Now you will conduct a microscopic study of red blood cells suspended in three solutions. The objective is to determine if these solutions have any effect on cell shape by promoting net osmosis.
1. Place a very small drop of physiologic saline on a slide. Using the medicine dropper, add a very small drop of animal blood to the saline on the slide. Tilt the slide to mix, cover with a coverslip, (make sure the smear is THIN) and, after blotting the slide with a kimwipe to be sure there is no fluid on the slide or cover slip, examine the preparation under the highest-power lens that does not say “OIL”. Notice that the red blood cells retain their normal smooth disc-like shape. Why do you think this happens? Keep this slide for comparison as you complete steps 2 and 3.
2. Prepare another wet mount of animal blood, but this time use 10% saline solution as the suspending medium. Carefully observe the red blood cells under high power AFTER at least 5 min.
Here, for prediction 5, write down what you actually see or what you expected to see any why.
What is happening to the normally smooth disc shape of the red blood cells? If you can’t tell, indicate here what you think should have happened.
What is this phenomenon called? ____________________________________
3. Put a drop of blood on a third slide. Get the blood cells in view at the highest power (not requiring oil) before having your partner add a drop of distilled water to the right edge of the coverslip by folding/twisting a kimwipe in half and place its folded edge at the opposite edge of the coverslip; it will absorb the saline solution and draw the distilled water across the cells. Immediately, watch the red blood cells as they float across the field. After about 5 minutes have passed, describe the change in their appearance compared to their shape before the distilled water was added and as you watched the cells float across the field. Do you see as many cells as you saw before?
What caused this immediate change to occur?
Did the RBCs begin or continue to disappear, or is there no change 5 minutes later? __________Why?
What is this phenomenon called? _____________________________________
Now, place the cover slips in the “Broken Glass” container. Place your blood-soiled slides and test tubes in the bleach or Lysol solution in the sink. Wash thoroughly and set the items out (use racks for tubes and paper towels for other items) to dry.
C. OSMOSIS THROUGH ANIMAL AND PLANT CELLS
I. Chicken eggs have been soaked in vinegar to dissolve the calcium carbonate eggshell. This leaves the selectively permeable membrane surrounding the albumin and yolk intact for this experiment.
1. Place your hand in the beakers and GENTLY examine the eggs in the distilled water beaker and in the glucose/corn syrup beaker. The eggs are fragile. Please handle gently and do not wear gloves.
2. Describe the feel and state of plumpness of the egg in:
40% Glucose or corn syrup:
3. Measure the circumference of each egg by GENTLY using a string and then measuring the length of string:
Egg in distilled water: _____________________________cm
Egg in 40% glucose: ______________________________cm
*For Prediction 6, write down what you actually observed here.
Which egg has the larger diameter? Why?
4. Describe the movement of water (osmosis) for each of the eggs. That is to say, which direction did water move in and why did it move in that direction (aside from the fact that solvent follows solute)?
Egg in distilled water:
Egg in 40% glucose or in corn syrup:
5. Could this process be reversed? _____________ If so, how?
What happens when cells are substantially overfilled with water?
6. What is the purpose of albumin (protein) in the egg white as it pertains to this lab and thinking about how cells in the body are surrounded by fluids?
II. Plant cells possess a cell wall and a plasma membrane. Carrots and Celery have been sliced to expose the plant cells and placed in two different solutions: tap water and 20% NaCl.
Complete Prediction 7 on the last page before proceeding.
- Feel and describe the texture of the carrots and celery in the tap water.
- Define TURGOR PRESSURE: