Various Types of Substances Moving Across The Plama Membrane

Movement of substances across the Plasma Membrane

              

Simple Diffusion (Passive Transport)

1. Diffusion is the net movement of substances from the higher concentration to the lower concentration region until a dynamic equilibrium is achieved.

2. The examples of simple diffusion

   a) Gaseous exchange in unicellular organisms such as Amoeba sp.

   b) Gaseous exchange between alveoli and blood capillaries during respiration.

   c) Gaseous exchange through the stomata of leaves .

   d) Small fat-soluble molecules such as fatty acids, glycerol, vitamin A,D,E,K 

      diffuse across the plasma membrane.

             

Osmosis (Passive Transport)

1. Osmosis is the diffusion of water molecules across a semi-permeable membrane until a dynamic equilibrium is achieved.

2. The example of osmosis

   a) The uptake of water from soil by the root hairs.

          

The short video below shows that how osmosis process works.

 

Facilitated Diffusion (Passive Transport)

1. Facilitated diffusion is the diffusion of certain substances through the cell 

   membrane with the help of carrier protein or pore protein.

2. In the facilitated diffusion, the substances will be transported down the gradient concentration until equilibrium is reached.

3. The examples of facilitated transport

   a) The absorption of glucose and amino acids from the ileum into the villus 

      through carrier protein.

   b) The absorption of mineral ions from the ileum into the villus through pore 

      protein.

 

Absorption of glucose molecules into the villus through carrier protein (facilitated diffusion)

Active Transport

1. Active transport is the movement of substances across the plasma membrane   against concentration gradient with the use of ATP energy and carrier proteins called pumps.
        
  

2. The phosphate bond in ATP molecules is broken down to release ADP, P, and
   energy.

3. Active transport can be slowed down or inhibited by respiratory poisons such
   as cyanide or a lack of oxygen.

4. The examples of active transport

   a) Absorption of mineral ions such as potassium ion, phosphate and nitrate by
      root hair.
   b) Sodium-potassium pump ( in nerve and animal cells ) that pump sodium ions
      out of the cell and potassium ions into the cell.
   c) Uptake of the sodium ion and glucose from the lumen of the tubules of
      kidney nephron.
   d) Accumulation of the iodine ions by algae, Nitella sp. Despite the
      concentration of iodine int he cell being higher than that of the sea.

Transport of the sodium ion out and potassium ion into a cell through a carrier protein (active transport)

                

Comparison between passive transport and active transport

              

Video below shows the processes of passive and active transport