The Plasma Membrane
The plasma membrane is a semi-permeable lipid bilayer found in all cells that controls water and certain substances in and out of the cell.
Function of the Plasma Membrane
- Protects the cell.
- Separates the intracellular components from the extracellular environment.
- Controls what enters and exits the cell
Necessities for the Movement of Substances across the Plasma Membrane
- To transport nutrients into the cell.
- For gases exchange
- To excrete metabolic waste.
- To maintain the pH value and ionic concentration of the cell.
Substances In and Out through the Membrane
- lipid bilayer
- pore protein
- carrier protein
What is diffusion?
Diffusion is the movement of particles from a high density region to a low density region. No energy is needed and no membrane involves in diffusion.
The Dynamic Equilibrium
Diffusion will continue until the concentration in all region is the same. When this happen, we say it has reached the dynamic equilibrium.
Factors Affecting the Rate of Diffusion (How fast diffusion happens)
Particles that Move Through the Plasma Membrane Through Diffusion
- Substances soluble in fat: fatty acid, glycerol, some vitamins (A,D,E,K)
- Neutral particles: water, oxygen, carbon dioxide,
What is Osmosis?
Osmosis is the diffusion of a water through a semi-permeable membrane, from a solution of low solute concentration to a solution with high solute concentration.It is a physical process in which a solvent moves, without input of energy, across a semi-permeable membrane separating two solutions of different concentrations.Important Points:
- It is the diffusion of water (normally) through a semi-permeable membrane.
- It is from a dilute solution to a more concentrated solution.
What is Facilitated Diffusion?
Facilitated diffusion is the passive transport of substances across the plasma membrane with the help of transport proteins such as the channel protein and the carrier protein.
Substances Pass through the Plasma Membrane through Facilitated Diffusion
Particles undergo facilitated diffusion are the particles that cannot diffuse through the phospholipid bilayer such as
- Large particles such as glucose, amino acids, proteins and nucleic acids
- Some ions such as the sodium ions and chloride ions
2 Types of Transport Protein
Facilitated diffusion occurs through 2 types of transport protein, namely
- Channel Protein
- Carrier Protein
What is Active Transport?
Active transport is the movement of substances across the plasma membrane of cells against the concentration gradient (From lower concentration to higher concentration).
Since it is against the concentration gradient, energy is needed in the process.
Video below shows how particles are transported through the carrier protein in active transport. Take notes that the process only happens when the carrier protein receives energy from an ATP.
Click the link below to watch the video.
What is Hypotonic Solution?
Hypotonic solution is the solution that has higher water potential than the other solution.
Water Concentration and Solute Concentration of a Cell in a Hypotonic Solution
Water concentration: Water concentration inside the cell is lower than outside the cell.
Solute Concentration: Solute concentration inside the cell is higher than outside the cell.
Effect of Hypotonic Solution on Animal Cell
- If an animal cell such as red blood cell is placed into a hypotonic solution, water molecules is transported into the red blood cells by osmosis (as shown in the diagram above).
- The red blood cells will inflate and finally burst because the thin membrane cannot withstand the high pressure inside the cell.
- The red blood cells are said to undergo haemolysis.
What is Isotonic Solution?
In isotonic solutions, both solutions have equal water potential.
Water Concentration and Solute Concentration of a Cell in a Isotonic Solution
Water concentration and solute concentration are equal in both solutions.
Effect of Isotonic Solution on Animal Cell
- If an animal cell such as red blood cell is placed into a isotonic solution, amount of water molecules is transported into the red blood cells by osmosis is equal to the amount of water molecules transported out from the cell (as shown in the diagram above).
- Therefore the amount of water in the cell remain unchanged.
- The red blood cells maintain their shape.
- If an animal cell such as red blood cell is placed into a hypertonic solution, water molecules is transported out from the red blood cells by osmosis (as shown in the diagram above).
- The red blood cells will shrink due to the lost of water from the cell and probably die.
- The red blood cells are said to undergo crenation .
The Youtube video above shows the effects of hypertonic solution on red blood cells. We can see that the cells finally shrink in hypertonic solution.