Photosynthesis

Ecological Significance

Ecological Significance Photosynthesis- the process that converts light

energy to chemical energy

Autotrophs- “self + feeders”

Photoautotrophs- “light + self + feeders”

Heterotrophs- “ other + feeders”

Consumers- eat other things

Decomposers- break down dead organic material

Chloroplast Structure Leaf Structure

The leaf is the major site of photosynthesis

Stomata- small pores in the leaf where CO2 enters an O2 and H2O leave

Mesophyll Tissue in center of the leaf Where chloroplasts are found

Chloroplast Structure Double Membrane

Stroma- fluid inside the inner membrane but outside the thylakoid

Thylakoid interconnected membranous sacks

Granna (granum)- stacks of thylakoids

Thylakoid Space- the space inside the thylakoid

Chlorophyll- green pigment found inside (embedded in) the thylakoid membrane

Chemical Context of Photosynthesis General Equation

6CO2 + 6H2O + light energy → C6H12O6 + 6O2

Redox Reaction

Reverse of cellular respiration

Electrons increase in potential energy as they move from water to sugar

Anabolic reaction- builds up large organic molecules from smaller ones

Requires energy that is supplied by the sun

Light and Pigments Pigments- molecules that absorb light

Visible Light- 750nm-380nm (ROYGBIV)

Absorbance vs. Transmittance/Reflection Absorbance- wavelengths that are absorbed

(colors that you don’t see)

Transmittance- wavelengths that bounce off or go through a substance (colors that you do see)

Plant Pigments Chlorophyll a- reflects blue-green wavelengths

(all others are captured)

Chlorophyll b- reflects yellow-green wavelengths (all others are captured)

Carotenoids- reflects yellow and orange wavelengths

Major function of carotenoids= photoprotection- absorbs excessive light energy that could otherwise be harmful

The Big Picture of Photosynthesis

Light Reactions “photo” = light

Also known as: Light Dependent Reactions

Location: thylakoid membrane (photosystems I & II and the electron transport chain)

Input: light (photons) + H2O + NADP+ + ADP + P

Output: O2 + NADPH + ATP

Reaction: light + H2O → O2

Calvin Cycle “synthesis”= make, put together

Also known as: Light Independent Reactions, Dark Reactions

Location: stroma

Input: NADPH + ATP + CO2

Output: G3P (later converted to glucose) + NADP+ + ADP + P

Reaction: CO2 → C6H12O6

The Light Reaction Photosystems- a protein complex embedded

in the thylakoid membrane that contains two parts:

Reaction Center- protein complex that holds a special chlorophyll a molecule and a primary electron acceptor

Light-harvesting complex- pigment molecules that capture light and transfer excited electrons to the special chlorophyll a molecues

Two Kinds of Photosystems Photosystem II:

Special chlorophyll a= P680 Functions 1st

Photosystem I: Special chlorophyll a= P700 Functions 2nd

P680 and P700 Very unstable when oxidized so electrons

must be replenished immediately

P700 is replenished with electrons moving down the ETC from P680

P680 is replenished by the splitting of water molecules

Noncyclic Electron Flow

Cyclic Electron Flow the calvin cycle uses more ATP than NADPH

a build up of NADPH triggers the switch from noncyclic to cyclic electron flow

Uses only PSI

Electrons cycle back from Ferredoxin (Fd) to the cytochrome complex to replenish P700

Does not produce NADPH or O2 but does produce ATP

Chemiosmosis in the Chloroplast Energy from sunlight, not food

Build up of H+ occurs in the thylakoid space

Enzyme: ATP synthase

Overall Result of the Light Reactions: solar power generates ATP and NADPH providing chemical energy and reducing power to the Calvin cycle

Overall Result of the Light Reaction Solar power generates ATP and NADPH

providing chemical energy and reducing power to the Calvin cycle

The Clavin Cycle Input: 3 CO2 (one at a time) + 9 ATP +

6NADPH

Output: glucose

Three Major Steps of the Calvin Cycle Carbon Fixation- carbon is incorporated into

organic forms from carbon dioxide

CO2 is converted into carbohydrates using the energy provided by ATP and NADPH from the light reactions

Back to the Big Picture of Photosynthesis