Cell: The Unit of Life (NCERT) - Vocabulary Flashcards

Key vocabulary terms and concise definitions covering prokaryotic cell structure, endomembrane system, organelles, plastids, nucleus, and plant cell wall components from the NCERT chapter on the Cell: The Unit of Life.

Bacterial cell envelope

Outer layers around a bacterium: glycocalyx (capsule/slime), a peptidoglycan cell wall, and the plasma membrane; Gram-negative bacteria may have an outer membrane.

Glycocalyx

An outer coating of polysaccharides (and sometimes proteins) that surrounds some bacteria; can be a capsule or slime layer and aids in protection and adhesion.

Capsule

A well-defined, thick layer of polysaccharide outside the cell wall that protects bacteria and helps in adherence and immune evasion.

Slime layer

A loosely attached, unorganized glycocalyx that aids adhesion and protects the cell but is not as well defined as a capsule.

Cell wall (bacteria)

Rigid layer primarily made of peptidoglycan; gives shape and protection; thicker in Gram-positive bacteria, thinner with an outer membrane in Gram-negative bacteria.

Peptidoglycan

A mesh-like polymer of sugars and peptides (NAG-NAM) that provides rigidity and strength to the bacterial cell wall.

Outer membrane

An extra lipopolysaccharide-containing membrane in many Gram-negative bacteria; provides barrier function and selective permeability.

Plasma membrane (bacteria)

Phospholipid bilayer enclosing cytoplasm; site of respiration in many bacteria; embedded proteins; fluid mosaic model.

Cytoplasm

The internal content of the cell excluding the nucleus; includes cytosol, ribosomes, and inclusions.

Nucleoid

Region in the bacterial cytoplasm where the circular chromosome resides; not a membrane-bound nucleus.

Circular DNA

The single, circular bacterial chromosome found in the nucleoid.

Plasmid

Small, circular, extra-chromosomal DNA carrying accessory genes (e.g., antibiotic resistance).

Ribosome (bacteria)

70S ribosome (composed of 30S and 50S subunits); site of protein synthesis; can form polyribosomes.

Polyribosome

Cluster of ribosomes translating a single mRNA molecule simultaneously.

Inclusion bodies

Storage bodies within the cytoplasm (e.g., glycogen, phosphate bodies, sulfur granules, lipid droplets).

Pili (fimbriae)

Hair-like appendages on bacterial surface used for adhesion to surfaces and, in some cases, DNA transfer (conjugation).

Flagellum (bacteria)

Long appendage used for locomotion; composed of filament, hook, and basal body; rotates to move the cell.

Basal body

The motor-portion of the bacterial flagellum embedded in the cell envelope; drives flagellar rotation.

Endomembrane system

Network of membranes in eukaryotic cells including ER, Golgi apparatus, lysosomes, and vesicles that synthesize, modify, and transport proteins and lipids.

Rough Endoplasmic Reticulum (RER)

ER studded with ribosomes; synthesizes and processes secretory and membrane proteins.

Smooth Endoplasmic Reticulum (SER)

ER lacking ribosomes; involved in lipid synthesis and detoxification processes.

Golgi apparatus

Organelle that modifies, sorts, and packages proteins and lipids from the ER; cis face receives, trans face ships.

Cis face

The side of the Golgi complex that receives transport vesicles from the ER.

Trans face

The side of the Golgi complex where vesicles depart to their destinations.

Vesicles

Small membrane-bound sacs that transport materials between organelles and to the plasma membrane.

Lysosome

Membrane-bound organelle with hydrolytic enzymes for digestion; acidic interior; involved in macromolecule turnover.

Mitochondrion

Double-membrane-bound organelle; site of cellular respiration; contains cristae (inner membrane folds) and matrix; has its own circular DNA and 70S ribosomes.

Cristae

Infoldings of the inner mitochondrial membrane that increase surface area for the electron transport chain.

Matrix

Gel-like interior of the mitochondrion housing enzymes for the TCA cycle.

Endosymbiotic theory

Idea that mitochondria and plastids originated as free-living bacteria that were taken inside a eukaryotic host cell and became organelles.

Plastids

A class of plant organelles with double membranes; includes chloroplasts, chromoplasts, and leucoplasts.

Chloroplast

Plastid responsible for photosynthesis; contains chlorophyll; has double membrane, thylakoids, grana, and stroma; contains 70S ribosomes and circular DNA.

Thylakoid

Flattened membrane-bound sacs inside chloroplasts where light-dependent reactions occur.

Grana

Stacks of thylakoid membranes within chloroplasts.

Stroma

Fluid surrounding the thylakoids inside chloroplasts; site of the Calvin cycle.

Leucoplast

Colored, non-pigmented plastids that store nutrients; subtypes include amyloplasts (starch) and elaioplasts (lipids).

Amyloplast

Leucoplast that stores starch.

Elaioplast

Leucoplast that stores lipids (oils).

Chromoplast

Pigment-containing plastids (carotenoids) giving red/orange/yellow colors to fruits and flowers.

Plasmodesmata

Cytoplasmic channels through plant cell walls that connect adjacent plant cells and enable transport and communication.

Plant cell wall

Rigid cellulose-based wall; primary wall in growing cells, secondary wall inside the primary in some cells; middle lamella cements adjacent cells.

Middle lamella

A pectin-rich layer rich in calcium that cements neighboring plant cell walls together.

Primary cell wall

Flexible cell wall formed in growing plant cells.

Secondary cell wall

Rigid layer deposited inside the primary wall in some cells; provides strength; not present in all cells.

Cytoskeleton

Network of protein filaments (microfilaments, intermediate filaments, microtubules) that supports cell shape, movement, and organization.

Microfilaments

Thin actin filaments involved in cell movement and shape changes.

Microtubules

Hollow tubules of tubulin that organize cell shape, organelle movement, and spindle formation during division.

Intermediate filaments

Rope-like filaments providing mechanical strength and structural support.

Centriole

Cylindrical structure within the centrosome of animal cells; composed of nine triplets of microtubules; organizes spindle apparatus during mitosis and forms basal bodies for cilia/flagella.

Centrosome

Microtubule-organizing center in animal cells; contains a pair of centrioles and pericentriolar material; organizes spindle fibers.

Pericentriolar material

Protein-rich matrix surrounding centrioles that nucleates and anchors microtubules.

Nucleus

Membrane-bound organelle in eukaryotes housing genetic material; contains a double membrane envelope, nucleolus, and chromatin.

Nuclear envelope

Double membrane surrounding the nucleus; contains nuclear pores for exchange with cytoplasm.

Nuclear pores

Protein channels in the nuclear envelope that regulate transport between nucleus and cytoplasm.

Nucleolus

Dense region within the nucleus where ribosomal RNA (rRNA) synthesis and ribosome assembly begin.

Chromatin

DNA associated with proteins (histones) that condenses to form chromosomes during cell division.

Heterochromatin

Tightly packed, transcriptionally inactive regions of DNA.

Euchromatin

Loosely packed, transcriptionally active regions of DNA.

Satellite chromosomes

Small chromosomal segments rich in repetitive DNA that constitute part of the nucleolar organizing regions.

Nucleolar organizer region (NOR)

Chromosomal regions containing clusters of ribosomal RNA genes; associated with nucleolus formation.