Chapter: 8 Photosynthesis

Transfer of Energy

• flows in an ecosystem (sunlight - leaves heat)

mesophyll

interior tissues of the leaf

• chloroplasts found

Transfer of Energy

• flows in an ecosystem (sunlight - leaves heat)

mesophyll

interior tissues of the leaf

• chloroplasts found

stomata

Co2 enters and O2 exits through these microscopic pores

stroma

chloroplasts has an envelope of two membranes surrounding a dense fluid called…

thylakoids

connected sacs in the chloroplast that compose a third membrane system

grana

thylakoids are stacked in collumns

chlorophyll

pigment that gives leaves their green color

• in the thylakoid membranes

Photosynthesis Chemical Formula

6 cycles of photosynthesis to build glucose

Cellular Respiration

photosynthesis splits water

chloroplasts splits H2O → hydrogen and oxygen → incorporates hydrogen electrons into sugar molecules → oxygen byproduct

Light is a form of energy

• can be reflected, transmitted, or absorbed

• pigments can absorb light

• unabsorbed light wavelengths → reflected back → what we see

chlorophyll a

the key light capturing pigment

chlorophyll b

an accessory pigment

carotenoids

a separate group of accessory pigments

photosystem II (PS II)

• functions first

• reaction-center of chlorophyll a of PS II is called P680 (best at absorbed at a wavelength of 680 nm)

photosystem I (PS I)

best at absorbing wavelength of 700 nm

• reaction - center = P700

Steps in Linear Electron Flow (1)

photon hits a pigment in a light-harvesting complex of PS II, and its energy is passed among pigment molecules until it excites P680

Steps in Linear Electron Flow (2)

An exited electron from P680 is transferred to the primary electron acceptor

• P680+

Steps in Linear Electron Flow (3)

H20 is split by enzymes, and the electrons are transferred from the hydrogen atoms to P680+, thus reducing it to P680

• H+ are released into the thylakoid space

• O2 is released as a by product

Steps in Linear Electron Flow (4)

Each electrons “falls“ down an electron transport chain from the primary electron acceptors of PS II to PSI. energy released by the fall drives the creation of a proton gradient across the thylakoid membrane

Steps in Linear Electron Flow (5)

Potential energy stored in the proton gradient drives production of ATP by chemiosmosis

• photophosphorylation

Steps in Linear Electron Flow (6)

In PS I (like PS II), transferred light energy
excites P700, which loses an electron to the
primary electron acceptor
• P700+ (P700 that is missing an electron) accepts an
electron passed down from PS II via the electron
transport chain

Steps in Linear Electron Flow (7)

Each electron “falls” down an electron
transport chain from the primary electron
acceptor of PS I to the protein ferredoxin (Fd)

Steps in Linear Electron Flow (8)

NADP+ reductase catalyzes the transfer of
electrons to NADP+, reducing it to NADPH
• The electrons of NADPH are available for the
reactions of the Calvin cycle
• This process also removes an H+ from the stroma Campbell Biology Figure 10.14

mitochondria

proton movements

matrix > intermembrane space > ATP synthase > matrix

chloroplast

proton movement

stroma > thylakoid space > ATP synthase > stroma

The Calvin Cycle uses…

ATP and NADPH → to reduce Co2 to sugar > G3P

Calvin Cycle (3 Phases)

1. Carbon Fixation - Carboxylation

2. Reduction

3. Regeneration of CO2 acceptor

Carbon Fixation (Carboxylation)

• 3 carbon dioxide molecules (one at a time)

• 5C sugar (RuBP) accepts Co2 → converts to an unstable 6C sugar

• instability causes a split into 2, 3C molecules

Reduction

Each 3C molecule is phosphorylated to 1 - 3 BPG

• NADPH reduces 1 - 3 BPG to G3P

Regeneration

3 Co2 enter per cycle → 6C molecule upon entering the cycle → splits into 2 3C molecules

• 1 G3P leave the cycle to assemble into glucose or other organic molecules

• 5 G3Ps used to regenerate RuBP