Tonicity, Water Potential, and Active Transport
This page delves into the concepts of tonicity, water potential, and active transport, which are crucial for understanding cellular processes and homeostasis in AP Biology Unit 2: cell structure and function.
Tonicity is introduced as a way to describe the osmotic gradient between solutions:
-
Isotonic: A state of equilibrium where the concentration of solutes is equal on both sides of a semipermeable membrane.
-
Hypertonic: A solution that has a higher concentration of solutes compared to the cell, causing the cell to shrivel due to water loss.
-
Hypotonic: A solution that has a lower concentration of solutes compared to the cell, causing the cell to swell as water enters.
The concept of water potential is explained as the tendency of water to flow from an area of higher water concentration to an area of lower water concentration. The relationship between water potential and concentration is expressed mathematically, with the constant R given as 0.0831.
Active transport is described as the movement of substances against their natural flow (typically from an area of lower concentration to an area of higher concentration). This process requires energy in the form of ATP. The sodium-potassium pump is presented as an example of active transport, where three sodium ions are moved out of the cell while two potassium ions are brought in.
Vocabulary: Tonicity - The ability of a solution to cause a cell to gain or lose water through osmosis.
Example: When a plant cell is placed in a hypotonic solution, it becomes turgid as water enters the cell, pressing the cell membrane against the cell wall.
Definition: Water potential is a measure of the potential energy of water per unit volume relative to pure water in reference conditions.
Highlight: The sodium-potassium pump is a crucial example of active transport, maintaining the electrochemical gradient necessary for nerve impulse transmission and other cellular functions.
Quote: "Active Transport: movement against natural flow (& to ↑ Concentration)"