Chapter 3: Movement substance across Plasma MembraneThe 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

Singer and Nicholson proposed the fluid mosaic model in 1972 to explain the structure of the plasma membrane

What is passive transport?Passive transport is the movement of substances across the cell membrane without the use of energy by the cell.During passive transport, substances move down their concentration gradient, hence no energy is required.Passive transports can happen through three different channels, namely 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

Example of Diffusion

Between alveoli and blood capillaries in the lung during gases exchange.

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 asLarge particles such as glucose, amino acids, proteins and nucleic acidsSome ions such as the sodium ions and chloride ions

2 Types of Transport Protein

Facilitated diffusion occurs through 2 types of transport protein, namelyChannel ProteinCarrier Protein

Concentration GradientFacilitated diffusion happens down a concentration gradient.

Similarities between Simple Diffusion and Facilitated DiffusionDown the concentration gradient (From high concentration to low concentration)No energy is required

Differences between Simple Diffusion and Facilitated Diffusion

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.Basic Requirements in Active TransportPresence of the carrier proteinPresence of ATP (Adenosine Triphosphate)

Function of the ATPATP is the source of energy in active transport. It supplies energy to the carrier protein to carry out the process. It is converted into ADP (Adenosine Diphosphate) after the reaction.Examples of Active TransportIntake of mineral ions by the root hairs of a plant.

When immersed in hypertonic region:-The solution is more concentrated than the cell sap -As a result, water diffuses from the cell sap into the solution -The net flow is negative, as the water flows out of the cell -Hence, the cell mass decreases, and flaccid/ crenation occurs When immersed in isotonic region:-The solution's concentration is similar to the cell sap -As a result, water diffuses equally in & out of the cell -This is because the net flow is zero -Hence, the cell mass does not changeWhen immersed in hypotonic region:-The solution is more diluted than the cell sap -As a result, water diffuses from the solution into the cell sap -The net flow is positive, as the water flows into the cell -Hence, the cell mass increases, leading to haemolysis/ cell turgidity