General Biology BIOL151 Unit 2 Learning Objectives and Key Terms

Comprehensive practice vocabulary flashcards covering General Biology BIOL151 Unit 2 Learning Objectives and Key Terms across Chapter 4 (Cell Structure and Function), Chapter 5 (Membrane Structure and Transport), and BioSkills (Microscopy, Metrics, and Scientific Literature).

Cell Theory

The foundational principle of cell biology stating that all organisms are composed of one or more cells, the cell is the fundamental structural and functional unit of life, and all cells arise from pre-existing cells.

Prokaryotic Cell

A unicellular organism lacking a membrane-bound nucleus and membrane-bound organelles, typically having its genetic material organized in a single circular chromosome within a nucleoid region.

Specialized Structures in Prokaryotic Cells

Unique, non-universal structures found in certain prokaryotic species, such as photosynthetic internal membranes, protective capsules, fimbriae or pili for attachment, flagella for motility, and extrachromosomal plasmids.

Cell Size Limitation

The physical constraint requiring cells to remain microscopic because as cell radius increases, volume increases much faster than surface area ($\text{surface area} \propto r^2$ vs. $\text{volume} \propto r^3$), limiting diffusion rates and the transport of nutrients and wastes across the membrane.

Eukaryotic Cell

A cell characterized by possessing a membrane-bound nucleus housing genomic DNA, specialized membrane-bound organelles, and a complex cytoskeleton.

Compartmentalization

The structural separation of cellular processes into distinct membrane-bound organelles within eukaryotic cells, allowing incompatible chemical reactions to occur simultaneously, concentrating reactants, and increasing biochemical efficiency.

Organelle

A specialized membrane-bound subunit or distinct structure within a cell that performs a specific metabolic or structural function.

Cell Organelle Dominance

The correlation between a cell's specialized physiological activity and its organellar composition, wherein cells specialized for specific functions contain a high abundance of the corresponding organelles (e.g., active secretion correlates with prominent RER and Golgi).

Endomembrane System

An interconnected network of internal eukaryotic membranes—including the nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vesicles, and plasma membrane—that coordinates protein and lipid synthesis, modification, and transport.

Protein Transport in the Endomembrane System

The targeted movement of newly synthesized proteins from ribosomes on the rough ER, through transport vesicles to the cis face of the Golgi apparatus, through Golgi cisternae, and out the trans face to destinations such as lysosomes or the plasma membrane.

Molecular "Zip Codes"

Specific amino acid sequences (such as signal peptides) or carbohydrate tags on proteins that direct them to their correct cellular destination or organelle during intracellular transport.

Lysosomal Recycling Pathways

The metabolic pathways that deliver internal or external materials to lysosomes for enzymatic breakdown and recycling, including autophagy, phagocytosis, and receptor-mediated endocytosis.

Autophagy

A lysosomal degradation pathway in which damaged or redundant cellular organelles are enclosed by a double membrane to form an autophagosome, which then fuses with a lysosome for hydrolytic digestion.

Cytoskeleton

A dynamic intracellular network of protein fibers extending throughout the cytoplasm of eukaryotic cells, providing structural support, maintaining cell shape, anchoring organelles, and facilitating cell motility.

Microfilaments

The thinnest cytoskeletal components ($\approx 7\,\text{nm}$ diameter), composed of polymer chains of actin subunits, responsible for cell shape maintenance, muscle contraction, amoeboid movement, and cytokinesis.

Intermediate Filaments

Rope-like cytoskeletal fibers ($\approx 8\text{ to }12\,\text{nm}$ diameter) constructed from fibrous proteins (such as keratins and lamins) that resist tensile stress, anchor the nucleus, and provide mechanical stability to the cell.

Microtubules

Hollow cylindrical cytoskeletal fibers ($\approx 25\,\text{nm}$ diameter) formed from $\alpha$- and $\beta$-tubulin dimers, serving as tracks for motor proteins, separating chromosomes during cell division, and forming the structural core of cilia and flagella.

Eukaryotic Flagella

Long, whip-like motile cell appendages constructed of an axoneme with a "$9 + 2$" microtubule arrangement surrounded by the plasma membrane, powered to bend in undulating waves by dynein motor proteins.

Motor Proteins

Specialized mechanochemical proteins (such as kinesin, dynein, and myosin) that hydrolyze ATP to generate mechanical movement along cytoskeletal filaments, transporting vesicles or driving cell motility.

Fluid-Mosaic Model

The widely accepted structural model of biological membranes describing the lipid bilayer as a dynamic, fluid sea of phospholipids in which various proteins, glycoproteins, and glycolipids are embedded and can diffuse laterally.

Membrane Fluidity

The physical property describing the viscosity and lateral mobility of lipid molecules and proteins within the plane of the biological membrane bilayer.

Factors Affecting Membrane Fluidity

Physical and chemical variables altering bilayer fluidity, including temperature, fatty acid tail saturation (unsaturated tails increase fluidity), tail length (shorter tails increase fluidity), and cholesterol concentration.

Phospholipid Bilayer

A two-layered sheet formed spontaneously by phospholipids in aqueous solutions, with hydrophobic fatty acid tails sequestered in the interior and hydrophilic phosphate heads facing outward toward the water.

Amphipathic

A chemical property describing a molecule that possesses both a hydrophilic (polar, water-soluble) region and a hydrophobic (nonpolar, water-insoluble) region.

Phospholipid

An amphipathic lipid consisting of a glycerol molecule linked to two hydrophobic fatty acid tails and a hydrophilic head group containing a negatively charged phosphate.

Integral Membrane Protein

A protein that is permanently attached to or embedded within the biological membrane, containing hydrophobic regions that interact directly with the lipid core.

Transmembrane Protein

A type of integral membrane protein that spans entirely across the phospholipid bilayer, possessing hydrophilic domains exposed to both the interior and exterior of the cell.

Peripheral Membrane Protein

A membrane protein that is temporarily attached to the surface of the lipid bilayer or to integral proteins via non-covalent interactions, without penetrating the hydrophobic core.

Glycoprotein

A membrane-bound protein covalently linked to carbohydrate oligosaccharide chains on the extracellular surface, functioning in cell-cell recognition, adhesion, and signaling.

Membrane Carbohydrates

Short, branched chains of sugars covalently linked to lipids (glycolipids) or proteins (glycoproteins) on the outer surface of the plasma membrane, serving as cellular identification tags.

Permeability

The capability of a biological membrane to permit the transit of substances, solutes, or water across its bilayer.

Selective Permeability

The property of biological membranes that allows certain substances (such as small nonpolar molecules) to pass through freely while preventing or regulating the transit of other substances (such as ions and large polar molecules).

Concentration Gradient

A difference in the concentration of a solute or ion across a physical space or between opposite sides of a biological membrane.

Diffusion

The spontaneous net movement of solute particles down their concentration gradient (from an area of higher concentration to an area of lower concentration) driven by random thermal motion.

Dynamic Equilibrium

The state reached when solute molecules become evenly distributed across a membrane, such that molecules continue to cross in both directions at equal rates with no net change in concentration.

Passive Transport

The movement of substances across a biological membrane down their concentration or electrochemical gradient without the expenditure of cellular metabolic energy ($\text{ATP}$).

Facilitated Diffusion

A form of passive transport in which polar, hydrophilic, or charged solutes cross a biological membrane down their concentration gradient through transmembrane channel or carrier proteins.

Channel Protein

A transmembrane protein that forms a continuous, hydrophilic passageway across the membrane, allowing specific ions or water molecules to diffuse rapidly down their gradient.

Ion Channel

A specialized pore-forming transmembrane protein that selectively permits the passage of specific ions ($\text{e.g., } Na^+$ or $K^+$) across the membrane, often regulated by voltage, ligands, or mechanical stress.

Carrier Protein

A transmembrane transport protein that selectively binds a specific solute, undergoes a reversible conformational change, and releases the solute on the opposite side of the membrane.

Glucose Transporter (GLUT-1)

A specific uniporter carrier protein in the plasma membrane that accelerates the passive, facilitated diffusion of glucose into cells down its concentration gradient.

Osmosis

The passive net diffusion of free water molecules across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Hypertonic

Describing an external solution that has a higher solute concentration compared to the interior of a cell, resulting in a net osmotic outflow of water and cell shrinkage.

Hypotonic

Describing an external solution that has a lower solute concentration compared to the interior of a cell, resulting in a net osmotic inflow of water and cell swelling.

Isotonic

Describing an external solution that has the same solute concentration as the interior of a cell, resulting in no net movement of water across the plasma membrane.

Active Transport

The transport of ions or solutes across a biological membrane against their concentration or electrochemical gradient, requiring an expenditure of cellular energy ($\text{ATP}$).

Primary Active Transport

An active transport process that directly hydrolyzes $\text{ATP}$ to pump ions or solutes across a membrane against their concentration or electrochemical gradient.

Secondary Active Transport

An active transport mechanism that couples the uphill transport of a solute against its gradient to the downhill movement of another solute or ion whose gradient was established by primary active transport.

Sodium–Potassium Pump

A primary active transport membrane protein ($Na^+/K^+\text{-ATPase}$) that hydrolyzes one $\text{ATP}$ to pump three $Na^+$ ions out of the cell and two $K^+$ ions into the cell against their respective concentration gradients.

Uniporter

An integral membrane transport protein that moves a single type of solute or ion across a membrane in one direction.

Symporter

A membrane transport protein (cotransporter) that carries two different solutes or ions across the membrane simultaneously in the same direction.

Antiporter

A membrane transport protein (exchanger) that transports two different solutes or ions across the membrane simultaneously in opposite directions.

Endocytosis

An active cellular transport process in which the plasma membrane invaginates around extracellular material, pinching off to form an internal membrane-bound vesicle.

Phagocytosis

A form of endocytosis ("cell eating") in which a cell engulfs large particulate matter, cellular debris, or microbes into a large internal vesicle called a phagosome.

Pinocytosis

A non-specific form of endocytosis ("cell drinking") in which the plasma membrane pinches inward to internalize droplets of extracellular fluid and dissolved solutes into small vesicles.

Receptor-Mediated Endocytosis

A highly selective form of endocytosis in which extracellular target molecules bind to specific cell-surface receptors, triggering the inward budding of coated vesicles.

Exocytosis

An active cellular export process in which internal membrane-bound vesicles fuse with the plasma membrane, discharging their contents into the extracellular space.

Cell Wall

A rigid structural layer located outside the plasma membrane in plants, fungi, and most prokaryotes, providing structural support, shape, and protection against osmotic lysis.

Chloroplast

A double-membrane-bound photosynthetic organelle found in plant cells and algae containing thylakoids and chlorophyll, responsible for converting light energy into chemical energy.

Mitochondria

Double-membrane-bound eukaryotic organelles that produce the majority of cellular $\text{ATP}$ through cellular respiration, possessing their own circular genome and ribosomes.

Endosymbiosis Theory

The evolutionary theory stating that eukaryotic mitochondria and chloroplasts originated as free-living prokaryotic organisms that were engulfed by an ancestral host cell and became permanent endosymbionts.

Cytoplasm

All the contents of a cell contained within the plasma membrane, excluding the nucleus in eukaryotic cells, encompassing the cytosol, organelles, and cytoskeleton.

Cytosol

The aqueous, semifluid fluid portion of the cytoplasm surrounding the organelles, where many intermediate metabolic reactions take place.

Ribosomes

Non-membrane-bound complexes of ribosomal RNA ($\text{rRNA}$) and proteins that carry out protein synthesis (translation) in both prokaryotic and eukaryotic cells.

Nucleus

The prominent double-membrane-bound eukaryotic organelle that encloses and protects the genomic DNA, coordinating gene expression, transcription, and replication.

Nuclear Envelope

The double-lipid bilayer membrane structure that encloses the eukaryotic nucleus, separating genetic material from the cytoplasm.

Nuclear Pores

Protein complexes spanning the nuclear envelope that regulate the selective bidirectional transit of macromolecules (such as RNA and proteins) between the nucleus and the cytoplasm.

Nucleolus

A dense, non-membrane-bound subnuclear region responsible for transcribing ribosomal RNA ($\text{rRNA}$) and assembling ribosome subunits.

Nucleoid

The irregularly shaped, non-membrane-enclosed region within a prokaryotic cell where the circular chromosomal DNA is concentrated.

Endoplasmic Reticulum

An extensive membranous network of tubules and flattened sacs (cisternae) continuous with the outer nuclear membrane, functioning in protein and lipid synthesis.

Rough Endoplasmic Reticulum (RER)

The portion of the endoplasmic reticulum studded with ribosomes on its outer surface, specialized for the synthesis, folding, and initial modification of secretory, membrane, and lysosomal proteins.

Smooth Endoplasmic Reticulum (sER)

The portion of the endoplasmic reticulum lacking bound ribosomes, specialized for lipid and steroid synthesis, carbohydrate metabolism, calcium storage, and detoxification of drugs and poisons.

Golgi Apparatus

An organelle consisting of stacks of flattened membranous sacs (cisternae) that receives, chemically modifies, sorts, and packages proteins and lipids arriving from the endoplasmic reticulum.

Lysosomes

Membrane-bound digestive organelles containing acidic hydrolytic enzymes that degrade macromolecules, old cellular components, and ingested foreign material.

Peroxisome

A membrane-bound eukaryotic organelle containing oxidative enzymes that transfer hydrogen to oxygen, producing hydrogen peroxide ($H_2O_2$), which is subsequently broken down into water.

Vacuole

A large membrane-bound organelle found in plant and fungal cells (and some protists) that functions in cellular storage, waste disposal, ion balance, and maintaining hydrostatic turgor pressure.

Cilia / Cilium

Short, numerous hair-like eukaryotic projections with a "$9 + 2$" microtubule core that beat rhythmically to move fluid across cell surfaces or propel single cells.

Flagella

Long, whip-like cellular appendages responsible for locomotion, differing structurally between prokaryotes (rotary motors of flagellin) and eukaryotes (membrane-bound "$9 + 2$" microtubule axonemes).

Plasma Membrane

The selectively permeable phospholipid bilayer embedded with proteins that encloses the entire cell, regulating molecular transit and separating the intracellular cytoplasm from the extracellular environment.

Cell Membrane

The biological membrane that surrounds the cytoplasm of all cells, acting as a dynamic barrier with selective permeability that maintains cellular homeostasis.

Light Compound Microscope

An optical instrument that uses visible light and a two-lens system (ocular and objective lenses) to magnify small biological specimens mounted on glass slides.

Ocular Lens

The lens at the top of a compound microscope through which the viewer looks, which typically provides a fixed magnification of $10\times$.

Objective Lenses

The set of primary optical lenses mounted on a rotating nosepiece positioned near the specimen, typically providing magnifications of $4\times$, $10\times$, $40\times$, and $100\times$.

Microscope Stage

The flat, horizontal platform of a microscope where the glass specimen slide is placed and held in position by stage clips for examination.

Coarse Focus Knob

The control knob on a microscope that moves the stage vertically in large increments to bring the specimen into initial approximate focus under low-power objectives.

Fine Focus Knob

The control knob that moves the microscope stage in minute increments to sharpen and precisely resolve specimen details, particularly under high-power objectives.

Condenser

A lens system located beneath the stage of a compound microscope that focuses and concentrates light from the illuminator onto the specimen.

Iris Diaphragm

An adjustable aperture mechanism on the condenser that regulates the diameter of the light cone passing through the specimen to adjust image contrast and resolution.

Total Magnification

The overall visual enlargement of a specimen under a microscope, calculated as the product of the ocular lens magnification and the active objective lens magnification ($\text{Total Magnification} = \text{Ocular Lens Magnification} \times \text{Objective Lens Magnification}$).

Magnification Range

The complete operational spectrum of total magnifications achievable with a microscope, typically from $40\times$ (using a $4\times$ objective) to $1000\times$ (using a $100\times$ objective) on a standard compound microscope.

Maximum Magnification

The highest enlargement achievable with a standard laboratory compound light microscope, equal to $1000\times$ using a $100\times$ oil immersion objective with a $10\times$ eyepiece.

Microbe Morphological Differentiation

The practice of identifying and distinguishing between prokaryotic and eukaryotic microbes based on structural characteristics, such as cell size, shape, and the presence or absence of an observable nucleus.

Metric Conversions in Biology

The mathematical conversion between metric units of length ($\text{powers of } 10$) used to quantify and compare the microscopic sizes of cells and organelles (e.g., $1\,\text{mm} = 1000\,\mu\text{m}$ and $1\,\mu\text{m} = 1000\,\text{nm}$).

Micrometer ($\mu\text{m}$)

A standard metric unit of length equal to $10^{-6}\,\text{m}$ (one-millionth of a meter), commonly used to express the dimensions of cells (prokaryotes at $\approx 1\text{ to }5\,\mu\text{m}$; eukaryotes at $\approx 10\text{ to }100\,\mu\text{m}$).

Nanometer ($\text{nm}$)

A metric unit of length equal to $10^{-9}\,\text{m}$ (one-billionth of a meter), standardly used to express the dimensions of macromolecular complexes, viruses, ribosomes ($\approx 25\,\text{nm}$), and membrane thicknesses ($\approx 7\text{ to }10\,\text{nm}$).

Popular Literature

Non-peer-reviewed written media (such as news outlets and general magazines) written by journalists for the general public, typically presenting second-hand overviews of scientific topics without primary citations.

Scholarly Literature

Academic and scientific publications written by researchers and experts for an academic audience, characterized by rigorous methodology, comprehensive citations, and formal peer review.

Primary Sources

Original, peer-reviewed scientific journal articles written by the researchers who conducted the study, presenting novel empirical data, detailed methodology, and original results.

Secondary Sources

Scholarly publications (such as review articles and meta-analyses) that summarize, analyze, and synthesize previously published primary research literature.

Tertiary Sources

Reference publications (such as encyclopedias, dictionaries, and textbooks) that compile, index, and summarize information from primary and secondary sources to provide broad overviews.