Cell Structure, Function, Membrane Transport, and Water Potential

Comprehensive vocabulary flashcards covering cell theory, microscopy, cell structure, organelle fractionation, membrane dynamics, transport mechanisms, and water potential calculations.

Apoptosis

The programmed process of cellular suicide.

Cell Theory

The foundational biological theory stating that all organisms are made up of cells, the cell is the basic living unit of organization for all organisms, and all cells come from pre-existing cells.

Robert Hooke

The first biologist/cytologist who observed cells in 1665 using an early microscope.

Light Microscope

A microscope that passes visible light through a specimen, achieves a resolution of approximately $0.2\,\mu m$ (about the size of a bacterium), and can be used to observe live cells.

Transmission Electron Microscope (TEM)

An electron microscope developed in the 1950s that achieves a resolution of $2.0\,nm$ (100 times greater than a light microscope) by directing an electron beam through a thin section of a dead specimen to reveal internal organelles.

Scanning Electron Microscope (SEM)

An electron microscope used to study surface structures by coating a specimen with a thin film of gold and exciting surface electrons, yielding an image with great depth of field that appears 3-D.

Atomic Force Microscope

An advanced microscopy technique that creates images of electron density and enables scientists to visualize individual chemical bonds between atoms.

Cell Fractionation

The laboratory technique of isolating and separating organelles from cells based on their variable densities using an ultracentrifuge that can spin up to $130{,}000\,\text{RPM}$ and generate forces greater than $1{,}000{,}000 \times g$.

Cytosol

The semi-fluid substance located inside the plasma membrane of all cells.

Cytoplasm

The entire cellular contents enclosed by the plasma membrane, consisting of the cytosol plus suspended organelles.

Nucleoid Region

The non-membrane-enclosed area in a prokaryotic cell where the chromosome/DNA is concentrated.

Ribosomes

Tiny structures found in all cells that synthesize proteins using the genetic instructions carried by genes.

Mycoplasmas

The smallest known bacteria, measuring $0.1\,\mu m$ to $1.0\,\mu m$ in size, representing the lower size limit for cellular life.

Surface-to-Volume Ratio

A geometric relationship that sets an upper limit on cell size because volume increases faster than surface area as a cell enlarges, making large cells unable to transport materials in and out fast enough to meet metabolic requirements.

Cellular Compartmentalization

The structural organization in eukaryotic cells wherein internal membranes partition the cell into distinct compartments with specialized lipid and protein compositions, creating unique local environments for specific metabolic processes.

Plasma Membrane

A selectively permeable boundary approximately $8\,nm$ thick composed of phospholipids, proteins, and other macromolecules that controls traffic into and out of the cell.

Fluid Mosaic Model

The structural model of cell membranes proposed in 1972 by S.J. Singer and G. Nicolson, describing membranes as a fluid phospholipid bilayer into which diverse proteins are inserted.

Peripheral Proteins

Membrane proteins that lack hydrophobic regions and are loosely bound to the surface of the lipid bilayer.

Integral Proteins

Membrane proteins that penetrate into the hydrophobic core of the lipid bilayer, often completely spanning the membrane as transmembrane proteins.

Membrane Carbohydrates

Carbohydrate chains located on the outer membrane surface that serve as markers for cell-cell recognition, crucial for tissue/organ development and the immune system's rejection of foreign cells.

Unsaturated Fatty Acid Tails (Membrane Fluidity)

Phospholipid tails containing double bonds that produce kinks, preventing tight molecular packing and maintaining membrane fluidity at lower temperatures (e.g., increased by winter wheat in autumn).

Simple Diffusion

The passive movement of non-polar, hydrophobic substances across a membrane directly down their concentration gradient from high to low concentration without cellular energy expenditure.

Facilitated Diffusion

The passive transport of polar, hydrophilic molecules across a membrane through specific protein channels down their concentration gradient without requiring energy.

Active Transport

The movement of substances against their concentration gradient from low to high concentration using membrane protein pumps and cellular energy in the form of $ATP$.

Osmosis

The diffusion of water across a semi-permeable membrane from a region of higher water concentration (higher water potential) to a region of lower water concentration (lower water potential).

Hypotonic Solution

An external environment having a lower solute concentration and higher water concentration relative to the cell, causing water to enter the cell and potentially lead to swelling or bursting.

Hypertonic Solution

An external environment having a higher solute concentration and lower water concentration relative to the cell, causing water to exit the cell and potentially lead to cell shriveling and death.

Isotonic Solution

An environment in which the solute and water concentrations are equal inside and outside the cell, resulting in no net movement of water.

Contractile Vacuole

A specialized organelle in freshwater protists like Paramecium that collects excess incoming water and pumps it out of the cell using $ATP$ to prevent lysis.

Plasmolysis

The phenomenon in which a plant cell placed in a solution with negative water potential ($-\Psi$) loses water, causing the plasma membrane to pull away from the cell wall and the plant to wilt.

Turgid

The firm, fully swollen state of a plant cell resulting from net water uptake when placed in a solution with positive water potential ($+\Psi$), structurally supported against bursting by its cell wall.

Bulk Flow

The overall mass movement of water in response to differences in potential energy, driven by gravity, pressure, or water potential, which requires a constant input of energy.

Water Potential ($\Psi$)

The difference in free energy of a water sample per unit mass or volume ($J\,m^{-3}$) relative to pure water at ambient pressure, which is assigned a baseline value of $0\,MPa$.

Solute Potential ($\Psi_s$)

The component of water potential (also known as osmotic potential) that depends on the concentration of dissolved substances, which decreases (becomes more negative) as solute concentration increases.

Pressure Potential ($\Psi_p$)

The component of water potential that depends on the physical hydrostatic pressure exerted on the water.

Megapascal ($MPa$)

A metric pressure unit used to express water potential, where $1\,MPa = 10\,\text{bars} = 10\,\text{atmospheres} = 7500\,\text{mmHg}$.

Solute Potential Formula

The equation $\Psi_s = -iCRT$, where $i$ is the ionization constant, $C$ is the molar concentration in $mol\,L^{-1}$, $R$ is the gas constant ($0.0831\,\text{liter}\cdot\text{bar}\,mol^{-1}\,K^{-1}$), and $T$ is the absolute temperature in Kelvin ($^\circ C + 273$).

Ionization Constant ($i$)

The factor in the solute potential formula representing the number of particles a solute forms in water, which equals $1$ for non-ionizing solutes such as sucrose.