Transport across membranes

• Active transport


  Movement of a substance from a region where it is in low in concentration to a region where it is high in concentration. this process requires the expenditure of metabolic energy in the form of ATP
• Bilayer


  a membrane consisting of two layers of phospholipids
• Carrier protein 


  A protein completely spanning the phospholipid bilateral which bind to ions or molecules then change shape in order to move these molecules across the membrane
• cell membrane


  a selectively permeable membrane surrounding the cell and controlling the entry and exit of materials
• cholesterol


  lipid that is an important component of cell-surface membranes because it adds strength. excess in the blood can lead to atheroma
• Fluid mosaic model


  the arrangement of the various molecules of the cell-surface membrane. Fluid because the individual phospholipid molecules can move relative to one another. Mosaic because the proteins vary in shape, size and pattern
• glycolipid

  a carbohydrate covalently bonded with a lipid. they act as recognition sites, help maintain the stability of the membrane and help cells attach to one another
• glycoprotein 


  carbohydrate chains attached to a protein (often extrinsic) which are part of the cell-surface membrane. they act as recognition sites, help cells attach to one another and allows cells to recognise one another
• partially permeable 


  also called semi-permeable. a partially permeable membrane allows water and other small molecules to pass through, but not larger molecules such as starch.
• Permeability


  How permeable A substance is depends on the size, polarity and charge of the molecule. If it’s small, non-polar and fat soluble it is very permeable and can pass through the cell membrane
• phospholipid

  triglyceride in which one of the fatty acid molecules is replaced by a phosphate molecule. phospholipids are important in the functioning and structure of plasma membrane
• plasma membrane


  membranes consisting of a phospholipid bilayer found around and within cells. the cell-surface membrane is the plasma membrane that surrounds cells.
• protein channel

  a protein completely spanning the phospholipid bilayer which form water-filled tubes to allow water-soluble one to diffuse across the membrane
• concentration

  the concentration of a solution tells us how much of a substance is dissolved in water. the higher the concentration, the more particles of the substance are present
• diffusion


  the net movement of molecules (or ions)from a region of high concentration to a region of low concentration. it is passive
• solvent


  the liquid in which the solute dissolves to form a solution
• Co-transport 


  The transport of one substance coupled with he transport of another substance across a plasma membrane in the same direction through the same carrier protein
• Facilitated diffusion 


  Diffusion involving the presence of a carrier protein molecules to allow the passive event of substances (usually large, polar or charged molecules) across a plasma membrane
• net


  overall
• passive transport


  transport of molecules that occurs as a result of the random movement of particles, so that there is a net movement from a higher to lower concentration. passive transport does not require energy
• cell sap


  the liquid found in the vacuole of plant cells , consisting of water with dissolved sugars, salts and amino acids
• cell wall

  outer structure which provides support and prevents the cell from bursting from the uptake of water by osmosis. plant, fugal and bacterial cell walls have different structures and chemical compositions
• cellulose


  a carbohydrate. it forms the cell wall in plant cells
• Cytoplasm


  The living substance inside the cell (not including the nucleus)
• dilute 


  a solution with low concentration
• dissolve


  when a substance breaks up and mixes completely with a solvent to produce a solution
• flaccid


  lacking turgor. lacking in stiffness or strength. soft and floppy
• isotonic

  a solution that has. the same water potential as the cell within it
• osmosis


  the passage of water from a region where there is a higher water potential to a region where there is a lower water potential through a selectively permeable membrane
• plasmolysed 


  description of a plant cell in which the vacuole has shrunk and the membrane has pulled away from the wall due to water loss by osmosis
• solute


  the dissolved substance inside a solution
• solution

  the mixture formed by a solute and solvent
• solvent 


  the liquid in which the solute dissolves to form a solution
• sucrose


  the disaccharide made from glucose and fructose. it is used as table sugar
• turgid


  enlarged and swollen with water. having turgor. description of a plant cell in which the vacuole has swollen due to water gain by osmosis
• vacuole


  a space within the cytoplasm of plant cells that contains cell sap
• volume


  refers to the amount of space inside the object
• water potential


  the pressure created by water molecules. the measure of the extent to which a solution gives out water. the greater the number of water molecules present, the higher the water potential. pure water has a water potential of zero
• Calibration curve


  A general method for determining the concentration of an unknown sample by comparing the unknown to a set of standard samples of known concentration
• serial dilution


  a set of solutions which increase/decrease in concentration by the same factor each time