Understanding Photosynthesis and Its Mechanisms

Photosynthesis

the conversion of light energy to chemical energy

Autotrophs

Organisms that produce their own food (organic molecules) from simple substances in their surroundings

Heterotrophs

Organisms unable to make their own food so they live off of other organisms

Cyanobacteria

early prokaryotes capable of photosynthesis that oxygenated the atmosphere of early Earth

Chloroplast

organelle for the location of photosynthesis, found in the mesophyll, the cells that make up the interior tissue of the leaf

Stomata

pores in leaves that allow CO2 in and O2 out

Stroma

aqueous internal fluid of chloroplasts

Thylakoids

structures that form stacks known as grana in chloroplasts

Chlorophyll

green pigment in thylakoid membranes

Photosynthesis Simplified Formula

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

Redox reaction

reaction involving complete or partial transfer of one or more electrons from one reactant to another

Oxidation

loss of electrons (e-)

Reduction

gain of electrons (e-)

Light

electromagnetic energy made up of particles of energy called photons

Wavelength

the distance from the crest of one wave to the crest of the next

Electromagnetic spectrum

the entire range of wavelengths of electromagnetic energy

Visible light

the range of light wavelengths from 380 nm to 750 nm

Photosynthetic Pigments

molecules that absorb visible light

Chlorophyll a

primary pigment involved in the light reactions, blue/green pigment

Chlorophyll b

accessory pigment, yellow/green pigment

Carotenoids

yellow/orange pigments that broaden the spectrum of colors that drive photosynthesis and provide photoprotection

Light Reactions

occur in the thylakoid membrane in the photosystems and convert solar energy to chemical energy

Photosystems

reaction center and light capturing complexes in the thylakoid membrane

Photosystem 2

reaction center P680 that absorbs light at 680 nm

Photosystem 1

reaction center P700 that absorbs light at 700 nm

Photosystem II

Initial stage of photosynthesis where light energy is absorbed.

P680

Chlorophyll a molecules in Photosystem II that absorb light.

Primary electron acceptor

Molecule that accepts excited electrons from P680.

H2O splitting

Process producing electrons, protons, and oxygen from water.

Linear electron flow

Pathway where electrons move from PS II to PS I.

ATP generation

Energy from electron flow used to synthesize ATP.

Photosystem I

Second stage of photosynthesis that further excites electrons.

P700

Chlorophyll a molecules in Photosystem I that absorb light.

NADP+ reductase

Enzyme that transfers electrons to NADP+, forming NADPH.

Calvin Cycle

Cyclic process using ATP and NADPH to synthesize sugars.

Carbon fixation

Incorporation of CO2 into organic molecules in Calvin Cycle.

Rubisco

Enzyme catalyzing the attachment of CO2 to RuBP.

3-phosphoglycerate

Product formed from CO2 and RuBP during carbon fixation.

G3P

3-carbon sugar produced in the Calvin Cycle.

Photorespiration

Inefficient process where Rubisco binds O2 instead of CO2.

C4 plants

Plants with spatial separation of carbon fixation steps.

CAM plants

Plants that fix CO2 at night to conserve water.

Electron transport chain

Series of proteins transferring electrons from PS II to PS I.

Thylakoid space

Compartment where protons accumulate during electron transport.

NADPH

Reduced form of NADP+, used in Calvin Cycle.

ATP synthase

Enzyme that synthesizes ATP using H+ gradient energy.

Oxygen release

By-product of water splitting during photosynthesis.

6 NADPH

Amount of NADPH needed to reduce 1,3-bisphosphoglycerate.

3 ATP

Amount of ATP used to regenerate RuBP in Calvin Cycle.

9 ATP

Total ATP required for one cycle of Calvin Cycle.

9 ADP

By-product of ATP usage in the Calvin Cycle.