Osmosis and Diffusion:

Diffusion is the process where molecules spread out from an area of high concentration to an area of low concentration. For example, if someone uncorks a bottle of perfume in a classroom, before long people on the other side of the classroom can smell the perfume because the perfume molecules have diffused, or spread out. This happens because the molecules collide and bounce off of one another.

  • Write a definition below of osmosis in your own words using your textbook and this worksheet.

For each of the following scenarios, write how you think the molecules would move.

  1. If you drop food coloring into a pitcher of water, and wait a while, what will happen to the molecules of food coloring in the pitcher?
  2. The air you breathe in has more oxygen than there is inside your lung cells. Since oxygen is a small molecule, itcan easily pass through cell membranes. Will oxygen enter or leave the cells in your lungs?
  1. If you have kidney failure, you might have to have a medical procedure called kidney dialysis. Blood from your body is run through dialysis tubing in a machine and then returned to you. The dialysis tubing is covered in liquid called dialysis fluid. If your kidneys are not working, a toxic compound called urea builds up in your blood. In order to get rid of the urea in your blood, how much urea should the dialysis fluid have in it and why?

Osmosis is the diffusion of water molecules. In a cell, the cell membrane prevents many large molecules and ions from moving into and out of the cell. Since water is small, it is able to pass directly through the cell membrane. If there is an uneven concentration of something inside and outside of a cell, water molecules will move through the cell membrane to make the concentration equal.

For example, if a red blood cell is placed in salt water, it will shrivel up because water will leave the cell to try and even out the salt concentration inside and outside of the cell. If a red blood cell is placed in pure water the reverse will occur; it will burst because water will flow into the cell to make it less concentrated.

  • Write a definition of osmosis in your own words using your textbook and the definition on this worksheet.
  1. A fresh water aquarium plant is placed in a salt water aquarium. What will happen to the cells of the plant?
  1. If you drink a large amount of salty ocean water, what will happen to the cells in your body? (hint: it is like when you swim in the water at Galveston)
  2. If you take a nice long bath, and you notice your skin is starting to look weird and wrinkly, what is happening to your skin cells? Is water flowing into or out of them?

Using the picture below and your textbook, write a definition for the words below. Then explain the picture below using the terms. Focus in on which way the water would have moved.

  1. Isotonic -
  1. Hypotonic -
  1. Hypertonic -
  • For questions 4,5 and 6 now add to the definition if they are isotonic, hypertonic, or hypotonic.

Facilitated Diffusion and Active Transport

  1. Some of the compounds your body needs are too large to pass through the cell membrane. One way cells get around this is through special proteins that act as channels for the substance to move through. This is called facilitated diffusion. For example, the cells in your intestines have special channel proteins that allow glucose to diffuse through the cell membrane. If you drink cool aid, what will happen to the sugar in the drink when it reaches the cells in your intestines?
  1. Some substances that cells need are in short supply. This means that in order to get them, the cells must use energy because they will not diffuse on their own. Anytime a cell has to use energy to move molecules or substances it is known as active transport. For example, your body needs calcium to build and maintain your bones. Since most food does not have that much calcium in it, your intestines actively pump any calcium into your cells using energy. Fresh water plants also use active transport to get rid of extra water. How do you think your body gets most of its vitamins – diffusion, osmosis, facilitated diffusion or active transport?

Write your own Scenarios

  1. Describe a situation in which diffusion would occur. Include an explanation of how the molecules would move.
  2. Describe a situation in which osmosis would occur. Include an explanation of how the water molecules will move.
  3. You have three different aquariums. Determine weather the environment the fish is in is hypotonic, hypertonic, or isotonic. Think about the size of the fish and which way the water would have moved and why.

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