Unit 3 – Cell: Structure and Functions (Vocabulary)

Vocabulary flashcards covering essential terms from Unit 3: Cell – Structure and Functions, including cell theory, organelles, prokaryotic and eukaryotic features, and related cellular concepts.

Biology

The scientific study of living organisms.

Cell Theory

Concept stating that all living organisms are composed of cells and that all cells arise from pre-existing cells.

Reductionist Biology

Physico-chemical approach that explains life processes by analyzing cells in molecular terms.

Cell

Fundamental structural and functional unit of all living organisms.

Unicellular Organism

A living organism composed of a single cell capable of independent existence.

Multicellular Organism

An organism composed of many cells that divide labor among specialized cell types.

Anton van Leeuwenhoek

First person to observe and describe live cells using a microscope.

Robert Brown

Scientist who discovered the cell nucleus (1831).

Matthias Schleiden

Botanist who proposed that all plants are made of cells.

Theodor Schwann

Zoologist who stated that animals are made of cells; co-formulated cell theory.

Rudolf Virchow

Pathologist who added that cells arise only from pre-existing cells—“Omnis cellula e cellula.”

Prokaryote

Cell lacking a membrane-bound nucleus and organelles; e.g., bacteria.

Eukaryote

Cell with a nucleus enclosed by a membrane and numerous membrane-bound organelles.

Cytoplasm

Semi-fluid matrix inside the cell where metabolic reactions occur.

Organelle

Specialized sub-cellular structure performing a specific function.

Ribosome

Non-membranous organelle that synthesizes proteins; 70S in prokaryotes, 80S in eukaryotes.

Centrosome

Animal-cell organelle containing a pair of centrioles; organizes spindle and basal bodies.

Mycoplasma

Smallest known prokaryotic cells; lack a cell wall.

Bacteria

Prokaryotic microorganisms with shapes such as bacillus, coccus, vibrio, and spirillum.

Glycocalyx

Outermost gelatinous layer of bacterial cell envelope; may form slime layer or capsule.

Cell Wall

Rigid outer layer in plants, fungi, and most bacteria that provides shape and protection.

Plasma Membrane

Selectively permeable phospholipid bilayer forming the cell’s boundary.

Mesosome

Infolding of prokaryotic plasma membrane involved in respiration and DNA distribution.

Plasmid

Small circular DNA molecules in bacteria that confer extra traits like antibiotic resistance.

Flagellum (Prokaryotic)

Long filamentous appendage enabling bacterial motility; composed of filament, hook, basal body.

Pilus

Elongated tubular surface structure in bacteria used for conjugation or attachment.

Fimbriae

Short bristle-like bacterial appendages that help in adhesion to surfaces.

Inclusion Body

Reserve material granule (e.g., glycogen, phosphate) lying free in prokaryotic cytoplasm.

Cell Envelope

Three-layered structure of bacteria: glycocalyx, cell wall, and plasma membrane.

Gram-Positive Bacteria

Bacteria with thick peptidoglycan cell wall that retain Gram stain.

Gram-Negative Bacteria

Bacteria with thin peptidoglycan and outer membrane; do not retain Gram stain.

Fluid Mosaic Model

Singer & Nicolson description of cell membrane as a fluid lipid bilayer with floating proteins.

Passive Transport

Movement of molecules across membrane along concentration gradient without energy input.

Osmosis

Diffusion of water through a selectively permeable membrane from high to low water potential.

Active Transport

Energy-requiring movement of substances against concentration gradient (e.g., Na⁺/K⁺ pump).

Endomembrane System

Coordinated group of organelles: ER, Golgi, lysosomes, and vacuoles.

Endoplasmic Reticulum (ER)

Network of membranous tubules; divides intracellular space into luminal and cytoplasmic compartments.

Rough ER (RER)

ER with ribosomes attached; synthesizes and transports proteins.

Smooth ER (SER)

ER lacking ribosomes; synthesizes lipids and steroid hormones.

Golgi Apparatus

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

Cis Face (Golgi)

Receiving side of Golgi apparatus where ER-derived vesicles fuse.

Trans Face (Golgi)

Maturing side of Golgi apparatus where processed vesicles bud off.

Lysosome

Single-membrane vesicle rich in hydrolytic enzymes for intracellular digestion.

Vacuole

Membrane-bound cavity (tonoplast) storing water, ions, or waste; large in plant cells.

Mitochondrion

Double-membrane organelle generating ATP via aerobic respiration; “powerhouse” of cell.

Crista

Fold of inner mitochondrial membrane that increases surface area for ATP production.

Plastid

Double-membrane plant organelle containing pigments or storage materials.

Chloroplast

Green plastid with chlorophyll; site of photosynthesis.

Thylakoid

Flattened membrane sac inside chloroplast where light reactions occur.

Granum

Stack of thylakoids within a chloroplast.

Stroma

Fluid matrix of chloroplast containing enzymes, DNA, and ribosomes.

Chromoplast

Plastid containing carotenoid pigments that impart yellow, orange, or red color.

Leucoplast

Colorless plastid specialized for storage (starch, oil, or protein).

Cytoskeleton

Network of microtubules, microfilaments, and intermediate filaments providing shape and movement.

Microtubule

Hollow protein filament composed of tubulin; forms spindle, cilia, flagella scaffold.

Microfilament

Thin filament of actin involved in cell motility and shape changes.

Cilium

Short hair-like projection moving fluid or the cell in a coordinated manner.

Flagellum (Eukaryotic)

Long whip-like projection enabling cell movement; shows 9+2 microtubule arrangement.

Axoneme

Core of cilia/flagella with 9 peripheral doublets and 2 central microtubules (9+2).

Basal Body

Centriole-derived structure anchoring cilium or flagellum to the cell.

Centriole

Cylindrical structure of nine triplet microtubules; forms spindle and basal bodies.

Nucleus

Double-membrane organelle housing DNA and controlling cellular activities.

Nuclear Envelope

Double membrane surrounding nucleus; outer layer continuous with RER.

Nuclear Pore

Opening in nuclear envelope allowing selective exchange of RNA and proteins.

Nucleolus

Dense, non-membranous nuclear body where rRNA synthesis and ribosome assembly occur.

Chromatin

DNA-protein complex in interphase nucleus that condenses into chromosomes during division.

Chromosome

Compact, visible DNA-protein structure formed during cell division.

Centromere

Primary constriction of chromosome where sister chromatids are joined.

Kinetochore

Protein disc on centromere where spindle fibers attach during mitosis.

Metacentric Chromosome

Chromosome with centromere in the middle producing equal arms.

Submetacentric Chromosome

Chromosome with centromere slightly off-center creating unequal arms.

Acrocentric Chromosome

Chromosome with centromere near one end resulting in a very short arm.

Telocentric Chromosome

Chromosome with centromere at the terminal end; essentially one arm.

Microbody

Small enzyme-containing vesicle such as peroxisome present in cytoplasm.