LAB 2: Diffusion

• Define hypotonic.

  The concentration of solute(s) is lower, compared to a reference solution.
• Define cyclosis.

  The cycling of the cytoplasm in the cell.
• Temperature is the measure of what?

  The average kinetic energy of the particles of a substance.
• • In a solid, particles vibrate without being displaced much.
  • In a liquid, the particles are moving faster (they have more kinetic energy) so that they bounced off of and move past each other.
  • In a gas, the particles have so much kinetic energy that they bounce farther and tend to be dispersed.
• The continuous random movement of particles in water is known as Brownian movement.
• Diffusion is the net (overall) movement of particles from an area of higher concentration to an area of lower concentration.
• • Molecular weight is just the mass of a molecule of a particular substance.
  • The rate of diffusion (how fast a substance will diffuse) depends on a number of factors including the size, shape and mass of the particles, and the temperature.
• Materials exchanged between a cell and its environment must cross this membrane, a phospholipid bilayer with specialized proteins.
• Materials may enter or exit the cell in one of several ways:

  • Passively: by diffusion (through the phospholipid bilayer) and by facilitated diffusion (through channels or carrier proteins)
  • Actively: by active transport and by cytosis
• Passive movement does not cost the cell any chemical energy.
• Diffusion: Molecules that can pass through the phospholipid bilayer of the plasma membrane may enter or leave the cell through simple diffusion.
• The plasma membrane is called semi-permeable (or selectively permeable).
• Osmosis: diffusion of water across a selectively permeable membrane
• Some small molecules that cannot pass through the phospholipid bilayer may still diffuse across the plasma membrane through channel proteins.
• Aquaporins are channel proteins that facilitate the movement of water.
• Larger molecules may still diffuse across the plasma membrane with the help of carrier proteins.
• Active movement costs the cell chemical energy.
• Active Transport: Some proteins will only move molecules in one direction across the plasma membrane, and will do so regardless of the concentration gradient.
• Some particles may be too large to be handled by any carrier protein. These particles may still be brought into the cell by cytosis: transport via a pocket in the membrane.
• Endocytosis: a particle outside the cell may be enveloped by part of the plasma membrane, forming a vacuole (containing the particle) inside the cell.
• Exocytosis: a particle inside the cell, in a vacuole, may be ejected from the cell when the vacuole fuses with the plasma membrane and releases its contents to the cell's environment.
• Solvent: The liquid in which something is dissolved. In cells this is water.
• Solute: The substance that is dissolved in a solvent. In a solution of sugar and water, sugar is the solute.
• Isotonic: The same concentration of solutes in the inside and outside of the cell.
• Hypertonic: The solution is more concentrated than the cell. The cell shrinks and the cell membrane swells.
• Hypotonic: A solution with a lower solute concentration than the cell.
• As the cells lose water they will tend to collapse like an empty bag, a process called plasmolysis in plant cells, or crenulation in blood cells.
• As the cells gain too much water they tend to swell and may burst (called haemolysis in blood cells).
• Cyclosis: the cycling of the cytoplasm in the cell, sometimes visible because the green chloroplasts are cycling with the rest of the cytoplasm.
• What is the difference between Brownian movement and diffusion

  The Brownian movement is a continuous random movement of particles. Diffusion is the movement from a higher concentration to lower concentration.
• How would the rate of diffusion of a substance be influenced by temperature? Explain.

  A higher temperature causes more kinetic energy and a substance will diffuse quicker.
• Phospholipid bilayer has a polar head and non-polar tails.
• In facilitated diffusion, molecules diffuse across the plasma membrane with assistance from membrane proteins, such as channels and carriers.
• ATP can power active transport to force molecules to go against their concentration gradient (from low to high).
• A lower water concentration likely means there is a greater solute concentration.
• Water moves to areas where there is a higher solute concentration, which means lower water concentration.
• If the cytosol of a bacterial cell is hypotonic to its environment, what would you expect to happen? Explain.

  The cell will begin to swell because water will diffuse into the cell.
• The right side of an aquarium has a solution of salt in water. The left side of this aquarium has a solution of sugar in water. If the right side is hypertonic to the left side, which way will the sugar diffuse?

  The sugar will diffuse to the right side.