Chapter 2: The Cellular Level of Organization

Vocabulary practice flashcards covering cell structure, transport, organelles, the cytoskeleton, cell division, and stem cells based on Chapter 2 lecture notes.

Cytology

The study of cell structure and function.

Cell Theory

The scientific concept stating that all living organisms are made of cells, cells are the basic structural and functional unit of life, cells arise from preexisting cells, all cells share the same basic chemical composition, organismal functions arise from cellular activity, and metabolism occurs within cells.

Metabolism

Internal chemical change within an organism involving taking in molecules, chemically altering them for energy or structure, controlling physiology, and excreting waste products.

Homeostasis

The capability of an organism to maintain a stable internal environment.

Development

A change in form or function over time that involves growth and differentiation.

Light Microscope (LM)

An optical instrument that uses visible light passing through thin tissue sections to produce magnified images.

Resolution

The ability of a microscope to reveal detail in an image.

Transmission Electron Microscope (TEM)

A high-resolution microscope that uses an electron beam to visualize ultrathin slices of a specimen.

Scanning Electron Microscope (SEM)

A high-resolution microscope that uses an electron beam to visualize the surface features of a specimen.

Squamous

A cell shape that is thin and flat.

Cuboidal

A cell shape that is approximately equal in height and width.

Columnar

A cell shape that is distinctly taller than it is wide.

Polygonal

A cell shape having irregularly angular shapes with four or more sides.

Stellate

A cell shape characterized by multiple pointed processes, giving it a starlike appearance.

Spheroidal

A cell shape that ranges from round to oval.

Discoidal

A cell shape that is disc-shaped.

Fusiform

A spindle-shaped cell structure that is elongated with a thick middle and tapered ends.

Fibrous

A cell shape that is long, slender, and threadlike.

Basal Surface

The lower surface of an epithelial cell that is anchored to deeper tissues.

Apical Surface

The upper surface of a cell that often faces an interior body cavity.

Lateral Surface

The side wall of a cell that adheres to neighboring cells.

Cytosol

The clear, viscous, water colloid fluid environment within the cell, also known as intracellular fluid (ICF).

Extracellular Fluid (ECF)

All body fluids located outside of cells, including blood plasma, lymph, cerebrospinal fluid, and interstitial fluid.

Interstitial Fluid

The extracellular fluid located specifically in the spaces between cells; also called tissue fluid.

Phospholipids

The most abundant membrane lipids ($75\%$), consisting of a 3-carbon glycerol backbone with two hydrophobic fatty acid tails and a hydrophilic phosphate head.

Cholesterol

Membrane lipids making up about $20\%$ of the plasma membrane that modulate membrane fluidity and stiffness.

Glycolipids

Lipids making up $5\%$ of the plasma membrane consisting of phospholipids with short carbohydrate chains on the extracellular face.

Transmembrane Proteins

Membrane proteins that pass completely through the phospholipid bilayer, most of which are glycoproteins.

Peripheral Proteins

Membrane proteins that do not protrude into the phospholipid bilayer but adhere to either the inner or outer face of the membrane.

Receptors

Transmembrane or surface proteins that bind chemical signals to trigger internal cellular responses.

Channel Proteins

Membrane proteins forming passages that allow water and hydrophilic solutes to cross the membrane.

Gated Channels

Channel proteins that open or close in response to specific stimuli.

Cell-Adhesion Molecules (CAMs)

Proteins that allow cells to adhere to one another and to extracellular materials.

Glycocalyx

A fuzzy sugary surface coat composed of carbohydrate moieties of glycolipids and glycoproteins that cushions, protects, and identifies cells.

Filtration

A transport process in which physical pressure forces fluid through a membrane.

Simple Diffusion

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

Osmosis

The net diffusion of water molecules through a selectively permeable membrane toward a region of higher nonpermeating solute concentration.

Aquaporins

Specialized channel proteins that facilitate the rapid passage of water through the cell membrane.

Facilitated Diffusion

Carrier-mediated transport of a solute across a membrane down its concentration gradient without energy expenditure.

Active Transport

Carrier-mediated transport that moves a solute up its concentration gradient utilizing ATP energy.

Vesicular Transport

The movement of large particles or fluid droplets across the membrane encased in bubblelike vesicles.

Pinocytosis

A form of endocytosis in which the cell pinches off vesicles containing droplets of extracellular fluid; known as 'cell drinking'.

Receptor-Mediated Endocytosis

A selective endocytosis process where specific molecules bind membrane surface receptors before the membrane pinches inward.

Phagocytosis

A form of endocytosis in which pseudopods surround and engulf large particles or microorganisms; known as 'cell eating'.

Microvilli

Short membrane extensions that increase cell surface area to maximize absorption, forming a brush border.

Cilia

Hairlike processes $7$ to $10\,\mu m$ long containing an axoneme core that function in sensory roles or move substances across epithelial surfaces.

Dynein

A motor protein responsible for the bending and movement of cilia.

Flagella

A long whiplike cell extension containing an axoneme, present in humans solely as the tail of a sperm cell.

Pseudopods

Continually changing, cytoplasm-filled extensions used in cell movement and phagocytosis.

Tight Junctions

Cellular junctions near the apical surface that interlock adjacent cells like a zipper to seal off the intercellular space.

Desmosomes

Patch-like protein structures with dense plaques that anchor cells firmly to one another to resist mechanical stress.

Hemidesmosomes

Half-desmosome structures that anchor epithelial cells to the underlying basement membrane.

Gap Junctions

Communicating junctions consisting of rings of transmembrane proteins surrounding a water-filled pore that allows small solutes and electrical signals to pass directly between cells.

Cytoskeleton

A structural network of protein microfilaments, intermediate filaments, and microtubules that supports cell structure, shape, and internal movement.

Microfilaments

Thin cytoskeletal elements ($6\,nm$ thick) composed of actin protein that form the terminal web and support microvilli.

Intermediate Filaments

Stiff cytoskeletal elements ($8\text{--}10\,nm$ in diameter) that give the cell shape, resist mechanical stress, and include keratin in skin cells.

Microtubules

Hollow cylinders ($25\,nm$ in diameter) composed of tubulin protein that radiate from the centrosome, guide organelle transport, and form cilia and flagella basal bodies.

Nucleus

The largest cellular organelle containing the cell's genetic material (chromosomes) enclosed in a double unit membrane nuclear envelope.

Chromatin

A complex of DNA and protein residing in the nucleoplasm that condenses into chromosomes during cell division.

Nucleolus

A dark-staining region within a non-dividing nucleus where ribosomal subunits are synthesized and assembled.

Rough Endoplasmic Reticulum

An interconnected system of membrane cisterns studded with ribosomes that synthesizes membrane lipids and proteins destinated for secretion or lysosomes.

Smooth Endoplasmic Reticulum

A network of membrane cisterns lacking ribosomes that synthesizes steroids and other lipids, detoxifies drugs and alcohol, and manufactures cell membranes.

Ribosomes

Small granules of RNA and protein that translate genetic code to assemble amino acids into proteins.

Golgi Complex

An organelle consisting of $4$ to $6$ flattened cisterns that receives, modifies, sorts, and packages proteins from the rough ER into vesicles.

Proteasomes

Hollow cylindrical protein complexes that degrade unwanted internal cell proteins tagged for destruction into short peptides and amino acids.

Lysosomes

Membrane-bound organelles containing digestive enzymes used for autophagy, intracellular digestion of microbes, and programmed cell death.

Autophagy

The enzymatic digestion and recycling of worn-out or surplus cellular organelles by lysosomes.

Apoptosis

Programmed cell death carried out by organelles such as lysosomes to dispose of defective or unneeded cells.

Peroxisomes

Organelles that break down fatty acids and organic molecules via oxidation, producing hydrogen peroxide that is subsequently converted to water and oxygen by catalase.

Mitochondria

Double-membrane organelles specialized for aerobic respiration and primary cellular ATP synthesis, containing internal folds called cristae.

Centrioles

Short cylindrical structures composed of microtubules arranged in pairs at the centrosome, participating in cell division and forming basal bodies.

Interphase

The portion of the cell cycle between divisions, encompassing the $G_1$, $S$, and $G_2$ phases.

First Gap (G1) Phase

The stage of interphase between cell division and DNA replication where the cell grows and performs normal physiological functions.

Synthesis (S) Phase

The stage of interphase during which the cell produces duplicates of its nuclear DNA and centrioles.

Second Gap (G2) Phase

The stage of interphase between DNA replication and mitosis where the cell synthesizes enzymes needed for cell division.

G0 Phase

A resting phase taken by cells that have temporarily or permanently departed from the cell cycle.

Mitosis

The process of somatic cell division in which one nucleus divides into two genetically identical nuclei through prophase, metaphase, anaphase, and telophase.

Prophase

The first phase of mitosis during which chromatin condenses into visible chromosomes, the nuclear envelope degenerates, and spindle fibers grow from migrating centrioles.

Metaphase

The phase of mitosis in which chromosomes line up along the cell's equatorial plane attached to spindle fibers at their kinetochores.

Anaphase

The phase of mitosis where centromeres divide and sister chromatids are pulled apart toward opposite poles of the cell.

Telophase

The final stage of mitosis where chromosomes uncoil at opposite poles, new nuclear envelopes assemble, nucleoli reappear, and spindle fibers break down.

Cytokinesis

The division of the cytoplasm into two distinct daughter cells, overlapping with late mitosis.

Developmental Plasticity

The capacity of stem cells to differentiate into one or more mature, specialized cell types.

Unipotent Stem Cells

Adult stem cells that possess the ability to develop into only one specific mature cell type.

Multipotent Stem Cells

Adult stem cells that can differentiate into multiple distinct mature cell types.

Pluripotent Stem Cells

Embryonic stem cells derived from embryos up to $150$ cells that can differentiate into any cell type in the body.