Photosynthesis

Ch. 10

Photosynthesis has two stages:

Light reactionsenergy from the sun is absorbed and converted into

ATPWater molecules are split and NADP+ picks up the free

hydrogen and electrons to make NADPHTakes place in the thylakoid membrane system

Calvin CycleATP gives energy to sites where glucose (C6H12O6) is

formedNADPH delivers hydrogenCO2 donates carbon and oxygenTakes place in the stroma

Photoautotrophs can only harness the wavelengths between 400 and 750 nanometers. This is also the range of visible light.

Pigments are the “molecular bridge” Absorb wavelengths of light and organisms use them

Chlorophylls are the main pigments of photosynthesis Absorb all wavelengths except very little of the green

and yellow-green ones

How do pigments work?

Each pigment has a light-catching set of atoms Electrons of a pigment’s light-catching area absorb

photons (packets of light energy) Electrons move to higher energy level, then back

down releasing energy The energy is passed on to “neighbors” called a

photosystem Energy is passed on and on until it reaches the

“reaction center”

SUMMARY 3 Things happen in light reactions

Pigments of photosystems absorb photon energy and give up excited electrons

Transfers of electrons and hydrogen through electron transport systems leads to ATP and NADPH formation

Pigments that gave up electrons get electron replacements

Noncyclic Photophosphorylation

Cyclic Photophosphorylation

Calvin Cycle

“Synthesis” part of photosynthesis ATP provides energy for the reactions NADPH supplies the hydrogen and electrons CO2 provides the carbon and oxygen

RESULT: sugar

C4 Plants

Modified for DRY environments Thrive in hot/sunny environments

Modified anatomy that allows them to minimize excess water loss and maximize sugar production

Pump CO2 deep into leaf in bundle-sheath cells before going though Calvin Cycle

This way, oxygen doesn't inhibit the Calvin Cycle Get away with having smaller stomata, thus losing less

water

CAM Plants

Also adapted to dry conditions Keep stomates closed during the day and open at night This is the reverse of how most plants behave Fixes CO2 at night and stores materials to use for

photosynthesis the next day (when stomata close)