A2.2 Cell Biology: Structure, Microscopy, and Cell Specialization

Comprehensive vocabulary flashcards covering IB Biology subtopic A2.2: cell theory, microscopy skills, technological developments, prokaryotic and eukaryotic organelles, unicellular life processes, plant/animal/fungal distinctions, and atypical cell structures.

Cell Theory

The foundational biological tenet consisting of three components: all living things are composed of cells, the cell is the basic unit of life, and cells come from preexisting cells.

Emergent Property (in Life)

A characteristic—such as life itself—that arises from the complex interactions of subcellular components at the cellular level, whereas the individual subcellular components on their own are not alive.

Inductive Reasoning (in Cell Theory)

The logical process of developing a general conclusion from specific repeated observations, exemplified by examining plant, animal, fungal, bacterial, and protist tissues to conclude that all living organisms consist of cells.

Scientific Theory

A well-substantiated explanation of an aspect of the natural world based on a body of facts repeatedly confirmed through rigorous observation and experiment, distinguishing it from an unsupported guess.

Magnification

The ratio indicating how much larger an image appears compared to the specimen's actual physical size.

Total Magnification Formula

The formula used to determine a light microscope's overall power: $\text{Total Magnification} = \text{Ocular Lens Magnification} \times \text{Objective Lens Magnification}$.

Wet Mount

A laboratory slide preparation method in which a specimen is suspended in a drop of water between a glass slide and a coverslip, lowered at an angle to prevent air bubbles.

Iodine Stain

A chemical stain commonly used to identify starch (which it stains brown or blue-black) and glycogen (which it stains red).

Methylene Blue

A histological stain useful for binding to and highlighting cell nuclei and DNA under a light microscope.

Gram Stain

A differential staining procedure that classifies bacteria into Gram-positive (stained purple) or Gram-negative (appearing pink) based on the size and composition of their peptidoglycan cell wall.

Field of View (FOV)

The diameter of the circular area that is visible when looking through the eyepiece of a microscope.

Magnification Formula (M = I / A)

The mathematical formula for calculating scale, magnification, or specimen size: $\text{Magnification} = \frac{\text{Image Size}}{\text{Actual Size}}$.

Resolution

The smallest interval or distance between two distinct points that can be distinguished by an optical instrument, determining the degree of image detail visible.

Compound Light Microscope

An optical device that bends visible light using multiple glass lenses to magnify specimens up to approximately $1500\times$ with a resolving power of $0.25\,\mu\text{m}$ to $0.3\,\mu\text{m}$, allowing living or dead cells to be observed in color.

Electron Microscope

An imaging instrument using beams of electrons focused by electromagnets that achieves magnifications between $100{,}000\times$ and $300{,}000\times$ and resolving power down to $0.001\,\mu\text{m}$, requiring specimens to be killed and chemically fixed.

Immunofluorescence

A microscopy technique developed in 1942 that uses fluorescently tagged antibodies to bind, visualize, and track specific target proteins within cells.

Freeze-Fracture

An electron microscopy preparation method developed in the 1960s where rapidly frozen cells are split along planes of weakness through the interior of membranes and metal-coated, demonstrating that integral proteins span the lipid bilayer.

Cryogenic Electron Microscopy (Cryo-EM)

A transmission electron microscopy technique developed in the 1980s that bombards frozen protein solutions with an electron beam to elucidate molecular structures at near atomic-level resolution.

Cytosol

The aqueous, gel-like liquid portion of the cytoplasm consisting of water and dissolved solutes such as salts, fatty acids, sugars, amino acids, and enzymes.

Svedberg Unit (s)

A unit of measure of sedimentation rate and particle density used to designate ribosomal size, distinguishing prokaryotic ($70\text{s}$) ribosomes from eukaryotic ($80\text{s}$) ribosomes.

Nucleoid

The irregularly shaped, non-membrane-bound region in the cytoplasm of a prokaryotic cell where the main circular, naked DNA molecule is located.

Plasmid

A small, circular, naked DNA molecule found in some prokaryotes that replicates independently of the nucleoid chromosome and frequently confers antibiotic resistance.

Pili

Hair-like surface appendages on prokaryotic cells that enable attachment to surfaces, exchange of DNA with other cells via conjugation, or uptake of DNA from the surrounding environment.

Nucleolus

A specialized dense structure within the eukaryotic nucleus where ribosomal RNA is transcribed and ribosome subunits are assembled.

Rough Endoplasmic Reticulum (RER)

A network of flattened, connected membranous sacs continuous with the nuclear envelope and studded with bound ribosomes, specialized for synthesizing and transporting polypeptides.

Smooth Endoplasmic Reticulum (SER)

A system of interconnected membranous sacs lacking ribosomes, responsible for synthesizing phospholipids and cholesterol for membrane formation and repair.

Golgi Apparatus

An organelle composed of flattened stacks that receives polypeptides from the RER, modifies them, and sorts, concentrates, and packages them into vesicles.

Lysosome

A single-membrane-bound spherical organelle containing hydrolytic digestive enzymes operating at acidic pH, functioning to break down old organelles and digest engulfed pathogens.

Cristae

The folds of the inner mitochondrial membrane that project into the matrix, providing expanded surface area for cellular respiration and ATP synthesis.

Central Vacuole

A large, permanent plant organelle enclosed by a single membrane called the tonoplast, occupying $30\% - 90\%$ of cell volume to store water and maintain internal turgor pressure against the cell wall.

Cytoskeleton

A non-organelle structural network composed of microtubules, actin microfilaments, and intermediate filaments that maintains cell shape, organizes organelles, and facilitates movement and cell division.

Centriole

A cylindrical organelle composed of nine groups of three microtubules arranged with radial symmetry; a pair forms the centrosome that organizes the mitotic spindle.

Basal Body

A modified centriole located at the base of eukaryotic cilia and flagella that serves as an anchor point at the cell membrane.

9+2 Pattern

The characteristic internal microtubule arrangement in eukaryotic cilia and flagella, consisting of nine outer doublet pairs surrounding two central single microtubules.

Microvilli

Tightly packed, finger-like projections of the animal plasma membrane that increase surface area for absorption and lack the $9+2$ microtubule arrangement of cilia.

Homeostasis

The active maintenance of a stable internal environment within a living organism despite changes in external conditions.

Contractile Vacuole

A specialized osmoregulatory organelle in freshwater unicellular organisms (such as Paramecium and Chlamydomonas) that periodically swells with excess water entering by osmosis and expels it through the cell membrane.

Catabolism

The set of exergonic metabolic reactions that breaks down complex molecules into smaller units, releasing chemical energy.

Anabolism

The set of endergonic metabolic reactions that builds larger, complex molecules from smaller precursors, requiring energy input.

Autotroph

An organism capable of synthesizing organic carbon compounds from simple inorganic substances using an external energy source, typically sunlight through photosynthesis.

Heterotroph

An organism that satisfies its nutritional requirements by obtaining preformed organic carbon compounds from other living organisms.

Excretion

The biological process by which metabolic waste products generated by cellular reactions are eliminated from an organism.

Holozoic Nutrition

A form of heterotrophic nutrition characteristic of animals involving the ingestion and subsequent internal enzymatic digestion of other organisms.

Saprotroph

An organism, characteristic of most fungi, that feeds by secreting extracellular digestive enzymes into its surrounding environment and absorbing the digested organic nutrients.

Chitin

The strong, structural polysaccharide that forms the protective cell wall of fungal cells.

Erythrocyte (Red Blood Cell)

A specialized vertebrate cell that discards its nucleus and mitochondria during maturation to maximize surface area to volume ratio for gas exchange and movement through capillaries.

Aseptate Fungal Hyphae

Fungal filaments lacking internal septa (cross-walls), resulting in a continuous, uninterrupted cytoplasm containing numerous nuclei.

Skeletal Muscle Fiber

An elongated contractile muscle cell formed by the fusion of multiple individual cells, resulting in a single continuous cytoplasm containing multiple nuclei and striations.

Sieve Tube Element

A conducting cell in plant phloem tissue that degrades its nucleus and major organelles during development to optimize sap transport, relying on adjacent companion cells for metabolic support.

Ultrastructure

The fine, detailed structural components and internal anatomy of a cell that are too small to be resolved by a light microscope and can only be visualized using an electron microscope.