Warm-upWarm-up

For thought: How do you get something as big as an oak tree from

an acorn?

1. Mesophyll

1. Mesophyll

A layer of cells that contain & are responsible for most of the plant’s photosynthesis

chloroplastschloroplasts

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2. Stomata

Openings in plant leaves that allow for to occur

(CO2) passes in and (O2) passes out.

COCO22

OO22

gas exchange

Carbon Dioxide Oxygen

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Mesophyll Cell

Chloroplast

The site of Photosynthesis

Double-membrane bound organelle

Inner membrane

Outer membrane

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6. Stroma7. Thylakoid

8. Grana

8. Grana

resides in these membranes

Chlorophyll

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Photosynthesis: Discoveries

Experiment:1 Seedling in dry soilOnly added water for five years

Results:Plant gained 75 kg

Conclusion:Plant mass comes from water.

Page 3Jan Van Helmont

Photosynthesis: Discoveries

Joseph Priestly Jan Ingenhousz

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Photosynthesis: Discoveries

Microbiologist who observed:

Purple sulfur bacteriaunderwent photosynthesis, but there was a big difference:

Cornelius Van Niel

H2S + CO2 C6H12O6 + S2

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Photosynthesis: Discoveries

• Van Niel theorized:

H2O is the source of Oxygen in Photosynthesis.

• How was his theory proven?

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H2O + CO2 C6H12O6 + O2

H2O + CO2 C6H12O6 + O2O

O

O

O

Pathway of Photosynthesis

On your own, balance this equation:

CO2 + H2O + (Light) C6H12O6 + O2

Reactants must equal Products

1166 6666

Carbon

Hydrogen

Oxygen

Carbon

Hydrogen

Oxygen

66

1212

66

1212

1818 1818

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Thylakoid

Label the image in your notes, and fill in the notes provided

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Photosynthesis: The Light Reaction

• are chemical factories powered by the sun.

• Their thylakoids transform light energy into the energy of

and .

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Chloroplasts

NADPH ATP

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The Nature of Light

• In addition to the wave-like nature of light, light consists of discrete particles called

.

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The Nature of Light

photons

Why are leaves green?Substances that absorb light are called

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Chlorophyll a

Chlorophyll b

Carotenoids

Chlorophyll absorbs and light, reflecting

pigments

red blue green

How do plants keep from losing all of this energy?

• A complex of proteins and other organic molecules called photosystems

Photosystems: Harvest LightPhoton

Transfer of Energy Antenna pigment molecules

Reaction Center Chlorophyll

Primary Electron AcceptorElectron Transfer

Protein complex

Protein complex

Protein complex

NADPH making enzyme

Mechanical analogy for the light reactions

1. Photon excites an electron

2. In Photosystem II

3. ATP is produced during this stage

4. The electron moves on to Photosystem I

5. An electron is excited by another photon

6. NADPH is produced

ATP Synthetase

• An enzyme embedded in the

• Hydrogen ionsbuild up here:

• ADP & Pi combine to form ATP here:

Thylakoid membrane

thylakoid membrane

thylakoid lumen

stroma

ProteinComplex

Enzyme

Summary of the Light Reaction

+ ++ +

+ +

ATPATP

+++

+

++

++

+

+

+

++

+

+

+

+

+

+

++

2e-4e-

NADPHNADPH

To the “Dark Reaction” – or the Calvin Cycle

• The Plant’s Dilemma: The Calvin Cycle uses more ATP than NADPH. How would you create more ATP, and no additional NADPH?

Cyclic Electron Flow

Protein complex

Dark Reaction:An Overview

• The General Formula for Photosynthesis is:

CO2 + H2O + (Light ) C6H12O6 +O2

• Which of these reactants has not been accounted for so far?

ATP & NADPH are used to convert CO2

into sugarNADPHNADPH

ATPATP

CO2

Sugar!

This is done in a three-phase cycle…

STEP 1: Carbon fixation

5-Carbon Sugar (RuBP)

+ CO2

+ the help of Rubisco (An enzyme)

2 3-Carbon Compounds (PGA)

RuBP PGA

ATP adds a phosphate

NADPH donatesan electron &

removes aphosphate

PGAL is the product

PGAL

PGAL

That doesn’t add up

• Glucose is a 6-Carbon sugar.

• PGAL is a 3-Carbon sugar.

• How many times must a chloroplast undergo the Calvin Cycle to create one glucose molecule?

PGA

PGAL