Transcript Inquiry into Life, Eleventh Edition

Honors Biology
Chapter 8
Photosynthesis
John Regan
Wendy Vermillion
Columbus State Community College
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Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
8.1 Overview of photosynthesis
• Flowering plants as photosynthesizers
– Photosynthesis occurs in the green parts of
plants
– Water is taken up by roots and transported to
leaves by veins
– Carbon dioxide enters through openings in
the leaves called stomata
– Light energy is absorbed by photopigments in
thylakoids of chloroplasts
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Chloroplast Anatomy
• Double membrane on outside
• Inner membrane-thylakoids
– Stacks of thylakoids- grana
– Chlorophyll and other pigments in thylakoid membranes
– Absorbs light
• Stroma- space between grana
– Carbohydrates made here
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Plants as photosynthesizers
• Fig
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Overview of photosynthesis cont’d.
• Photosynthetic reaction
Solar energy + 6CO2 + 6H2O  C6H12O6 + 6O2
– Carbon dioxide is reduced to form glucose, therefore
oxygen in glucose comes from CO2
– Water is oxidized to form oxygen, therefore the oxygen
given off by photosynthesis comes from water
• Two set of reactions
– Photosynthesis consists of 2 sets of reactions
– The light reactions occur first followed by the Calvin
cycle
– NADP+ carries hydrogens from the light reactions to
the Calvin cycle
– ATP formed in the light reactions is used in the Calvin1-5
Overview of photosynthesis
• Fig
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8.2 Solar energy capture
• Visible light
– Visible light is a part of the electromagnetic
spectrum
– Visible light includes the colors violet,blue
green, yellow, orange, and red
– Blue-violets have the shortest wavelengths
and the highest energy content
– Photopigments chlorophyll a and b and
carotenoids absorb specific portions of the
light spectrum
– Blue, violet, and red are best absorbed
– Green is reflected
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The electromagnetic spectrum and
visible light
• Fig
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Photosynthetic pigments and
photosynthesis
• Fig
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Solar energy capture cont’d.
• Light reactions
– 2 types of photosystems (PS I and PS II)
composed of photopigments
– Composed of chlorophyll a and b and
carotenoids
– Reaction center of each photosystem is
chlorophyll a
– Electrons of chlorophyll a absorb light energy
and move to an electron acceptor molecule
– Electrons then pass down one of 2 paths- 1-10
noncyclic or cyclic
Solar energy capture cont’d.
• The noncylic pathway
–
–
–
–
Produces ATP and NADPH
Light energy is absorbed by chlorophyll a in PSII
Excited electrons are removed
Those electrons are replaced by splitting a water
molecule
2H2O  4H+ + 4e- + O2
– High energy electrons removed from PSII pass down
an ETC releasing energy to build a chemiosmotic
gradient
– ATP is produced
– Electrons are picked up by NADP+ to make NADPH
– Electrons lost by PSI chlorophyll a can be replaced by
those from PSII
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The light reactions: the noncyclic
electron pathway
• Fig 8.6
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Solar energy capture cont’d.
• Cyclic pathway
– Generates only ATP
– PSI absorbs solar energy and electrons from
chlorophyll a are removed
– Electrons pass down an ETC
– Energy released is stored in an
electrochemical gradient for chemiosmosis
– ATP is produced
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The light reactions: the cyclic electron
pathway
• Fig 8.7
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Solar energy capture cont’d.
• Organization of thylakoid
– Thylakoid space acts as reservoir of
hydrogen ions
– Hydrogen ions flow down gradient
through an ATP synthase complex in
thylakoid membrane to produce ATP
– Thylakoid membranes contain the
following complexes:
• PS I and II
• ETC
• ATP synthase complexes
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Organization of the thylakoid
• Fig
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Light Reaction In/Out Table
In
H2O
Out
O2
NADP+
NADPH
ADP + P
ATP
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8.3 Carbohydrate synthesis
• Stages of the Calvin cycle
1. Carbon fixation
• carbon fixation occurs when a reaction
occurs that attaches CO2 to an organic
compound
• Ribulose biphosphate (RuBP) combines
with CO2 to form a 6C molecule
• Enzyme which catalyzes this reaction is
RuBP carboxylase
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The Calvin cycle reactions
• Fig
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Stages of the Calvin Cycle
2. Reduction of carbon dioxide
– 6C molecule breaks into 2 3C 3PG molecules
– Each undergoes reduction to G3P in a 2 step
process
– CO2 is reduced to a carbohydrate and
NADPH is oxidized to NADP+
– ATP provides the energy
– Every 3 turns of the Calvin cycle produce 6
G3P; one molecule leaves the pathway to
synthesize carbohydrates
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Stages of Calvin Cycle
3. Regeneration of RuBp
– Constant supply of RuBP needed to keep the
Calvin cycle turning
– For every 3 turns of the Calvin cycle 5 G3P
molecules are used to reform RuBP
– This reaction also requires energy from ATP
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Calvin Cycle In/Out Table
In
NADPH
ATP
CO2
Out
NADP+
ADP + P
Glucose
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Carbohydrate synthesis cont’d.
• Importance of the Calvin cycle
– G3P is the Calvin cycle product that can be converted
to glucose phosphate
– Glucose phosphate can then be converted into many
different organic molecules
Glucose phosphate
Glucose and starches
Amino acids
Fatty acids and glycerol
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8.5 Photosynthesis versus cellular
respiration
• Photosynthesis vs cell respiration
– Both plant and animal cells carry out cell
respiration
– Only plant cells photosynthesize
– Both processes utilize an electron transport
chain and chemiosmosis for ATP production
– Photosynthesis reduces CO2 to carbohydrates
and releases O2
– Respiration utilizes O2 and gives off CO2
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Photosynthesis vs cell
respiration
• Fig
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Objectives Chapters 7
1. Know the equation for aerobic cellular respiration.
2. Know the 4 stages of aerobic respiration and where
each happens.
3. Know the terms oxidation, reduction.
4. Know how many ATPs are made from NADH and
FADH2 in ETC.
5. Know the 2 categories of metabolism and whether they
are exergonic or endergonic.
6. Know the efficiencies of aerobic and anaerobic
respiration.
7. Know the 2 types of fermentation.
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Objectives Chapter 8
1. Know the equation for photosynthesis.
2. Know what colors of light have the most energy.
3. Know what colors of light are absorbed the best by
chlorophyll.
4. Know the structure of a chloroplast.
5. Know the source of oxygen released by
photosynthesis.
6. Know the 2 stages of Photosynthesis.
7. Know the reactants and products of the light reaction
and Calvin cycle.
8. Know the differences between the cyclic and noncyclic
electron pathways.
9. Know how RuBP is used in the Calvin cycle.
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10. Compare photosynthesis and cellular respiration.