1.4 Membrane Transport Flashcards
Ways for particles to move across the membrane
Simple diffusion, facilitated diffusion, osmosis and active transport
Diffusion
The passive movement of particles from a region of high concentration to a region of low concentration (down a concentration gradient).
Passive movement = does not require ATP
Simple diffusion
The passive movement of particles from a region of high concentration to a region of low concentration (down a concentration gradient).
- occurs when substances (except water) move across the phospholipid bilayer (not through protein channels)
- substances that move across the membrane are usually small non-charged particles (i.e. Oxygen, Carbon Dioxide, and Nitrogen)
Facilitated diffusion
The passive movement of particles from a region of high concentration to a region of low concentration (down a concentration gradient).
- Specific ions and other particles that cannot move through the phospholipid bilayer move across protein channels
- each protein channel structure allows only one specific molecule to pass through the channel (e.g. magnesium ions only allow magnesium ions to pass through)
Active transport
Movement of substances across membranes using energy from ATP from an area of low concentration to an area of high concentration (against their concentration gradient).
- different protein pumps are used for active transport
- each pump only transports a particular substance -> cells can control what is absorbed and what is expelled
- pumps work in a specific direction - substances enter only on one side and exit through the other side
- substances enter the pump from the side with a lower concentration
- energy from ATP is used to change the shape of the pump
- the specific particle is released on the side with a higher concentration and the pump returns to its original shape
Osmosis
Passive movement of water molecules, across a semi-permeable membrane, from a region of lower solute concentration to a region of higher solute concentration (dilute to concentrate).
- solute molecules can not pass through the membrane due to their properties
Hypotonic solutions
- a solution with a lower solute concentration compared to the other solution
- cells in this solution - causes the water molecules to move into the cell (increase in cell mass)
Plant cells: the cell does not burst due to the cell wall and the pressure from the extra water causes the cell to remain turgid
Animal cells: don’t have a cell wall; cells will lyse/burst
Hypertonic solutions
- a solution with a higher higher solute concentration compared to the other solution
- cells in this solution - causes the water molecules to leave the cell
Animal and plant cells: the cytoplasm’s volume will shrink (decrease in cell mass) and will plasmolyse
Isotonic solution
A solution that has the same concentration as the other solution
Water molecules move at the same rate inside and out of the cell - no change in mass (graph: x=0)
Tissues/organs used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis
Bulk transport
- fluidity of membranes allows materials to be taken into cells by bulk transport (endocytosis & exocytosis)
- fluidity of membrane allows the membrane to easily attachment/remove, leading to the formation of vesicles
- vesicles move materials within cells
Endocytosis
Movement into the cell
- membrane folds in, engulfing materials too large to enter the cell directly through the plasma membrane
- cell membrane reattaches because amphipathic characteristics of the phospholipids
- vesicle buds of containing particles
Exocytosis
Movement out of the cell
- After a vesicle created by the rough ER enters the Golgi apparatus, it is modified again and another vesicle is budded from the end of the Golgi apparatus, which moves towards the cell membrane
- vesicle migrates to the plasma membrane and fuses with the membrane - releasing the protein outside the cell
- amphipathic properties of the phospholipids and the fluidity of the membrane allows the phospholipids from the vesicle to combine with the plasma membrane
