Wendy Moore
EDU 235
Microteaching
Dr. Leonard
April 24, 2006
Biology – Diffusion and Osmosis
Introduction/Review: We have been learning about the body and what makes up everything in the body as well as any other living organism – cells. One of the key processes that the body carries out is diffusion and osmosis. We have already talked about diffusion and now we are going to talk about osmosis. Review diffusion.
Essential Questions:
What is osmosis and how does it relate to the body
Teacher Input:
Osmosis – the movement of water molecules across a semi permeable membrane (cell membrane) from an area of high concentration to an area of low concentration
So osmosis is just the diffusion of water.
The size of the solute molecules doesn’t matter because the water molecules is moving
Cells are completely semi permeable to water
There are three types of solutions:
· Hypertonic – high concentration of solute relative to another solution (cytoplasm). When a cell is in hypertonic solution, the water diffuses out of a cell causing to shrivel.
· Hypotonic – low concentration of solute relative to another solution (cytoplasm). When cell is in hypotonic solution, the water diffuses into the cell causing it to swell or perhaps burst
· Isotonic – contain same concentration of solute as another solution. When cell is placed into isotonic solution, the water diffuses in and out of cell at same rate
How does osmosis relate to the body?
Cell membranes regulate the flow of substances into and out of the cell through osmosis
Osmosis is seen greatly in the excretory system:
Small intestines – this is where secretion and absorption of water occurs because small intestines is the portal of absorption of virtually all nutrients into the blood
Functions of excretory system:
· Collect water and filter body fluids
· Remove and concentrate waste products from the body fluids and return other substances to body fluids as necessary (homeostasis)
· Eliminate excretory products from body
Guided practice:
Lab: explaining the procedure of osmosis using the dialysis tubing and showing the process.
Set up three dishes
Dialysis tubing represents semi-permeable membrane.
Hypertonic – place 40% syrup solution tube in pure syrup. Water diffuses out into bowl and causes cell to shrink
Hypotonic – place 40% syrup solution tube in pure water. Water diffuses into tube making it swell
Isotonic – place 40% solution tube in same 40% solution. Diffusion is equal across membranes.
Independent practice:
Let students observe the lab, make measurements, and record observations
Closure:
Reiterate what we learned and ask if there are any questions.
Evaluation:
Ask the students questions on the difference between the isotonic, hypertonic, and hypotonic solution and ask them to explain what happened. Collect their lab work. Then based on their answers and work, observe how well they learned the material. This will also tell how well I taught and explained information.