Photosynthesis Acquiring Energy From Light

PhotosynthesisAcquiring Energy From Light

•Photosynthesis is a two stage process by which Light, Water and Carbon dioxide are used to make high energy compounds Glucose (carbohydrates).

PHOTOSYNTHESIS:Chemical equation:Reactants (needed) Products (what is produced)

12H2O +6CO2 C6H12O6 + 6O2 + 6H2OSimplified: 6H2O + 6CO2 [C6H12O6] + 6O2

sunlight energy-

What is Photosynthesis? Click me

Light- Dependent Reactions(photophosphorylation)

Light- Independent Reactions(Calvin Cycle)

Light

H20

CO2

O2

C6H12 O6

Light energy Chemical energy SUGARS SUN ATP, NADPH (C6H1206)

ATP, NADPH

“chemical energy”

“chemical energy”

Chloroplast

Light

3O2

Sugars

CO2

Light-Dependent Reactions

CalvinCycle

NADPH

ATP

ADP + PNADP+

Chloroplast

6H2O + 6CO2 ---sunlight energy-- C6H12O6 + 6O2

Figure 8-7 Photosynthesis: An Overview

Light-Independent Reactions

Calvin Cycle

Light Dependent Reactions

NADPH+

ADP+P

ATP

NADPH

6H2O

Light

6CO2

C6H12O6

Where Do These Reactions Take Place?

click me

Chloroplast

Thylakoid membranes

Occurs in the chloroplast of plant and other autotrophs

Photosynthesis starts in the (thylakoid membrane system) of the chloroplasts

Light Dependent Reaction

The Making of Chemical Energy: PHOTOPHOSPHORYLATION

Light energy is used to split water molecules (PHOTO)6 Water molecules are split into atoms of Hydrogen and atoms of Oxygen Step 1-photolysis (click me)6 H2O 12 H and 6 O2Oxygen (O2) is by product in this reaction

Step 2-phosphorylation

H+ (hydrogen ions) from water are used to generate

“Chemical energy” in the form of ATP and NADPH

ADP ATP NADP+ + HNADPH

HydrogenIon Movement

Photosystem II

InnerThylakoidSpace

ThylakoidMembrane

Stroma

ATP synthase

Electron Transport Chain Photosystem I ATP Formation

Chloroplast

Section 8-3

Figure 8-10 Light-Dependent Reactions

The products of the light dependent reaction:Oxygen, ATP

The Role of Chlorophyll click me

• Light trapping pigment Chlorophyll is required for photosynthesis

• Chlorophyll absorbs all light energy EXCEPT GREEN, green wavelengths are reflected, this is why leaves are perceived as green in color.

• Fall colors of leaves result from the absence of chlorophyll and the presence of other pigments which reflect their respective colors

• Ex. Carotene (reflects orange and red wavelengths of light).

Absorption of Light byChlorophyll a and Chlorophyll b

V B G YO R

Chlorophyll b

Chlorophyll a

Section 8-2

Figure 8-5 Chlorophyll Light Absorption

Light Independent reactions(Calvin Cycle)

LIGHT INDEPENDENT REACTIONS: Also known as “Calvin cycle” and "Carbon Fixation "

-does not depend on sunlight for energy and proceeds in the absence of sunlightThe energy made in the light dependent reaction in the form of (ATP, NADP+H) reaction are “spent” to convert carbon compounds found in the plant cells into sugars like (glucose) C6H12O6 a carbohydrate end product.

Video 5CARBON FIXATION

The first step involves CO2 (carbon dioxide) combining

with RUBP- a 5 carbon compound found in plants

ChloropIast

CO2 Enters the Cycle

Energy Input

5-CarbonMoleculesRegenerated

Sugars and other compounds

6-Carbon SugarProduced

The Light-Independent Reactions “Carbon Fixation”Step 1) Carbon dioxide from the air is combined with a 5-carbon sugar RuBP (Ribulose biphosphate)

3 CO2 + 3 RuBP------> 6 PGA (each cycle)

This forms a 6-carbon molecule PGA (Phosphoglycerate)

Step 2) 12 ATP are "spent" to convert PGA to PGAL a 3-carbon molecule and 12 H (hydrogen) are added to the molecule

6 PGA + [Chemical Energy] 12 PGAL [12 ATP12 ADP]

[12 NADP+H 12 NADP]

=Phosphoglyeraldehyde

“spending energy”

Step 3) 6 additional ATP are "spent" to convert PGAL into sugar and recycle RuBP

PGAL + PGAL--------> C6H12O6 + RuBP [6 ATP---> 6ADP] “energy spent”

Summary:18 ATP made in the light dependent reactions are "spent" in the light independent reaction to make one molecule of PGALTwo cycles of the Calvin Cycle = 2PGALTotal cost is 36 ATP+2PGAL=1glucose (sugar)

Photosynthesis

includes

of

take place intakes place in uses

to produce to produce

use

Light-dependentreactions

Calvin cycle

Thylakoidmembranes Stroma CO2ATP

NADPH

Energy fromsunlight

ATP NADPH O2 Chloroplasts High-energysugars

Section 8-3

Concept Map

H2O