Cell Transport

Homeostasis

Need of an organism to stay stable by regulating internal conditions. A dynamic equilibrium is maintained which means it is not always the same, but things stay within a range.

Stimulus

Change in environment.

Response

A change in the organism as a result of a stimulus.

Feedback Mechanisms

Evolved to help maintain homeostasis in organisms as they respond to stimuli.

Positive Feedback Loop

The output or product of a system intensifies the response. Example is childbirth where hormones released intensify contractions.

Negative Feedback Loop

The output or product of a system causes a counter response to return to a set point. Example is sweating to get back to normal body temperature.

Selectively Permeable

Picky about what goes in and out.

Membrane Access

Things that are small, nonpolar, hydrophobic, and or neutral, as well as water.

Hard Membrane Access

Polar and or large molecules.

Passive Transport

Requires no energy. Molecules move from high concentration to low concentration areas down the concentration gradient.

Passive Transport Examples

Simple diffusion, facilitated diffusion, and osmosis.

Active Transport

Requires extra energy in the form of ATP to bring materials into the cell or expel materials out of the cell moving from low to high concentration against the concentration gradient.

Active Transport Examples

Molecular pumps, exocytosis, and endocytosis.

Solute

What gets dissolved. Example is lemonade powder.

Solvent

Does the dissolving. Example is water.

Solution

Uniform mixture of two or more substances. Example is lemonade.

Concentration

Amount of solute dissolved in solvent. Symbol for abbreviation is [ ].

Concentration Gradient

Difference in concentration of a substance from one location to another.

Simple Diffusion

Type of passive transport. The spreading out of molecules across a membrane until equilibrium is reached. Molecules move down a concentration gradient, from high concentration to an area of low concentration.

Facilitated Diffusion

Type of passive transport. A transport protein helps to facilitate the diffusion of molecules that normally could not pass through the cell membrane. Molecules move down a concentration gradient, from high concentration to an area of low concentration. Transport proteins can act as a channel or a carrier.

Osmosis

The simple diffusion of water across the cell membrane. Water molecules move down a concentration gradient, from high water concentration to an area of low water concentration until equilibrium is reached.

Hypertonic Solutions

Water concentration is lower than the cell’s cytoplasm. Net movement of water out of the cell causes the cell to shrivel.

Hypotonic Solutions

Water concentration is higher than the cell’s cytoplasm. Net movement of water into the cell causes the cell to swell.

Isotonic Solutions

Identical water concentration to the cell’s cytoplasm, so the cell stays the same.

Molecular Pumps

A type of active transport. Uses energy to pump molecules across the membrane, against the concentration gradient, through a protein channel.

Endocytosis

Type of active transport. Uses vesicles to move large particles into the cell.

Exocytosis

Type of active transport. Uses vesicles to export materials out of the cell.

Phagocytosis

Type of endocytosis. Cell “eating.” The cell engulfs solids into a vesicle and digests them.

Pinocytosis

Type of endocytosis. Cell “drinking.” The cell engulfs liquids into a vesicle and digests them.