Diffusion and Osmosis (Miro Bedrousi)

Title: Diffusion and Osmosis

Principle(s) Investigated:

Diffusion, Osmosis , Hypotonic/Hypertonic/Isotonic Solution , semi-permeable membrane

Standards:

MS-LS1-2. Develop and use a model to describe the function of a cell as a whole and ways parts of cells contribute to the function

Materials:

• Gummy bears
• Clear Plastic Cups
• Distilled water
• Salt
• Pen/Pencil
• Quick-write

Procedure:

• Assign students in groups of 3. Each group will need 3 clear plastic cup, 3 gummy bears, 2 teaspoons of salt.
• Label the plastic cups A,B,C
• Pour 50ml of distiled water in Cup B and place a gummy bear in there.
• Pour 50ml of Distilled water, 2 teaspoons of salt in cup "C" and stir the solution. After stirring the solution place a gummy bear in there.
• Place a gummy bear in cup A, with no water or salt. This is going to be our Control.
• Make sure you have your group name written on the cups.
• Set the cups aside, we will observe them tomorrow.
• Meanwhile, predict what will happen to the gummy bears in Cup B and Cup C.

Student prior knowledge:

Students need to know the basic structure of the cellular membrane and it's semi-permeability and what solvent, solute and solutions are.

Explanation:

• Spray air freshener in front of the class, away from students. Have students raise their hands as soon as they smell the air freshener and have them identify the smell if possible.
• Introduce the concept of diffusion. (Google slides)
  • Diffusion is the movement of molecules from a region of high concentration to a region of lower concentration.
  • The reason it happens is because these molecules have energy and they are moving around randomly because of something called brownian motion. What will happen eventually that the molecules will bounce off each other and fill out the entire room. That way they are energetically happy and stable.
• Introduce the concept of diffusion. (Google slides)
  • Net movement of water molecules from a region of high water concentration (dilute solution) to a region of lower water concentration (Concentrated solution) through a partially permeable membrane.
  • Hypotonic solution: A hypotonic solution is one in which the concentration of solute inside the cell is greater than outside of it.
  • Hypertonic solution: A hypertonic solution is one in which the concentration of solute inside the cell is less than outside of it.
  • Isotonic solution: An isotonic solution is when two solutions, separated by a semipermeable membrane, have the same concentrations of solutes and water.
• Allow students to observe their lab results the next day, or in this case, provide them with previously prepared lab and have them incorporate what they learned in their observation.
  • In cup B, the gummy bear has more concentration of solute, in this case sugar, so the distilled water will move in to the hypertonic environment of the gummy bear and it will make it heavier and larger in size.
  • In Cup C; the water from inside the gummy bear's hypotonic environment , will move out to the gummy bear because of high solute (salt) concentration in the outside solution.

Questions & Answers:

• What would happen if we drink sea water to survive? Would you be less thirsty after you drink sea water?
  • When you drink too much seawater, the saltiness outside your cells will increase rapidly and the cells force water molecules out in order to restore balance. So even if you are already dehydrated, drinking sea water will cause your cells to release more water and you will end up peeing out more liquid than you take in.
• What would happen if you chug massive amount of pure water?
  • if you chug a massive amount of pure water, the exact opposite will happen. The saltiness outside your cells will decrease rapidly and water will be forced into your cells. This can cause the cells to swell and burst, which in extreme cases leads to seizures, coma and sometimes death!
• What will happen if you put a freshwater fish in salt water?
  • Freshwater fish cell have hypotonic environment compare to the salt water, meaning they have less of an ion concentration within their cells. Therefore, if placed in saltwater, water will leave their cells through the gills and they will dehydrate.
• Why do grocery stores spray their fresh produce with water?
  • Spraying them with water keeps the produce hydrated.By spring them with water the outside environment tuners into a more hypotonic environment than the inside of the plant cell which allows water to move into the cells in the and fill them with water and maintain its turgidity of the vegetables. This also allows the produce to weight more and appear larger.

Applications to Everyday Life:

Preserving food. For thousands of years, perishable foods such as fish, olives, and vegetables have been preserved in salt or brine. The high salt concentration is hypertonic to bacteria cells, and kills them by dehydration before they can cause the food to spoil. Preserving fruit in sugar principle. (Science Clarified Website)

Super market spraying their produce with water. By doing that the concentration of solute on the surface compare to the inside environment of the plants decreases, therefore water move inside of teh cell where the solute concentration is higher, causing the plants to look fresh and more presentable.

Gas exchange in our lungs. Oxygen and Carbon dioxide are moved in and out of our body though are lungs. At the smallest branches of the bronchi, called bronchioles, there are little sacs known as alveoli, which are surrounded by tiny blood vessels called capillaries. The oxygen from alveoli enters the capillaries where the carbon dioxide moves from the capillaries to the alveolar and out of the lungs

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