Plasma Membrane and Cellular Transport
Structure of the Plasma Membrane
1. Why do you think it is important to have a membrane surrounding each of our trillions of cells? Expect varying answers, but the idea is have the students understand the plasma membrane separates the cells from their environment and each other while also regulating the material within each cell. 2. What are two distinctive physical features of phospholipids? Heads are polar (water soluble, hydrophilic) and tails are nonpolar (water hydrophobic).
Describe the conformation of the phospholipid bilayer of the plasma membrane. What abundant fluid leads to his conformation? Because the phospholipids heads are polar and the tails are nonpolar, their orientation is directly influenced by their polar/nonpolar interaction with water. By forming a bilayer, the nonpolar tails point into the space between the layers and can avoid water while the polar heads point towards the outside of each layer and so they can orient towards water. 4. What molecule in the plasma membrane directly affects the membrane’s fluidity? The phospholipids of the bilayer aren’t static, they move laterally around, like a fluid. Cholesterol can reduce or improve the fluidity of the plasma membrane. 5. What is the function of the glycoproteins and glycolipids of the plasma membrane? Glycoproteins and glycolipids serve as cellular identifiers or signatures. They help the cell recognize friend and foe.
Use the illustration to identify the following components of the plasma membrane: cholesterol, glycoprotein, phospholipids, membrane protein, and glycolipid.
Houston Community College
Cellular Transport: Diffusion and Osmosis
1. Define cellular homeostasis. How does the plasma membrane contribute to cellular homeostasis? Cellular homeostasis is the maintenance of a constant environment within a cell, in which the plasma membrane regulates the passage of molecules across it.
2. Define diffusion. Diffusion is the movement of particles from a region of high concentration to a region of lower concentration.
3. What is the concentration gradient? The concentration gradient is a difference in concentration between a region of higher concentration and region of lower concentration. 4. The cell continually produces carbon dioxide as a by-product of cellular respiration. How does the cell keep carbon dioxide from building up in the cytoplasm and poisoning the cell? Carbon dioxide diffuses across the plasma membrane into the extracellular fluid where its concentration is lower than in the cell. 5. What distinguishes osmosis from diffusion? Osmosis is the diffusion of water, whereas diffusion can be applied to any molecule. 6. If the concentration of protein in one solution (Solution A) is greater than a second solution (Solution B), in which solution is the concentration of water greater? Use the illustration to answer the following questions about osmosis.
In which direction will water move through the membrane? If the proteins could diffuse, in which direction would they move? Water will move from B to A. Proteins would diffuse from A to B, if they could.
Osmotic pressure is the pressure exerted by water on its container as it moves by osmosis into a region of lower water concentration. What do you think might happen if a pressure equivalent to osmotic pressure was applied to side A?
e water would not move from side B to side A; the unequal concentrations would remain the same. 8. Fill in the summary tables for each type of solutions. 8a. What is an isotonic solution?
The concentration of dissolved substances is equal inside the cytoplasm and in the extracellular fluid. Isotonic Solution Concentration of dissolved substances (solute) Concentration of water (solvent) What...