Modules 8 & 9: Cellular Respiration and Photosynthesis

Vocabulary flashcards covering the key concepts, stages, reactions, and adaptations of Cellular Respiration (Module 8) and Photosynthesis (Module 9).

Cellular Respiration

The metabolic process by which organisms break down organic molecules to generate $ATP$.

Redox Reaction

A chemical reaction involving the transfer of electrons, consisting of oxidation (the loss of electrons) and reduction (the gain of electrons).

Aerobic Respiration

An exergonic pathway that consumes oxygen and organic molecules to produce energy, summarized by the equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{ATP}$.

Electron Carriers ($NAD^+$ and $FAD$)

Molecules that function as electron shuttles, accepting high-energy electrons during cellular respiration to form $NADH$ and $FADH_2$ and delivering them to the electron transport chain.

Glycolysis

The first stage of cellular respiration ('sugar splitting') occurring in the cytoplasm without requiring oxygen; it breaks down glucose into a net output of pyruvate, $ATP$, and $NADH$.

Pyruvate Oxidation (The Link Reaction)

The transitional stage occurring in the mitochondria where pyruvate is converted into acetyl CoA before entering the Citric Acid Cycle, yielding acetyl CoA, $CO_2$, and $NADH$.

Citric Acid Cycle (Krebs Cycle)

The mitochondrial stage of respiration that takes in acetyl CoA to complete the breakdown of glucose, releasing $CO_2$ and producing $ATP$, $NADH$, and $FADH_2$.

Oxidative Phosphorylation

The final stage of cellular respiration, consisting of the electron transport chain and chemiosmosis, which produces the vast majority of cellular $ATP$.

Electron Transport Chain (ETC)

A series of protein complexes in the inner mitochondrial membrane that accept electrons from $NADH$ and $FADH_2$ and transfer them to the final electron acceptor ($O_2$), pumping protons to establish an $H^+$ gradient.

Chemiosmosis

The process in which energy stored in a proton gradient (proton-motive force) drives $ATP$ Synthase to synthesize $ATP$.

Proton-Motive Force

The electrochemical gradient of protons ($H^+$) generated across the inner mitochondrial membrane by the electron transport chain.

Fermentation

An anaerobic pathway that occurs in the absence of oxygen whose primary goal is to regenerate $NAD^+$ so that glycolysis can continue producing $ATP$.

Alcoholic Fermentation

A type of anaerobic fermentation that converts pyruvate into end products of ethanol and $CO_2$.

Lactic Acid Fermentation

A type of anaerobic fermentation in which pyruvate is directly reduced by $NADH$ to form lactate (lactic acid) as the end product.

Photosynthesis

The endergonic process by which autotrophs capture light energy and convert it into chemical energy stored in organic molecules.

Thylakoid

Flattened, membranous sacs inside a chloroplast that contain chlorophyll and other pigments, serving as the site of the light-dependent reactions.

Stroma

The dense fluid within the chloroplast surrounding the thylakoid membranes, serving as the site of the Calvin Cycle (light-independent reactions).

Light-Dependent Reactions

The initial reactions of photosynthesis that take place in the thylakoid membranes, using light, water, $ADP$, and $NADP^+$ to generate $O_2$, $ATP$, and $NADPH$.

Photolysis of Water

The splitting of water molecules in Photosystem II during light reactions, which produces electrons to replace those lost by chlorophyll, protons ($H^+$), and molecular oxygen ($O_2$).

Calvin Cycle (Light-Independent Reactions)

The second stage of photosynthesis occurring in the stroma; it uses $CO_2$, $ATP$, and $NADPH$ across carbon fixation, reduction, and regeneration to produce sugars.

RuBisCO

The enzyme that catalyzes the initial carbon fixation step of the Calvin Cycle by combining $CO_2$ with ribulose bisphosphate (RuBP).

Photorespiration

A wasteful metabolic pathway that occurs under hot, dry conditions when RuBisCO binds $O_2$ instead of $CO_2$, consuming energy without producing sugar.

$C_4$ Plants

Plants (such as corn) that have adapted to minimize photorespiration through spatial separation of carbon fixation and the Calvin Cycle.

CAM Plants

Plants (such as cacti) that minimize water loss and photorespiration through temporal separation, opening stomata to fix carbon at night and running the Calvin cycle during the day.