Fluid Mosaic Model

Posted: March 25, 2011 in Uncategorized


Active Transport

Posted: March 25, 2011 in Uncategorized

Active Transport

– movement of molecules or ions from a region of lower concerntration to a higher concerntration.

require the use of carrier protein and cellular energy(ATP).

-one active site of carrier protein binds with a particular molecule or ion and another active site of carrier protein   bind with ATP molecule and this will transport the molecule or ions to the region of higher concerntration.


Type of Passive Transport

Posted: March 24, 2011 in Uncategorized

Passive Transport

  • simple diffusion
  • osmosis
  • facilitated diffusion

~Simple Diffusion~

1. Diffusion is the movement of molecules in air or in solution from a region of high concentration to a region of low concentration.

2. Oxygen in the inspired air must diffuse across the membrane of the alveoli and the wall of the capillaries before it gets into the blood. Oxygen would then be transported to all the cells in the body by the circulatory system.

3. When oxygen reaches the cells, it has to diffuse across the capillary wall and the plasma membrane of the cells before it can enter the cells.

4.Conversely, CO2 that is produced by the cells diffuses out into the blood circulation that transport it to the lungs. There, CO2 diffuses from the capillaries into the lungs and is expelled out.



1. Osmosis is the movement of water from a region of low solute concentration to a region of high solute concentration.

2. eg.:  ~water absorption from the intestine

~water reabsorption from the kidney tubules

~water uptake from the soil by the root hairs


~Facilitated Diffusion~

1. Some substances cannot diffuse passively across the membrane because they are either insoluble in lipid or too big to pass through the pores.

2. Some molecules in the membrane can “carry” these substances across. These “carrier molecules” consist of membrane proteins.

3.The products of digestion such as glucose and amino acids have to cross the wall of the epithelial cells lining the intestine and the wall of the capillaries to get into the circulartory system.

4. These nutrients are lipid-insoluble and they are too large to pass through yhe pores in the membrane. Fortunately, some carrier proteins in the membrane are able to trap these nutrients and carry them across the membrane via facilitated diffusion.

5. This occur in almost all body cells, especially along the villi of the epithelial cells lining the small intestine. The nutrients are then distributed to all the cells in the body. On reaching the cells, the nutrients cross the capillary wall and the plasma membrane of the cells via facilitated diffusion.



A hypertonic solution is one with a high concentration of solutes when compared to another solution which is separated from it by a semipermeable membrane . The property of tonicity is often used to illustrate the biology of the body, with the solute concentration of cells and surrounding fluids being used as an example. Tonicity is related to osmosis , in which fluids flow back and forth across a semipermeable membrane; osmolarity differs from tonicity in that it considers the concentration of solutes that penetrate the membrane and those that do not, while tonicity only considers those that do not penetrate.

If a solution is hypertonic, it means that fluid will flow across the membrane and into the hypertonic solution until an isotonic state is reached. In an isotonic state, the solutions on either side of the membrane have the same distribution of solutes. Conversely, with a hypotonic solution, the concentration of solutes is lower than that of a solution on the other side of a membrane, which means that water will be drawn out of the hypotonic solution and into a hypertonic solution.


In the general sense, two solutions are isotonic when they contain the same amounts of solutes, or dissolved substances, and therefore have the same osmotic pressure. As commonly used in the medical field, though, isotonic solutions are solutions which have the same concentration of solute as the cells in the human body. A cell placed in an isotonic solution will neither gain nor lose water.

When two aqueous solutions of different concentrations or tonicities are separated by a semi-permeable membrane such as a cell wall, water will migrate from the less concentrated, or hypotonic, side to the more concentrated, or hypertonic, side in an attempt to bring both sides into equilibrium. This process is known as osmosis. The greater the difference in the two solutions’ concentrations, the higher the osmotic pressure will be, and the quicker the osmotic transfer will be.


A solution which has a lower osmotic concentration (high water potential) than another solution is said to be hypotonic. If two solutions are of equal concentration they are isotonic.
A plant cell behaves differently from an animal cell when placed in a hypotonic solution. Since the cell sap has a lower water potential than that of the solution outside the living cell, water enters the cell by osmosis (endosmosis). Note, that the partially permeable membrane here is the plasma membrane and not the cellulose cell wall. The cellulose cell wallis permeable and allows most dissolved substances to pass through.
As water enters the cell the vacuole increases in size and pushes the cell contents against the cellulose wall. The plant cell does not burst because the cell wall is strong and relatively inelastic. It prevents over expansion of the cell by exerting an opposing pressure preventing the entry of more water. When the cell is in this state, it becomes rigid or turgid. This rigidity of the cell with water is called turgor. The pressure exerted by the water on the cell wall is the turgor pressure.
On the other hand an animal cell will swell and may burst in a hypotonic solution.

The structure of plasma membrane

Posted: February 17, 2011 in Uncategorized

A mosaic is a structure made up of many different parts. Likewise, the plasma membrane is composed of different kinds of macromolecules. The components of a plasma membrane are integral proteins, peripheral proteins, glycoproteins, phospholipids, glycolipids, and in some cases cholesterol, lipoproteins.

Integral membrane proteins are inserted into the lipid bilayer, whereas peripheral proteins are bound to the membrane indirectly by protein-protein interactions. Most integral membrane proteins are transmembrane proteins, with portions exposed on both sides of the lipid bilayer. The extracellular portions of these proteins are usually glycosylated, as are the peripheral membrane proteins bound to the external face of the membrane.


Diffusion is the net movement of material from an area of high concentration to an area with low concentration. The difference between the two area is often term as the concentration gradient and diffusion will continue until this gradient has been eliminated.

Facilitated diffusion also called carrier-mediated diffusion, is the movement of molecule across the cell membrane via special transport protein that are embedded within the cellular membrane. Many large molecules, such as glucose, are insoluble in lipids and too large to fit through the membrane pores. Therefore, it will bind with its specific carrier proteins, and the complex will then be boned to a receptor site and move through the cellular membrane.

Osmosis is the diffusion of water molecule from a area of low solute concentration to area of high solute concentration. Examples of movement of water via asmosis in organisms include:

water absorption from the intestine, water reabsorption from the kidney tubules, water uptake from the soil by the root hairs


Water and minerals get into the root hair of plants from the soil. The concentration of minerals in the root hair is higher than that in the soil. That makes it easy for the water to move in via osmosis. The minerals, however, get into the root of  hair via active transport after they dissolve in water in the soil. This requires energy provided by ATP.

Hello world!

Posted: February 9, 2011 in Uncategorized

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