LAB EXAM Flashcards
Why is it important to replicate an experiment?
To ensure accurate, repeatable results (not due to errors in procedure or other set of environmental conditions present)
Describe an egg in a solution with a high concentration of sucrose (reference tonicity, appearance)
Solution is hypertonic (higher concentration of sucrose in solution than in cell); membrane is permeable to water (and not sucrose), so water moves from low [sucrose] to high [sucrose] (i.e. moves from cell to outside); cell appears shriveled, smaller (loss of weight)
Describe an egg in a solution with a low concentration of sucrose (reference tonicity, appearance)
Solution is hypotonic (lower concentration of sucrose in solution than in cell); membrane is permeable to water (and not sucrose), so water moves from low [sucrose] to high [sucrose] (i.e. moves from outside to cell); cell appears bloated/larger (gain weight), may lyse (explode)
Describe an egg in a solution with a normal concentration of sucrose (reference tonicity, appearance)
Solution is isotonic (same concentration of sucrose in solution and in cell); no difference in [sucrose], so no net water movement (dynamic equilibrium, so water moves, but no NET movement) (minimal/no change in weight)
Is the membrane permeable to water?
Yes, we are assuming that the membrane is permeable to water, and thus is impermeable to the solutes; for mass to change, water is diffusing in/out of the egg (since membrane is impermeable to solutes), so must be permeable to water
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Is the membrane permeable to sucrose?
No, cell wants to keep solutes within; therefore must be impermeable to sucrose
If permeable to sucrose, sucrose would be able to diffuse out of egg
The mass of an egg increased by an average of 1.30 g. Is the solution hypertonic, hypotonic, or isotonic?
The solution is hypotonic
- Mass increased
- Membrane only permeable to water, so water must enter cell
- Therefore lower concentration of solutes in solution (higher concentration of water)
- Water diffuses into cell, increases mass
The mass of an egg decreased by an average of 1.20 g. Is the solution hypertonic, hypotonic, or isotonic?
The solution is hypertonic
- Mass decreased
- Membrane only permeable to water, so water must leave cell
- Therefore higher concentration of solutes in solution (lower concentration of water)
- Water diffuses out of cell, decreases mass
The mass of an egg increased by an average of 0.01 g. Is the solution hypertonic, hypotonic, or isotonic?
The solution is isotonic
- Mass relatively the same
- Minimal change in mass=minimal water movement
- Therefore similar/same concentration of solutes in solution and cell
- Minimal/no water movement, minimal/no change in mass
What is a partition coefficient? How is it related to polarity?
Partition coefficient = Solubility in oil/Solubility in water;
-Value closer to 1 = high solubility in oil, low solubility in water
-Value close to 0 = low solubility in oil, high solubility in water
-Polar solvents dissolve polar solutes
-Water = polar –> high solubility in water = more polar (partition coefficient closer to 0)
-Oil = non-polar –> high solubility in oil = less polar (partition coefficient closer to 1)
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Why does a solute’s solubility in oil affect its ability to cross the RBC membrane?
High solubility in oil = low polarity –> Low polarity = less attraction to polar molecules in solution (i.e. water), phosphate heads –> Crosses membrane faster
How do very polar molecules and strongly charged ions cross cell membranes?
Via membrane transport proteins –> Channels and Carriers
- Carriers typically have 2 shapes; 1 with solute, 1 without
- Channels allow specific solutes to pass through a “pore” the proteins forms on the membrane
Define independent and dependent variables
Independent –> Variable that is being manipulated
Dependent –> Variable being measured
How is it possible that two solutions with the same solute concentration have different results in terms of lysis time?
They have different permeabilities (i.e. the more permeable the membrane is to the solute, the faster the lysis, so different solutions = different permeabilities = different lysis times)
If the lysis time of solute X is twice as fast as that of solute D, what does it mean with regards to the permeability of the membrane to solute X and D?
The membrane is twice as permeable to solute X as to solute D because solute X (and the water that followed) was able to enter the cell twice as fast
Why does a solution of distilled water cause lysis faster than a solution of 0.3M ethylene glycol?
Because for lysis in the ethylene glycol solution, solute has to enter the cell, and then have water follow it (moving down its concentration gradient)
For distilled water, the water can directly enter the cell and thus cause lysis faster
What is the purpose of a negative control?
To ensure that a confounding variable (a complicating factor) doesn’t interfere with the results
