Photosynthesis: An Overview

Warm up 11/12 Define these words

Pigment Chlorophyll Thylakoid Stroma Light dependent reactions Light independent reaction

Learning Objectives Explain the role of light and pigments in photosynthesis. Explain the role of electron carrier molecules in

photosynthesis. State the overall equation for photosynthesis.

Light

• Light energy from the sun must be captured for photosynthesis to occur.

• Sunlight is “white” light—actually a mixture of different wavelengths. (ROY-G-BIV)

Pigments

Pigments – plants gather the suns energy with light absorbing molecules called pigment

What role do pigments play in the process of photosynthesis?• Photosynthetic organisms capture energy from sunlight

with pigments

Chlorophyll

Photosynthetic organisms capture energy from sunlight with pigments—principally with chlorophyll.

Chlorophyll – green pigments

2 main types of chlorophyll• Chlorophyll a and Chlorophyll b

• Absorbs light very well in the blue-violet spectrum and red regions of visible spectrum

• Chlorophyll a – found in all plants, algae, and cyanobacteria

• Chlorophyll b – found in all plants, and green algae

Chlorophyll

Photosynthesis takes place inside organelles called chloroplasts.

Plant Cell

Chloroplast

Chloroplast

Chloroplasts contain• Thylakoids- saclike photosynthetic membranes

• Chlorophyll is located in thylakoid membrane• Grana – thylakoids are interconnected and arranged

in stacks known as grana• Stroma – fluid portion of the chloroplast, outside of the

thylakoids

Chloroplast

In plants, photosynthesis takes place inside chloroplasts.

ThylakoidGranum

Thylakoid membrane

Stroma

Chloroplasts and light transmission

What is so special about chlorophyll that makes it so important for photosynthesis?

• light is a form of energy, any compound that absorbs light absorbs energy

High Energy Electrons

The high-energy electrons produced by chlorophyll are highly reactive and require a special “carrier.”

High Energy Electrons

An electron carrier is a compound that can accept a pair of high-energy electrons and transfer them, along with most of their energy, to another molecule.

NADP+ accepts and holds 2 high energy electrons, along with a hydrogen ion (H+) NADP+ NADPHThis is one way in which energy from sunlight can be trapped in chemical form.

High Energy Electrons

NADPH can carry the high-energy electrons that were produced by light absorption in chlorophyll to chemical reactions elsewhere in the cell.

An Overview of Photosynthesis

Photosynthesis uses the energy of sunlight to convert water and carbon dioxide (low-energy reactants) into high-energy sugars and oxygen (products).

Carbon dioxide + Water → Sugars + Oxygenlight

light+ → +

C6H12O66CO2 6H2O 6O2

Photosynthesis and Light

Photosynthesis involves two sets of reactions: Light-dependent reactions Light-independent reactions

Light-Dependent Reactions

Light-dependent reactions require the direct involvement of light and light-absorbing pigments.

Water

Oxygen

• Uses energy from sunlight to produce energy rich compounds like ATP

• Takes place in the Thylakoid

• Input: Water• Output:

Oxygen (O2)

Light-Independent ReactionsLight-independent reactions use ATP and NADPH molecules produced in the light-dependent reactions to produce high-energy sugars from carbon dioxide

Sugars andCarbohydrates

Carbon Dioxide

• No light is required • Take place outside the

thylakoids, in the stroma• Input: CO2

• Output: sugar

Interdependence of ReactionsLight-dependent and light-independent reactions have an interdependent relationship.

work together to capture the energy of sunlight and transform it into energy rich compounds like carbohydrates