How do you prepare phenolphthalein solution for the diffusion indicator?

Weigh 1 gram of phenolphthalein and add it to a beaker containing 100 milliliters of 95% ethanol. Stir until the phenolphthalein fully dissolves into the ethanol. This solution serves as the diffusion indicator and will be added to the agar later to visualize pH changes during the experiment.

What is the correct procedure for preparing a 0.1 molar sodium hydroxide solution?

Measure 80 milliliters of water into a beaker and add 0.4 grams of NaOH. Stir until the solute dissolves completely, then bring the total volume to 100 milliliters with additional water. This creates a 0.1 molar basic solution used in the agar preparation.

How should you prepare the agar with phenolphthalein indicator?

Weigh 20 grams of dehydrated agar powder and add to 1 liter of water. Heat to near boiling until fully clear, then cool to 55°C. Add 10 milliliters of phenolphthalein ethanol solution and slowly add the 0.1 molar sodium hydroxide until the agar turns vibrant pink. Pour to 3 centimeters depth in a tray and refrigerate for several hours.

What steps are involved in preparing a 1% starch solution?

Weigh 10 grams of soluble starch and add to 500 milliliters of distilled water on a magnetic stir plate. Allow the starch to dissolve completely, then bring the final volume to 1 liter with additional distilled water. This solution is used as a test substance in dialysis tubing experiments.

How do you prepare 1 molar NaCl and dextrose solutions?

For 1M NaCl, dissolve 58.4 grams in 500 milliliters of distilled water in a 1-liter container, then bring volume to 1 liter. For 1M dextrose, add 180.2 grams of dextrose powder to 500 milliliters of distilled water in a 1-liter beaker, then bring to 1 liter. Both solutions are used to test osmotic effects through dialysis tubing.

How should dialysis tubing be prepared and stored?

Cut dialysis tubing into 20-centimeter pieces and soak them in distilled water, keeping them moist at all times. Excess tubing can be stored at 4°C in 20% ethanol to prevent bacterial growth. Proper preparation ensures the tubing remains flexible and functional for osmosis experiments.

What is the correct ratio and procedure for preparing hydrochloric acid solution?

Measure 25 milliliters of HCl and add to 475 milliliters of water to create approximately 500 milliliters of dilute acid solution. This diffusing acid is used to test how substances move across agar and demonstrates principles relevant to macromolecules identification using indicator solutions.

Diffusion and Osmosis

Concepts Instructor Prep Student Protocol

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Diffusion and osmosis are important concepts that explain how water and other materials that cells need are transported across cell membranes.

Let's talk about diffusion first. It is defined as the net movement of particles from an area of high concentration to an area of lower concentration. The graduated change in concentration between the two areas is referred to as the concentration gradient. Although diffusion is net directional, the particles are constantly moving in both directions due to random motion, so even at equilibrium when the particle density is the same throughout the concentration gradient, particles continue to move in both directions at a constant exchange rate.

Similarly, water moves across cell membranes by diffusion in a process called osmosis, but not everything can freely pass through cell membranes, which is why they are referred to as semi-permeable. This is important, because it means that cells can regulate and maintain different concentrations of solutes inside versus outside their membranes. Depending on the relative solute concentrations of solutions separated by semi-permeable membranes we refer to them as hypotonic, isotonic or hypertonic. Hypotonic is when the solute concentration is greater inside the cell in comparison to outside. Isotonic is when the inside solute concentration equals the outside concentration. Hypertonic is when the outside solute concentration exceeds the inside solute concentration. This can affect the movement of water into and out of the cell as water moves to the area of greater solute concentration. In turn, this can affect the shapes of the cells causing cell bloating in hypotonic solutions, no shape changes in isotonic solutions and the cell shrivels in the presence of hypertonic solutions.

The capacity for water to move into cells is different between plant and animal cells because of the presence of the additional plant cell wall. Cell walls are rigid and only permeable to small molecules. When water moves into plant cells the membrane gets pushed up against the cell wall creating hydrostatic or turgor pressure. This pressure limits the amount and rate at which water can enter the cell.

Diffusion is also a major limiting factor to cell size and helps explain why unicellular organisms are generally very small. Multi-cellular organisms are made up of many small cells giving a greater total surface area to volume ratio and increasing diffusion rates. Many aspects of our physiology, like breathing and digestion rely on diffusion. For example, human lungs have many small alveoli which are like small pockets. This extra surface area makes the lung more efficient at diffusion of gases in and out of the bloodstream.

In this lab, you will use two cell models, agar cube and dialysis tubing to test the principles of diffusion and osmosis.

At the end of this lab, students should know...

$$\rightleftharpoonup{xx}$$ $$\longleftharp{xx}$$, $$\longrightharp{xx}$$,

What is diffusion?

Diffusion is the net movement of particles from an area of high concentration to one of lower concentration.

How is movement of molecules into and out of cells regulated?

Movement of molecules into and out of cells is mediated by the semi-permeable cell membrane.

What is osmosis?

Water moving across cell membranes by diffusion is referred to as osmosis.

How do plant cell walls affect osmosis?

In plant cells, the additional cell wall means the amount of water that can enter a cell is limited by turgor pressure.

How does diffusion affect cell size and physiology?

Increased diffusion rates at larger cell sizes means unicellular organisms are typically very small. In multicellular organisms, physiology may be adapted for greater surface area in organs where diffusion is necessary.