Unit 2 Concept 2🧬✅

Science

Homeostasis

The need of an organism to stay stable by regulating internal conditions.

Dynamic Equilibrium

A condition maintained in homeostasis where internal parameters are not always identical, but stay within a balanced range.

Stimulus

A change in the environment that evokes a response in an organism.

Response

A change in an organism that occurs as a result of a stimulus.

Positive Feedback Loop

A feedback mechanism in which the output or product of a system intensifies or amplifies the response, such as in human childbirth or fruit ripening.

Negative Feedback Loop

A feedback mechanism in which the output or product of a system causes a counter response to return the system to a set point and achieve stabilization, such as thermoregulation, osmoregulation, or blood sugar regulation.

Selectively Permeable

A characteristic of the cell membrane meaning it is picky about what goes in and out, allowing small, nonpolar, hydrophobic, or neutral molecules and $H_2O$ to pass easily while restricting polar or large molecules.

Passive Transport

Cellular transport that requires no extra energy by the cell because molecules move down the concentration gradient from an area of high concentration to an area of low concentration.

Active Transport

Cellular transport that requires extra energy ($\text{ATP}$) to move materials into or out of the cell against the concentration gradient from low concentration to high concentration.

Solute

The substance that gets dissolved in a solution, such as lemonade powder.

Solvent

The substance that does the dissolving in a solution, such as water.

Solution

A uniform mixture of two or more substances, such as lemonade.

Concentration

The amount of solute dissolved in a solvent, abbreviated by the symbol $[\text{ }]$.

Simple Diffusion

The spreading out of small, nonpolar molecules across a membrane down a concentration gradient from high to low concentration until equilibrium is reached.

Facilitated Diffusion

Passive transport where a transport protein (channel or carrier) helps diffuse large molecules like glucose ($C_6H_{12}O_6$) or polar ions like calcium ($Ca^{2+}$) down a concentration gradient across the cell membrane.

Osmosis

The simple diffusion of water molecules ($H_2O$) across a cell membrane down a concentration gradient from high water concentration (low solute) to low water concentration (high solute).

Hypertonic Solution

A solution where the water concentration is lower than the cell's cytoplasm, causing net movement of water out of the cell and leading the cell to shrivel.

Hypotonic Solution

A solution where the water concentration is higher than the cell's cytoplasm, causing net movement of water into the cell and leading the cell to swell.

Isotonic Solution

A solution with a water concentration identical to the cell's cytoplasm, resulting in no net movement of water so the cell stays the same size.

Molecular Pump

An active transport mechanism where a cell uses energy ($\text{ATP}$) to pump charged ions like potassium ($K^+$), chlorine ($Cl^-$), and sodium ($Na^+$) across the membrane through a protein channel against their concentration gradient.

Endocytosis

Active transport that uses vesicles to move large particles into the cell, such as white blood cells engulfing bacteria to fight infection.

Exocytosis

Active transport that uses vesicles to export materials out of the cell, such as nerve cells secreting neurotransmitters to send signals.