Biology: Cellular Respiration and Photosynthesis Vocabulary

A comprehensive vocabulary flashcard set covering key terms, structures, and pathways from Raven's Biology Chapter 7 (Cellular Respiration) and Chapter 8 (Photosynthesis).

Autotrophs

Organisms capable of producing their own organic molecules from inorganic sources through processes like photosynthesis.

Heterotrophs

Organisms that obtain energy and organic compounds by consuming other organisms or their products.

Cellular Respiration

A series of metabolic reactions used by organisms to extract chemical energy from organic molecules to synthesize ATP.

Dehydrogenation

An oxidation reaction in which lost electrons are accompanied by protons, resulting in the net loss of hydrogen atoms (1 electron and 1 proton).

Nicotinamide Adenosine Dinucleotide ($\text{NAD}^+$)

A coenzyme and electron carrier that reversibly accepts 2 electrons and 1 proton to form NADH during cellular energy harvest.

Aerobic Respiration

A cellular respiration pathway that requires molecular oxygen ($\text{O}_2$) as the final electron acceptor, with a theoretical free energy change of $\Delta G = -686\,\text{kcal/mol}$ of glucose.

Anaerobic Respiration

A cellular respiration pathway where an inorganic molecule other than oxygen ($\text{O}_2$), such as nitrate, sulfate, or carbon dioxide, serves as the final electron acceptor.

Fermentation

An anaerobic cellular pathway in which the final electron acceptor is an organic molecule, allowing the recycling of $\text{NAD}^+$ without oxygen.

Substrate-level Phosphorylation

The direct transfer of a phosphate group from a phosphorylated metabolic intermediate to ADP to form ATP, occurring during glycolysis and the citric acid cycle.

Oxidative Phosphorylation

The synthesis of ATP by ATP synthase using energy derived from a proton electrochemical gradient created by an electron transport chain.

Glycolysis

A 10-step biochemical pathway in the cytoplasm that breaks down 1 6-carbon glucose molecule into 2 3-carbon pyruvate molecules, yielding a net gain of 2 ATP and 2 NADH.

Pyruvate Oxidation

The multi-enzyme conversion of pyruvate to acetyl-CoA in the mitochondrial matrix (or plasma membrane in prokaryotes) catalyzed by pyruvate dehydrogenase, yielding 1 $\text{CO}_2$, 1 NADH, and 1 acetyl-CoA per pyruvate.

Citric Acid Cycle

A 9-step pathway in the mitochondrial matrix that oxidizes acetyl-CoA, producing 2 $\text{CO}_2$, 3 NADH, 1 $\text{FADH}_2$, and 1 ATP per acetyl-CoA while regenerating oxaloacetate.

Electron Transport Chain

A series of membrane-bound protein complexes embedded in the inner mitochondrial membrane that transfer high-energy electrons and pump protons into the intermembrane space.

Chemiosmosis

The movement of protons down their electrochemical gradient back into the mitochondrial matrix through ATP synthase, driving the phosphorylation of ADP to ATP.

ATP Synthase

A rotary motor enzyme complex consisting of a membrane-bound $F_0$ complex and a catalytic $F_1$ complex that uses proton flow to synthesize ATP.

P/O Ratio

The phosphate-to-oxygen ratio, representing the amount of ATP synthesized per oxygen molecule reduced during oxidative phosphorylation.

Phosphofructokinase

A key regulatory enzyme in glycolysis that is allosterically inhibited by high levels of ATP or citrate.

Methanogens

Anaerobic prokaryotes that use carbon dioxide ($\text{CO}_2$) as a final electron acceptor, reducing it to methane ($\text{CH}_4$).

Ethanol Fermentation

A fermentation process in yeast that decarboxylates pyruvate to acetaldehyde and reduces it to ethanol, regenerating $\text{NAD}^+$ and producing $\text{CO}_2$.

Lactic Acid Fermentation

A fermentation process occurring in animal muscle cells where electrons from NADH are transferred directly to pyruvate to form lactate, regenerating $\text{NAD}^+$.

Deamination

The chemical removal of an amino group ($-\text{NH}_2$) from an amino acid, allowing the remaining carbon skeleton to enter glycolysis or the citric acid cycle.

$\beta$-Oxidation

An oxygen-dependent metabolic pathway that sequentially cleaves 2-carbon acetyl units from fatty acids to form acetyl-CoA, producing NADH and $\text{FADH}_2$.

Oxygenic Photosynthesis

Photosynthesis carried out by cyanobacteria, algae, and land plants that splits water ($\text{H}_2\text{O}$) to produce oxygen ($\text{O}_2$), ATP, and NADPH.

Light-Dependent Reactions

The initial stage of photosynthesis taking place in the thylakoid membranes where light energy is captured to form ATP and reduce $\text{NADP}^+$ to NADPH.

Carbon Fixation Reactions

Light-independent reactions occurring in the stroma that use ATP and NADPH from light-dependent reactions to convert $\text{CO}_2$ into organic molecules.

Thylakoid Membrane

The internal phospholipid membrane network within chloroplasts that contains photosynthetic pigments, electron transport chains, and photosystems.

Stroma

The semiliquid fluid matrix surrounding the thylakoid membrane system inside a chloroplast, where the Calvin cycle reactions occur.

Photon

A discrete packet or quantum of light energy whose energy content is inversely proportional to its wavelength.

Photoelectric Effect

The phenomenon in which light photons strike a molecule and cause the ejection or removal of an electron.

Electromagnetic Spectrum

The complete range of all frequencies and wavelengths of electromagnetic radiation, from gamma rays ($0.001\,\text{nm}$) to radio waves ($100\,\text{m}$).

Absorption Spectrum

The specific range and efficiency of light wavelengths absorbed by a particular pigment molecule.

Action Spectrum

A graph plotting the relative efficiency or rate of photosynthesis promoted by different wavelengths of light across the visible spectrum.

Chlorophyll a

The primary photosynthetic pigment in plants and cyanobacteria; it absorbs violet-blue and red light and is the only pigment directly involved in converting light energy to chemical energy.

Chlorophyll b

An accessory pigment that absorbs blue and red-orange light wavelengths not absorbed by chlorophyll a, transferring its captured energy to chlorophyll a.

Porphyrin Ring

The light-absorbing complex ring structure of chlorophyll containing alternating single and double bonds with a central magnesium ion ($\text{Mg}^{2+}$).

Carotenoids

Accessory pigments with carbon rings linked to alternating single and double bonds that absorb a broad range of light wavelengths and protect cells by scavenging free radicals.

Antenna Complex

A web of hundreds of accessory pigment molecules bound in the thylakoid membrane that absorb photons and funnel excitation energy to the reaction center.

Reaction Center

A transmembrane protein-pigment complex in a photosystem containing chlorophyll a molecules that pass excited electrons to a primary electron acceptor.

Cyclic Photophosphorylation

An anoxygenic photosynthetic process in sulfur bacteria using a single photosystem ($P_{870}$) where electrons return to the reaction center, generating ATP via a proton gradient without generating NADPH or $\text{O}_2$.

Photosystem II (P680)

A photosystem complex in thylakoid membranes that absorbs photons, excites electrons, and uses a manganese cluster to oxidize water, producing $\text{O}_2$ and protons.

Photosystem I (P700)

A photosystem complex that accepts low-energy electrons from photosystem II via plastocyanin, re-excites them with photons, and transfers them to ferredoxin to reduce $\text{NADP}^+$ to NADPH.

Noncyclic Photophosphorylation

The two-stage pathway using photosystems II and I in series to produce both ATP and NADPH while splitting water to yield $\text{O}_2$.

Rubisco

Ribulose bisphosphate carboxylase/oxygenase; the key stroma enzyme that fixes $\text{CO}_2$ to RuBP in the Calvin cycle, but can also bind $\text{O}_2$ during photorespiration.

Calvin Cycle

The 3-phase metabolic pathway (carbon fixation, reduction, regeneration of RuBP) in the stroma that uses ATP and NADPH to synthesize glyceraldehyde 3-phosphate (G3P) from $\text{CO}_2$.

Photorespiration

A wasteful metabolic process occurring when Rubisco binds $\text{O}_2$ instead of $\text{CO}_2$ to RuBP under hot, dry conditions with closed stomata, releasing $\text{CO}_2$ and consuming energy.

C4 Plants

Plants that bypass photorespiration by spatially separating carbon fixation (PEP carboxylase in mesophyll cells) from the Calvin cycle (bundle-sheath cells).

CAM Plants

Succulent plants that avoid photorespiration by temporally separating carbon fixation, opening stomata at night to fix $\text{CO}_2$ into organic acids and closing them during the day to run the Calvin cycle.

PEP Carboxylase

An enzyme present in C4 and CAM plants that fixes $\text{CO}_2$ onto phosphoenolpyruvate (PEP) to form oxaloacetate; it has high affinity for $\text{CO}_2$ and lacks oxygenase activity.