Biology: Cell Types, Structures, and Modifications

A comprehensive vocabulary set covering prokaryotic and eukaryotic cell anatomy, three-domain classification, membrane models, organelle functions, and specialized cell modifications in plants and animals.

Prokaryotic Cells

The simplest and most ancient forms of life that developed about $3.5$ years ago, lacking a membrane-bound nucleus and measuring between $1$ to $10\,\mu \text{m}$ in diameter.

Eukaryotic Cells

Complex cells that contain a nucleus and other membranous organelles, typically measuring $10-100\,\mu \text{m}$ in diameter.

Carl Woese

A microbiologist who in 1977 studied key molecules in many cell types, leading to the organization of life into three domains.

Domain Bacteria

The most abundant and diverse organisms on Earth, which have existed longer than any other groups and play roles as decomposers and producers.

Domain Archaea

Prokaryotic organisms that are mostly one-celled and build their cells out of biochemicals different from those in bacteria or eukaryotes.

Domain Eukarya

The domain containing organisms with complex cells, including animals, plants, protists, and fungi.

Glycocalyx

An outer layer of a prokaryotic cell that provides protection, acts as a virulence factor, and exists as a rigid capsule or an unstructured slime layer.

Cell Wall (Prokaryotic)

A structure composed of peptidoglycan that confers rigidity and shape to the cell, located outside the plasma membrane.

Plasma Membrane

A phospholipid bilayer that prevents the loss of water and electrolytes while regulating the entry of substances into the cell.

Plasmid

A small, circular, extrachromosomal $DNA$ molecule found in the cytoplasm of bacteria, separate from chromosomal $DNA$.

Nucleoid

The region within a prokaryotic cell where the circular $DNA$ is concentrated.

Ribosome

A non-membrane-bound structure consisting of proteins and $RNA$ that serves as the site where proteins are synthesized.

Pilus (plural: pili)

A short, hairlike appendage on the surface of bacteria used for adhesion to host cells or the transfer of genetic material via a sex pilus.

Flagellum (plural: flagella)

A long, threadlike appendage anchored in the cell wall that rotates like a propeller to facilitate cell movement.

Fimbriae

Bristle-like fibers shorter than pili that are primarily used for bacterial attachment to tissue surfaces.

Nucleus

The most visible part of a eukaryotic cell where nucleic acids are synthesized and hereditary factors are stored.

Nuclear Pores

Selective channels in the nuclear membrane that allow molecules to move between the cytoplasm and the inside of the nucleus.

Nucleoplasm

A dense, protein-rich, spherical substance found inside the nucleus.

Nucleolus

A structure rich in proteins and nucleic acids responsible for the formation and assembly of ribosomes.

Chromatin

A combination of $DNA$ and proteins found in the nucleus that forms chromosomes during cell division.

Chromosomes

Structures containing genes inherited by offspring; humans have a specific count of $46$ chromosomes.

Classical Model (1930)

A cell membrane hypothesis proposed by Hugh Davson and James Danielli suggesting a phospholipid bilayer sandwiched between distinct layers of proteins.

Fluid Mosaic Model (1972)

Proposed by Jonathan Singer and Garth Nicolson, this model describes the membrane as a thin fluid layer containing a variety of proteins, glycolipids, and cholesterol.

Tight Junction

A cell-to-cell connection that joins cells tightly together to form a leak-proof sheet.

Adhesion Junction

A connection that acts like screws together with cytoskeletal fibers to form strong sheets between cells.

Gap Junction

A specialized protein complex that allows small molecules to flow directly between neighboring animal cells.

Endoplasmic Reticulum (ER)

A network of membrane-enclosed sacs and tubules serving as an intracellular highway for molecule transport.

Rough ER

A portion of the endoplasmic reticulum with ribosomes on its surface that produces proteins for membranes or export.

Smooth ER

A tubular organelle involved in steroid synthesis, toxic substance breakdown, and calcium level regulation.

Golgi Apparatus

A system of flattened sacs that processes, packages, and sorts secretory materials received from the $ER$ into vesicles.

Mitochondrion

The 'power plant' of the cell that produces $ATP$ through the chemical oxidation of food molecules; it contains its own $DNA$ and ribosomes.

Lysosomes

Small, spherical, membrane-bound organelles containing enzymes that digest proteins, lipids, and pathogens.

Centrosome

A part of the cytoplasm in animal cells that produces microtubules and forms centrioles for cell division.

Cytoskeleton

A network of filaments and tubules, including microtubules and microfilaments, providing the cell with motility and strength.

Central Vacuole

A large organelle in mature plant cells that degrades molecules, stores nutrients, and maintains turgor pressure.

Peroxisome

A membrane-bound organelle originating from the $ER$ that contains enzymes to break down toxic substances.

Chloroplast

A plant organelle containing chlorophyll and thylakoids where sunlight is converted into chemical energy ($glucose$).

Plasmodesmata

Microscopic channels passing through plant cell walls that allow water, nutrients, and signaling molecules to flow between adjacent cells.

Centriole

Cylindrical structures within the centrosome that help organize microtubules and give rise to cilia and flagella.

Cilia

Short, numerous extensions resembling a fringe that enable cells, such as Paramecium, to swim.

Microvilli

Tiny cytoplasmic extensions that increase surface area for nutrient absorption in the small intestine.

Nerve Cells (Neuron)

Elongated, slender cells designed to transmit nerve impulses between the brain, spinal cord, and the rest of the body.

Red Blood Cells (RBCs)

Biconcave, flexible discs that lose their nucleus at maturity to maximize space for oxygen transport.

Chromatophores

Specialized pigment-containing cells in animals like squids and octopuses used for camouflage or communication.

Nematocysts

Specialized stinging cells in jellyfish and Hydra that utilize a needle-like structure to inject toxins for defense or prey capture.

Root Hair Cells

Elongated extensions of plant root epidermal cells that increase surface area for absorbing water and minerals.

Guard Cells

Specialized cells that surround the stomata to regulate gas exchange and water loss by opening and closing the pores.