Facilitated Diffusion

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What is facilitated diffusion? In membrane, there are protein channels (pores) that allow polar molecules (soluble in water but not soluble in lipids) to move through them. The molecules that move through these channels never come into contact with the hydrophobic layer or the membrane's polar surface because these channels provide a continuous pathway for molecules that are moving through them. In this type of diffusion, like simple diffusion, no energy is consumed. Large and polar molecules require help to pass through the membrane. This help is done by a type of protein called carrier (transport) protein . To pass through the membrane, a molecules binds (temporarily) with carries protein in lipid bilayer and is transported from an area of higher concentration to an area of lower concentration.  Related topics: Simple Diffusion
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What is cell?Difference between prokaryotic and eukaryotic cell and parts of cell-The Knowledge

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What are cells?

Cells 

Cells are the organizational units of life.In other words we can say that cells are fundamental units of life,in which all of the chemical reactions necessary for the maintenance and reproduction  of life takes place.Because all animals are made of cells,the cell is as fundamental to an understanding of zoology as atom is to an understanding of chemistry.Cells are smallest independent units of life.Structurally speaking,cells are either prokaryotic are eukaryotic.

Types of cells on the basis of structure 

There are two types of cells on the basis if structure.
Prokaryotic cell
Eukaryotic cell  

Difference between prokaryotes and eukaryotes 

 
 All prokaryotes(“before nucleus”) are independent,single-celled organisms(e.g.,bacteria)The word “prokaryote” describe cells in which DNA is localized in a region but is not bound by a membrane.                                                                                                                                                                              All eukaryotes(“true nucleus) have cells with a membrane-bound nucleus containing DNA.In addition, eukaryotic cells contain many other structures called organelles (“little organs”)that perform specific functions.Eukaryotic cells also have network of specialized structures called filaments and tubules organized into the cytoskeleton, which gives shape to the cell and allows intra-cellular movement. 

 

Parts of a cell

All eukaryotic cells have have three basic parts.

1.The plasma/cell membrane

Cell membrane is the outer boundary of the cell.It separates the internal metabolic events from the environment and allows them to proceed in organized,controlled ways.The plasma membrane also has specific reception for external molecules that alter the cells function.(Read in Detail)

2.Cytoplasm

Cytoplasm (Greek.kytos, hollow vessel + plasm, fluid) is the portion of the cell outside the nucleus.The semi-fluid portion of the cytoplasm is called the cytosol.Suspended within the cytosol are the organelles.

3.Nucleus

Nucleus (pl.,nuclei) is the cell control center.It contains the chromosomes and is separated from the cytoplasm by its own nuclear envelop.The nucleoplasm is the semi-fluid material in the nucleus.Because cells vary so much in form and function, no “typical” cell exists.

 

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