BIOL 1001 Exam 2 Review: Cell Membranes, Bioenergetics, Photosynthesis, and Cellular Respiration

Comprehensive vocabulary flashcards covering the key concepts, mechanisms, and diagrams for BIOL 1001 Exam 2, including membrane dynamics and transport, thermodynamics, enzymes, photosynthesis, and cellular respiration.

Phospholipid Bilayer

The fluid portion of the plasma membrane, consisting of polar hydrophilic heads oriented outward toward watery environments and nonpolar hydrophobic fatty acid tails oriented inward away from water.

Unsaturated Fatty Acid Kinks

Bends in fatty acid tails resulting from double or triple carbon bonds that hinder tight molecular packing and increase cell membrane fluidity.

Cholesterol (Membrane Stabilizer)

A steroid lipid embedded within animal cell membranes that modulates membrane fluidity across fluctuating temperatures and decreases permeability to biological solutes.

Receptor Protein

A membrane protein that binds an extracellular signaling molecule (such as a hormone), changing shape to initiate an intracellular chemical response.

Passive Transport

The net movement of substances across a biological membrane down a concentration gradient without requiring cellular energy expenditure, encompassing simple diffusion, facilitated diffusion, and osmosis.

Simple Diffusion

The passive, unassisted movement of small nonpolar molecules (such as $O_2$ and $CO_2$) and minor quantities of water directly across the phospholipid bilayer.

Facilitated Diffusion

The passive movement of ions or large, polar, water-soluble molecules across a membrane through specialized channel or carrier proteins.

Osmosis

The net diffusion of water across a selectively permeable membrane, either directly across the lipid bilayer or through specialized aquaporin channels.

Isotonic Solution

A surrounding fluid possessing an equal solute concentration relative to the cell's interior, causing no net flow of water across the membrane.

Hypertonic Solution

A solution characterized by a higher solute concentration (and lower water concentration) relative to the cell interior, driving water out of the cell.

Hypotonic Solution

A solution characterized by a lower solute concentration (and higher water concentration) relative to the cell interior, causing water to enter and swell the cell.

Red Blood Cell Osmotic Responses

Red blood cells maintain regular biconcave morphology in isotonic solution, shrivel (crenate) as water leaves in hypertonic solution, and swell or burst as water enters in hypotonic solution.

Turgor Pressure

Hydrostatic pressure exerted by fluid inside a plant cell's central vacuole pushing the cytoplasm against the rigid cell wall to maintain structural support.

Plasmolysis

The detachment and retraction of a plant cell's plasma membrane away from its rigid cell wall caused by net osmotic loss of water into a hypertonic extracellular fluid.

Active Transport

An energy-dependent transport mechanism where membrane proteins utilize ATP hydrolysis to move ions or molecules (such as $Ca^{2+}$) against their concentration gradient.

Pinocytosis

A category of endocytosis colloquially referred to as 'cell drinking' wherein the plasma membrane forms dimples to engulf extracellular fluid into small vesicles.

Phagocytosis

A category of endocytosis colloquially known as 'cell eating' where the cell projects pseudopods to encircle and enclose large particles or microorganisms into food vacuoles.

Exocytosis

An active cellular process wherein membrane-bound vesicles migrate to and fuse with the plasma membrane, releasing their enclosed contents into the extracellular fluid.

Desmosomes

Anchoring intercellular junctions in animals that link adjacent cells together through cytokeratin-bound protein filaments, common in flexible tissues like the small intestine.

Tight Junctions

Intercellular protein barrier junctions in animals that knit membranes tightly together to prevent fluid leakage between cells, prominent in the urinary bladder.

Gap Junctions

Protein channel assemblies in animal cells that establish direct cytoplasmic bridges between adjoining cells, facilitating coordinated intercellular communication.

Plasmodesmata

Membrane-lined cytoplasmic channels crossing plant cell walls that allow direct molecular communication and transport between neighbouring plant cells.

Potential Energy

Stored energy capable of performing work, including chemical energy sequestered within molecular bonds or electrical gradients across membranes.

Kinetic Energy

The energy of active motion, exemplified by heat, radiant light, electrical flow, or moving physical masses.

First Law of Thermodynamics

The law of conservation of energy stating that energy cannot be created or destroyed, only altered from one physical or chemical form into another.

Second Law of Thermodynamics

The principle stating that every energy conversion reduces the total amount of useful, organized energy, inevitably increasing the entropy of the universe.

Entropy

A quantitative physical measure of the randomness, disorder, or statistical unpredictability present within a thermodynamic system.

Exergonic Reaction

A spontaneous chemical reaction that releases free energy, in which the starting reactants possess higher free energy than the resultant products.

Endergonic Reaction

A non-spontaneous chemical reaction requiring an input of energy, in which the produced molecules possess higher free energy than the starting reactants.

Activation Energy

The initial minimum energy barrier required to destabilize existing chemical bonds and initiate a chemical transformation.

Coupled Reaction

A linked biochemical pairing wherein an exergonic reaction (such as ATP hydrolysis) supplies the energy needed to power an endergonic process (such as protein synthesis).

Active Site

The specialized, pocket-like binding domain on an enzyme that accommodates specific substrate molecules and stabilizes the reaction transition state.

Competitive Inhibition

An enzyme regulation mechanism where an inhibitory molecule competes directly with the substrate by binding reversibly to the enzyme's active site.

Noncompetitive Inhibition

An enzyme inhibition mechanism where an effector molecule binds to an allosteric site separate from the active site, inducing a conformational shape change that prevents catalysis.

Feedback Inhibition

A negative feedback mechanism in a metabolic pathway where the accumulation of an end product (such as isoleucine) allosterically inhibits an early pathway enzyme (enzyme 1).

Human Enzyme Optimal Ranges

The narrow physical boundaries for enzyme activity in humans, typically peaking near body temperature ($37\,^{\circ}\text{C}$ / $98.6\,^{\circ}\text{F}$) and specific pH levels (e.g., pH $2$ for pepsin, pH $7.4$ for cellular enzymes, pH $8$ for trypsin).

Chicxulub Asteroid Impact

A $15\,\text{km}$-wide asteroid that slammed into Mexico $65\text{ million}$ years ago at $20\times$ the speed of a bullet, unleashing an explosion equivalent to $1\text{ billion}$ Hiroshima bombs that triggered global winter and wiped out dinosaurs.

Engelmann’s Experiment

An investigation revealing that photosynthesis proceeds most actively under violet-blue and red light, demonstrated by aerobic bacteria clustering in those specific wavelengths along an illuminated algal filament.

Stoma (plural: Stomata)

Microscopic epidermal leaf pores flanked by guard cells that open to allow $CO_2$ influx when guard cells are swollen/turgid and close when flaccid to reduce water loss.

Thylakoid and Granum

A thylakoid is a flattened, disc-like membranous sac within a chloroplast housing chlorophyll pigments, and a granum is a stacked column of multiple thylakoids.

Phototropism

Plant directional growth toward light mediated by auxin, which migrates to the shaded side of the stem to promote asymmetric cell elongation and cause bending toward the light source.

Light Reactions of Photosynthesis

The first phase of photosynthesis occurring in thylakoid membranes, which captures photon energy to split water, release $O_2$, and generate ATP and NADPH.

Calvin Cycle (Dark Reactions)

The stroma-localized, light-independent stage of photosynthesis that utilizes ATP and NADPH from the light reactions to fix $CO_2$ into glucose ($C_6H_{12}O_6$).

Photosystem II (PS II)

A multiprotein light-harvesting complex in thylakoid membranes that initiates photosynthetic electron transport, catalyzes water photolysis, and establishes a proton gradient.

Photosystem I (PS I)

A photosynthetic complex in the thylakoid membrane that absorbs light energy to re-energize electrons for the reduction of $NADP^+$ into NADPH.

$C_4$ Pathway

A photosynthetic adaptation in plants like corn and sugar cane that spatially separates carbon fixation between mesophyll and bundle sheath cells to conserve water in hot, dry environments.

CAM Pathway

A photosynthetic carbon fixation adaptation in succulents like cacti and pineapples that fixes $CO_2$ into organic acids at night and runs the Calvin cycle during the day within the same mesophyll cell.

Oxidation and Reduction (LEO / GER)

Redox principles where oxidation represents the loss of electrons ($\text{LEO}$) and reduction represents the gain of electrons ($\text{GER}$).

Glycolysis

The initial anaerobic cytoplasmic stage of glucose catabolism that breaks down one glucose molecule into two molecules of pyruvate, generating a net of $2\,\text{ATP}$ and $2\,\text{NADH}$.

Krebs Cycle

A cyclic series of enzymatic reactions within the mitochondrial matrix that oxidizes acetyl groups derived from pyruvate into $CO_2$, producing ATP, NADH, and $FADH_2$.

ATP Yield of Cellular Respiration

The total energy production from the complete aerobic breakdown of one glucose molecule, yielding approximately $36\text{ to }38\,\text{ATP}$ at an overall thermodynamic efficiency of $39\%$.

Lactic Acid Fermentation

An anaerobic metabolic pathway that reduces pyruvate to lactate in overtaxed muscle cells or dairy bacteria in order to regenerate $NAD^+$ for continued glycolysis.

Alcoholic Fermentation

An anaerobic pathway in yeasts such as Saccharomyces that converts pyruvate to ethanol and $CO_2$, regenerating $NAD^+$ without producing additional ATP.

Industrial Fermentation Products

Commercial fermentation pathways where microorganisms convert pyruvic acid into distinct goods: Propionibacterium ($CO_2$, propionic acid / Swiss cheese), Lactobacillus (lactic acid / yogurt), Saccharomyces ($CO_2$, ethanol / wine, beer), and Acetobacter (acetic acid / vinegar).