General Biology I – Exam #2 Study Guide

Vocabulary flashcards covering membrane transport, bioenergetics, enzymes, photosynthesis, and cellular respiration for BIO 121 Exam #2.

Selectively permeable membrane

A biological membrane that allows some substances to cross more easily than others while blocking the passage of certain molecules.

Membrane protein

Protein embedded in or attached to the membrane that performs functions such as transport, signal reception, enzymatic activity, cell-cell recognition, and attachment.

Diffusion

The passive movement of molecules down their concentration gradient from an area of higher concentration to lower concentration.

Facilitated diffusion

Passive transport of polar or charged substances across a membrane via specific transport proteins.

Osmosis

The diffusion of water across a selectively permeable membrane toward the higher solute concentration.

Tonicity

The ability of a surrounding solution to cause a cell to gain or lose water.

Hypertonic solution

Solution with a higher solute concentration than the cell; water exits the cell.

Hypotonic solution

Solution with a lower solute concentration than the cell; water enters the cell.

Isotonic solution

Solution with equal solute concentration to the cell; no net water movement.

Lysis

The bursting of an animal cell placed in a hypotonic solution.

Crenation

Shriveling of an animal cell placed in a hypertonic solution.

Turgid

Firm state of a plant cell in a hypotonic environment; cell wall prevents bursting.

Plasmolysis

Shrinkage of the cytoplasm in a plant cell placed in a hypertonic solution; plasma membrane pulls away from the wall.

Osmoregulation

Control of water balance in organisms living in hyper- or hypotonic environments.

Active transport

Energy-requiring movement of substances against their concentration gradient via transport proteins.

Exocytosis

Bulk transport process that expels materials from a cell by fusion of a vesicle with the plasma membrane.

Endocytosis

Bulk uptake of material into the cell by forming vesicles from the plasma membrane.

Phagocytosis

‘Cell eating’; engulfment of large particles or organisms by the cell.

Receptor-mediated endocytosis

Highly specific endocytosis that uses receptor proteins to take in particular molecules.

Kinetic energy

Energy of motion; examples: heat, light moving photons.

Potential energy

Stored energy due to position or structure; example: chemical energy in bonds.

Light energy

Kinetic energy carried by photons of electromagnetic radiation.

Thermal energy

Kinetic energy associated with the random movement of atoms or molecules (heat).

Chemical energy

Potential energy stored in chemical bonds of molecules.

First Law of Thermodynamics

Energy cannot be created or destroyed, only transferred or transformed.

Second Law of Thermodynamics

Every energy transfer increases the entropy (disorder) of the universe.

Entropy

Measure of disorder or randomness in a system.

Endergonic reaction

Chemical reaction that absorbs free energy; products have more energy than reactants.

Exergonic reaction

Reaction that releases free energy; products have less energy than reactants.

Energy coupling

Use of exergonic processes to drive endergonic ones, often via ATP.

Metabolism

Sum of all chemical reactions in an organism.

ATP (adenosine triphosphate)

Cell’s main energy currency composed of adenine, ribose, and three phosphates.

ATP cycle

Continuous regeneration of ATP from ADP and Pi using energy from catabolism.

Enzyme

Protein catalyst that speeds up reactions by lowering activation energy.

Activation energy

Energy barrier that must be overcome for a chemical reaction to proceed.

Substrate

Specific reactant an enzyme acts upon.

Active site

Region on an enzyme where the substrate binds.

Product (enzyme reaction)

Molecule(s) produced from an enzymatic reaction.

Induced fit

Enzyme’s active site changes shape slightly to fit the substrate snugly.

Optimal enzyme conditions

Temperature, pH, and other factors at which an enzyme works best.

Cofactor

Non-protein helper (metal ion or molecule) required for enzyme activity.

Coenzyme

Organic cofactor such as vitamins NAD⁺ or FAD.

Competitive inhibitor

Molecule that binds the active site and blocks substrate access.

Noncompetitive inhibitor

Molecule that binds elsewhere on enzyme, altering its shape and activity.

Photoautotroph

Organism that uses light energy to make organic molecules from CO₂.

Photosynthesis

Process that converts light energy, CO₂, and H₂O into glucose and O₂.

Chloroplast

Organelle where photosynthesis occurs in plants and algae.

Thylakoid membrane

Internal chloroplast membrane where light reactions and photosystems reside.

Stroma

Fluid inside chloroplast surrounding thylakoids; site of Calvin Cycle.

Thylakoid space

Internal compartment enclosed by the thylakoid membrane; accumulation of H⁺.

Intermembrane space (chloroplast)

Space between the chloroplast’s inner and outer membranes.

Mesophyll

Photosynthetic tissue of a leaf located between upper and lower epidermis.

Stomata

Pores on leaf surface that allow gas exchange of CO₂ and O₂.

Chlorophyll

Green pigment that absorbs light mainly in blue and red wavelengths.

Carotenoid pigment

Accessory pigments that absorb excess light and give autumn colors.

Electromagnetic radiation

Energy that travels in waves; includes visible light, UV, IR, etc.

Wavelength

Distance between two successive peaks of a wave; inversely related to energy.

Visible light spectrum

Portion of EM spectrum perceived as colors; violet (short, high energy) to red (long, low energy).

Light-dependent reactions

Stage of photosynthesis that converts light energy to ATP and NADPH, releasing O₂.

Calvin Cycle

Light-independent reactions that fix CO₂ into G3P using ATP and NADPH.

NADP⁺ / NADPH

Electron carrier; NADP⁺ accepts electrons to form NADPH in light reactions.

Carbon fixation

Incorporation of CO₂ into organic molecules during the Calvin Cycle.

Rubisco

Enzyme that catalyzes the first step of carbon fixation in the Calvin Cycle.

Photosystem II

First photosystem that splits water and passes electrons to ETC, producing O₂.

Photosystem I

Second photosystem that re-energizes electrons to reduce NADP⁺ to NADPH.

G3P (glyceraldehyde 3-phosphate)

Three-carbon sugar product of the Calvin Cycle; two G3P form glucose.

Photorespiration

Process in which Rubisco fixes O₂ instead of CO₂, wasting energy and reducing sugar output.

C4 pathway

Photosynthetic adaptation that fixes CO₂ into a 4-carbon compound to minimize photorespiration; e.g., corn, sugarcane.

CAM pathway

Adaptation where stomata open at night, storing CO₂ for use during the day; e.g., cacti, pineapples.

Greenhouse effect

Warming caused by atmospheric gases (mainly CO₂) trapping heat radiating from Earth.

Cellular respiration

Catabolic process that converts glucose and O₂ into CO₂, H₂O, and ATP.

Oxidation

Loss of electrons or hydrogen; releases energy.

Reduction

Gain of electrons or hydrogen; stores energy.

Glycolysis

First stage of respiration that splits glucose into pyruvate in the cytoplasm, producing small ATP and NADH.

Pyruvate oxidation

Preparatory step converting pyruvate to acetyl-CoA, yielding NADH and CO₂ in the mitochondrial matrix.

Krebs cycle (citric acid cycle)

Cycle in matrix that oxidizes acetyl-CoA to CO₂, producing NADH, FADH₂, and ATP.

Oxidative phosphorylation

Electron transport chain and chemiosmosis that generate most ATP in mitochondria.

NAD⁺

Electron carrier that becomes NADH when reduced during respiration.

FAD

Electron carrier reduced to FADH₂ in the Krebs cycle.

Chemiosmosis

ATP production driven by the flow of H⁺ down its gradient through ATP synthase.

ATP synthase

Enzyme complex that uses proton motive force to convert ADP + Pi into ATP.

Fermentation

Anaerobic pathway that regenerates NAD⁺ from NADH allowing glycolysis to continue.

Lactic acid fermentation

Fermentation producing lactate; occurs in muscle cells and lactic acid bacteria.

Alcoholic fermentation

Fermentation producing ethanol and CO₂; used by yeast in brewing and baking.

Facultative anaerobe

Organism that can make ATP by aerobic respiration or fermentation depending on O₂ availability.

Obligate anaerobe

Organism that is poisoned by O₂ and relies solely on anaerobic metabolism.

Uncoupler

Chemical that dissipates the H⁺ gradient across the inner mitochondrial membrane, preventing ATP synthesis and releasing energy as heat.