AP Biology Unit 3: Cellular Energetics Flashcards

Vocabulary flashcards covering enzyme mechanics, thermodynamics, light-dependent reactions, and the Calvin cycle based on the AP Biology Unit 3 study guide.

First Law of Thermodynamics

The principle stating that energy cannot be created or destroyed; it can only be transformed or transferred.

Denaturation

The structural alteration of an enzyme caused by excessive heat or extreme pH, which disrupts its shape and alters or inactivates the active site.

Competitive Inhibition

A form of enzyme inhibition where the inhibitor binds to the active site, competing with the substrate and blocking substrate binding.

Noncompetitive / Allosteric Inhibition

A form of enzyme inhibition where the inhibitor binds to a site away from the active site, changing the enzyme shape and reducing active-site function.

Substrate Saturation

The point at which all enzyme active sites are occupied by substrate, causing the reaction rate to plateau so that adding more substrate does not increase activity.

Catalase Assay (Floating Filter-Paper Disks)

An experimental procedure where faster floating filter-paper disks indicate a faster reaction rate because $\text{O}_2$ bubbles form more quickly.

Photoautotroph

An organism that uses light for energy and $\text{CO}_2$ as a carbon source.

Overall Photosynthesis Equation

The summary chemical equation for photosynthesis: $6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$.

Carotenoids

Accessory pigments in photosynthetic organisms that provide photoprotection by dissipating excess light energy.

Photosystem II (PSII)

A photosynthetic protein complex that absorbs light first; energized electrons enter the electron transport chain, and water is split to replace electrons, releasing $\text{H}^+$ and $\text{O}_2$.

Electron Transport Chain (Photosynthesis)

A series of membrane proteins that transfers electrons from PSII toward PSI and uses their energy to move $\text{H}^+$ into the thylakoid lumen.

Photosystem I (PSI)

A photosynthetic protein complex that re-energizes electrons with light; these electrons ultimately help reduce $\text{NADP}^+$ to $\text{NADPH}$.

ATP Synthase (Photosynthesis)

An enzyme complex through which $\text{H}^+$ flows from the thylakoid lumen to the stroma, driving ATP production.

Thylakoid Lumen

The internal space of the thylakoid membrane where $\text{H}^+$ accumulates during the light-dependent reactions to create a proton gradient.

Stroma

The fluid-filled space of the chloroplast surrounding the thylakoid membranes, which serves as the location for the Calvin cycle.

Oxidation and Reduction in Photosynthesis

In photosynthesis, water is oxidized as it supplies electrons, and $\text{NADP}^+$ is reduced to $\text{NADPH}$.

Carbon Fixation Phase

The first phase of the Calvin cycle in which Rubisco attaches $\text{CO}_2$ to $\text{RuBP}$; the unstable product splits into $\text{3-PGA}$.

Rubisco

The enzyme that catalyzes the attachment of inorganic $\text{CO}_2$ to $\text{RuBP}$ during the carbon fixation phase of the Calvin cycle.

Reduction Phase (Calvin Cycle)

The second phase of the Calvin cycle in which ATP and $\text{NADPH}$ convert $\text{3-PGA}$ into $\text{G3P}$.

RuBP Regeneration Phase

The third phase of the Calvin cycle in which ATP helps rearrange molecules to regenerate $\text{RuBP}$ so the cycle can continue.

Photorespiration

A pathway that occurs when Rubisco binds $\text{O}_2$ instead of $\text{CO}_2$, consuming energy and releasing previously fixed carbon without producing sugar.

$\text{C}_4$ Adaptation

A photosynthetic adaptation utilizing spatial separation: $\text{CO}_2$ is first fixed into a four-carbon compound in mesophyll cells, then delivered to bundle-sheath cells for the Calvin cycle.

CAM Adaptation

A photosynthetic adaptation utilizing temporal separation: stomata open at night to store $\text{CO}_2$ in organic acids, which is released for the Calvin cycle during the day.

Stomatal Closure Response

A defense mechanism against water loss where stomata close, reducing internal $\text{CO}_2$, slowing the Calvin cycle, and decreasing $\text{G3P}$ and sugar production.