Week of Introductions

Welcome to General Biology II at Vanier College.

The primary function of this website is to provide you with study questions and provide you with a open means to communicate solutions to given problems. This way, you can see where your classmates are at, and you can solve these questions as a group.

cell

First Study Topic: Cell Membranes

  1. If a eukaryotic cell has a diameter that is 10 times that of a bacterial cell, proportionally how much more surface area would the eukaryotic cell have? Proportionally how much more volume would it have?
  2. In your own words, describe the molecular structure of the plasma membrane.
  3. A solution of 1 molar (M) glucose is separated by a selectively permeable membrane from a solution of 0.2 M fructose and 0.7 M sucrose. The membrane is not permeable to the sugar molecules. Indicate which side initially has more free water molecules, and which side has fewer. What is the result in volumes (higher or lower) for sides A and B after osmosis has occurred?Osmosis question

4. The ratios of saturated to unsaturated phospholipids in an organism’s membranes can change in response to changes in environmental conditions. In warm environments, how would you expect the fatty acid tails of the membrane phospholipids of tropical plants to be different than those of fish living in cold waters? (HINT: consider how permeability and fluidity of a membrane that contains a low percentage of unsaturated phospholipids compare with those of a membrane that contains a high percentage of unsaturated phospholipids.)

5. Use your knowledge of how the concentration of solutions outside cells affects cell shape to explain why salting meat is an effective way to preserve it (and keep bacteria from rotting it).

6. Tough Question: How is cholesterol transported into human cells? Explain why cholesterol accumulates in the blood of individuals with the disease familial hypercholesterolemia?

 

Published by Stephanie

3 thoughts on “Week of Introductions”

  1. 1. assuming that the shape of a cell is similar to that of a sphere and considering that the formula for the surface area of a sphere is 4(pi)r^2 and that the formula of the volume of a sphere is 4/3(pi)r^3 I would say that the surface area would be 10^2 times larger and the volume would be 10^3 times larger because the radius is now 10^1 times larger.

    2. The plasma membrane is a membrane composed of two phospholipid layers, hence the term phospholipid bilayer. the Phospholipids arrange themselves with the hydrophilic heads positioned towards the outside of the cell as well as towards the inside of the cell leaving the hydrophobic tails to meet in the middle. cholesterol, which is a steroid, is found within the plasma membrane and has the role of ensuring proper arrangement and spacing of the phospholipids. in short the cholesterol keeps the phospholipids from bunching together if temperature decreases and prevents them from dispersing if the temperature increases. proteins are another component of the plasma membrane. there are proteins that go through the membrane and others that rest within it. their purpose is to allow compounds and molecules to permeate the membrane.

    3. the side with the sucrose and fructose has more free water initially since that side has an overall concentration of 0.9 M compared to the side with glucose which has a concentration of 1.0 M. After osmosis has occurred side A will rise and side B will lower since water flows from low to high concentration in order to even the concentrations out.

    (I started out by doing my best at answering the first half of the questions)

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  2. 4. I believe that when the outside solution is hypertonic, meaning it has higher concentration that the inside of the cell, by means of osmosis, the water will travel from the cell to the outside and this will cause the cell to shrivel. When the outside solution is hypotonic, water will travel from the outside to the inside of cell and the cell will expand and can burst. When the solution outside is isotonic, the water will no travel since the concentrations of solute outside and inside the cell are equal.
    Therefore, to preserve meat, salt is used because it will draw the water away from the meat since the outside is more concentrated with NaCl molecules. The bacteria that are present will die because the salt has taken the moisture from their habitat.

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