Biolab 2

• The maintenance of a constant internalenvironment in a cell or organism, also known ashomeostasis, necessitates a constant entrance ofmaterials into the cell and the passage of othersubstances out of it.
• The movement of substances through the plasma membrane involves several processes. These include passive transport or diffusion (simple and facilitated), active transport, and bulk transport (phagocytosis, pinocytosis)
• Diffusion is the spontaneous movement ofmolecules of different substances
• Osmosis is a special form of diffusion. It is themovement of water from a dilute solution (hypoosmotic)to a more concentrated (hyperosmotic) one through asemi-permeable or selectively permeable membrane
• The process of diffusion of crystalloidsolute through such membrane on the other hand, isknown as dialysis
• Temperature affects diffusion. In this section, a comparison will be made on the rate of diffusion of potassium permanganate crystals between two beakers having different temperatures.
• Passive Transport - occurs without the input of cellular energy
• Passive transport goes from high concentration to low concentration
• Simple diffusion: oxygen
• Facilitated diffusion: channel and carrier mediated
• Active Transport - requires the input of energy from the cell
• Active Transport - used ATP and protein pumps to transport molecules against the concentration gradient (low to high gradients)
• Sodium-potassium pump - cell to cell communication, action potentials, nervous system functions
• Exocytosis and endocytosis - too large to be diffused or pumped from and to the cell, enzymes bacteria, and waste materials, engulfing of particles by the cell membrane
• Temperature and Diffusion Rate - directly proportional
• Molecular Weight and Diffusion Rate - inverse proportional
• Steepness of Concentrated Gradient and Diffusion Rate - directly proportional
• Membrane Surface Area and Diffusion Rate - directly proportional
• Membrane Permeability and Diffusion Rate - directly proportional
• Solutions used: potassium permanganate, starch solution, iodine solution, cellulose sac