transport across the cell membrane

• (simple diffusion)

  diffusion is a passive process that involves the spreading out of particles so that they are evenly distributed over the available space
• (simple diffusion)

  diffusion occurs from the random movement of ions and molecules as they bump into each other / the container, causing them to change directions. Molecules moving to an area of lower concentration move for longer as there are less obstacles
• (simple diffusion)

  net diffusion is the movement of molecules from a place of high concentration to lower concentration (going along a concentration gradient)
• (simple diffusion)

  osmosis is a special type of diffusion of a solvent through a semipermeable membrane in order to balance the concentration of another substance
• (simple diffusion)

  osmotic pressure is the pressure due to differences in the level of water on either side of a semipermeable membrane. a higher concentration of a solute has a higher osmotic pressure
• (facilitated)

  facilitated transport requires proteins (carrier or channel) in the cell membrane that allow molecules to be transported across the membrane.
• (facilitated)

  water-soluble molecules must pass through protein channels so they do not come in contact with the hydrophobic tail. Very small, water ions can pass through like this but larger molecules can't
• (facilitated)

  carrier proteins are open on one side, the molecule binds to the binding site which is when the protein opens on the other side and then releasing the substance on the other side
• (facilitated)

  carrier proteins are specific - they only bind to particular molecules (carrier for glucose cannot transport anything else)
• (facilitated)

  facilitated diffusion is when a substance is transported through a protein along the concentration gradient and is a passive process
• (facilitated)

  active transport is when substances are transported against the concentration , this is an active process
• (vesicular)

  vesicular transport is the movement of substances across the cell membrane in vesicles, it is an active process as energy from the cell is needed to make vesicles
• (vesicular)

  endocytosis is taking liquids or solids into the cell by vesicular transport

  1. the membrane folds around the droplet of liquid or solid until it is completely enclosed
  2. the vesicle pinches off and is suspended in the cytoplasm
• (vesicular)

  pinocytosis - taking in liquids
• (vesicular)

  phagocytosis - taking in solids
• (vesicular)

  exocytosis is content from inside the cell is passed to the outside

  1. vesicle forms inside the cell
  2. vesicle migrates to cell membrane
  3. vesicle fuses with membrane
  4. contents is pushed out into extracellular fluid
• (facilitated)

  carriers can become saturated - when all available carriers are occupied, increase in concentration of molecules will not increase the rate of movement
• (facilitated)

  activity is regulated by substances (e.g. hormones) - hormones are important in coordinating activities of carrier proteins
• water, oxygen, carbon dioxide use simple diffusion
• glucose and amino acids use facilitated diffusion
• glucose, amino acids and certain ions use active transport
• cholesterol, iron ions, micro-organisms and cell debris (only certain specialised cells) use endocytosis
• secretions like mucus or digestive juices use exocytosis
• it is advantageous to use active transport as it does not depend on the concentration gradient meaning substances can be taking in or out of the cell regardless of the concentration on either side