Unit 4: Photosynthesis, Respiration, and Cellular Energetics

Photosynthesis Overall Reaction

The biochemical process converting light energy into chemical energy: $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.

Thylakoid

A flattened membrane-bound sac inside chloroplasts containing chlorophyll pigments; site of the light-dependent reactions.

Stroma

The protein-rich fluid surrounding grana within the chloroplast; site of the light-independent reactions (Calvin cycle).

Photolysis

The splitting of water molecules by light energy during the light-dependent reactions: $2\text{H}_2\text{O} \rightarrow 4\text{H}^+ + 4e^- + \text{O}_2$.

Calvin Cycle

Light-independent reactions in the stroma using $\text{ATP}$ and $\text{NADPH}$ to reduce $\text{CO}_2$ into $\text{G3P}$ and glucose.

RuBisCO

The enzyme ribulose-1,5-bisphosphate carboxylase-oxygenase that catalyzes the fixation of atmospheric $\text{CO}_2$ to $\text{RuBP}$.

Cellular Respiration Overall Reaction

The catabolic pathway releasing biochemical energy from glucose: $\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + 36\text{--}38\,\text{ATP}$.

Glycolysis

The anaerobic cytoplasmic breakdown of one glucose molecule into two pyruvate molecules, yielding a net $2\,\text{ATP}$ and $2\,\text{NADH}$.

Krebs Cycle

The mitochondrial matrix pathway that oxidizes acetyl-CoA, producing $2\,\text{ATP}$, $6\,\text{NADH}$, $2\,\text{FADH}_2$, and $4\,\text{CO}_2$ per glucose molecule.

Oxidative Phosphorylation

The process along the inner mitochondrial membrane where electron transport and chemiosmosis power $\text{ATP}$ synthase to generate $32\text{--}34\,\text{ATP}$.

Lactic Acid Fermentation

An anaerobic pathway occurring in animal muscles and bacteria where pyruvate is reduced directly to lactate to regenerate $\text{NAD}^+$.

Alcoholic Fermentation

An anaerobic pathway in yeast and plants where pyruvate is converted into ethanol and $\text{CO}_2$ to regenerate $\text{NAD}^+$.

Adenosine Triphosphate (ATP)

The primary energy carrier of cells, composed of adenine, ribose sugar, and three phosphate groups joined by high-energy phosphoanhydride bonds.

ATP Hydrolysis

An exergonic reaction breaking the terminal phosphate bond of $\text{ATP}$ to release free energy for cellular work: $\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{energy}$.