1. Section Objectives
Relate the structure of chloroplasts to the events in photosynthesis
Describe light-dependent reactions.
Explain the reactions and products of the light-independent Calvin cycle.

2. Photosynthesis: Life from Light and Air

3. Trapping Energy from Sunlight
The process that uses the sun’s energy to make simple sugars is called photosynthesis.

4. AN OVERVIEW OF PHOTOSYNTHESIS
Photosynthesis is the process by which autotrophic organisms use light energy to make sugar and oxygen gas from carbon dioxide and water
PHOTOSYNTHESIS

5. Plants are energy producers
Like animals, plants need energy to live
unlike animals, plants don’t need to eat food to make that energy
Plants make both FOOD & ENERGY
animals are heterotrophs(consumers)
plants are autotrophs (producers)

6. How do plants make energy & food?
Plants use the energy from the sun
to make ATP energy
to make sugars
glucose, sucrose, cellulose, starch, & more
sun
ATP
sugars

7. Building plants from sunlight & air
Photosynthesis
2 separate processes
ENERGY building reactions
collect sun energy
use it to make ATP
SUGAR building reactions
take the ATP energy
collect CO2 from air & H2O from ground
use all to build sugars
ATP
H2O +
CO2
sugars
carbon dioxide
CO2
water
H2O
sugars
C6H12O6 +

8. What do plants need to grow?
The “factory” for making energy & sugars
chloroplast
Fuels
sunlight
carbon dioxide
water
The Helpers
enzymes
Make ATP! Make sugar! I can do it all… And no one even notices!
sun
CO2
ATP
enzymes
sugars
H2O

9. So what does a plant need?
Bring In
light
CO2
H2O
Let Out O2
Move Around
sugars
leaves
shoot
roots
6CO2
6H2O
C6H12O6
6O2
light
energy  +

10. Photosynthesis ATP ADP ENERGY building reactions
sun
Photosynthesis
ENERGY building reactions
ADP
ATP
SUGAR building reactions
used immediately to synthesize sugars
H2O
sugar
CO2

11. Chloroplasts absorb sunlight & CO2 Leaf Leaves CO2
Chloroplasts in cell
Chloroplast
Chloroplast
Chloroplasts
contain
Chlorophyll
make ENERGY & SUGAR

12. Stomates & Guard Cells in the leaf
Function of stomates
CO2 in
O2 out
H2O out
gets to leaves for photosynthesis
Function of guard cells
open & close stomates
guard cell
stomate

13. An overview of photosynthesis
Chloroplast
Light
CO2
H2O
NADP+
ADP +P
LIGHT REACTIONS (in grana
CALVIN CYCLE (in stroma
ATP
NADPH O2 O2
Sugar

14. Trapping Energy from Sunlight
Photosynthesis happens in two phases.
The light-dependent reactions convert light energy into chemical energy. (ATP)
2. The molecules of ATP produced in the light-dependent reactions are then used to fuel the Calvin Cycle or light-independent reactions that produce simple sugars.
The general equation for photosynthesis is written as CO2 + 6H2O→C6H12O6 + 6O2

15. THE LIGHT REACTIONS: CONVERTING SOLAR ENERGY TO CHEMICAL ENERGY Visible radiation drives the light reactions
Certain wavelengths of visible light drive the light reactions of photosynthesis
X-rays
Micro- waves
Radio
waves
Gamma rays UV
Infrared
Visible light
Wavelength (nm)

16. pigments in the chloroplast
To trap the energy in the sun’s light, the thylakoid membranes contain pigments, molecules that absorb specific wavelengths of sunlight.
Wavelengths that are NOT absorbed are reflected (bounce off) or transmitted (pass through)
So the material in which the pigment is found appears to be the color of the wavelengths that are NOT absorbed
Photosynthetic pigments: can absorb light energy & make it available for conversion to chemical energy .
Light
Reflected light
Chloroplast
Absorbed light

17. pigments in the chloroplast
Chlorophyll a: most common pigment in chloroplast (absorbs blue &red light and reflects green light thus giving the chloroplast a green color)(chloro = green phylla + leaf)
Accessory pigments: additional pigments that absorb different wavelengths (carotene, chlorophyll b, & xanthophyll)

19. Light-Dependent Reactions absorption of light energy by chlorophyll
As sunlight strikes the chlorophyll molecules in a photosystem of the thylakoid membrane, the energy in the light is transferred to electrons.
These highly energized, or excited, electrons are passed from chlorophyll to an electron transport chain, a series of proteins embedded in the thylakoid membrane.
At each step along the transport chain, the electrons lose energy.

20. Energy from the energized electrons pump
H+ ions and change NAPD+ to NADPH.
The H+ ions move from high to low and turn
the ATP synthase and change ADP + P to ATP
Energized electrons
Oxygen
by-product
Photolysis

21. Light-Dependent Reactions
Chemiosmosis: This “lost” energy can be used to form ATP from ADP, or to pump hydrogen ions into the center of the thylakoid disc. .

22. Light-Dependent Reactions
The electrons are transferred to the stroma of the chloroplast. To do this, an electron carrier molecule called NADP is used.
NADP can combine with two excited electrons and a hydrogen ion (H+) to become NADPH.
NADPH will play an important role in the light-independent reactions.

23. Restoring electrons
To replace the lost electrons, molecules of water are split in the first photosystem. This reaction is called photolysis.
The O2 liberated by photosynthesis is made from the oxygen in water
Chlorophyll
O2 + 2H+ 2
2e-
H2O
H2O ®2H+ +
O2 + 2e-

24. Restoring electrons
The oxygen produced by photolysis is released into the air and supplies the oxygen we breathe.
The electrons are returned to chlorophyll.
The hydrogen ions are pumped into the thylakoid, where they accumulate in high concentration.

25. Light Dependent Reactions: Summary
Absorptions of light energy by chlorophyll-takes place in thylakoid
1. Split water molecule (PHOTOLYSIS) Oxygen combines with other oxygen to produce O2 which is given off as a by-product
2. Hydrogen produced by splitting of water is attached to hydrogen carrier NADP -> NADPH (energy in this molecule)
3. Then energy from “excited electrons”is used to take ADP + P ->ATP

26. Light Independent Reactions or The Calvin Cycle
CO2 put into organic molecules called Carbon fixation
Does not require light but must have ATP and NADPH which are produced by light dependent reactions
Called Calvin Cycle (Melvin Calvin won Nobel prize in chemistry)
Takes place in stroma of chloroplast

27. Light Independent Reactions or The Calvin Cycle
The Calvin cycle constructs G3P (a sugar) using
carbon from atmospheric CO2
electrons and H+ from NADPH
energy from ATP
Energy-rich sugar (G3P) is then converted into glucose
INPUT
CALVIN CYCLE
OUTPUT:

28. So what does a plant need?
Bring In
light
CO2
H2O
Let Out O2
Move Around
sugars
leaves
shoot
roots
6CO2
6H2O
C6H12O6
6O2
light
energy  +

29. An overview of photosynthesis
Chloroplast
Light
CO2
H2O
NADP+
ADP +P
LIGHT REACTIONS (in grana
CALVIN CYCLE (in stroma
ATP
NADPH O2
Sugar

30. Factors Affecting Rate of Photosynthesis
Temperature: increases rate up to a certain point
Light Intensity: increases rate up to a certain point
CO2 level: Increases rate up to a certain point
Water: decrease water, decrease photosynthesis
Minerals; Ex. Magnesium, Nitrogen