Cell Structure and Function

Vocabulary practice flashcards covering cell biology, organelle structure, plasma membrane composition, microscopy, and transport processes.

Cell

The smallest unit of a living thing and the basic building block of all organisms.

Microscope

An instrument that magnifies an object.

Micrograph

An image taken using a microscope.

Antony van Leeuwenhoek

A Dutch shopkeeper who observed moving protists and sperm in the 1600s, which he termed 'animalcules'.

Robert Hooke

A scientist who viewed cork tissue in 1665 and coined the term 'cell' from the Latin word 'cella', meaning 'small room'.

Unified Cell Theory

A theory proposed in the late 1830s by Matthias Schleiden and Theodor Schwann stating that all living things are composed of one or more cells, the cell is the basic unit of life, and all new cells arise from existing cells.

Plasma Membrane

An outer covering made of a phospholipid bilayer with embedded proteins that separates the internal contents of the cell from its surrounding environment.

Cytoplasm

The contents of a cell between the plasma membrane and the nuclear envelope, comprising gel-like cytosol, organelles, the cytoskeleton, and various chemicals.

Ribosomes

Cellular structures responsible for protein synthesis that can be free-floating in the cytoplasm or attached to membranes.

Prokaryotic Cell

A simple, single-celled organism that lacks a nucleus or any other membrane-bound organelles, typically ranging in size from $0.1 - 5.0\text{ }\frac{\text{m}}{\text{s}}$.

Nucleoid

The central, darkened region of a prokaryotic cell where its chromosomal DNA is localized.

Eukaryotic Cell

A cell that possesses a membrane-bound nucleus and other membrane-bound organelles, typically ranging in size from $10 - 100\text{ }\frac{\text{m}}{\text{s}}$.

Organelles

Membrane-bound compartments or sacs inside eukaryotic cells that carry out specialized functions.

Microvilli

Fingerlike projections formed by folding of the plasma membrane that increase surface area to enhance absorption.

Cytoskeleton

A network of protein fibers that maintains cell shape, secures organelles in position, facilitates cytoplasm and vesicle movement, and enables unicellular organisms to move independently.

Microfilaments

The thinnest cytoskeleton fibers (also called actin filaments) that move cellular components and maintain microvilli structure.

Intermediate Filaments

Cytoskeleton fibers of intermediate diameter that carry out structural functions such as maintaining cell shape and anchoring organelles.

Microtubules

The thickest cytoskeleton fibers consisting of hollow tubes that dissolve and reform quickly; they guide organelle movement, pull chromosomes during cell division, and form flagella and cilia.

Flagella

Long, hair-like structures extending from the plasma membrane used to move an entire cell.

Cilia

Short, hair-like structures present in large numbers along the cell surface that move entire cells or move substances along the outer surface of the cell.

Endomembrane System

A group of eukaryotic membranes and organelles—including the nuclear envelope, lysosomes, vesicles, endoplasmic reticulum, and Golgi apparatus—that work together to modify, package, and transport lipids and proteins.

Nucleus

The eukaryotic organelle that houses genetic DNA in the form of chromatin and directs the synthesis of ribosomes and proteins.

Nuclear Envelope

A double-membrane structure punctuated with pores that constitutes the outermost boundary of the nucleus and regulates the passage of ions, molecules, and RNA.

Nucleolus

The darkly stained area inside the nucleus that aggregates ribosomal RNA.

Rough Endoplasmic Reticulum

A series of interconnected membranous tubules studded with ribosomes on its cytoplasmic surface that synthesize and modify proteins and produce phospholipids for the cell membrane.

Smooth Endoplasmic Reticulum

Membranous tubules continuous with the RER that lack ribosomes; functions include synthesis of carbohydrates, lipids, and steroid hormones, detoxification of poisons, alcohol metabolism, and storage of calcium ions.

Golgi Apparatus

A series of flattened membranous sacs that sort, tag, package, and distribute lipids and proteins.

Lysosomes

Membrane-bound vesicles containing digestive enzymes that break down proteins, polysaccharides, lipids, nucleic acids, and worn-out organelles.

Vesicles and Vacuoles

Membrane-bound sacs that function in cellular storage and transport; vesicles can fuse with other membranes, whereas vacuoles are larger and do not fuse with other organelles.

Mitochondria

Organelles referred to as the 'powerhouses' of the cell that produce ATP ($\text{adenosine triphosphate}$), contain their own DNA, and carry out cellular respiration.

Peroxisomes

Small, round organelles enclosed by single membranes that carry out oxidation reactions breaking down fatty acids and amino acids, safely neutralizing the byproduct hydrogen peroxide ($H_2O_2$) into water and oxygen.

Cell Wall

A rigid external covering composed primarily of cellulose that protects, provides structural support, and gives shape to plant, fungal, and some protist cells.

Chloroplasts

Plant organelles containing thylakoids and stroma that perform photosynthesis, converting carbon dioxide, water, and light energy into glucose and oxygen.

Central Vacuole

A large plant cell organelle that regulates cell water concentration and produces turgor pressure against the cell wall to keep the plant firm and upright.

Endosymbiosis

The concept that mitochondria and chloroplasts originated as bacterial cells engulfed by a larger cell, developing a mutually beneficial symbiotic relationship.

Extracellular Matrix

A structural network made of glycoproteins and collagen proteins that holds animal cells together to form tissues and allows intercellular communication.

Fluid Mosaic Model

A structural depiction of the plasma membrane as a fluid combination of phospholipids, cholesterol, proteins, and carbohydrates whose components can flow and change position.

Passive Transport

A naturally occurring process in which substances move down a concentration gradient from an area of higher concentration to lower concentration without expending energy.

Concentration Gradient

The difference in the concentration of a substance across two regions or solutions.

Diffusion

The passive movement of a substance from an area of high concentration to an area of low concentration until its concentration is equal across the space.

Facilitated Transport

The movement of materials across the plasma membrane down their concentration gradient using transmembrane proteins without cellular energy expenditure.

Osmosis

The diffusion of water across a semipermeable membrane from an area of higher water concentration to an area of lower water concentration.

Tonicity

A description of the solute concentration of a solution relative to the internal solute concentration of a cell.

Hypotonic

Describes an extracellular solution that has a lower solute concentration than the cell interior, causing water to enter the cell (which may cause animal cells to lyse).

Hypertonic

Describes an extracellular solution that has a higher solute concentration than the cell interior, causing water to leave the cell (which causes animal cells to crenate or shrivel).

Isotonic

Describes a condition where extracellular and intracellular fluids have equal solute concentrations, resulting in equal movement of water in and out of the cell.

Active Transport

Mechanisms requiring cellular energy (ATP) to move ions, charged molecules, or large particles against their concentration gradient (from low to high concentration).

Electrochemical Gradient

A dual gradient consisting of a chemical concentration difference and an electrical charge difference across a plasma membrane.

Sodium-Potassium Pump

A primary active transport mechanism that expends ATP to pump sodium ions out of the cell and potassium ions into the cell against their electrochemical gradients.

Endocytosis

A type of active transport that moves large particles or cells into a cell by invaginating the plasma membrane to form a pocket that pinches off into a vacuole or vesicle.

Phagocytosis

A form of endocytosis ('cell eating') by which large particles, such as pathogenic bacteria or whole cells, are taken in by a cell.

Pinocytosis

A form of endocytosis ('cell drinking') by which small volumes of fluid are surrounded and taken into the cell via vesicles.

Receptor-Mediated Endocytosis

A targeted form of endocytosis where specific target particles bind to cell-surface receptor proteins, triggering membrane invagination and vesicle internalization.

Exocytosis

The active transport process of expelling a particle from a cell when its intracellular vesicle fuses with the plasma membrane to release contents outside.