Properties of Water, Cell Membrane Structure, and Transport

Comprehensive vocabulary flashcards reviewing the chemical properties of water, the fluid mosaic structure of cell membranes, mechanisms of passive and active cell transport, tonicity, and the biological importance of surface area-to-volume ratio in cell size.

Polar Bond (in Water)

A covalent bond formed by the unequal sharing of electrons between atoms, giving the oxygen atom a partial negative charge and the hydrogen atoms partial positive charges.

Hydrogen Bond

A weak intermolecular attraction formed between water molecules due to the partial electrical charges generated by unequal electron sharing.

Cohesion

The tendency of water molecules to stick to other water molecules because of hydrogen bonding, keeping water molecules together to form droplets.

Adhesion

The attraction that causes water molecules to stick to substances other than water due to the attraction of opposite electrical charges.

Capillary Action

The tendency of water to move along the surface of a substance due to adhesion, allowing water molecules to pull each other upward through narrow spaces such as from plant roots to leaves.

Surface Tension

A special form of cohesion that causes the surface layer of water to resist rupture, allowing certain insects to walk across water.

Universal Solvent

A property describing water's capability to dissolve many diverse substances owing to the partial positive and negative charges across its polar structure.

Specific Heat

The amount of heat energy required to raise the temperature of a substance; water possesses a high specific heat because energy must first break its hydrogen bonds.

Hydrophobic

Describing substances that do not dissolve in or mix with water ("water fearing"), such as nonpolar oils.

Hydrophilic

Describing substances that readily dissolve in or attract water ("water loving"), such as salt and sugar.

Homeostasis

The maintenance of stable internal conditions inside cells and living organisms, regulated at the cellular level by the cell membrane.

Phospholipid

The primary structural molecule of the cell membrane, consisting of a hydrophilic (water-loving) phosphate head and two hydrophobic (water-fearing) fatty acid tails.

Fluid Mosaic Model

A structural model describing the cell membrane where components can move dynamically ("fluid") and are composed of an assortment of phospholipids, proteins, carbohydrates, and cholesterol ("mosaic").

Semipermeable (Selectively Permeable)

A membrane characteristic that selectively allows certain molecules to cross while preventing other substances from passing through.

Concentration Gradient

The difference in the concentration of a chemical substance from one region to another, such as between the interior and exterior of a cell.

Passive Transport

The cellular movement of substances across a biological membrane down their concentration gradient (from high to low concentration) without consuming metabolic energy.

Simple Diffusion

The passive transport of small, nonpolar, uncharged molecules (such as oxygen and carbon dioxide) straight through the phospholipid bilayer from high to low concentration.

Facilitated Diffusion

The passive movement of molecules from an area of higher concentration to lower concentration through the assistance of specific channel or carrier membrane proteins.

Osmosis

The diffusion of water across a semipermeable membrane down its concentration gradient (from high water concentration to low water concentration), occurring directly or through aquaporins.

Isotonic Solution

A solution whose solute concentration outside the cell equals the solute concentration inside the cytosol, resulting in equal movement of water and no change in cell size.

Hypotonic Solution

A solution whose solute concentration outside the cell is lower than inside the cell, causing water to enter the cell and leading to swelling, turgor in plant cells, or lysis in animal cells.

Hypertonic Solution

A solution whose solute concentration outside the cell is higher than inside the cell, driving water out and resulting in cellular shrinking, crenation in animal cells, or plasmolysis in plant cells.

Active Transport

The energy-requiring movement of substances across a cell membrane against (up) their concentration gradient, moving from low to high concentration.

Sodium Potassium ($\text{Na}^+/\text{K}^+$) Pump

A membrane protein pump that hydrolyzes $\text{ATP}$ to transport sodium ions out of the cell and potassium ions into the cell, which is essential for sending signals in the nervous system.

Bulk Transport

A form of active transport requiring energy to package and transport large particles or large quantities of substances into or out of cells using vesicles.

Endocytosis

An active transport process where the plasma membrane folds inward around external particles or fluid droplets to engulf them into an internal vesicle.

Exocytosis

An active transport process wherein intracellular vesicles migrate to and fuse with the plasma membrane to secrete substances, such as hormones like insulin, or eliminate waste.

Surface Area-to-Volume Ratio ($\text{SA:V}$)

The mathematical relationship comparing a cell's outer membrane surface area to its interior volume; smaller cells have a higher ratio, allowing faster and more efficient diffusion across the membrane.