Photosynthesis

Overview

6 CO2 + 6 H20 C6H12O6 + 6 O2

Structure of a Leaf

Photosynthesis• Process by which plants and other

autotrophs store the energy of sunlight into sugars.

• Occurs in the leaves of plants in organelles called chloroplasts.

• Requires sunlight, water, and carbon dioxide.

Structure of a Chloroplast

It’s a TWO part process!

• Process #1: Requires Light (Light Reactions)• Process #2: Does NOT require light (Dark

Reactions)

Misnomer: Dark reactions don’t require “dark.” They can take place independent of light.

Overview

Light Reactions

individual cell

chloroplasts

Elodea leaf cells, 100 X

So where are pigments?Groups of pigments called PHOTOSYSTEMS are located on the surface of the thylakoid.

Pigments

Chlorophyll b is one of many different versions of chlorophyll.

Photosynthesis requires chlorophyll and other pigments to absorb solar energy.

Plants containing chlorophyll

appear green. Why?

Because chlorophyll absorbs everything but green!

GREEN is being

reflected back to your

eye.

Some Light Reflected, Some Light Absorbed

Absorbs Certain Colors

Reflected Colors are what you see

Think some more!

Why does a plant need to use both

primary and accessory pigments?

Animationhttp://www.pbs.org/wgbh/nova/nature/

photosynthesis.html

Light Reactions in Detail

“Energy cannot be created nor destroyed, only transformed!”

A photosystem can be considered a “light-harvesting complex.”

A bunch of them together make a “light-gathering antenna.”

Photon = packet of light energy!Photon = packet of light energy!

But there are TWO photosystems!

Figure 7.8A

Light

StromaPhotosystem II

Thylakoidspace

Th

ylak

oid

mem

bra

ne Primary

acceptor

Primaryacceptor

P680 P700

Photosystem I

Light NADP NADPHElectron transport chainProvides energy for

synthesis of ATP

by chemiosmosis

21

H2O

3

1

2

45

6

H

O2 H 2

Photosystem II and I Animation

• http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120072/bio13.swf::Photosynthetic%20Electron%20Transport%20and%20ATP%20Synthesis

What are the two main products of the light reactions (both photosystems)?

These are both sent to the Calvin Cycle (dark reactions/light independent reactions).

1.)

2.)

Photosynthesis Part Two

The Calvin Cycle

Textbook page 116

How are the two parts linked?

By ATP and

NADPH

By ATP and

NADPH

Calvin Cycle Animation

• http://highered.mcgraw-hill.com/sites/0070960526/student_view0/chapter5/animation_quiz_1.html

Do NOT worry about the specific molecule names. Pay close attention to how the light reactions interact with the dark reactions.

What are the start and end points and “materials” used?

My Movie Clip Notes• Location? _____________________________

• What enters the Calvin Cycle? ____________

• What is used from the light reactions? _____________________________________

• What is formed? ________________________

STROMA

CO2

Producing glucose…

To synthesize one glucose molecule, the Calvin Cycle uses 6 CO2 molecules,

18 ATP, and 12 NADPH.

Mini “Quiz”Directions: Grab a white board and marker. Answer each of the following questions individually. Reveal your answer when directed by holding up your board.

Question #1

What is the main purpose of the light

reactions?ANSWER : To Produce ATP and NADPH

Question #2

What is the main purpose of

photosynthesis?

Question #3

What is the main purpose of cellular

respiration?

Question #4

What is the main purpose of

fermentation?

Question #5

The Calvin Cycle takes place in the ________ of chloroplasts.

A)matrixB)stromaC)thylakoid membraneD)inner membraneE)outer membrane

Question #6

The Calvin Cycle uses ________, which are products of the light reactions of

photosynthesis.

A)CO2 and H2O

B)RuBP and O2

C)ADP and NADH

D)ATP and NADPH

E)3-phosphoglycerate and glucose

Question #7

How do gases enter and exit the plant cell in photosynthesis?

A)veins B)roots C)stomata D)mesophyllE)choroplasts

Question #8

Predict (and draw) what the graph would look like relating

the rate of photosynthesis to the concentration of carbon dioxide.