Photosynthesis

• Converts sunlight energy into chemical

energy

Chemical Equation

• 6CO2 + 6H2 O +light energy C6 H 12 O 6 + 6O2

• Carbon dioxide and water are the reactants and glucose and oxygen are the products.

• Chlorophyll is the pigment necessary to run the reaction.

Requirements

• Light Energy (Sun)• Chlorophyll a,b and accessory

pigments (these absorb wavelengths of light)

• Raw materials (CO2 and H2O )

• Enzyme: NADP (taxi cab)

Cross Section of a Leaf

• Leaf has many layers of specialized cells.

• Notice the location of the chloroplasts.

Stomata

• Stomata (leaf mouth) allows gas exchange (O2 and CO2)

• guard cells create the stomata

Inside the Chloroplast

• Saclike membranes called thylakoids contain chlorophyll and accessory pigments.

• Stacks of Thylakoids

are called Grana. • Stroma is the fluid

filled space.

Chloroplast Again

• Chloroplast

Below

Notice the granaare stacks of

thylakoids

The Two Phases of Photosynthesis

• Phase I - Light Dependent Reaction (occurs in thylakoids)– Light energy is absorbed and converted to

chemical energy in the form of ATP and NADPH.

• Phase II - Dark Reaction (Calvin Cycle) (occurs in stroma)– NADPH and ATP that were formed during light

dependent reactions are used to make glucose.

Light ReactionsOverview:

1. Light energy is absorbed in the THYLAKOID.

2. Water is split or pulled apart: 2H and ½ O2

3. CO2 is NOT involved yet.4. ATP is formed.5. Reactants: chlorophyll, light energy, water,

and NADP.

Light Reactions Steps:1. Light energy is absorbed by chlorophyll.2. Electrons in chlorophyll become “excited”

(high energy) and split H2O apart.

H2O: 2H + ½ O2 * 6 molecules of water total are split apart:

12 H+ , 6, ½ O2 (released into air as a byproduct).

3. An electron is released into the electron transport system.

Light Reactions

4. NADP picks up the H + and electrons

and transports them across the thylakoid membrane into the stroma.

NADP + H + NADPH

* 6 H2O are split: 12 NADPH are formed by the Light Reaction.

5. Hydrogen protons (H+) move across the thylakoid into the stroma to create ATPs from ADPs.

Products of Light Reactions

• 6, ½ O2 are released into the air via stomata.

• NADPH and ATP go to the stroma for Phase II (The Calvin Cycle).

Calvin Cycle or Dark Reaction

• Reactants: • ATP and NADPH from Light Reactions• 6 CO2

• 6 RuBP (ribulose bisphosphates)• Products: Glucose (C6H12O6) and 6

RuBP• Takes place in the stroma.

Steps of the Calvin Cycle (Dark Reaction)

• CO2 Fixation:

CO2 combines with RuBP 6CO2 + 6RuBP 12 PGA

PGA is a 3-Carbon molecule and is

UNSTABLE!

Total: 6 CO2 + 6 RuBP 12 PGA

Calvin Cycle

12 PGA + 12 ATP + 12 NADPH

12 G3P + 12 ADP + 12 NADP

* What happens to NADP? ADP?

* PGA and PGAL are 3 Carbon molecules.

Calvin Cycle Con’t.

• Formation of glucose:

2G3P 2Glucose

C3H6O3 + C3H6O3 C6H12O6

* Recall: G3P is a 3- Carbon molecule.

Calvin Cycle

Importance of Photosynthesis

• Forms glucose which is necessary for cellular respiration.

• Forms the source of oxygen we breathe.

Factors that Affect Photosynthesis

• 1. Amount of water• 2. Temperatures• 3. Light Intensity• 4. Amount of CO2

Summary of Photosynthesis