Photosynthesis

Introduction

6 CO2 + 6 H2O +

light energy → C6H12O6 + 6 O2

Photosynthesis consists of two independent pathways called the light-dependent reaction (light reaction) and the light-independent reaction (dark reaction).

IntroductionLight Reactions: the energy in sunlight is trapped, O2 is released, and both ATP and NADPH + H+ (hydrogen-carrier molecule) are formedDark Reactions: the ATP and NADPH + H+ react with CO2 from the atmosphere and form glucoseThe entire process results in the transformation of light energy from the sun into energy stored in the bonds of the glucose molecule.

Structure of a Chloroplast

The light reactions take place in the thylakoid membrane

The dark reactions take place in the stroma

Structure of a Chloroplast

Electromagnetic Spectrum

Why are plants green?

Pigments

Pigments are light-absorbing compounds.

Pigments appear colored because they absorb light of certain wavelengths and reflect that of others.

Chlorophyll a is the primary pigment in green plants that absorbs red and blue/violet light and reflects green light.

Structure of Chlorophyll

Accessory Pigments

Chloroplasts also contain other pigments called accessory pigments.

Accessory pigments trap wavelengths of light that cannot be absorbed by chlorophyll a and then transfer the energy to chlorophyll a molecules for use in photosynthesis. In this way, accessory pigments enable plants to use a greater amount of the sun’s energy than is available to chlorophyll alone.

Light Reaction

Light Reaction

Also called Light Dependent ReactionPigments that are in the chloroplasts intercept light and begin the light reactions of photosynthesis.The light reactions occur in two photosystems (located in the thylakoid membrane):

Photosystem: a unit of several hundred chlorophyll a molecules and associated acceptor molecules

-photosystem I (PSI) -photosystem II (PSII)

Photosystems

Excited Electrons

NADPH

NADP+ is an electron acceptor

NADP+ + 2 e- + 2 H+ NADPH + H+

ATP

Synth

ase

PSII

PSI

Water (H2O)

Oxygen (O2)

Hydrogen Ion (H+)

Electron

Lumen

PrimaryElectronAcceptor

Proton Pump

ATP Synthase

Thylakoid

ETC

Step 1

Step 2

Step 3

Step 3

Step 3

Step 3

Step 3

Step 3

Step 4

~

e

high

low

Step 4

Step 4

Step 4

Step 4

Step 4

Step 5

Step 5

Step 5

Step 5

Step 5

Step 5

NADP+

NADPH+ H+

Step 6

high

low

Step 6

Step 6

Step 6

Step 6

Step 6

~

e

ADP + P

ATP

Reactants

ADP + P

NADP+

Products ATP

NADPH+ H+

O2 isreleasedinto the

atmosphere

DR

Dark Reaction

Dark ReactionThe dark reaction is also known as the Calvin Cycle, after an American scientist (Melvin Calvin) who figured out the pathway.The dark reaction is also known as the C3 Cycle because the first stable products of this pathway are molecules that contain three carbon atoms.The Calvin Cycle occurs in the stroma.

12 NADPH + H+

~

e12 ADP + P

12 ATP

12 NADP+

e-

10 PGAL

~

e6 ADP + P

6 ATP

6 CO2C

6 RuBPC C C C C

12 PGAC C C

12 PGALC C C

2 PGALC C C

GlucoseC C C C C C

C C C C C C

unstablecompound

The following The following slides areslides are

ONLY for Level I!ONLY for Level I!

C4vs.

CAM

Hint for Level I TestShort Answer Question

The End!