Where do we get our energy from?

Photosynthesis: An Overview

Some details:

LightReaction

Dark Reaction

Sunlight

Water Oxygen

Carbon Dioxide

Glucose

ATP NADH

Today’s Goal!

To explain how energy is transferred from sunlight to glucose via the light and dark reactions of photosynthesis.

The Formula for Photosynthesis

ThylakoidsThylakoids

(Light DEPENDENT)(Light DEPENDENT)

StromaStroma

(Light INDEPENDENT)(Light INDEPENDENT)

CALVINCALVIN

Inner and outer Inner and outer membrane ofmembrane of chloroplastchloroplast

THE CHLOROPOPLASTTHE CHLOROPOPLAST

Light dependent and light Light dependent and light independent reaction locationsindependent reaction locations

Pigments- Important for the absorption of light energy

Three types:

1. Chlorphyll a- absorbs all spectrum of light except for green

2. Chlorophyll b- absorbs most spectrum of light except orange, yellow or red

3. Carotene- absorbs most spectrum of light except for orange

So why are plant leaves green?

Another Question: Why are leaves a different color in the fall? See the next slide for the answer from a celebrity presenter.

1. In the Fall the strength of the sun decreases.

2. Plants will decrease their production of chlorophyll a in order to conserve more sugar for the winter months. (remember that when the body builds something it requires energy)

3. The remaining pigments will reflect different spectrum of light depending on the species.

Thanks David!

Hey! Its David Ortiz…maybe he can explain why the leaves change color in the fall.

Light Reactions-Does this picture look familiar?

Electron CarriersWhat do they do?• Electron carriers take high energy electrons (stored

on H) and bring them to electron transport chains (more on these later)

• The electrons become high energy when exposed to sunlight

Examples:

1. With electronsNADPH or FADH2

2. Without electrons NADP+ or FAD+

Light Reactions

e-NADP+

FAD+

e-e-

e-

e-

e-

e-

NADPH

FADH2+

1. Sunlight hits chlorphyll and excites the electrons (woo hoo!)

2. These electrons are transferred to electron carriersReally

excited electrons

Electron carriers

3. These electrons are used to split water molecules (this is why plants produce oxygen)

e-e- e-e-

e- Excited electrons splitting H20 molecule into its base elements

H+H+

O- leaves the plant via stomata

H+’s used to help carry electrons (FAD+ becomes FADH2 when it carries electrons)

This is a close-up shot of the pathway the light energy traveled…from beginning to end.

4. These Hydrogen ions are also shot across an electron transport chain (against the proton gradient…remember the sledding example)

- - - - - - - - - - - - - - - - - - -

++

+++

++ +

+

H+

The Electron Transport Chain is represented by the dashed line and has one side which is highly positive…shooting the Hydrogen ions against the positive gradient creates energy.

H+ H+ H+ H+ H+ H+ H+

5. This produces enough energy to make a small amount of ATP which will be used in the Calvin Cycle

ATP

ATP

SYNTHASE

ADP + P

Energy from electron transport chain Note the H+ ions returning

through ATP Synthase…Oxygen picks up these ions and forms H20…more on this when we get to cellular respiration

This is a close-up shot of the pathway the light energy traveled…from beginning to end.

Light-dependent Reaction-Takes Place in Thykaloid

1. Sunlight hits chlorphyll and excites the electrons (woo hoo!)

2. These electrons are transferred to electron carriers

3. These electrons are used to split water molecules (this is why plants produce oxygen)

4. Hydrogen ions are also shot across an electron transport chain (against the gradient…remember the sledding example)

5. This produces enough energy to make a small amount of ATP which will be used in the Calvin Cycle

Dark Reactions (Calvin Cycle)

1. The plant “breaths in” C02 via stomata

Electron micrograph photo of stomata(s)

CO2

CO2 CO2

CO2CO2

CO2

Plant taking in CO2

Lets zoom in

2. The ATP and NADPH produced in the light reaction is used to break apart the CO2 into its base elements

Energy from ATP and NADPH

Carbon Dioxide being split into base elements

O-

O-C

3. With enough C02 and H (remember when the water molecule was split?) a glucose molecule is formed (what was that formula again?)

O-

O-

O-

O-

O-

O-

C

C

CC

C

C

+ +H+

H+

H+

H+

H+

H+ H+

H+

H+

H+

H+

H+

C6H12O6

Aka: Glucose

Oxygen’s from the splitting of H20

Carbon’s from Carbon Dioxide

Hydrogen’s from the splitting of H20

The processes we have talked about are how carbon and energy enter the food chain.

Calvin Cycle-takes place in Stroma

2. The ATP and NADPH produced in the light reaction is used to break apart the CO2 into its base elements

1. The plant “breaths in” C02

3. With enough C02

and H (remember when the water molecule was split?) a glucose molecule is formed (what was that formula again?)

Using your notes and the diagram below, explain how energy is transferred from one form (Sunlight) to one that is stored (Glucose). Use the reactions involved in Photosynthesis in your explanation.