BIO CO5

Energy

The ability to promote change or do work

Chemical Energy

Energy stored within the chemical bonds between atoms and molecules

Solar Energy

Radiant energy harvested directly from the sun

Metabolism

The sum of all chemical reactions occurring within a cell or organism

Catabolism

Metabolic breakdown of large molecules into smaller units; an exergonic (energy-releasing) process

Anabolism

Metabolic synthesis of complex molecules from smaller units; an endergonic (energy-requiring) process

Exergonic Reaction

A chemical reaction that net releases energy

Endergonic Reaction

A chemical reaction that requires or absorbs energy

Adenosine Triphosphate (ATP)

The primary energy "currency" and intermediate molecule in cells, composed of adenine, ribose, and three phosphate groups

ATP Hydrolysis

The exergonic reaction where water breaks ATP's outer phosphoanhydride bond, forming ADP and inorganic phosphate Pi to release energy for cellular work

ATP Synthesis (Condensation)

The endergonic joining of ADP and Pi with the loss of a water molecule to store energy as ATP

ATP-ADP Cycle

The continuous cycle of consuming ATP for cellular work and regenerating ATP using energy from cellular respiration

Cellular Respiration

Energy-yielding pathways (aerobic/anaerobic respiration and fermentation) that power ATP production

Phototrophic Energy Metabolism

Reactions that obtain energy primarily from sunlight

Chemotrophic Energy Metabolism

Reactions that obtain energy through oxidation-reduction processes

Oxidation

The loss of electrons, loss of hydrogen atoms, or gain of oxygen atoms

Reduction

The gain of electrons, gain of hydrogen atoms, or loss of oxygen atoms

Oxidizing Agent

A reactant that accepts/gains electrons and becomes reduced

Reducing Agent

A reactant that donates/loses electrons and becomes oxidized

NAD+/NADH

Nicotinamide Adenine Dinucleotide in its oxidized (NAD+)and reduced (NADH) electron-carrier states

Oxygenic Photosynthesis

The redox process converting light energy into chemical energy to synthesize organic molecules from CO2 and H2O, releasing oxygen

Photoautotrophs

Organisms that use light as an energy source and inorganic compounds CO2 as a carbon source

Photoheterotrophs

Organisms that use light as an energy source and organic compounds as a carbon source

Chloroplast

The organelle that serves as the site of photosynthesis in plants

Mesophyll Cells

Interior leaf cells containing the primary concentration of chloroplasts

Stomata

Microscopic pores on leaf surfaces that allow CO2 to enter and O2 to exit

Stroma

The dense fluid matrix inside the chloroplast surrounding thylakoids

Thylakoids

Membrane-bound sacs inside chloroplasts where light-dependent reactions take place

Grana

Stacks of thylakoid membranes

Chlorophyll

Green light-absorbing pigments in thylakoid membranes that absorb red and violet-blue light while reflecting green and yellow light

Chlorophyll a

The primary photosynthetic pigment

Chlorophyll b

An accessory photosynthetic pigment

Photoexcitation

The transfer of photon energy to pigment electrons, boosting them from a ground state to an excited state

Fluorescence

The release of photons when excited electrons drop back down to their ground state

Light-Dependent Reactions

The thylakoid stage of photosynthesis that converts light energy into ATP and NADPH while splitting water and releasing O2

Photosystem

A functional unit in thylakoid membranes composed of chlorophylls, accessory pigments, and proteins

Photosystem II (PSII / P680)

Photosystem utilizing P680 reaction-center chlorophyll to initiate linear electron flow and water splitting

Photosystem I (PSI / P700)

Photosystem utilizing P700 reaction-center chlorophyll to re-excite electrons for NADPH formation

Primary Electron Acceptor (PEA)

A molecule in the reaction center that receives high-energy electrons from photoexcited chlorophyll (P680 or P700)

H2O Photolysis

The light-driven splitting of water by PSII into 2e-, 2H+ and O2

P680⁺

The oxidized form of P680; an extremely powerful biological oxidizing agent that pulls electrons from water

Electron Transport Chain (ETC)

A series of electron carriers (Plastoquinone/Pq, Cytochrome complex, Plastocyanin/Pc) transferring electrons from PSII to PSI

Proton Ion Gradient

A concentration difference of H+ pumped across the thylakoid membrane by the Cytochrome complex to fuel ATP synthesis via chemiosmosis

P700⁺

The oxidized P700 electron acceptor that receives replacement electrons coming from the first ETC

Second ETC

Redox chain transferring electrons from PSI's PEA through Ferredoxin (Fd) to NADP+ reductase without generating a proton gradient or ATP

Ferredoxin (Fd)

An electron-carrier protein in the second electron transport chain

NADP+ Reductase

Enzyme catalyzing electron transfer from Fd and H+ to NADP+, generating NADPH

NADP+ / NADPH

Nicotinamide Adenine Dinucleotide Phosphate in its oxidized NADP+ and reduced (NADPH) states; NADPH holds high-energy electrons for the Calvin cycle

Calvin-Benson Cycle (Light-Independent Reactions)

The stroma process using ATP and NADPH to convert CO2 into carbohydrates across Carbon Fixation, Reduction, and Regeneration

Carbon Fixation

Phase 1 of the Calvin cycle where $\text{CO}_2$ is combined with RuBP by Rubisco, forming an unstable 6-carbon intermediate that immediately splits into two 3-PGA molecules

Rubisco

Ribulose bisphosphate carboxylase/oxygenase; the enzyme that catalyzes carbon fixation

3-Phosphoglycerate (3-PGA)

Three-carbon compound produced during carbon fixation

1,3-Bisphosphoglycerate

Intermediate formed when 3-PGA receives a phosphate group from ATP

Glyceraldehyde-3-Phosphate (G3P)

Three-carbon sugar formed when NADPH reduces 1,3-bisphosphoglycerate; the direct final carbohydrate output of photosynthesis

Ribulose Bisphosphate (RuBP)

Five-carbon CO2 acceptor molecule regenerated in Phase 3 using 5 G3P molecules and 3 ATPs