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
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
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)
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
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.
Different pigments absorb different colors of light
This allows plants to use most of the available light