Cell: The Unit of Life – Key Vocabulary

A comprehensive set of vocabulary flashcards covering major terms, structures, and concepts from the lecture on cell structure and function.

Biology

The study of living organisms, their structure, function, growth, and evolution.

Cell Theory

Principle stating that all living organisms are made of cells and all cells arise from pre-existing cells.

Reductionist Biology

Physico-chemical approach that explains life processes by analyzing molecular components in cell-free systems.

Unicellular Organism

A living entity composed of a single cell capable of independent existence and performing all life functions.

Multicellular Organism

An organism composed of many specialized cells that cooperate and divide labor.

Prokaryotic Cell

Cell lacking a membrane-bound nucleus and organelles; exemplified by bacteria and cyanobacteria.

Eukaryotic Cell

Cell possessing a true nucleus and membrane-bound organelles; found in protists, fungi, plants, and animals.

Antonie van Leeuwenhoek

Scientist who first observed and described living cells using a microscope.

Robert Brown

Botanist who discovered the cell nucleus in plant cells.

Schleiden and Schwann

Scientists who jointly formulated the original cell theory in 1838-39.

Rudolf Virchow

Pathologist who added ‘Omnis cellula e cellula’ – cells arise from pre-existing cells – to cell theory.

Plasma Membrane

Selectively permeable phospholipid bilayer enclosing the cell cytoplasm.

Cell Wall

Rigid outer layer in plants, fungi, and most prokaryotes providing shape and protection.

Glycocalyx

Outer polysaccharide coating of many bacteria, existing as a slime layer or capsule.

Gram-Positive Bacteria

Bacteria whose thick peptidoglycan cell wall retains crystal violet stain.

Gram-Negative Bacteria

Bacteria with thin peptidoglycan and outer membrane that do not retain crystal violet stain.

Mesosome

Plasma-membrane infolding in prokaryotes involved in respiration, DNA replication, and cell wall formation.

Plasmid

Small circular DNA molecule in bacteria that confers extra traits such as antibiotic resistance.

Flagellum (Bacterial)

Thin filamentous appendage providing motility; composed of filament, hook, and basal body.

Pilus

Tubular protein appendage in bacteria used for conjugation or attachment.

Fimbriae

Short bristle-like bacterial surface structures aiding in adhesion to surfaces or host tissues.

Ribosome (70S)

Prokaryotic protein-synthesizing particle composed of 50S and 30S subunits.

Polysome

Chain of ribosomes simultaneously translating the same mRNA molecule.

Inclusion Bodies

Non-membranous storage granules in prokaryotes, e.g., phosphate, glycogen, or gas vacuoles.

Endomembrane System

Coordinated set of organelles—ER, Golgi, lysosomes, vacuoles—responsible for intracellular trafficking.

Endoplasmic Reticulum (ER)

Network of membrane tubules dividing cytoplasm into luminal and extra-luminal compartments.

Rough ER (RER)

ER studded with ribosomes; site of protein synthesis and export.

Smooth ER (SER)

ER lacking ribosomes; synthesizes lipids and steroid hormones.

Golgi Apparatus

Stack of cisternae that modifies, sorts, and packages proteins and lipids for transport.

Cis Face (Golgi)

Convex ‘receiving’ side of the Golgi apparatus that accepts vesicles from ER.

Trans Face (Golgi)

Concave ‘maturing’ side of the Golgi that dispatches processed vesicles.

Lysosome

Single-membrane vesicle rich in acidic hydrolase enzymes for intracellular digestion.

Vacuole

Membrane-bound (tonoplast) compartment in cytoplasm; stores water, ions, and wastes; large in plants.

Tonoplast

Selectively permeable membrane surrounding a plant cell vacuole.

Mitochondrion

Double-membrane organelle with cristae; site of aerobic respiration and ATP production.

Crista

Inner-membrane infolding of mitochondrion increasing surface area for oxidative enzymes.

Matrix (Mitochondrial)

Internal fluid containing enzymes, circular DNA, RNA, and 70S ribosomes.

Plastid

Plant cell organelle containing pigments or storage products; includes chloroplasts, chromoplasts, leucoplasts.

Chloroplast

Green plastid with thylakoids and stroma; performs photosynthesis.

Granum

Stack of thylakoids within a chloroplast where light-dependent reactions occur.

Stroma

Chloroplast matrix housing enzymes for carbon fixation, DNA, and ribosomes.

Leucoplast

Colourless plastid specialized for storage of starch (amyloplast), oils (elaioplast), or proteins (aleuroplast).

Fluid Mosaic Model

Singer and Nicolson description of membranes as fluid lipid bilayers with embedded proteins.

Integral Protein

Membrane protein embedded within or spanning the lipid bilayer.

Peripheral Protein

Protein loosely attached to membrane surface.

Passive Transport

Energy-independent movement of molecules down their concentration gradient across a membrane.

Osmosis

Diffusion of water through a selectively permeable membrane from higher to lower water potential.

Active Transport

ATP-dependent transport of molecules against their concentration gradient, e.g., Na⁺/K⁺ pump.

Plasmodesma

Cytoplasmic channel traversing plant cell walls for intercellular communication.

Cytoskeleton

Network of microtubules, microfilaments, and intermediate filaments providing support and motility.

Cilium

Short hair-like projection with 9+2 microtubule axoneme; moves cell or fluid over surface.

Flagellum (Eukaryotic)

Long whip-like extension with 9+2 axoneme driving cell movement.

Basal Body

Centriole-derived structure anchoring cilia and flagella.

Centrosome

Animal-cell organelle containing a pair of perpendicular centrioles; organizes spindle fibres.

Centriole

Cylindrical microtubule triplet structure forming basal bodies and spindle apparatus.

Nucleus

Double-membrane organelle housing DNA, nucleolus, and chromatin; controls cellular activities.

Nuclear Pore

Opening in nuclear envelope regulating bidirectional traffic of RNAs and proteins.

Chromatin

DNA-protein complex appearing as extended fibres during interphase; condenses into chromosomes in mitosis.

Centromere

Primary chromosome constriction where sister chromatids attach and kinetochore forms.

Metacentric Chromosome

Chromosome with centrally located centromere and equal arms.

Acrocentric Chromosome

Chromosome with centromere near one end, producing one very long and one very short arm.

Microbody

Small single-membrane vesicle (e.g., peroxisome) containing specialized enzymes for metabolic reactions.