Transport cross cell membranes

• What is the fluid-mosaic model of membrane structure?

  Molecules move laterally in phospholipid bilayer
• What components make up the cell membrane?

  Phospholipids, proteins, glycoproteins, glycolipids

  
• What is the basic structure of all cell membranes?

  Same for cell-surface and eukaryotic organelle membranes
• How are phospholipids arranged in a cell membrane?

  Bilayer with fatty acid tails facing inwards

  
• What type of proteins span the phospholipid bilayer?

  Intrinsic or integral proteins

  
• Where are extrinsic proteins located in the membrane?

  On the surface of the membrane
• What are glycolipids?

  Lipids with polysaccharide chains attached
• What are glycoproteins?

  Proteins with polysaccharide chains attached
• What role does cholesterol play in cell membranes?

  Increases rigidity and decreases fluidity
• How do phospholipids behave in the presence of water?

  Fatty acid tails point away from water
• What is the significance of the hydrophobic fatty acid tails?

  They repel water and point inward
• What is the role of hydrophilic phosphate heads?

  They are attracted to water and point outward
• How does the fluidity of the membrane affect its function?

  Allows bending for vesicle formation
• What role do glycoproteins and glycolipids play in cell membranes?

  Act as receptors and antigens

  
• What substances can move across membranes by simple diffusion?

  Lipid-soluble or very small substances
• How do substances move during simple diffusion?

  From higher to lower concentration
• What type of transport is simple diffusion?

  Passive transport requiring no energy
• What limits movement across the phospholipid bilayer?

  Hydrophobic fatty acid tails restrict polar substances

  
• What substances move across membranes by facilitated diffusion?

  Water-soluble or slightly larger substances

  
• How do substances move during facilitated diffusion?

  Down a concentration gradient
• What proteins are involved in facilitated diffusion?

  Specific channel and carrier proteins

  
• How do channel proteins facilitate diffusion?

  They provide a hydrophilic pore for substances

  
• What is the role of carrier proteins in facilitated diffusion?

  Change shape to transport complementary substances
• How does osmosis occur across membranes?

  Water moves through a partially permeable membrane
• What is the direction of water movement during osmosis?

  From high to low water potential
• What is water potential?

  Measure of likelihood of water movement
• What is required for active transport?

  Hydrolysis of ATP and carrier proteins
• How do substances move during active transport?

  From lower to higher concentration
• What happens during the hydrolysis of ATP in active transport?

  Releases energy for protein shape change
• What is co-transport?

  Simultaneous movement of two substances via a protein
• How does sodium ion absorption illustrate co-transport?

  Na+ moves with glucose against its gradient

  
• What is the effect of increasing surface area on transport rates?

  Increases rate of movement across membranes
• How does the number of channel proteins affect transport rates?

  More proteins increase facilitated diffusion rates

  
• How does increasing concentration gradient affect transport rates?

  Increases rates of diffusion and osmosis
• What happens when all channel proteins are saturated?

  Transport rate becomes limited
• How does water potential gradient affect osmosis rates?

  Increasing gradient increases rate of osmosis
• What adaptations do specialized cells have for transport?

  Increased surface area and more protein channels
• Why is it important to control variables in experiments?

  Ensures accurate and reliable results
• What is the purpose of calculating % change in mass?

  Enables comparison of different samples
• Why should plant tissue be blotted dry before weighing?

  Removes excess water for accurate mass