Cell: The Unit of Life - Vocabulary Flashcards

Comprehensive vocabulary flashcards covering key terms, cell organelles, historical discoveries, and structural components from Chapter 8 (Cell: The Unit of Life).

Reductionist Biology

A physico-chemical approach to study and understand living organisms by applying concepts and techniques of physics and chemistry to describe biological processes in molecular terms.

Ramachandran Plot

A plot devised by G.N. Ramachandran used for the analysis of the allowed conformations of proteins.

Cell Theory

A fundamental theory formulated by Matthias Schleiden and Theodore Schwann, and later modified by Rudolf Virchow, stating that all living organisms are composed of cells and products of cells, and all cells arise from pre-existing cells.

Omnis cellula-e cellula

A concept first explained by Rudolf Virchow (1855) meaning that cells divide and new cells are formed from pre-existing cells.

Unicellular Organisms

Organisms composed of a single cell that are capable of independent existence and performing the essential functions of life.

Multicellular Organisms

Organisms composed of many cells working together to carry out life processes.

Eukaryotic Cells

Cells that possess membrane-bound nuclei as well as other membrane-bound organelles.

Prokaryotic Cells

Cells that lack a membrane-bound nucleus and membrane-bound organelles.

Cytoplasm

A semi-fluid matrix that occupies the volume of both prokaryotic and eukaryotic cells, serving as the main arena of cellular activities.

Mycoplasmas

The smallest known living cells, measuring only $0.3\,\mu m$ in length, which lack a cell wall.

Plasmids

Small, circular DNA molecules present in many bacteria outside the genomic DNA that confer unique phenotypic characters such as antibiotic resistance.

Mesosome

A specialized differentiated form of cell membrane characteristic of prokaryotes, formed by infoldings of the plasma membrane into the cell in the form of vesicles, tubules, and lamellae.

Glycocalyx

The outermost layer of the bacterial cell envelope, which can exist either as a loose sheath called a slime layer or as a thick and tough layer called a capsule.

Gram Stain

A staining procedure developed by Gram used to classify bacteria into Gram positive (those that take up the stain) and Gram negative (those that do not).

Flagellum (Bacterial)

A thin filamentous extension from the bacterial cell wall responsible for motility, composed of three parts: filament, hook, and basal body.

Pili

Elongated tubular surface structures on bacteria made of a special protein that do not play a role in motility.

Fimbriae

Small bristle-like fibres sprouting out of the bacterial cell that help attach the bacteria to rocks in streams and to host tissues.

Polysome (Polyribosome)

A structure formed when several ribosomes attach to a single mRNA molecule to translate it into proteins.

Inclusion Bodies

Non-membrane-bound reserve materials stored free in the cytoplasm of prokaryotic cells, such as phosphate granules, cyanophycean granules, and glycogen granules.

Fluid Mosaic Model

A model of cell membrane structure proposed by Singer and Nicolson (1972) stating that the quasi-fluid nature of lipid enables lateral movement of proteins within the overall bilayer.

Passive Transport

The movement of neutral solutes or water across the cell membrane along a concentration gradient without any requirement of energy.

Osmosis

The movement of water across a selectively permeable membrane by diffusion from a region of higher concentration to lower concentration.

Active Transport

An energy-dependent process in which ions or molecules are transported across a membrane against their concentration gradient using ATP (e.g., $Na^+/K^+$ Pump).

Middle Lamella

A layer consisting mainly of calcium pectate that holds or glues neighbouring plant cells together.

Plasmodesmata

Cytoplasmic channels that traverse the cell wall and middle lamella, connecting the cytoplasm of neighbouring plant cells.

Endomembrane System

A coordinated group of eukaryotic membrane-bound organelles that includes the endoplasmic reticulum, Golgi complex, lysosomes, and vacuoles.

Rough Endoplasmic Reticulum (RER)

Endoplasmic reticulum bearing ribosomes on its outer surface, actively involved in protein synthesis and secretion.

Smooth Endoplasmic Reticulum (SER)

Endoplasmic reticulum lacking ribosomes, serving as the major site for the synthesis of lipids and steroidal hormones.

Cisternae

Flat, disc-shaped sacs of $0.5\,\mu m\text{ to }1.0\,\mu m$ diameter stacked parallel to each other in the Golgi apparatus.

Lysosomes

Membrane-bound vesicular structures formed by the Golgi apparatus that are rich in hydrolytic enzymes (lipases, proteases, carbohydrases) active at acidic pH.

Tonoplast

The single membrane bounding the vacuole in plant cells that facilitates the transport of ions and other materials against concentration gradients.

Cristae

Infoldings of the inner mitochondrial membrane extending into the matrix that increase the surface area for enzymatic activities.

Amyloplasts

A type of leucoplast that stores carbohydrates (starch), such as in potato tubers.

Elaioplasts

A type of leucoplast that stores oils and fats.

Aleuroplasts

A type of leucoplast that stores proteins.

Thylakoids

Organized flattened membranous sacs arranged in stacks (grana) or singly within the stroma of chloroplasts that contain chlorophyll pigments.

Svedberg's Unit ($S$)

A unit used in measuring ribosomes that stands for the sedimentation coefficient, serving as an indirect measure of density and size.

Cytoskeleton

An elaborate network of filamentous proteinaceous structures (microtubules, microfilaments, intermediate filaments) in the cytoplasm involved in mechanical support, motility, and maintenance of cell shape.

Axoneme

The core of eukaryotic cilia and flagella containing a $9+2$ array of radially arranged peripheral microtubule doublets and a central pair of microtubules.

Centrosome

An organelle usually containing two cylindrical structures called centrioles arranged perpendicular to each other and surrounded by amorphous pericentriolar materials.

Chromatin

Highly extended and elaborate nucleoprotein fibres present in the interphase nucleus (named by Flemming) containing DNA, histones, non-histone proteins, and RNA.

Kinetochores

Disc-shaped structures located on the sides of the primary constriction (centromere) of a chromosome.

Metacentric Chromosome

A chromosome possessing a middle centromere that forms two equal arms.

Sub-metacentric Chromosome

A chromosome with a centromere situated slightly away from the middle, resulting in one shorter arm and one longer arm.

Acrocentric Chromosome

A chromosome with a centromere situated close to its end, forming one extremely short and one very long arm.

Telocentric Chromosome

A chromosome possessing a terminal centromere.

Satellite

A small fragment of a chromosome formed by the presence of a non-staining secondary constriction at a constant location.

Microbodies

Membrane-bound minute vesicles containing various enzymes present in both plant and animal cells.