Chapter 8: PhotosynthesisChapter 8: Photosynthesis

ATP: The Energy unit of the Cell

ATP (adenosine triphosphate,三磷酸腺苷）

O O O O CH2

H

OH OH

H

N

H H

O

NC

HC

N CC

N

NH2Adenine

RibosePhosphate groups

O

O O

O

O

O

-

- - -

CH

Cell Energy use in Active Transport

• Energy is released from ATP (-30.54 kJ/mol)– When the 3rd phosphate bond is broken

Trapping Energy from Sunlight

• The process that uses the sun’s energy to make simple sugars is called photosynthesis

• Bases of all ecosystems on Earth

6 CO2 + 6 H2O + Light energy C6H12O6 + 6 O2

Vein

Leaf cross section

Mesophyll

CO2 O2

Stomata

Where Does CO2 come from?•Enters leafs through the stomata

Where does H2O come from?•Absorbed by roots and pulled up to the leaves by cohesion and adhesion

(transpiration)

Where does Light Energy come from?

• Energy from the sun must be absorbed by pigments, light absorbing molecules

• Inside a chloroplasts are thylakoids and inside their membranes are pigments

• What wavelength of light do the pigments not absorb?– Green; reason why plants

are green

Photosynthesis: 2 Reaction Set

1) Light-dependent reactions chemical reactions driven by light energy absorbed by pigments

2) Light-independent reactions chemical reactions that use ATP and NADPH to create sugars out of CO2

H2O CO2

Light

LIGHT REACTIONSCALVINCYCLE

Chloroplast

[CH2O](sugar)

NADPH

NADP

ADP

+ P

O2

ATP

The Light-Dependent reactions

LightReflectedLight

Chloroplast

Absorbedlight

Granum

Transmittedlight

Pigments- light absorbing moleculesChlorophyll main light absorbing pigment

Light-dependent reactions are broken into two systems:Photosystem II and Photosystem I

Photosystem II• Chlorophyll absorbs light energy

into electrons

• Electrons passed through protein carriers (Electron Transport Chain)

• Energy used to move H+ into thylakoid

• Photosystem II breaks water (photolysis) to get more electrons and H+ produces O2

Photosystem I• Electrons re-energized by chlorophyll

in the photosystem

• Electrons passed to enzyme to change NADP+ (nicotinamide adenin dinucleotide phosphate) into NADPH

• NADPH carries H+ and energized electrons to light-independent reactions

• ATP synthase uses H+ ions in thylakoid to make ATP

ATP-Synthase

• Makes ADP + Pi into ATP

• Powered by Chemiosmosis:– Movement of chemicals across a

selectively- permeable membrane

– H+ concentration gradient was made by photosystem II, now it is used to make ATP through facilitated diffusion

3H+= 1 ATP

The Light-Dependent reactions

Photolysis

H2O CO2

Light

LIGHT REACTIONSCALVINCYCLE

Chloroplast

[CH2O](sugar)

NADPH

NADP

ADP

+ P

O2

ATP

The Light-Independent reactions

Final NumbersUse Produce

Light-Dependent Reactions

Sunlight NADPH

H2O ATP

NADP+/ADP/Pi O2

Use Produce

Light-Independent Reactions

(Calvin Cycle)

NADPH

RuBP

RuBP (recycled to keep

cycle going)

ATP PGAL (Which form sugars)

CO2 NADP+/ADP/Pi

Alternate Pathways: C4 and CAM

• Plants in hot/dry areas lose H2O quickly if they open their stomata but they need CO2

• 2 Pathways to fix this:1) C4 allows plant to change O2 into

CO2 but it costs ATP so it is less energy efficient• Corn and sugar cane

2) CAM Collect CO2 at night and store it as an acid then use the acid to make CO2 during the day time• Pineapple trees and cactus plants

P 242

Homework

• Read Ch. 9 and do Ch. 9 vocabulary

• Ch. 8 Apply Vocabulary and Questions 1-18 on p. 205-206