Biology form 4 chapter 3

Topics: Diffusion, Adenosine triphosphate, Molecular diffusion Pages: 5 (656 words) Published: April 11, 2014
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

1. lipid bilayer
2. pore protein
3. 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

1. Substances soluble in fat: fatty acid, glycerol, some vitamins (A,D,E,K) 2. Neutral particles: water, oxygen, carbon dioxide,

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 as

1. Large particles such as glucose, amino acids, proteins and nucleic acids 2. 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

1. Channel Protein
2. Carrier Protein

Concentration Gradient

Facilitated diffusion happens down a concentration gradient.

Similarities between Simple Diffusion and Facilitated Diffusion

1. Down the concentration gradient (From high concentration to low concentration) 2. 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.

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. Basic Requirements in Active Transport

1. Presence of the carrier protein
2. Presence of ATP (Adenosine Triphosphate)

Function of the ATP

ATP 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.

Mechanism of Active Transport

The video below shows how sodium ions and potassium ions are transported through the plasma membrane by a carrier protein. Examples of Active Transport

Intake of mineral ions by the root hairs of a plant.

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

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