plant cell nucleus chloroplast cytosol cell wall
TRANSCRIPT
Plant Cell
nucleus
chloroplast
cytosol
cell wall
All photosynthetic reactions take place in the chloroplast
Light is captured in the chloroplasts with green pigments called cholorphylls
Plant Cell
nucleus
chloroplast
cytosol
cell wallChloroplast
The Chloroplast
Outer membrane
Inner membrane
Stroma
Thylakoid
Granum
Thylakoid
Thylakoid (contains chlorophyll)
Stroma
Lamella (connects grana)
Thylakoid Space (Lumen)
PHOTOSYNTHESIS
Stages of Photosythnesis
There are 2 main stages of photosynthesis:
Light Reactions Dark Reactions
makesmakes
NADPH ATP
some
glucoseglucose
DON’T BE FOOLED!!Both light and dark reactions occur
during the day. The “Dark” reactions don’t REQUIRE light while the “Light” reactions do!
PHOTOSYNTHESIS
Stages of Photosynthesis
There are 2 main stages of photosynthesis:
Light Reactions Dark Reactions
makesmakes
NADPH ATP
some
glucoseglucose
Light-Dependent Reactions Light - Independent Reactions
The full range of wavelengths of light emitted from the sun is known as the electromagnetic spectrum
Visible light is between 400-700nm Light has properties of both waves and particles
The Electromagnetic Spectrum
Light ~ as a particle?
Light travels in bundles of energy called photons
The energy from photons is used to initiate photosynthesis
PhotonPhoton
Photon
Photon
Photon
Capturing Light For the Light Reactions
Photosynthetic pigments absorb light Each pigment can absorb light (photons) within a
specific range of wavelengths
Wavelengths that are not absorbed are said to be transmitted or reflected• This is the light we see
◦ determines what colour we see
Chlorophyll a
Chlorophyll b
The most common pigments in plants are Chlorophyll a and Chlorophyll b
Capturing Light For the Light Reactions
Absorbance:
absorbed absorbed
Chlorophyll a
Chlorophyll b
The most common pigments in plants are Chlorophyll a and Chlorophyll b
Capturing Light For the Light Reactions
GREENWhat we see
Reflection:
reflected
Absorption Spectra for Chlorophyll
Absorption Spectra for Chlorophyll
Other pigments
Though chlorophylls are the most common pigments, other pigments are present in plants to absorb at other wavelengths:
Carotenoids Phycobilins Xanthophylls
Other pigments
Harnessing Solar Energy!
How do plants store energy from photons into the chemical bonds of high energy molecules?
It starts in the thylakoids of the chloroplasts!
a
The Light Reactions(light-independent reactions)
Groups of molecules responsible for the light reactions are called photosystems Each photosystem has:
1. antenna pigments• 200-400 chlorophyll b molecules, accessory pigments (ex. carotenoids)
2. reaction centre• a specialized chlorophyll a molecule with associated proteins
3. primary electron acceptor
PS II
Electron Accepto
r
How Photosystems Capture Light Energy
2 photosystems in plants:
Photosystem I (PS I) & Photosystem II (PS II)Other names (used by text)
PS I absorbs best at 700nm; called P700 PS II absorbs best at 680nm; called P680
* Difference in absorbance is due to differences in proteins associated with chlorophyll a
Thylakoid
PS I PS IIP700 P680
How Photosystems Capture Light Energy
1. Photons of light are absorbed by antenna pigments causing them to move from ground state to an excited state.
2. “Excitation” energy is passed along chlorophyll molecules until it reaches the reaction centre.
3. Chlorophyll a in the reaction centre absorbs the energy.
4. The high-energy state of chlorophyll a causes it to emit 2 electrons.
5. The primary electron acceptor takes the electrons from chlorophyll a. this process is called photoexcitation
Thylakoid
PS I PS IIa aa
Electron Accepto
r
Homework
Read Section 3.3 up to “The Calvin Cycle” Do section review 1-4 on pg.94 Explain the difference between the cyclic and non-
cyclic pathway
Tomorrow we get into the nitty gritty details of how plants make ATP and Glucose! Excited?
Still to come
Time permitting I will show you a video that will show you plants as you’ve never seen them. It is made by my hero, Sir David Attenborough… sneak peak…
Non-Cyclical Electron Pathway
Photosystem II aquires a supply of electrons by using the sun’s energy to hydrolyze water.
This is called photolysis.
PS II
High
Low
En
ergy
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H2O
H+H+
O2
H+
H+
H+
H+
Stroma
Thylakoid Lumen
ThylakoidMembrane
Non-Cyclical Electron Pathway
The reaction center passes electrons through an electron transport system containing a cytochrome complex (cytochrome b6f)
This complex generates a proton gradient
PS II
High
Low
En
ergy
H+
H+
H+
H+
ThylakoidMembrane
Stroma
Thylakoid Lumen
E T C
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
PS I
O2
ATP
Electrons are re-energized at photosystem I The high energy electrons are involved in a redox
reaction to generate the high energy NADPH molecule
The proton gradient is used to generate ATP through ATP Synthase
Non-Cyclical Electron Pathway
PS II
High
Low
En
ergy
H+
H+
H+
H+
ThylakoidMembrane
Stroma
Thylakoid Lumen
E T C
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+H
+H
+
H+
H+
H+
H+
PS I
ATP
NADP+
NADPH
The End Result
These end products of the light reaction can now be used to synthesize glucose
ATPNADPH
Cyclical Electron Pathway
High
Low
En
ergy
H+
H+
H+
H+
Membrane
E T C
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
PS IATP
Simple organisms like bacteria are able to meet their energy demands by using PS I alone to generate ATP
In this way they generate cellular energy without synthesizing glucose.
Cyclical Electron Pathway
High
Low
En
ergy
H+
H+
H+
H+
Membrane
E T C
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
H+
PS IATP
ATP
The Dark Reaction
The Whole Process