The Cell Membrane and Cell Transport The Master of Homeostasis

Terms to Know Homeostasis Diffusion Osmosis Active Transport Passive Transport Cell membrane Selectively permeable Gradient Equilibrium Hypotonic solution Hypertonic solution Isotonic solution

Homeostasis An organism keeping its internal structures at constant levels is homeostasis One of the main structures of a cell responsible for maintaining homeostasis is the cell membrane

The Cell Membrane The cell membrane or plasma membrane is a flexible boundary between the cell and its environment It is the outermost structure (except in cells with cell walls)

The Cell Membrane The cell membrane allows certain things into the cell, such as water and nutrients, and other things out of the cell. Functions of the Cell Membrane include The cell membrane is selectively permeable. This means the cell membrane only lets specific things in or out. The cell membrane also protects and supports the cell.

The Cell Membrane

The Cell Membrane The cell membrane is made of a phospolipid bi-layer. The outer parts are phosphates and the inside is made of fatty acids. On the outside there are carbohydrates molecules that help with cell recognition. Also on the membrane are large protein molecules that help move materials in and out of the cell.

Phospholipid Bi-layer

Cell Membrane and Homeostasis Because of the selective permeability of the cell membrane, the cell only allows good things in and keeps bad things out of the cell. This helps the organism stay healthy and stay alive.

Mini Partner Quiz Review Question: What are two examples of eukaryotic organisms. Review Question: What is the difference between prokaryotic and eukaryotic cells? Review Question: True/False Both plant and animal cells have mitochondria and cell membranes. List 2 functions of the cell membrane. Explain why the cell membrane is largely responsible for homeostasis.

Passive Transport Passive transport is when a cell transports things across the membrane without energy. Things always move from high concentration to low concentration when no energy is used.

An Example of Passive Transport is Diffusion Diffusion is the movement of particles from an area of high concentration (more particles) to an area of low concentration (less particles). Ex: the smell of chocolate chip cookies moving throughout the room. The concentration of the smell is high by the oven but then moves throughout the room where there is low concentration. Activity: in a beaker, fill with corn syrup and place a few drops of food coloring on the top of the syrup in one location. Discuss that the concentration of food coloring particles is very high where the drops are located and that the particles of corn syrup and food coloring are randomly moving, even though you cannot see the individual particles moving. Ask the students what will happen if you leave the mixture overnight. Discuss that because of the net movement of particles from an area of higher concentration to an area of lower concentration, the food coloring should distribute itself evenly throughout the mixture until it reaches equilibrium.

Diffusion in Cells Movement of particles from areas of high concentration to low concentration are said to be moving “down the concentration gradient” The particles move until they are evenly distributed, which is called “equilibrium” Like floating down a river. It requires no energy.

A specific type of Diffusion that deals with water is Osmosis The diffusion of water molecules across a selectively permeable membrane is known as osmosis. The water moves from high concentration to low concentration. Still doesn’t require energy.

Hypotonic Water is always going to move where there is less water. If there is more dissolved solute on the inside of the cell that means that there is less water on the inside of the cell. Water will move from high to low concentration, it will move into the cell. This is called a hypotonic solution. The cell will swell up big like a hippo.

Hypotonic

Hypertonic If the concentration of dissolved solute is higher on the outside of a cell then that means there is less water on the outside of the cell. The water will move out of the cell until equilibrium is reached. This cell is said to be in a hypertonic solution where there is more particles outside of the cell. As water moves out of the cell, the cell will shrink.

Hypertonic

Isotonic If the concentration of dissolved solute outside the cell are the same as inside of the cell, water will move both directions equally. A cell in this case is said to be in an isotonic solution where the concentration of dissolved particles is the same on both sides of the cell membrane.

Isotonic

Osmosis Type of Solution Solution (outside) concentration Cell (Inside) concentration Where is there more water? Which way will water move? Hypotonic More water Less water Hypertonic Isotonic Same amount Same Amount

Osmosis with Blood Cells

Active Transport Sometimes the cell needs to get things inside and outside of the cell against the concentration gradient This requires energy from the cell and is called active transport

Some Molecules are Moved Across the Membrane using Protein Pumps They are powered by ATP, an energy source made by the mitochondria. Like paying money to lift up the arm at the parking garage.

Protein Pumps

Another Form of Active Transport is Exocytosis Materials leaving the cell by way of vesicles.

Last Form of Active Transport is Endocytosis Materials entering the cell by way of vesicles.

What is the main goal of all these processes? To maintain homeostasis.