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