Unit 20 C: Photosynthesis

Vocabulary flashcards covering the key terms, organelle structures, and biochemical processes of photosynthesis and cellular respiration from Unit 20 C.

Electromagnetic Radiation (EMR)

A form of energy that travels as waves of varying lengths and frequencies, ranging from high-energy gamma rays to low-energy radio waves.

Photon

A packet of light energy corresponding to a unit of electromagnetic radiation with a specific wavelength.

Visible Light Spectrum

The narrow range of electromagnetic radiation spanning from approximately $380\,\text{nm}$ (violet) to $750\,\text{nm}$ (red) that photosynthetic organisms harness for energy.

Chlorophyll

The light-absorbing, green-coloured pigment found in photosynthetic organisms that initiates the process of photosynthesis.

Chlorophyll a

The primary blue-green photosynthetic pigment in all photosynthetic organisms; it is the only pigment that can transfer light energy directly to the chemical reactions of photosynthesis.

Chlorophyll b

An accessory yellow-green pigment that absorbs photons at wavelengths poorly absorbed by chlorophyll a and transfers the captured energy to chlorophyll a.

Carotenoids

Accessory photosynthetic pigments that absorb yellow, orange, and red wavelengths not well absorbed by chlorophylls and transfer their captured energy to chlorophyll a.

Chloroplast

A double-membrane-bound organelle found in green plant and algal cells that carries out the reactions of photosynthesis.

Stroma

The protein-rich, semiliquid fluid filling the interior space of a chloroplast surrounding the thylakoid membranes; site of the Calvin cycle.

Thylakoid

A system of flattened, interconnected membrane sacs forming a separate internal compartment within the stroma of a chloroplast.

Grana

Dense stacks of thylakoid sacs located within the chloroplast that increase membrane surface area for light-capturing reactions (singular: granum).

Lamellae

Unstacked, membranous thylakoid segments connecting adjacent grana within a chloroplast (singular: lamella).

Thylakoid Membrane

The lipid bilayer within a chloroplast housing light-gathering pigments, photosystems, electron transport chains, and ATP synthase.

Thylakoid Lumen

The water-filled internal space enclosed by the thylakoid membrane where protons accumulate during electron transport.

Photosystem

A light-harvesting cluster of photosynthetic pigments and proteins embedded in the thylakoid membrane that absorbs photons.

Photosystem II (PSII)

The pigment-protein complex that absorbs photons to excite electrons removed from water molecules, initiating the thylakoid electron transport chain.

Photosystem I (PSI)

The pigment-protein complex that re-energizes electrons using solar energy and facilitates their transfer to $\text{NADP}^+$ to yield $\text{NADPH}$.

Photolysis

The solar-driven splitting of water molecules in the thylakoid lumen that produces $H^+$ ions, electrons, and $O_2$ gas: $2H_2O_{(l)} + \text{energy} \rightarrow 4H^+ + 4e^- + O_{2(g)}$.

Electron Transport Chain (in photosynthesis)

A series of progressively stronger electron acceptors in the thylakoid membrane that transfers excited electrons and harnesses released energy to pump protons.

Oxidation

A chemical reaction in which an atom, ion, or molecule loses one or more electrons.

Reduction

A chemical reaction in which an atom, ion, or molecule gains one or more electrons.

ATP (Adenosine Triphosphate)

A nucleotide containing three high-energy phosphate bonds that functions as the immediate energy-transferring molecule in living cells.

ADP (Adenosine Diphosphate)

A lower-energy nucleotide containing two phosphate groups that is phosphorylated to form ATP upon the addition of an inorganic phosphate group ($P_i$).

$$\text{NADP}^+$$

A coenzyme that acts as the terminal electron acceptor in the light-dependent reactions, taking up two electrons and one proton ($H^+$) to form $\text{NADPH}$.

$$\text{NADPH}$$

A reduced coenzyme and electron donor generated in the light-dependent reactions that provides reducing power and hydrogen atoms to the Calvin cycle.

Light-Dependent Reactions

The first phase of photosynthesis occurring in thylakoid membranes, in which captured solar energy excites electrons, generates ATP, and reduces $\text{NADP}^+$ to $\text{NADPH}$.

ATP Synthase Complex

A specialized membrane-bound enzyme channel that harnesses the flow of $H^+$ ions from the lumen into the stroma to synthesize ATP from ADP and $P_i$.

Chemiosmosis (in photosynthesis)

The process of synthesizing ATP using the potential energy of an electrochemical proton ($H^+$) gradient established across the thylakoid membrane.

Light-Independent Reactions

The second phase of photosynthesis (the Calvin cycle) that takes place in the stroma and uses ATP and $\text{NADPH}$ to synthesize carbohydrates without directly requiring solar energy.

Carbon Fixation

The enzymatic incorporation of inorganic carbon from $CO_2$ into organic compounds such as carbohydrates in the stroma.

Calvin Cycle

A cyclic series of light-independent reactions occurring in the stroma that utilizes ATP and $\text{NADPH}$ to fix $CO_2$ into sugar molecules.

RuBP (Ribulose Bisphosphate)

The five-carbon compound in the stroma that binds with incoming $CO_2$ during the carbon fixation phase of the Calvin cycle.

Rubisco

The key stromal enzyme that catalyzes the attachment of inorganic $CO_2$ to RuBP during the initial step of the Calvin cycle.

3-PGA (3-Phosphoglycerate)

The stable three-carbon molecule formed when the unstable six-carbon intermediate splits during carbon fixation; it is subsequently energized and reduced to form G3P.

G3P (Glyceraldehyde-3-Phosphate)

A high-energy three-carbon carbohydrate produced by the reduction of 3-PGA; two molecules exit the Calvin cycle to assemble one glucose molecule.

C3 Plants

Plants that fix carbon dioxide directly into three-carbon molecules ($3\text{-PGA}$) as the first stable product of the Calvin cycle.