Unit 3 – Cell Structure & Functions Vocabulary

Vocabulary flashcards summarizing key terms and definitions from Unit 3, Chapter 8 lecture notes on the cell as the unit of life.

Cell Theory

Biological principle stating that all organisms are composed of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells (Schleiden, Schwann, Virchow).

Prokaryotic Cell

Small, rapidly multiplying cell lacking membrane-bound nucleus and organelles; examples include bacteria, blue-green algae, mycoplasma, PPLO.

Eukaryotic Cell

Cell type possessing a true, membrane-bound nucleus and membrane-bound organelles.

Bacillus

Rod-shaped bacterium.

Coccus

Spherical bacterium.

Vibrio

Comma-shaped bacterium.

Spirillum

Spiral-shaped bacterium.

Cell Envelope

Triple-layered protective covering of a prokaryotic cell consisting of glycocalyx, cell wall, and plasma membrane.

Glycocalyx

Outermost viscous layer of certain bacteria; may appear as loose slime layer or tough capsule.

Peptidoglycan

Modified sugar–peptide polymer forming the rigid framework of bacterial cell walls.

Gram-Positive Bacteria

Bacteria retaining crystal violet stain after alcohol wash due to thick peptidoglycan layer.

Gram-Negative Bacteria

Bacteria that lose crystal violet stain after alcohol wash; possess thin peptidoglycan and outer membrane.

Mesosome

Plasma-membrane infolding in prokaryotes associated with respiration and other metabolic activities.

Ribosome (70S)

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

Polysome

Chain of several ribosomes bound to a single mRNA molecule.

Inclusion Body

Reserve material granule in prokaryotes, e.g., phosphate, glycogen, cyanophycean granules.

Plasmid

Small, circular, extra-chromosomal DNA molecule in bacteria.

Nucleoid

Irregularly shaped region in prokaryotes where the chromosome (DNA) is located.

Bacterial Flagellum

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

Pilus / Fimbria

Short hair-like protein projection aiding bacterial attachment to surfaces or tissues.

Fluid Mosaic Model

Singer & Nicolson (1972) description of dynamic lipid bilayer with embedded and peripheral proteins.

Passive Transport

Membrane movement of substances down their concentration gradient without energy expenditure.

Active Transport

Energy-requiring movement of molecules across membranes against a concentration gradient via carrier proteins.

Middle Lamella

Calcium pectate-rich layer cementing adjacent plant cell walls.

Primary Cell Wall

Elastic first-formed cell wall layer in young, growing plant cells.

Secondary Cell Wall

Rigid inner wall layer deposited after cell growth ceases; may contain pits.

Plasmodesma

Cytoplasmic strand linking adjacent plant cells through cell wall pores.

Endoplasmic Reticulum (ER)

Continuous membranous network connected to nuclear envelope; divides intracellular space into lumenal and extra-lumenal compartments.

Rough ER (RER)

ER with ribosomes attached; site of protein synthesis and secretion.

Smooth ER (SER)

Ribosome-free ER; major site of lipid and steroid hormone synthesis.

Golgi Apparatus

Stack of flattened cisternae (cis and trans faces) responsible for modification, packaging, and secretion of materials.

Lysosome

Single-membrane vesicle rich in hydrolytic enzymes; functions in intracellular digestion at acidic pH.

Vacuole

Large membrane-bound sac in plant cells containing cell sap; bounded by tonoplast.

Tonoplast

Semi-permeable membrane surrounding a vacuole, regulating its contents.

Mitochondrion

Double-membrane, ATP-producing ‘powerhouse’ organelle; contains cristae and matrix with circular DNA and 70S ribosomes.

Crista

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

Oxysome (F₁F₀ particle)

Peg-like ATP synthase complex on mitochondrial cristae involved in ATP formation and proton pumping.

Plastid

Double-membrane, semi-autonomous plant organelle with its own DNA; includes chloroplasts, chromoplasts, leucoplasts.

Leucoplast

Colourless plastid specialized for storage (amyloplast—starch, elaioplast—lipids, aleuroplast—proteins).

Chromoplast

Coloured plastid containing carotenoid pigments (yellow to red).

Chloroplast

Green plastid containing chlorophyll; site of photosynthesis.

Granum

Stack of thylakoids within a chloroplast.

Thylakoid

Flattened membranous sac in chloroplast where light reactions occur.

Stroma

Protein-rich fluid matrix of chloroplast housing enzymes for dark reactions, DNA, and ribosomes.

Ribosome (80S)

Eukaryotic cytoplasmic ribosome consisting of 60S and 40S subunits; site of protein synthesis.

Nuclear Envelope

Double membrane enclosing nucleus, perforated by nuclear pores and continuous with RER.

Nucleoplasm

Gel-like matrix inside nucleus containing chromatin and nucleolus.

Chromatin

DNA-protein complex forming chromosomes; exists as euchromatin (light, active) and heterochromatin (dark, inactive).

Nucleolus

Dense, membrane-less nuclear region associated with NOR; site of rRNA synthesis and ribosome assembly.

Centromere

Primary constriction of a chromosome where sister chromatids are joined and kinetochores form.

Kinetochore

Protein disc on each side of centromere that attaches chromosome to spindle fibres.

Metacentric Chromosome

Chromosome with centromere in the middle, producing equal arms.

Submetacentric Chromosome

Chromosome with centromere slightly off centre, yielding unequal arms.

Acrocentric Chromosome

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

Telocentric Chromosome

Chromosome with centromere at terminal end; only one arm visible.

Cytoskeleton

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

Microtubule

Tubulin-based hollow filament involved in cell shape, organelle transport, and spindle formation.

Microfilament

Actin-based thin filament supporting cell shape and enabling cytoplasmic streaming and muscle contraction.

Intermediate Filament

Fibrous protein filament (e.g., keratin) providing tensile strength to cells.

Cilium

Short, numerous hair-like projection (9+2 axoneme) generating fluid currents or cell movement.

Flagellum (Eukaryotic)

Long, usually solitary whip-like appendage (9+2 axoneme) propelling cells.

Axoneme

Core of cilium/flagellum with 9 peripheral doublet microtubules and 2 central singlets (9+2).

Basal Body

Centriole-derived organelle that nucleates cilium or flagellum.

Centriole

Cylindrical structure with nine triplet microtubules arranged around a hub and spokes; forms centrosome components.

Centrosome

Microtubule-organizing centre in animal cells, usually containing a pair of centrioles and pericentriolar material.

Pericentriolar Material

Amorphous protein matrix surrounding centrioles that nucleates microtubules.

Spindle Apparatus

Microtubule structure assembled from centrosomes to segregate chromosomes during cell division.