AP Biology: Cellular Respiration, Photosynthesis, and Energetics

Comprehensive vocabulary flashcards covering thermodynamics, enzyme kinetics, cellular respiration, fermentation, evolutionary energetics, photosynthesis, and macromolecule fuel integration.

Entropy

The degree of disorder, or a measure of the number of positions and motions a molecule can take.

Exergonic Reactions

Spontaneous chemical reactions that release energy and feature a negative change in free energy ($\Delta G < 0$).

Endergonic Reactions

Non-spontaneous chemical reactions that require an input of energy and feature a positive change in free energy ($\Delta G > 0$).

Gibbs Free Energy

The available amount of energy in a system to do work.

Transition State

A highly unstable molecular intermediate state with a large amount of free energy through which reactants must proceed in both endergonic and exergonic reactions.

Allosteric Enzymes

Enzymes that bind activators or inhibitors at regulatory sites other than the active site to change enzyme shape and activity; frequently positioned at the start or crossroads of metabolic pathways.

Metabolism

The entire set of chemical reactions within a cell that convert molecules into other molecules and transfer energy.

Substrate-Level Phosphorylation

The direct transfer of a phosphate group from an organic substrate molecule to ADP to synthesize ATP, as seen in glycolysis.

Glycolysis

An ancient biochemical pathway occurring in the cytoplasm that breaks down glucose into pyruvate, yielding a net gain of $2\text{ ATP}$ and $2\text{ NADH}$.

Krebs Cycle

A cyclic pathway in the mitochondria that completely oxidizes the acetyl group of acetyl-CoA, producing $1\text{ molecule of ATP}$, $3\text{ molecules of NADH}$, and $1\text{ molecule of FADH}_2$ per complete turn.

Respiratory Electron Transport Chain

A series of four protein complexes embedded in the inner mitochondrial membrane that accept electrons from reduced carriers (NADH and $FADH_2$) to pump protons into the intermembrane space.

Proton Electrochemical Gradient

A reservoir of potential energy created by the accumulation of protons in the intermembrane space across the inner mitochondrial membrane, driving ATP synthesis by ATP synthase.

Fermentation

An ancient, oxygen-independent metabolic process that regenerates $NAD^+$ by reducing pyruvate or its derivatives in the absence of oxygen.

Lactic Acid Fermentation

An anaerobic pathway in which pyruvate is directly reduced to lactic acid coupled with the oxidation of NADH to $NAD^+$.

Anaerobic Cellular Respiration

A respiratory process that utilizes an electron transport chain with an inorganic final electron acceptor other than $O_2$.

Cyanobacteria

Organisms that evolved approximately $2.4\text{ billion years ago}$ with the novel capacity to use water as an electron donor in photosynthesis, producing oxygen gas as a byproduct.

Hemoglobin

An ancient iron-containing transport protein in red blood cells that reversibly binds and releases oxygen gas, with fetal hemoglobin exhibiting a higher binding affinity than adult hemoglobin.

Myoglobin

A specialized oxygen-binding protein in muscle cells that binds and stores oxygen, enhancing oxygen delivery to muscle mitochondria for physical activity.

Photosystem II

The photosynthetic protein complex that absorbs light energy to extract electrons from water molecules, releasing oxygen gas and protons.

Photosystem I

The photosynthetic protein complex that absorbs light energy to energize electrons, ultimately reducing $NADP^+$ to produce NADPH.

Calvin Cycle

The light-independent pathway occurring in the stroma consisting of carbon fixation ($CO_2$ attached to RuBP via rubisco), reduction (using ATP and NADPH to form triose phosphates), and RuBP regeneration.

Glycogen

A large, highly branched polymer of glucose molecules attached to a central protein that functions as the primary carbohydrate energy storage molecule in animals.

Starch

A large, branched storage polysaccharide composed of glucose molecules found in plants such as potatoes, wheat, and corn.

Triacylglycerols

Lipid energy-storage molecules containing fatty acids that can be broken down to feed into cellular respiration pathways.