Osmosis in Action Mrs. Stewart Biology

Table Talk Watch this video. As a group discuss the answers to these questions: What organism is this? What kind of environment do you think it’s in? What is happening?

Objectives Predict the movement of water when a cell is placed in environments with varying solute concentrations Recognize the importance of homeostasis as a survival mechanism

Quick Review Solutions have: Concentration: Osmosis: Solvent: Solute(s): Concentration: Osmosis: The liquid that dissolves the solute. The substance that gets dissolved. the amount of a substance in a given volume When water moves from high to low concentration.

Cell Transport Passive Transport Active Transport Diffusion Osmosis Facilitated Diffusion Does NOT require energy, moves from HIGH concentrations to LOW concentrations DOES require energy, moves from LOW concentrations to HIGH concentrations, moves LARGE molecules (glucose) via transport proteins Moves small molecules, like CO2 & O2 gases, directly through the membrane Movement of water across the membrane Uses transport proteins to move large molecules through the membrane WITHOUT energy 3 Types of Solutions Hypertonic Isotonic Hypotonic Water moves out of the cell & it shrinks Water moves into the cell & it swells Water moves equally in and out of the cell; it stays the same size Protein Pumps Endocytosis Exocytosis Transport proteins that require energy to do work. Example: Sodium / Potassium Pumps are important in nerve responses. Materials ENTER the cell through a vesicle formed by the membrane Materials EXIT the cell through a vesicle formed by the Golgi Body Controlled via the Cell Membrane

So What? Cells live in solutions, both in the environment and in the body. So we’ve named the three types of solutions: Isotonic Hypertonic Hypotonic

Isotonic Isotonic: What happens: Concentrations of solutes are the same inside and outside of the cell. Water is at an equilibrium so it moves freely into and out of the cell at the same rate. The cell stays the same – no change

Hypertonic Hypertonic What happens? Concentrations of solutes are higher outside the cell than inside. Water moves outside the cell in order to create a dynamic equilibrium. Cells shrivel up and may die (in plants this is called plasmolysis.)

Hypotonic Hypotonic: What happens: Concentrations of solutes are lower outside the cell than inside. Water moves into the cell in order to create a dynamic equilibrium. Cells expand and may burst (this is called cytolysis.)

Summary Good graphic on page 99.

Review Watch this video again. As a group discuss the answers to these questions: What organism is this? What kind of environment do you think it’s in? What is happening?

Quick Review Isotonic – solutes are __________ within the solution in comparison to the cell Hypertonic – solutes are __________ within the solution in comparison to the cell Hypotonic – solutes are ___________ within the solution in comparison to the cell Equal Higher Lower

Objectives Predict the movement of water when a cell is placed in environments with varying solute concentrations Recognize the importance of homeostasis as a survival mechanism

Cell Responses to Osmosis Land Organisms: Saltwater Organisms: Freshwater organisms: Cells inside our bodies are in slightly hypotonic environments. No problems under normal conditions. Live in a hypotonic environment.

Hypotonic Environment Defenses Single-cell organisms: Contractile Vacuole: Multi-celled organisms: Solute Pumps: a sac that stores water and when it is full the sac contracts and the water is expelled. (If it fails the paramecium will die.) Proteins in the cell membrane can pump solutes out of the cell, making the concentrations of water more equal.

Plant Cells Hypotonic Environments: Turgor Pressure Hypertonic Environments: Plasmolysis As the plant cell swells, the pressure of the water is not enough to break the cell wall. This gives soft plants rigidity. (this is why plants stand tall) As plant cells lose water, the cell membrane pulls away from the cell wall and turgor pressure is lost and the plant wilts.

No Defenses Some cells have no defense against osmosis. Example: Red Blood Cells - hypotonic Red Blood Cells - hypertonic

Review Watch this video again. As a group discuss the answers to these questions: What organism is this? What kind of environment do you think it’s in? What is happening?

Objectives Predict the movement of water when a cell is placed in environments with varying solute concentrations Recognize the importance of homeostasis as a survival mechanism