Energy, Photosynthesis, and Cellular Respiration Vocabulary

A complete set of vocabulary flashcards covering key bioenergetics, photosynthesis, and cellular respiration concepts.

Enzyme

A macromolecule, typically a protein, that acts as a biological catalyst to speed up specific chemical reactions without being consumed.

Substrate

The specific reactant molecule upon which an enzyme acts during a catalyzed reaction.

Enzyme-substrate complex

A temporary intermediate structure formed when an enzyme binds non-covalently to its specific substrate.

Active site

The specific pocket or groove on an enzyme where the substrate binds and where chemical catalysis occurs.

Catalyst

A chemical agent that increases the rate of a chemical reaction without undergoing any permanent chemical change itself.

Ph

A logarithmic measure of the hydrogen ion concentration in a solution, indicating its relative acidity or alkalinity.

Denature

The structural modification of a protein or other biological macromolecule that alters its native shape and destroys its functional activity, often caused by extreme heat or pH.

Atp

Adenosine triphosphate, the primary energy-transfer molecule of living cells, composed of adenine, ribose, and three phosphate groups.

kinetic energy

The form of energy associated with the motion of matter, particles, or objects.

Potential energy

The stored energy that matter possesses as a result of its spatial location, arrangement, or chemical structure.

Energy

The capacity to do work or to cause change within a system.

Exergonic reaction

A spontaneous chemical reaction that involves a net release of free energy ($\Delta G < 0$).

Endergonic reaction

A non-spontaneous chemical reaction that requires an input of free energy from the surroundings ($\Delta G > 0$).

Catabolic pathway

A metabolic pathway that releases energy by breaking down complex molecules into simpler compounds.

Anabolic pathway

A metabolic pathway that consumes energy to construct complex macromolecules from simpler starting units.

Activation energy

The initial investment of energy required to contort reactant molecules so bonds can break and start a chemical reaction.

Laws of thermodynamics

Fundamental physical principles establishing that energy cannot be created or destroyed (First Law) and that every energy transformation increases the entropy of the universe (Second Law).

C4 plant

A plant that prefaces the Calvin cycle with reactions that incorporate $CO_2$ into a four-carbon compound, reducing photorespiration in hot, dry environments.

Light capturing complexes

Protein-pigment assemblies situated in the thylakoid membrane that absorb photons of light and funnel the excitation energy toward a reaction center.

Nadph

The reduced form of nicotinamide adenine dinucleotide phosphate, functioning as a key electron carrier and reducing agent in photosynthetic pathways.

Light

A form of electromagnetic radiation that travels in rhythmic waves and consists of discrete particles of energy known as photons.

Stomata

Microscopic pores bordered by guard cells on leaf surfaces that regulate the gas exchange of $CO_2$, $O_2$, and water vapor.

Stroma

The dense fluid within the chloroplast surrounding the thylakoids, serving as the site of the Calvin cycle.

Thylakoid

A flattened, membranous sac inside a chloroplast containing chlorophyll and the molecular machinery for light-dependent reactions.

Reaction center

A protein complex within a photosystem that contains a special pair of chlorophyll a molecules and a primary electron acceptor to initiate the light reactions.

Chlorophyll

The principal photosynthetic pigment located within chloroplasts that absorbs light energy, primarily within the blue and red regions of the visible spectrum.

Redox reaction

A chemical oxidation-reduction reaction that involves the transfer of one or more electrons from one reactant to another.

Oxidation

The loss of electrons, loss of hydrogen, or increase in oxidation state by a chemical substance during a reaction.

Pigments

Light-absorbing molecules that absorb light energy at specific wavelengths and reflect or transmit all other visible wavelengths.

Photosynthesis

The biological process of capturing light energy to synthesize organic molecules, such as sugars, from carbon dioxide and water.

Photons

Discrete quanta or packets of electromagnetic energy that make up light.

Wavelength

The spatial distance between crests or identical points of adjacent waves of electromagnetic radiation.

Reduction

The addition of electrons, addition of hydrogen, or decrease in oxidation state by a chemical substance during a reaction.

Photoprotection

The biological mechanism by which accessory pigments absorb and safely dissipate excessive light energy that would otherwise damage chlorophyll or form harmful reactive oxygen species.

Heterotrophs

Organisms that cannot produce their own organic food molecules and must obtain nutrition by consuming other organisms or organic substances.

Calvin cycle

The cyclic series of biochemical reactions occurring in the chloroplast stroma that incorporates $CO_2$ into carbohydrates using ATP and NADPH.

Chloroplast

A double-membrane organelle found in plant and algal cells that serves as the site for photosynthesis.

Grana

Stacks of thylakoid discs (singular: granum) located inside the chloroplast.

Photosystems

Light-harvesting complexes surrounding a reaction-center complex located within the thylakoid membrane that convert light energy into chemical energy.

Mesophyll

The specialized interior photosynthetic tissue of a leaf situated between the upper and lower epidermis.

Photorespiration

A metabolic pathway that consumes oxygen and ATP while releasing $CO_2$ without producing sugar, occurring when rubisco binds $O_2$ instead of $CO_2$.

G3p

Glyceraldehyde 3-phosphate, a three-carbon carbohydrate produced as the direct carbohydrate output of the Calvin cycle and an intermediate in glycolysis.

CAM plant

A plant that adapts to hot, arid conditions by opening stomata at night to fix $CO_2$ into organic acids and closing them during the day to prevent water loss while performing the Calvin cycle.

Cellular respiration

The catabolic pathway of aerobic and anaerobic processes that breaks down organic fuel molecules to generate ATP via an electron transport chain.

NAD+

Nicotinamide adenine dinucleotide, an oxidized coenzyme that serves as an electron carrier in cellular respiration and metabolic redox reactions.

FADH

A reduced flavin nucleotide electron carrier (commonly denoted as FADH or $FADH_2$) that delivers electrons to the mitochondrial electron transport chain.

Glycolysis

A series of reactions that splits glucose into two molecules of pyruvate in the cytoplasm, generating a net yield of two ATP and two NADH without requiring oxygen.

Pyruvate oxidation

The conversion of pyruvate into acetyl-CoA, carbon dioxide, and NADH within the mitochondrial matrix, connecting glycolysis to the citric acid cycle.

Citric acid cycle

An eight-step metabolic cycle in the mitochondrial matrix that completes the breakdown of glucose derivatives by oxidizing acetyl-CoA to $CO_2$, producing NADH, $FADH_2$, and ATP.

Chemiosmosis

An energy-coupling mechanism that uses energy stored in a transmembrane proton gradient to drive cellular work, such as the synthesis of ATP.

ATP synthase

A membrane-bound protein complex that harnesses the flow of protons passing down their electrochemical gradient to phosphorylate ADP into ATP.

Anaerobic respiration

A form of cellular respiration that uses an electron transport chain with an inorganic molecule other than molecular oxygen as the final electron acceptor.

Fermentation

A catabolic process that makes a limited amount of ATP from glucose without an electron transport chain or oxygen, by recycling $NAD^+$ through the reduction of organic molecules.