Transcript Chapter 10 Photosynthesis
Chapter 10 Photosynthesis
• Autotrophs can be separated by the source of energy that drives their metabolism.
–
Photo
autotrophs use light as the energy source.
– Photosynthesis occurs in plants, algae, some other protists, and some prokaryotes.
–
Chemo
autotrophs harvest energy from oxidizing inorganic substances, including sulfur and ammonia.
– Chemoautotrophy is unique to bacteria.
Fig. 9.1
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6CO
2
+ 6H
2
O ----------> C
6
H
12
O
6
+ 6O
2
2. The light reactions and the Calvin cycle cooperate in converting light energy to chemical energy of food: an overview
• • Photosynthesis is two processes, each with multiple stages.
• The
light reactions
convert solar energy to chemical energy .
The
Calvin cycle
incorporates CO 2 atmosphere into an organic molecule from the and uses energy from the light reaction to reduce the new carbon piece to sugar .
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• In the light reaction light energy absorbed by chlorophyll in the thylakoids drives the transfer of electrons and hydrogen from water to
NADP +
(nicotinamide adenine dinucleotide phosphate), forming NADPH .
– NADPH, an electron acceptor, provides energized electrons, reducing power, to the Calvin cycle .
• The light reaction also generates ATP by
photophosphorylation
for the Calvin cycle.
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Light Dependent Reactions Carbon Fixation Dark Reaction Light Independent Reactions
NADPH NADP+
• The Calvin cycle is named for Melvin Calvin who worked out many of its steps in the 1940s with his colleagues.
• It begins with the incorporation of CO 2 organic molecule via
carbon fixation
.
into an • This new piece of carbon backbone is reduced with electrons provided by NADPH.
• ATP from the light reaction also powers parts of the Calvin cycle.
• While the light reactions occur at the thylakoids, the Calvin cycle occurs in the stroma.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The entire range of electromagnetic radiation is the
electromagnetic spectrum
.
• The most important segment for life is a narrow band between 380 to 750 nm,
visible light
.
Fig. 10.5
• A
spectrophotometer
measures the ability of a pigment to absorb various wavelengths of light.
– It beams narrow wavelengths of light through a solution containing a pigment and measures the fraction of light transmitted at each wavelength.
– An
absorption spectrum
plots a pigment’s light absorption versus wavelength.
Fig. 10.7
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420 nm = BLUE
• The action spectrum of photosynthesis was first demonstrated in 1883 through an elegant experiment by Thomas Engelmann.
– In this experiment, different segments of a filamentous alga were exposed to different wavelengths of light.
– Areas receiving wavelengths favorable to photosynthesis should produce excess O 2 .
– Engelmann used the abundance of aerobic bacteria clustered along the alga as a measure of O 2 production.
Fig. 10.8c
• Below is an absorption spectrum for an unknown pigment molecule. What color would this pigment appear to you?
– violet – blue – green – yellow – red
photo activation
• • Excited electrons are unstable.
Generally, they drop to their ground state in a billionth of a second, releasing heat energy.
• Some pigments, including chlorophyll, release a photon of light, in a process called fluorescence, as well as heat.
Fig. 10.10
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• • In the thylakoid membrane, chlorophyll is organized along with proteins and smaller organic molecules into
photosystems
.
A photosystem acts like a light-gathering “antenna complex” consisting of a few hundred chlorophyll
a,
chlorophyll
b,
and carotenoid molecules.
Fig. 10.11
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Figure 10.12 How a photosystem harvests light Thylakoid Photon
Photosystem
Light-harvesting complexes STROMA Reaction center Primary election acceptor
e
– Transfer of energy Special chlorophyll
a
molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID)
Light-dependent reactions create energy molecules (ATP and NADPH) that are used to drive the Light-independent reactions (Calvin Cycle).
Light-dependent Reactions
Composed of two parts: • 1. cyclic photophosphorylation and • 2. non-cyclic photophosphorylation • Occurs in the grana
Cyclic photophosphorylation- the electron is cycled back to P700
P700
Cyclic Photophosphorylation uses the energy from the electron flow to make ATP Refer to p178
1. Electrons flowing through the ETC provide energy to pump H+ into the thylakoid space Electron transport chain 2. The build up of H+ in the interior thylakoid space causes them to flow out through an ATP synthesizing enzyme.
Figure 8-10 Light-Dependent Reactions Section 8-3
Inner Thylakoid Space Thylakoid Membrane Stroma H+ H+ Photosystem II H H+ Hydrogen Ion Movement H+ ATP synthase Chloroplast e e ATP Electron Transport Chain H+ Photosystem I ATP Formation
Figure 10.12 How a photosystem harvests light Thylakoid Photon
Photosystem
Light-harvesting complexes STROMA Reaction center Primary election acceptor
e
– Transfer of energy Special chlorophyll
a
molecules Pigment molecules THYLAKOID SPACE (INTERIOR OF THYLAKOID)
Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H 2 O CO 2 Light NADP + ADP LIGHT REACTIONS ATP NADPH CALVIN CYCLE O 2 [CH 2 O] (sugar) Primary acceptor
2
e
Light
1
P680
Photosystem II (PS II)
Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H 2 O CO 2 Light NADP + ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O 2 [CH 2 O] (sugar)
H 2 O
Primary acceptor
e
2
1 ⁄ 2 2 H + +
O 2 3
e
e
Light
1
P680
Photosystem II (PS II)
Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H 2 O CO 2 Light NADP + ADP LIGHT REACTIONS ATP NADPH CALVIN CYCLE O 2 [CH 2 O] (sugar) Light
1 H 2 O
Primary acceptor
2
e
1 ⁄ 2 2 H + +
O 2 3
e
e
P680 Pq
4
Cytochrome complex
5
Pc ATP
Photosystem II (PS II)
Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H 2 O CO 2 Light NADP + ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH [CH 2 O] (sugar) O 2 Light
1 H 2 O
Primary acceptor
e
2
1 ⁄ 2 2 H + +
O 2 3
e
e
P680 Pq
4
Cytochrome complex
5
Pc Primary acceptor
e
P700
6
Light ATP
Photosystem I (PS I) Photosystem II (PS II)
Figure 10.13 How noncyclic electron flow during the light reactions generates ATP and NADPH H 2 O CO 2 Light NADP + ADP CALVIN CYCLE LIGHT REACTIONS ATP NADPH O 2 [CH 2 O] (sugar) Light
1 1 H 2 O
Primary acceptor
e
2
1 ⁄ 2 2 H + +
O 2 3
e
e
P680 Pq
4
Cytochrome complex
5
Pc Primary acceptor
e
P700
7
Fd
e
e
8
NADP + reductase
6 6
Light NADP + + 2 H + NADPH + H + ATP
Photosystem I (PS I) Photosystem II (PS II)
Figure 10.14 A mechanical analogy for the light reactions
e –
ATP
Z Scheme
e – e –
NADPH
e – e – e –
Mill makes ATP
e –
Photosystem I Photosystem II
PGAL
Rubisco
NADPH NADP+
NADPH NADP+
Problems for Photosynthesis
Click to go to site for photosynthesis problems
Diagram on Page 184
Problems for Photosynthesis
Click to go to site for photosynthesis problems set 2
Chapter 10
Photosynthesis
Below is an absorption spectrum for an unknown pigment molecule. What color would this pigment appear to you?
– violet – blue – green – yellow – red
• In green plants, most of the ATP for synthesis of proteins, cytoplasmic streaming, and other cellular activities comes directly from – photosystem I.
– the Calvin cycle.
– oxidative phosphorylation.
– noncyclic photophosphorylation.
– cyclic photophosphorylation.
• What portion of an illuminated plant cell would you expect to have the lowest pH? – nucleus – vacuole – chloroplast – stroma of chloroplast – thylakoid space
• A new flower species has a unique photosynthetic pigment. The leaves of this plant appear to be reddish yellow. What wavelengths of visible light are
not
being absorbed by this pigment?
– red and yellow – blue and violet – green and yellow – blue, green, and red – green, blue, and violet
• Some photosynthetic organisms contain chloroplasts that lack photosystem II, yet are able to survive. The best way to detect the lack of photosystem II in these organisms would be – to determine if they have thylakoids in the chloroplasts. – to test for liberation of O 2 – to test for CO 2 in the light. fixation in the dark. – to do experiments to generate an action spectrum. – to test for production of either sucrose or starch.
• Assume a thylakoid is somehow punctured so that the interior of the thylakoid is no longer separated from the stroma. This damage will have the most direct effect on which of the following processes?
– the splitting of water – the absorption of light energy by chlorophyll – the flow of electrons from photosystem II to photosystem I – the synthesis of ATP – the reduction of NADP +
• In an experiment studying photosynthesis performed during the day, you provide a plant with radioactive carbon ( 14 C) dioxide as a metabolic tracer. The 14 C is incorporated first into oxaloacetic acid. The plant is best characterized as a – C 4 – C 3 plant. plant. – CAM plant. – heterotroph. – chemoautotroph.
• Which of the following conclusions does
not
follow from studying the absorption spectrum for chlorophyll
a
and the action spectrum for photosynthesis? – Not all wavelengths are equally effective for photosynthesis. – There must be accessory pigments that broaden the spectrum of light that contributes energy for photosynthesis. – The red and blue areas of the spectrum are most effective in driving photosynthesis. – Chlorophyll owes its color to the absorption of green light. – Chlorophyll
a
has two absorption peaks.
• Which of the following processes could still occur in a chloroplast in the presence of an inhibitor that prevents H + from passing through ATP synthase complexes? – sugar synthesis – generation of a proton-motive force – photophosphorylation – the Calvin cycle – oxidation of NADPH
The diagram below represents an experiment with isolated chloroplasts. The chloroplasts were first made acidic by soaking them in a solution at pH 4. After the thylakoid space reached pH 4, the chloroplasts were transferred to a basic solution at pH 8. The chloroplasts are then placed in the dark. Which of these compounds would you expect to be produced?
* – ATP – NADPH + H + – G3P – ATP and NADPH + H + – ATP, NADPH + H + , and G3P