Photosynthesis

Overview of Photosynthesis

•During photosynthesis, autotrophs/producers use the sun’s energy to make carbohydrate molecules from water and carbon dioxide, releasing oxygen as a by-product

Equation: 6CO2 + 6H20 +light energy C6H12O6 + 6O2

Reactants products

6CO2 + 6H20 C6H12O6 + 6O2

•This equation means: 6 molecules of carbon dioxide

plus 6 molecules of water, with the help of light energy are converted into glucose and six molecules of oxygen.

Chloroplasts • Photosynthesis occurs in the chloroplast of

the plant cell

membrane

Inside the thylakoids is chlorophyll

• Chlorophyll is a green pigment • Pigment: molecule that absorbs certain

wavelengths of light and reflects others. The reflected wavelength is what determines what color you see.

• Chlorophyll absorbs violet, blue, and red and reflects green.

Photosynthesis occurs in two stages:

Stage 1: Light dependant

Reactions– occurs in thylakoid

membranes of the chloroplast

Picture Overview • What are the two main parts of the

chloroplast where the reactions occur?

2: STROMA

Stage 1:

Thylakoid

membranes

Light dependent reaction

• https://www.youtube.com/watch?v=RFl25v

SElaE

6-12

Solar energy boosts electrons

to a higher energy level

• In the thylakoid membrane, photosystems

contain:

1. A pigment complex that absorbs solar

energy

2. An electron-acceptor molecule

• A pigment complex consists of antenna

molecules and a reaction center.

– Antenna chlorophyll molecules absorb light

and pass energy to the reaction center.

– In the reaction center, excited electrons are

passed to electron acceptors.

6-13 Figure 6.4

6.4 Solar energy boosts electrons

to a higher energy level

6-14

Photosystems

• Two types of photosystems participate in

the light reactions:

– Photosystem I (PS I)

• Reaction center in PS I absorbs light with a

wavelength of 700 nm

– Photosystem II (PS II)

• Reaction center in PS II absorbs light with a

wavelength of 680 nm

• Chloroplasts use electrons energized by solar energy to generate ATP.

• First step-Light/solar energy is converted into energy in chlorophyll a electrons (e-) (PSII)

• When the light hits the chlorphyll pigments it “charges” their electrons up. Charged/excited electrons leave the chlorophyll and go down an electron transport chain of pigments

• PS I- This is where the escaped electrons move to a different electron-acceptor molecule and NADP+ → NADPH

Restoring PSII

• When electrons leave the chlorophyll a in photosystem II, they need to be replaced by more!

• The photons that hit PSII also provide energy for photolysis-the splitting of water with light.

•

• Photolysis-Requires the reactants water and sunlight

• Every 2 Water molecules are broken down into 3 pieces by a special enzyme:

1) Four Hydrogen protons – (H+) – build up inside thylakoid compartment of chloroplast

2) Oxygen gas (O2) – is released from the plant chloroplast as a waste product

3)Four Excited Electrons (e-)– go to the group of pigments called photosystem II to replace the electrons lost from the electron transport C

Light reaction: 6CO2 + 6H20 C6H12O6 + 6O2

6-18

Animated summary of light

reaction in thylakoid of grana http://highered.mheducation.com/olc/dl/1200

72/bio13.swf

The proton pump is an indirect active transport used by chloroplasts to produce ATP. The enzyme “pumps” hydrogen protons through the thylakoid and out to the stroma. It gets its energy from the potential energy of the high concentration gradient of H+ protons inside thylakoid created by splitting the water. When hydrogen protons go from higher to lower concentration, ATP is produced.

*Remember theFour Hydrogen protons from water? (H+) – build up inside thylakoid compartment of chloroplast.

6-21 Figure 6.5

The purpose of the light reaction: • Energy from the light, electron transport

chain and proton pump is used to make NADPH in addition to ATP. These energy molecules are needed in the next stage

Stage 2 of photosynthesis: Calvin Cycle – AKA Light Independent-

6CO2 + 6H20 C6H12O6 + 6O2

• Happens in the stroma of the chloroplast • Requires the ATP and NADPH energy from

the light dependant reactions as well as the gas reactant CO2

• 6 CO2 are required to build one carbohydrate, “glucose” (C6H12O6 )

• THE PURPOSE OF THIS REACTION IS TO “FIX” CARBON FROM CO2 INTO GLUCOSE.

Light

Granum/Thylakoid

Chlorophyll and

photosystems

Water Oxygen

Carbon Dioxide (CO2)

ATP and NADPH

Calvin/light

independent cycle

Glucose

(C6H12O6

Chloroplast Stage 1: Light dependent

reaction

Stage 2: Light independent

reaction:

Photosynthesis Flow Map RAW Materials/Reactants

Products

Photo-lysis of light dependent

reaction:

1)

Makes the energy

molecules, _______here.

2)

Made with

Uses the energy

molecules:

This process is called:

Occurs in the:

Enters through the

_____

& used in

_________

Gas waste from the

_________reaction

3)

Occurs in the: