1.1 Cell Membrane and Transport

Vocabulary flashcards covering cell theory, cell membrane structure (fluid mosaic model), passive transport (diffusion, osmosis), active transport, and the significance of surface-area-to-volume ratio.

Cell theory

A theory stating that cells are the basic unit of structure in all organisms, the basic unit of reproduction, and that all cells come from pre-existing cells.

Fluid mosaic phospholipid bilayer model

The generally accepted structure of the cell membrane, comprised of a double layer of lipids with the ability to flow and change shape, embedded with specialized protein molecules.

Phospholipid

A type of lipid represented by a hydrophilic phosphate head and two hydrophobic fatty acid tails.

Hydrophilic

Water loving; able to absorb or dissolve in water.

Hydrophobic

Water repelling; avoid or are unable to dissolve in water.

Cholesterol

A type of lipid found in animal cell membranes that stabilizes and strengthens the membrane and maintains its fluidity.

Phytosterol

A lipid compound found in plant cell membranes that is similar to cholesterol.

Adhesion proteins

Membrane proteins that link cells together.

Receptor proteins

Proteins that bind hormones and other substances which change cell activities.

Recognition proteins

Proteins that act as markers allowing the immune system to determine between self and non-self cells.

Transport proteins

Proteins that assist certain substances to cross the cell membrane.

Differentially permeable

A feature of the cell membrane that allows only certain molecules to pass through while regulating the concentrations of substances.

Passive transport

The movement of materials into and out of the cell without the use of energy.

Diffusion

The net movement of molecules from a region of high particle concentration to a region of lower particle concentration.

Concentration gradient

The difference in particle concentration between two regions.

Equilibrium

A state reached when particles are evenly distributed throughout a system and move at equal rates in all directions.

Facilitated diffusion

A form of diffusion requiring substances to be assisted across a cell membrane by transport proteins, such as carrier or channel proteins.

Carrier proteins

Transport proteins that bind to specific molecules on one side of a membrane, change shape, and release the substance on the other side.

Channel proteins

Proteins that form passageways through which ions of a specific size and shape can move across quickly.

Osmosis

The movement of water across a selectively permeable membrane from a region of high water concentration (low solute) to a region of low water concentration (high solute).

Solute

A substance that is dissolved in a solvent to form a solution, such as salt.

Isotonic

A solution where the intra and extracellular fluids of a cell contain equal concentrations of solute.

Hypotonic

A solution with a lower solute concentration compared to another solution.

Hypertonic

A solution with a higher solute concentration compared to another solution.

Turgid

A state in plant cells where the vacuole swells until it is tight due to water entering via osmosis in a hypotonic environment.

Plasmolysis

The process in which the cell membrane pulls away from the cell wall as water moves out of the cell into a hypertonic environment.

Lysis

The process where an animal cell swells and eventually bursts when placed in a hypotonic solution.

Contractile vacuole

A regulatory mechanism in unicellular animal cells that collects and removes excess water to prevent lysis.

Active transport

The process of using energy to move a substance across a membrane from a region of low concentration to a region of higher concentration.

Mitochondria

An organelle whose function is to make energy available to the cell by building up ATP.

ATP (adenosine triphosphate)

The short-term energy storage molecule in cells used as the energy source for active transport.

Sodium-potassium pump

An example of active transport that moves $Na^+$ and $K^+$ ions in opposite directions across the cell membrane in animal cells.

Endocytosis

A form of active transport that moves large polar molecules into the cell via vesicle formation because they cannot pass through the hydrophobic membrane.

Phagocytosis

A form of endocytosis where solids are transported into a cell via vesicle formation.

Exocytosis

The movement of solids or liquids from inside a cell to the external environment via vesicle formation.

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

A relationship that determines a cell's efficiency in exchanging substances; as a cell grows, the volume increases faster than the surface area, decreasing this ratio.

Surface area of a sphere formula

$$SA = 4 \times \text{π} \times r^2$$

Volume of a sphere formula

$$V = \frac{4}{3} \times \text{π} \times r^3$$