IB Biology: Cell Structure and Microscopy

Vocabulary practice flashcards covering cell theory, microscopy skills, prokaryotic and eukaryotic ultrastructures, functions of life, atypical cells, endosymbiotic theory, and multicellular evolution for IB Biology.

Cell Theory

A foundational biological principle stating that all living organisms are composed of one or more cells, the cell is the basic structural and functional unit of life, and all new cells arise from pre-existing cells through division.

Deductive Reasoning

A scientific logical approach that progresses from general ideas or existing theories to hypothesis generation, testing, and specific conclusions.

Inductive Reasoning

A scientific logical approach that begins with specific observations and pattern recognition to develop general conclusions or theories.

Magnification

The measure of how many times larger an image produced by a microscope or drawing appears compared to the real-life size of the specimen, calculated as $\text{Magnification} = \frac{\text{Image Size}}{\text{Actual Size}}$.

Resolution

The ability to distinguish between two points that are close together as separate structures, determining the smallest interval distinguishable and the degree of detail visible in an image.

Optical (Light) Microscope

A microscope that directs light through biological material and lenses to view living or dead specimens in colour, limited by the wavelength of visible light ($400\text{--}700\,\text{nm}$) to a maximum resolution of approximately $0.2\,\mu\text{m}$ ($200\,\text{nm}$) and useful magnification up to $\times 1500$.

Transmission Electron Microscope (TEM)

An electron microscope that transmits a focused beam of electrons through thin, dead specimens in a vacuum, providing high-resolution cross-sectional images of internal cellular ultrastructure with a resolving power of approximately $0.0002\,\mu\text{m}$ ($0.2\,\text{nm}$).

Scanning Electron Microscope (SEM)

An electron microscope that scans a beam of electrons across the surface of a specimen to detect reflected electrons, producing three-dimensional images of external surfaces.

Eyepiece Graticule

A small transparent glass disc engraved with an uncalibrated scale placed into the eyepiece of a microscope to serve as a measuring ruler across the field of view.

Stage Micrometer

A microscope slide engraved with an accurate, known scale used to calibrate the units of an eyepiece graticule for each specific objective lens.

Scale Bar

A straight line drawn on a biological drawing or micrograph that represents a specific, stated actual dimension of the original specimen before magnification.

Cryogenic Electron Microscopy

A microscopy technique involving flash-freezing solutions of biological molecules and imaging them with electrons, using computer software to reconstruct high-resolution 3D models of proteins and complexes at near-atomic resolution.

Freeze Fracture

A preparation technique where a rapidly frozen sample is fractured along internal structural planes of weakness (such as the middle of lipid bilayers) in a vacuum and coated to produce a replica for electron microscopy.

Immunofluorescence

A technique using fluorescently labelled antibodies that bind selectively to target molecules, allowing their specific cellular distribution and movement to be visualized under ultraviolet light.

Emergent Property

A property that arises as a consequence of complex interactions among constituent components at the cellular level; for example, life itself is an emergent property exhibited by intact cells, whereas subcellular components on their own are not alive.

Nucleoid

The non-compartmentalized region in the cytoplasm of a prokaryotic cell that contains the primary genetic material in the form of a naked, circular single loop of DNA.

Plasmid

A small, circular, autonomous loop of naked DNA in prokaryotic cells that replicates independently of the main chromosome and often carries non-essential adaptive genes, such as those conferring antibiotic resistance.

Peptidoglycan (Murein)

A cross-linked polymer of sugars and amino acids that forms the rigid bacterial cell wall, protecting the cell from osmotic lysis and maintaining its shape.

Pili

Short, thin, hair-like protein appendages on the surface of some prokaryotes used for cellular adhesion to surfaces, escaping host phagocytes, and facilitating bacterial conjugation.

70S Ribosomes

Smaller ribonucleoprotein complexes found in prokaryotes, mitochondria, and chloroplasts that catalyze translation during polypeptide synthesis, consisting of a large and small subunit quantified in Svedberg units ($\text{S}$).

80S Ribosomes

Larger protein-synthesising complexes found in eukaryotic cells, either free within the cytosol or bound to the membrane of the rough endoplasmic reticulum.

Nuclear Envelope

The double membrane perforated by nuclear pores that surrounds the eukaryotic nucleus, physically segregating transcription within the nucleus from translation in the cytoplasm.

Nucleolus

A densely staining region inside the eukaryotic nucleus responsible for synthesizing ribosomal RNA (rRNA) and assembling ribosome subunits.

Rough Endoplasmic Reticulum (RER)

A membrane-bound network of flattened sacs (cisternae) continuous with the nuclear envelope and studded with 80S ribosomes, responsible for processing and packaging synthesized polypeptides into transport vesicles.

Smooth Endoplasmic Reticulum (SER)

A network of membranous tubular sacs continuous with the RER that lacks ribosomes, functioning in the synthesis of phospholipids, cholesterol, and other lipids for membrane formation and repair.

Golgi Apparatus

An organelle consisting of stacks of flattened membrane-bound cisternae that modifies, sorts, and packages proteins and lipids into vesicles targeted for lysosomes, the plasma membrane, or external secretion.

Lysosome

A spherical, single membrane-bound vesicle containing hydrolytic digestive enzymes operating at low pH, adapted to degrade worn-out cell parts, recycle macromolecules, and break down engulfed pathogens.

Mitochondrion

A double-membraned eukaryotic organelle featuring folded cristae and an enzyme-rich matrix containing 70S ribosomes and circular DNA, serving as the site of aerobic respiration to produce ATP.

Chloroplast

A double-membraned photosynthetic plant plastid containing chlorophyll-filled thylakoid membranes stacked into grana and an aqueous stroma containing 70S ribosomes and circular DNA.

Tonoplast

The selectively permeable single membrane surrounding the large permanent central vacuole in mature plant cells.

Cytoskeleton

An internal cellular structural network composed of microtubules, actin microfilaments, and intermediate filaments that organizes organelles, maintains cell shape, and facilitates movement and cell division.

Microtubules

Hollow protein cylinders approximately $25\,\text{nm}$ in diameter formed from dimers of $\alpha$-tubulin and $\beta$-tubulin, utilized for intracellular transport tracks, spindle fiber formation during mitosis, and structural support.

Centrioles

Paired cylindrical structures organized in a centrosome, composed of nine triplets of microtubules ($9 \times 3$ arrangement) with radial symmetry, that arrange the mitotic spindle during animal cell division and act as basal bodies.

Flagellum

A long, whip-like cell surface projection containing microtubules in a characteristic $9+2$ doublet arrangement anchored by a basal body, moving independently to propel eukaryotic cells or male gametes through fluid.

Microvilli

Tightly packed, finger-like projections of the plasma membrane that lack a $9+2$ microtubule arrangement, functioning to maximize cell surface area for efficient absorption of nutrients.

Homeostasis

The continuous physiological maintenance and regulation of internal bodily conditions (such as water volume, solute concentrations, and temperature) within narrow, tolerable limits despite external fluctuations.

Metabolism

The sum of all enzyme-catalysed chemical reactions occurring within a living organism or cell, encompassing anabolic energy-consuming pathways and catabolic energy-releasing pathways.

Contractile Vacuole

A specialized organelle in freshwater unicellular organisms (such as Paramecium and Chlamydomonas) that rhythmically accumulates excess intracellular water from osmosis and pumps it through pores out of the cell to regulate osmotic balance.

Striated Muscle Fibre

An atypical, fused multinucleate eukaryotic cell enclosed by a single sarcolemma that reaches up to $300\,\text{mm}$ in length, challenging the traditional cell theory notion that cells function as autonomous single units.

Aseptate Fungal Hyphae

Tubular fungal filaments lacking dividing internal cross-walls (septa), producing a continuous multinucleated cytoplasm that challenges the concept of organisms being divided into distinct cellular units.

Erythrocyte (Red Blood Cell)

A vertebrate blood cell specialized for oxygen transport that eliminates its nucleus and mitochondria during maturation to achieve a flexible biconcave shape with maximum hemoglobin capacity.

Phloem Sieve Tube Element

A specialized plant cell with perforated sieve plates that loses its nucleus, ribosomes, and most organelles to optimize sap transport, depending entirely on companion cells for metabolic survival.

Saprotroph

An organism (characteristic of most fungi) that feeds by secreting hydrolytic digestive enzymes into its external environment to digest complex organic material outside the body, subsequently absorbing the released nutrients.

Paramecium

Focuses on its role as a unicellular freshwater heterotroph carrying out all functions of life, highlighting its coordinated ciliary beating for movement, food vacuoles for internal digestion, contractile vacuoles for osmoregulation (homeostasis), and anal pore for excretion.

Chlamydomonas

A genus of unicellular photosynthetic green algae that carries out all functions of life, highlighting autotrophic nutrition via a large chloroplast, light sensing using a sensitive eyespot, motility via two flagella, osmoregulation through contractile vacuoles, and simple diffusion across the plasma membrane for excretion.

Temporary Mount (Wet Mount)

A slide preparation method in which a specimen is suspended in a drop of liquid between a microscope slide and a coverslip, lowered carefully at an angle to prevent air bubbles from being trapped.

Biological Staining

The application of coloured chemical compounds to specimens to enhance visual contrast under a microscope, such as methylene blue for cell nuclei and DNA, iodine solution for starch and glycogen, or Gram stain for bacterial cell walls.

Gram-Positive Bacteria

A group of eubacteria, including Bacillus and Staphylococcus, possessing a thick peptidoglycan cell wall that retains crystal violet stain and appears purple or blue under an optical microscope.

Universal Structures of All Cells

The four fundamental cellular components shared by all living organisms on Earth: a lipid bilayer plasma membrane, an aqueous cytoplasm (cytosol), DNA as genetic material, and ribosomes for polypeptide synthesis.

Cellular Compartmentalization

The organization of eukaryotic cytoplasm into membrane-bound organelles, which concentrates enzymes and substrates, sequesters potentially damaging enzymes, maintains optimal local conditions such as pH, and allows flexible organelle adaptation.

Microfilaments (Actin Filaments)

Narrow cytoskeletal protein fibres approximately $7\,\text{nm}$ in diameter formed from actin subunits, functioning in maintaining cell shape, supporting cell motility, driving cytoplasmic streaming, and forming the cleavage furrow during cytokinesis.

Nutrition

A fundamental process of life involving the acquisition of chemical energy and organic building blocks, accomplished either by synthesizing organic compounds from inorganic materials (autotrophy) or by ingesting and digesting external organic matter (heterotrophy).

Excretion

The biological process of eliminating toxic metabolic waste products produced by intracellular chemical reactions, such as carbon dioxide from cellular respiration, nitrogenous wastes, or oxygen produced during photosynthesis.

Growth

A universal process of life characterized by a permanent, irreversible increase in the physical size and dry biomass of an organism, achieved through cell enlargement and cell division.

Response to Stimuli

The ability of all living organisms to perceive environmental changes or external/internal cues via cellular receptor mechanisms and initiate appropriate adaptive reactions to survive.

Reproduction

The biological generation of new offspring, occurring either asexually to produce genetically identical daughter cells through mitosis or binary fission, or sexually involving the fusion of haploid gametes to create genetic variation.

Movement

The capacity of whole organisms or their internal subcellular structures to change position or orientation, encompassing motile swimming via cilia and flagella, plant phototropism, and intracellular cytoplasmic streaming.

Plastids

A family of double-membrane organelles unique to plant cells and algae involved in the synthesis and storage of food molecules, including chloroplasts for photosynthesis and leucoplasts/amyloplasts for starch storage.

Structural Differences: Animals, Plants, and Fungi

Plants contain cellulose cell walls, large permanent vacuoles, and plastids, storing carbohydrate as starch; fungi possess chitin walls, small temporary vacuoles, lack plastids, and store glycogen; animals lack cell walls and plastids, possess small temporary vacuoles and centrioles, and store glycogen.

Biological Drawing Conventions

Scientific illustration standards requiring clear, single, unshaded pencil lines, large diagrams filling at least half the page, an informative title with magnification/scale bar, and straight, horizontal, uncrossed label lines without arrowheads.

High-Power Field of View Diameter Calculation

The mathematical formula used to determine the field of view diameter when moving to a higher lens power: $\text{FOV}_{\text{HP}} = \frac{\text{FOV}_{\text{LP}} \times \text{Magnification}_{\text{LP}}}{\text{Magnification}_{\text{HP}}}$, reflecting an inversely proportional relationship.