Lab 4: Diffusion & Osmosis

Objectives:

Use calculated surface area-to-volume ratios to predict which cell(s) might eliminate wastes or procure nutrients faster by diffusion.
Explain how cell size & shape affect the overall rate of nutrient intake and the rate of waste elimination.
Use representations & models to pose scientific questions about properties of cell membranes and selective permeability based on molecular structure.
Construct models that connect the movement of molecules across membranes with membrane structure & function.
Investigate whether dynamic homeostasis is maintained by active movement of molecules across membranes.

Answer the 3 pre-lab questions in your notebook ahead of time.
Make sure your answer the questions for each section of the lab (if called for).
Create your data tables in your notebooks, not on a separate sheet of paper.
Remember we are not doing any of the "open inquiry" parts to save class time.
We will be part 1 first, then part 3 and ending with part 2.
You need to be on task in this lab or you will not be able to finish in time.

Celery in saltwater and deionized water solutions.

Obtain agar cubes. Do not scratch the surface of the cubes.
Use a ruler and measure the dimensions of each cube and record your measurements.
Place 3 cubes carefully in a plastic cup. Add white vinegar until cubes are submerged. Use a plastic spoon to keep cubes submerged for 10 min (turning the cubes if needed).
Calculate surface area, volume and surface area-to-volume ratio for each cube.
After 10 minutes, use a spoon to remove cubes and blot dry on a paper towel.
Observe cubes. Measure distance white vinegar diffused into each cube.
- Measured from the white edge of the cube to the pink edge.
Calculate rate of diffusion for each cube in cm / min.
Graph rate of diffusion to surface area-to-volume ratio.
Calculate volume each portion that has not changed color (ie. the remaining pink part of the cube)
Calculate the extent of diffusion into each cube as a percentage of the total volume.
Graph the extent of diffusion relative to surface area-to-volume ratio.

Obtain 5 pieces of pre-soaked dialysis tubing. Tie a tight knot in 1 end of each piece.
- String is available too if needed.
Open tubing.
Pour 10 mL of prepared solution into tube. Leave space for expansion but minimal amount of air in tubing.
Tie knot on open end of tubing.
Repeat steps 2 - 4 for remaining tubes with appropriate solutions.
Fill beakers with 100 mL of solutions to pair with cells.
- Water or saltwater are your only options!
Record initial mass of "cell" (a.k.a. the tubing)
Immerse cell into paired solution (beaker) and record any observations.
Record your predictions based on what you know.
Soak for 30 minutes. Record observations.
After 30 minutes, remove from solutions and pat dry. Weigh each cell and determine its final mass.
- Do not throw out solutions in beaker!
Calculate percentage change in mass and record results.

The mystery sucrose solutions ranging from 0M to 1.0M

Make potato cores or use pre-made cores.
Weigh each core and measure the length of each core. Create and table and record.
Place one or more potato cores in each of the mystery sucrose solutions.
Record your observations.
Wait 30 minutes.
After 30 minutes, reweigh cores and calculate the change in mass and percent change in mass for each sample. Record data.

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