Overview:

• Energy from light is used to convert CO2, H2O into sugar

• O2 is a byproduct or “leftover” and is released

Photosynthesis:

• In: 6CO2 + 6H2O + Energy

• Out: C6H12O6 + 6O2

Photosynthetic Organisms

• Includes plants, algae, some protisits and cyanobacteria

Cyanobacteria

• a.k.a blue-green algae• Unicellular, grow in colonies large enough to see• Evolved between 2.5 and 3.4 billion years ago,

they were probably the first organisms to use sunlight in the production of organic compounds from water and CO2

Cyanobacteria and their relatives are responsible for a major part of photosynthesis in oceans

• What does it look like?

• Function of leaves

Leaf functions:• “Trap” sunlight• Perform photosynthesis• Move food to storage

areas in the plant• Absorb CO2 from the air• Minimize water loss from

evaporation

Leaf structure is related to function…

Parts of a leaf:

Cuticle = water resistant coating on top of leaf

Chloroplast = contains chlorophyll

Guard cells = create the microscopic openings called stomata

Stomata = opening that regulate the exchange of CO2 and O2

Why are leaves green?

Because….

• Their cells are full of chloroplast!• Chloroplasts contain chlorophyll (a pigment that reflects

green light…which we see….so we see leaves as green)

Chloroplast structure:

Summary of chloroplast structure

• Enclosed in a double membrane

• Grana = a bunch of Thylakoid disks

• Thylakoid contains the pigments (chlorophyll)

• Stroma = the liquid part of chloroplasts (containing electron transport system and “loose” enzymes)

Photosynthesis takes place in 2 stages :

• Light Dependent Reactions

• Light Independent Reactions (Calvin-Benson Cycle)

So let’s learn about light……..

Where does the light come from?

• What are photons?– Light particles– No mass– Travel as a wave

• Photons & Energy– The smaller the

wavelength, the higher the energy per photon

Sunlight is a mixture of the colors of the rainbow

Photosynthetic Pigments: Light energy captors

• Embedded in membranes of thylakoid disks

• Includes different varieties of chlorophylls and other accessory pigments (ex: beta-carotene)

Pigments

• Pigments absorb light energy and convert it to chemical energy.

• Chlorophyll: GREEN (most important in photosynthesis)

• Carotenoids: YELLOW, ORANGE & RED.

• Photosynthesis only takes place when chlorophyll is present.

Photosynthetic pigments absorb the energy in specific colors of light

Different pigments absorb different colors of light

This allows plants to use most of the available light