IB Biology: Cell Structure, Membranes, Organelles, and Specialization

Vocabulary practice flashcards covering cell structure (A2.2), membranes and membrane transport (B2.1), organelles and compartmentalization (B2.2), and cell specialization (B2.3).

Amphipathic

The property of having both hydrophilic (water-attracting, polar) and hydrophobic (water-repelling, non-polar) parts within the same molecule, characteristic of membrane phospholipids.

Osmosis

The net passive movement of water molecules across a selectively permeable membrane from a region of lower solute concentration to a region of higher solute concentration.

Aquaporins

Integral membrane proteins that act as specialized water channels, facilitating the rapid diffusion of water molecules across cell membranes.

Channel proteins

Transmembrane integral proteins with hydrophilic interior pores that allow specific ions or polar molecules to pass across the membrane down their concentration gradient by facilitated diffusion.

Facilitated diffusion

The passive transport of substances down their concentration gradient across a biological membrane facilitated by transmembrane channel or carrier proteins, requiring no metabolic energy.

Selective permeability

The ability of a membrane to regulate which substances can cross into or out of a cell, governed by the hydrophobic lipid bilayer and specialized channel and pump proteins.

Cholesterol (in cell membranes)

A lipid component of animal cell membranes that acts as a fluidity modulator, disrupting regular hydrocarbon packing to prevent crystallization at low temperatures while restricting phospholipid movement at higher temperatures.

Glycoproteins and glycolipids

Membrane proteins and lipids with attached carbohydrate chains facing the extracellular surface, functioning in cell-cell recognition, adhesion into tissues, and cell signaling.

Sodium-potassium pump

An integral active transport exchange protein that hydrolyzes ATP to export three sodium ions ($3\text{ Na}^+$) out of the axon and import two potassium ions ($2\text{ K}^+$) into the axon against their concentration gradients.

Potassium channel (in axons)

A voltage-gated transmembrane protein in nerve cell axons that facilitates the rapid passive diffusion of potassium ions ($\text{K}^+$) out of the axon during repolarization.

Sodium-dependent glucose cotransporter

A transport protein that carries out indirect (secondary) active transport by coupling the downhill movement of sodium ions along their concentration gradient with the uphill transport of glucose into the cell.

Endocytosis

An active cellular process reliant on membrane fluidity where the plasma membrane invaginates and pinches off to form internal vesicles, engulfing external fluids or macromolecules.

Exocytosis

An active cellular process where intracellular vesicles fuse with the plasma membrane to expel their contents into the extracellular environment while adding vesicle membrane to the cell membrane.

Cell theory

The unifying biological principle stating that all living organisms are composed of one or more cells, cells are the basic structural and functional units of life, and all cells arise from pre-existing cells.

Nuclear pore (Structure X)

A large protein-lined channel spanning the nuclear envelope that selectively regulates macromolecular trafficking, such as RNA and proteins, between the nucleus and the cytoplasm.

Freeze-fracture electron microscopy

A preparation technique where rapidly frozen biological specimens are cracked along internal planes of weakness (such as the middle of lipid bilayers) to visualize transmembrane protein distribution.

Cryogenic electron microscopy (Cryo-EM)

A microscopy technique in which biological samples are flash-frozen in vitreous ice and imaged at cryogenic temperatures to deduce three-dimensional molecular structures at near-atomic resolution.

Prokaryote

A simple unicellular organism lacking a membrane-bound nucleus and compartmentalized organelles, characterized by $70\text{S}$ ribosomes and a nucleoid containing naked circular DNA.

Eukaryote

An organism whose cells feature a membrane-bound nucleus, membrane-enclosed compartmentalized organelles, and $80\text{S}$ ribosomes in the cytoplasm.

Atypical cell structures

Cellular structures that diverge from conventional cell theory, including multinucleated striated skeletal muscle fibers, non-septate fungal hyphae with continuous cytoplasm, and anucleate mature red blood cells.

Organelle compartmentalization

The isolation of specific cellular processes within discrete membrane-bound subunits in eukaryotic cytoplasm, enabling localized chemical conditions, optimal enzyme-substrate concentrations, and separation of incompatible reactions.

Endosymbiotic theory

The evolutionary model explaining that mitochondria and chloroplasts originated as free-living independent prokaryotes that were engulfed by ancestral host cells and became mutualistic endosymbionts.

Totipotent stem cells

Undifferentiated cells capable of differentiating into any cell type of the entire organism, including both embryonic tissue and extraembryonic tissues such as the placenta.

Pluripotent stem cells

Stem cells that can differentiate into any of the body's cell types originating from the three embryonic germ layers, but cannot form extraembryonic structures.

Multipotent stem cells

Adult stem cells that can differentiate into a narrow range of closely related, specialized cell types within a specific tissue (e.g., hematopoietic stem cells).

Stem cell niche

A specialized local microenvironment within adult tissues that maintains stem cells in an undifferentiated state and regulates their self-renewal and lineage differentiation.

Surface area-to-volume ratio (SA:V)

The proportion of a cell's outer surface area relative to its internal volume, which decreases as cell size increases ($\text{SA} \propto r^2$, $\text{V} \propto r^3$) and imposes an upper constraint on cell size.

Type I pneumocytes

Extremely thin, flattened squamous alveolar cells adapted to form an ultra-thin barrier that maximizes the rate of gas exchange ($\text{O}_2$ and $\text{CO}_2$) between the alveoli and blood capillaries.

Type II pneumocytes

Cuboidal epithelial cells in the alveoli adapted to secrete pulmonary surfactant, a lipid-protein complex that reduces surface tension to prevent alveolar collapse during expiration.

Exocrine gland cells of pancreas

Specialized animal cells adapted for protein synthesis and secretion, containing high quantities of rough endoplasmic reticulum, extensive Golgi apparatus, and numerous secretory zymogen granules.

Palisade mesophyll cells

Densely packed, columnar plant cells situated beneath the upper epidermis of a leaf, containing numerous chloroplasts positioned to maximize photon absorption for photosynthesis.

LUCA (Last Universal Common Ancestor)

The single ancestral form of life from which all modern cellular life evolved, evidenced by shared universal features such as DNA, genetic code codons, and ATP usage.

Cisternal maturation model

A model of Golgi apparatus transport wherein Golgi cisternae physically progress and mature from the cis face to the trans face while resident enzymes are retrogradely transported by vesicles.

Lytic cycle

A viral reproductive cycle in which the viral genome directs the host cell to assemble new virions, culminating in the lysis of the host cell membrane and release of progeny.

Lysogenic cycle

A viral cycle wherein the viral DNA integrates into the host cell's genome as a prophage or provirus, replicating alongside host DNA without immediately destroying the host cell.