Cell Biology, Organelles, Microscopy, and Membrane Transport

Comprehensive vocabulary flashcards covering cell theory, light and electron microscopy, prokaryotic and eukaryotic structures, organelle functions, the endomembrane system, and cellular transport mechanisms (diffusion and osmosis).

Cell Theory

The foundational biological principle stating that: 1. All living things are composed of one or more cells; 2. The cell is the basic unit of structure and organization/function in living things; and 3. All cells arise from preexisting cells.

Robert Hooke

The scientist who first observed and named cells while examining cork under a microscope.

Anton van Leeuwenhoek

The scientist who was the first to observe living cells and microorganisms.

Matthias Schleiden

The botanist who concluded that all plants are composed of cells.

Theodor Schwann

The zoologist who concluded that all animals are composed of cells.

Rudolf Virchow

The scientist who stated that all cells come from preexisting cells.

Resolution

The minimum distance between two objects before they are seen as one object; the ability of a microscope to distinguish two close points as separate.

Compound Light Microscope (CLM)

A light microscope that focuses visible light through glass lenses to examine thinly sliced sections or living specimens via an eyepiece; provides lower magnification and resolution than electron microscopes.

Dissecting (Scanning) Microscope

A light microscope used to study entire organisms in 3D at low magnification ($30\times$).

Transmission Electron Microscope (TEM)

An electron microscope that uses electromagnets to pass an electron beam through a thinly sliced, heavy metal-stained specimen, displaying detailed 2D images of internal cellular structures on a screen; specimens must be dead.

Scanning Electron Microscope (SEM)

An electron microscope that scans the surface of a specimen with an electron beam to generate detailed, 3D-looking images of exterior features; specimens must be dead.

Coarse Adjustment Knob

The control on a light microscope used under low power to make large vertical stage adjustments and bring the specimen into general focus.

Fine Adjustment Knob

The control on a light microscope used for precise focusing and sharpening the image under medium and high power objective lenses.

Surface Area-to-Volume Ratio ($SA:\text{Vol}$)

The physical relationship that constrains cell size; as a cell increases in size, its volume expands faster than its surface area, decreasing the ratio and reducing the efficiency of nutrient intake and waste expulsion.

Prokaryote

A simple, single-compartment cell (analogous to a one-room efficiency apartment) lacking a nucleus and membrane-bound organelles, characterized by free-floating circular DNA (pro = before, karyon = nucleus/kernel).

Eukaryote

A large, complex cell (analogous to a multi-room mansion) containing a membrane-bound nucleus and specialized membrane-bound organelles with extensive compartmentalization (eu = true, karyon = nucleus/kernel).

Coccus

A spherical- or ball-shaped bacterial cell.

Bacillus

A rod-shaped bacterial cell.

Spirillum

A spiral- or wavy-shaped bacterial cell.

Prokaryotic Cell Envelope

The three-layered protective boundary of a bacterial cell, ordered from innermost to outermost: 1. Plasma membrane, 2. Cell wall, and 3. Capsule.

Nucleoid

The open, non-membrane-enclosed region inside a prokaryotic cell where the circular bacterial chromosome resides.

Plasmid DNA

Small, circular pieces of extrachromosomal DNA in prokaryotes that replicate independently and carry accessory genetic information, such as antibiotic resistance genes.

Sex Pili

Hollow external appendages that connect bacterial cells to transfer plasmid DNA from one bacterium to another.

Cell Capsule

A sticky, gel-like coating external to the bacterial cell wall that protects the bacterium and facilitates attachment to surfaces.

Endosymbiotic Hypothesis

The theory that mitochondria and chloroplasts evolved from independent prokaryotes engulfed by ancestral eukaryotic cells, supported by their double membranes, independent circular DNA, bacterial-like ribosomes, and self-replication via binary fission.

Plasma Membrane

A flexible phospholipid bilayer embedded with proteins and cholesterol that forms the cell's outer boundary, selectively regulating the entry and exit of substances; analogous to a factory security fence.

Nucleus

The double-membrane-bound eukaryotic organelle containing nuclear pores that encloses and protects genetic material (DNA) and controls cellular activities; analogous to the factory control room.

Nucleolus

A dense non-membrane-bound structure located inside the nucleus where ribosomal RNA and proteins are assembled into ribosome subunits.

Ribosome

A cellular structure consisting of two subunits that reads mRNA transcripts and joins amino acids together to build proteins; free in cytoplasm or bound to rough ER; analogous to factory assembly workers.

Rough Endoplasmic Reticulum (Rough ER)

A network of folded membranous cisternae studded with ribosomes that folds, processes, and packages synthesized proteins into transport vesicles; functions as part of the cellular production line.

Smooth Endoplasmic Reticulum (Smooth ER)

A tubular, ribbon-like membranous network continuous with the rough ER that synthesizes lipids (including steroid hormones) and detoxifies drugs and harmful chemicals.

Golgi Apparatus

A series of flattened membranous sacs (cisternae) possessing cis and trans faces that receives, modifies, sorts, and packages proteins and lipids into vesicles; analogous to a factory shipping department.

Transport Vesicles

Small, spherical membrane-bound sacs that ferry proteins, lipids, and other cellular packages between organelles and to the cell surface; analogous to items to be shipped in a factory.

Endomembrane System

The coordinated eukaryotic pathway that manufactures and distributes biological molecules: DNA in the nucleus directs mRNA synthesis, ribosomes on rough ER build proteins, vesicles transfer them to the Golgi for sorting, and final vesicles deliver them to the membrane or outside.

Mitochondrion

A double-membrane eukaryotic organelle featuring folded inner membranes (cristae) and a fluid matrix that produces ATP through cellular respiration; analogous to the power generator of a factory.

Chloroplast

A double-membrane plant organelle containing stacked thylakoids (grana), stroma fluid, and chlorophyll that captures solar energy to synthesize sugars via photosynthesis.

Lysosome

A membrane-bound organelle containing digestive enzymes that breaks down cellular wastes, foreign materials, and worn-out cell parts; analogous to factory custodians.

Peroxisome

A metabolic organelle enclosed by a lipid bilayer containing enzymes that break down fatty acids and neutralize toxins by converting harmful hydrogen peroxide into water and oxygen.

Central Vacuole

A large plant organelle bounded by the tonoplast that stores water, nutrients, and waste products while exerting turgor pressure against the cell wall; analogous to a storage warehouse.

Centrioles / Centrosome

Paired cylindrical structures composed of microtubule triplets located near the nucleus in animal cells that organize microtubules and assist in cell division.

Plasmodesmata

Narrow membrane-lined channels passing through plant cell walls that link the cytoplasm of neighboring cells and facilitate direct intercellular transport and signaling.

Cytoskeleton (Microtubules)

Hollow structural protein cylinders made of tubulin dimers that maintain cell shape and serve as directional tracks for motor proteins such as kinesin and dynein.

Cilia

Short, hair-like external eukaryotic appendages that beat in coordinated back-and-forth waves to propel the cell or move extracellular fluids and particles.

Diffusion

The net passive movement of solute particles across a membrane from an area of higher concentration to an area of lower concentration down a concentration gradient.

Osmosis

The net movement of water molecules across a selectively permeable membrane from an area of high water concentration (dilute solution) to an area of low water concentration (concentrated solution).

Hypertonic Solution

An external environment having a higher solute concentration (and lower water concentration) relative to the intracellular fluid, driving net water outflow from the cell.

Hypotonic Solution

An external environment having a lower solute concentration (and higher water concentration) relative to the intracellular fluid, driving net water influx into the cell.

Isotonic Solution

An external environment possessing an equal solute and water concentration relative to the inside of the cell, resulting in no net movement of water across the membrane.

Crenation

The shriveling and shrinking of an animal cell caused by excessive net water loss when exposed to a hypertonic extracellular solution.

Lysis

The osmotic swelling and bursting of an animal cell resulting from excessive net water influx when exposed to a hypotonic extracellular environment.

Plasmolysis

The process where a plant cell loses water to a hypertonic solution, causing its protoplast and plasma membrane to pull away and shrink from the rigid cell wall.

Turgid

The swollen, pressurized, firm state of a plant cell whose internal vacuole fills with water in a hypotonic medium, with lysis prevented by the rigid cell wall.

Contractile Vacuole

A specialized osmoregulatory organelle in freshwater unicellular protists (such as Paramecium) that collects and expels excess water entering the organism from its hypotonic surroundings.