
ADP + Pi + energy
In mitochondria, the energy
released from the catabolism
of glucose is used to make
ATP from ADP and Pi .
The process is called
phosphoryllation.
ATP
Overview of Photosynthesis
6 CO2
+
1 2H2 O
Carbon water
dioxide
+
Solar
energy
C6 H1 2 O6
Glucose
+
6 O2
+
oxygen
In photosynthesis, energy from the
sun (in packets called photons) is
absorbed by pigment molecules
(primarily chlorophyll) and used to
produce glucose from CO2
6H 2 O
Photoautotrophs: Use sunlight to produce food molecules;
includes plants and cyanobacteria
Photosynthesis takes place in the
chloroplasts of plant cells
Leaf cross-section
Leaves contain millions of chloroplasts
Cells containing
chloroplasts
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Photosynthesis Review
• Occurs in the chlorplast
• Chlorophyll and accessory pigments
capture electromagnetic energy by
absorbing photons of light.
• The energy from light is captured and
converted to chemical energy which is
stored in the bonds of a biomolecule.
• Chemical energy is harvested to make
ATP during cellular respiration.
Different plant pigments absorb different
wavelengths of light.
Amount of light absorbed
Chlorophyll a
Chlorophyll b
Carotenoids
400
500
600
Wavelength of light (nm)
700
Pigments include chlorophyll (a and b), carotenoids, xanthophylls
and anthocyanins.
Figure 10.9 Location and structure of chlorophyll molecules in plants
Pigments are found in chloroplasts.
Outer
membrane
Inner
membrane
Thylakoids
Granum
Stroma
Inner membrane
Outer membrane
Stroma
Granum
Thylakoid
Factors affecting the rate of
photosynthesis
*LIGHT INTENSITY
*TEMPERATURE
*CO2 LEVEL
Photosynthesis: The Big Picture
• Light Dependent Reactions
– Occur in thylakoid membranes of grana
– Energy from the high energy electron of chlorophyll
is used to make ATP and NADPH
• Light Independent Reactions (Calvin Cycle)
– Occur in enzyme-rich stroma
– ATP and NADPH are used to make glucose
from CO2 (carbon fixation)
Photosynthesis Equation
6CO2 + 12 H2O + Light
energy
C6H12O6 + 6O2 + 6 H2O
Two components:
Light-dependent reactions
Light
energy
H2O
O2
Chemical
energy
(ATP,
NADPH)
Energy Harvest
Light-independent reactions
Chemical
energy
(ATP,
NADPH)
CO2
Synthesis
Chemical
energy
(C6 H12O6)
When a photon of light strikes
chlorophyll, an electron can be
promoted to a higher energy state
Electrons can be
promoted to
discrete highenergy states:
e–
Blue photons excite electrons to a
higher energy state
e–
Red photons excite electrons to a
high-energy state
Photons
0
1
Energy state of electrons in chlorophyll
2
Light
excites
e- in
chl.a in
PSII
e- move to
electron
acceptor
E- from PSI enter
second e.t.c. which
ends by making
NADPH
e- transferred
along electron
transport
chain; as they
lose energy,
H+ protons
move into
thylakoid
Light
excites e- in
chl a of PSI.
Moving Electrons
• LEO = lose electrons “oxidized”
• GER = gain electrons “reduced”
OR
OIL RIG
Oxidized is lost ……….Reduced is gained
Replacing electrons
• Water molecules inside the thylakoid
membranes are split by an enzyme
• Process is called photolysis
• Results:
• 2H2O  4H+ + 4e- + O2
Chemiosmosis
The movement
of protons (H+)
into the stroma
releases energy
which is used to
phosphoryllate
ADP + Pi to form
ATP.
SUMMARY
Alternative Carbon Pathways
• C3 plants = Fix carbon exclusively through the
Calvin cycle (see previous slide)
• C4 plants = used when CO2 levels are low (hottest
part of the day, stomates closed)
– Includes corn, sugar cane, grasses
– Can produce same amount of carbs with half the water
loss
• CAM plants = “crussulacean acid metabolism”
– CO2 incorporated into organic acids at night and released
for fixation during the day
– Includes cacti, pineapples
Cellular Respiration Overview
Glycolysis
• Occurs in the cytoplasm
• Use 2 ATP to break 6-carbon sugar into two 3-carbon
pyruvate; produces 4 ATP (net gain of 2) and 2 NADH
• If oxygen present, pyruvates continue to Krebs cycle
• If no oxygen present, pyruvates continue to fermentation
(lactic acid or alcohol)
Alcohol fermentation: no oxygen present
• Pyruvate is converted to ethanol and CO2 is released.
• Glycolysis is believed to have been what ancient
prokaryotes used for energy production long before oxygen
levels were high enough to support electron transport chain.
Lactic Acid fermentation
• Pyruvate is directly reduced by NADH to form
lactate. (NADH becomes NAD+)
• Used in human muscle cells when there is not enough
oxygen
getting to the muscles
such as during
strenuous exercise. A
chemical pathway
removes lactic acid as
oxygen becomes
available.
The Krebs cycle is the first part of cellular
respiration.
• Pyruvate is oxidized
to form acetyl CoA
– carbon dioxide
released
– NADH produced
– coenzyme A (CoA)
bonds to two-carbon
molecule
The Krebs cycle
• Produces
energy-carrying
molecules
including
ATP
NADH and
FADH2
• Citric acid is
formed and CO2
is released
Electron Transport Chain
• The second part of cellular respiration when protein
carriers are used to make NADH and FADH2 and ATP.
– high-energy electrons enter electron transport chain
– energy is used to transport hydrogen ions across the inner
membrane
– hydrogen ions
flow through a
channel in the
membrane
– One glucose nets up to 36 ATP
– Water is released as a waste product.