3.4 - Photosynthesis

How does light energy play a role in photosynthesis?

plants rely on white light (a combination of all the lights) to power photosynthesis

Pigments

a molecule that selectively reflects some light while absorbing others; will appear the color being reflected

Chlorophyll a

green blue pigment; responsible for initiating reactions for photosynthesis

Chlorophyll b

lime pigment

Structural comparison between the two different types of chlorophylls

-vary slightly in ring portion of structure

- both have hydrophobic tails that anchor them to the phospholipid bilayer

Leaf Structure - Top

chloroplast dense; when most photosynthesis occurs

Leaf Structure - Bottom

stomata (pores) that regulate the exchange of gases in and out of the leaf

Chloroplast

double membrane organelle

Stroma

internal space of chloroplast; location of Calvin cycle

Thylakoids

membrane bound structures stacked on top of one another

Photosystem

clusters of photosynthetic pigments embedded in thylakoid membrane

Thylakoid Space

internal space of thylakoids; interconnected with all other thylakoids in the chloroplast

What does the thylakoid space provide a location for?

location for a concentration gradient of hydrogen ions (essential for ATP production)

Granum

a stake of thylakoids

Where do the Light Dependent Reactions occur?

thylakoid membrane

What happens to the electrons in photosystem II?

light strikes photosynthetic pigments, boosting electrons to a higher energy level and leave the system to ETC

What is the process of producing waste produces in Photosystem II?

water splits to replace lost electrons, oxygen bonds and are liberated

Electron Transport Chain (ETC)

series of proteins embedded in thylakoid membrane

How does the ETC transport electrons from Photosystem II to Photosystem I?

electrons are passed by embedded proteins

What do the travelling electrons generate while in the ETC?

ATP

How does the ETC produce ATP?

the electrons power the active transport of protons into the thylakoids (high concentration) which then move back out via facilitated diffusion of ATP Synthase

Where does ATP go after produced?

to stroma to power Calvin cycle

Once in Photosystem I, what happens to the electrons?

boosted to a higher level (light)

2 electrons, along with a proton, are transported to an electron carrier (NADP+), the addition of electrons and protons reduces NADP+ into NADPH

Where does NADPH go?

to stroma to power Calvin cycle

Carbon Fixation

carbon (from CO2) bonds to RuBP (becomes unstable with extra carbon) breaks down into two 3 carbon and phosphate molecule

Reduction

ATP adds a phosphate to 3-carbon molecule

NADPH rearranges 3-carbon, removes phosphate, delivers electrons

creates six G3P

Where does G3P go after Reduction?

1 leaves, other 5 stay to be regenerated into RuBP

Regeneration

ATP rearranges G3P into 3 molecules of RuBP

What can G3P be used for?

synthesis of all macromolecules and more

Photorespiration

when CO2 levels drop; RuBP fixes to O2 , can't produce G3P

Spatial Separation

fixes CO2 to an acid which is then transported to another part of the cell to complete the cycle

Temporal Separation

stomata are open at night, during the day, stomata close, light dependent reactions start