4: Exchange & Transport

• Name the three factors influencing rate of diffusion?

  Surface area, concentration difference & membrane thickness
• What is Fick's law?

  Rate of diffusion is directly proportional to surface area multiplied by concentration difference divided by membrane thickness
• How does increasing surface area affect diffusion rate?

  Increases it
• How does increasing mebrane thickness affect diffusion rate?

  Decreases it
• How does increasing the concentration gradient affect diffusion rate?

  Increases it
• Why are some diffusion surfaces linked to transport systems?

  To maintain a concentration gradient
• How does a small lipid-soluble molecule move across a phospholipid bilayer mebrane?

  Simple diffusion
• What is the main component of a cell membrane?

  Phospholipids
• How are the phospholipids in a cell membrane arranged?

  In a bilayer with hydrophobic hydrocarbon tails facing in and hydrophilic phosphate heads out
• What may stop something diffusing freely in or out of a cell membrane?

  If its polar, charged, not lipid-soluble or large
• What do peripheral proteins on a cell membrane do?

  Act as receptors
• What do integral proteins in a cell mebrane do?

  Act as protein channels
• What does cholesterol in a cell membrane do?

  Increases flexibility
• What is a glycoprotein?

  A carbohydrate attached to a protein
• What is a glycolipid?

  A carbohydrate attached to a lipid
• What do glycoproteins in a cell membrane do?

  Act as recognition sites & allow cell adhesion
• What do glycolipids in a cell membrane do?

  Act as recognition sites & help maintain cell stability
• What is the name of the model used to describe the cell membrane?

  Fluid mosaic model
• Can water, oxygen and carbon dioxide freely diffuse out of a cell membrane?

  Yes
• Can glucose, amino acids and urea freely diffuse out of a cell membrane?

  no
• If a molecule cannot freely diffuse out of a cell membrane, how will it be moved across?

  Using a channel or carrier protein, known as facilitated diffusion
• What is passive transport?

  A type of membrane transport which doesn't require any energy to move substances across
• If simple diffusion an example of passive or active transport?

  Passive
• Is facilitated diffusion an example of passive or active transport?

  Passive
• Is osmosis an example of passive or active transport?

  Passive
• During simple diffusion, do molecules move from a high to low or low to high concentration?

  High to low
• What provides the energy for simple diffusion?

  Kinetic energy of the molecules diffusing
• What is active transport?

  A type of membrane transport which requires energy to move substances across a membrane
• Is active transport an example of passive or non-passive transport?

  Non-passive
• Are active transport and non-passive transport the same?

  Yes
• Is bulk transport an example of passive or non-passive transport?

  Non-passive
• During active transport, do molecules move from a low to high or high to low concentration gradient?

  Low to high
• What is the energy source for active transport?

  ATP
• What is bulk transport?

  The transport of solids or liquids by vesicles at the cell surface membrane
• What is the energy source for bulk transport?

  ATP
• What type of protein does facilitated diffusion require?

  Channel
• What is osmosis?

  The net movement of water molecules from a region of higher water concentration to a region of lower water concentration across a partially permeable membrane
• What does it mean for water molecules to be held stationary?

  Water molecules collect around a dissolved substance making the water less likely to move across a cell membrane
• Why is water a good solvent?

  Water molecules are polar
• What is meant by hypotonic?

  Lower solute concentration (high water concentration) than in cell