Photosynthesis Sections 4.2-4.3

The overall process of

photosynthesis produces

sugars that store chemical

energy.

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Overview • All energy on earth comes from the sun.

• We depend on:

– Plants

– Algae (underwater plants)

– Cyanobacteria (photosynthetic bacteria)

• To provide this energy to us!

Overview

Overview • Photosynthetic organisms are producers.

• Producers make their own source of

chemical energy.

• Plants use photosynthesis and are

producers.

• Photosynthesis captures energy from

sunlight to make sugars.

Overview • Carbon dioxide and water are taken in by

plants

• Plants absorb light energy and convert it to a usable form. – ATP

• Energy is used to “fix” carbon dioxide into sugar molecules – Chemical energy

• Sugar is converted to starch and stored for use by the plant, and by animals when they eat plants.

Chlorophyll

• Chlorophyll is a

molecule that

absorbs light

energy.

• In plants,

chlorophyll is

found in organelles

called

chloroplasts. leaf

leaf cell

chloroplast

Plants are green because of the pigment chlorophyll.

(which absorbs light energy)

• During the fall, the green chlorophyll

pigments are greatly reduced revealing

the other pigments, this is the reason

leaves turn brown in the fall.

• Carotenoids are pigments that are

either red or yellow.

• Photosynthesis

takes place in two

parts of

chloroplasts.

–grana

(thylakoids)

–stroma

chloroplast

stroma

grana (thylakoids)

Chloroplasts • Have TWO

membranes

– A “bi-bilayer!”

• The inner membrane is called the thylakoid.

• The thylakoid is folded and looks like stacks of coins called granum (grana=singular).

• The stroma is the space surrounding the granum.

Image source: http://www.daviddarling.info/encyclopedia/C/chloroplasts.html

Chloroplasts • Chlorophyll

molecules are

embedded in the

thylakoid membrane

• Act like a light

“antenna”

• These molecules

can absorb sunlight

energy. Image from Biology 11: College Preparation. Pg 73. Nelson,

Toronto. 2003.

Light (dependent)Reactions

• Happen ONLY in sunlight

– Hence they depend on light!

– Water is also required

1. Light energy is absorbed by chlorophyll

molecules in the thylakoid

2. The energy generates molecules of ATP

(ADP converted to ATP)

3. Convert NADP+ to NADPH (Electron

Carriers)-Energy then goes to Light

Independent reaction

4. Produce Oxygen (O2) gas

Light (dependent)Reactions

Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto. 2003.

Light (dependent)Reactions

Light Independent Reactions

(formerly the “dark reactions”) • Happen in sunlight, and in the dark.

– Hence “independent of light”

– Makes sugars

1. Takes place in the stroma.

2. CO2 enters from the atmosphere

3. ATP generated by sunlight drives the Calvin Cycle.

4. Monosaccarides (eg. glucose) are manufactured in the

cycle.

5. Monosaccarides are used to “build” polysaccharides (eg.

Starch).

Light Independent Reactions

(formerly the “dark reactions”)

Image from: Biology 11: College Preparation. Pg 74. Nelson, Toronto. 2003.

Light Independent Reactions

(formerly the “dark reactions”)

Overall Reaction What is the equation for photosynthesis?

carbon dioxide + water glucose + oxygen + energy

6CO2 + 6H2O C6H12O6 + 6O2 + energy

C6H12O6

granum (stack of thylakoids)

thylakoid

1 six-carbon sugar

6H2O

6CO2

6O2

chloroplast 1

2

4 3

energy

stroma (fluid outside the thylakoids)

Factors that affect the rate

of Photosynthesis are…

• Availability of Water

• Temperature

• Intensity of Light

• Concentration of CO2

S

u

n

L

I

G

H

T

H2O CO2

Light

Dependent

Reactions

Calvin Cycle

CHLOROPLAST

Sugars O2