1styear BIOLOGY Notes Chapter-2

Chapter-2
BIOLOGICAL MOLECULES

BIOCHEMISRTY
Biochemistry is a branch of biology, which deals with the study of chemical components and chemical processes in living organisms.

WATER (H2O)
MAIN CHARACTERISTICS OF WATER
• Chemically it is “Dihydrogen oxide”
• It is the most abundant component in living cell.
• Its amount varies approximately from 70 to 90% and life activities occur in the cell due to the presence of water.
• It is a polar molecule, means that it has a very slightly negative end (the oxygen atom) and a very slightly positive end (the hydrogen atom).
• Due to its polarity, H2O molecules form hydrogen bonds.

IMPORTANT BIOLOGICAL PROPERTIES OF WATER
(1) BEST SOLVENT
• Water is an excellent solvent for polar substances, when ionic substances dissolved in water, dissociate into positive and negative ions.
• Non-ionic substances, having charged groups in their molecules, are dispersed in water.
• Because of solvent property of water, almost all reactions in cells occur in aqueous media.
(2) HIGH HEAT CAPACITY
• Water has great ability of absorbing heat due to its high specific heat capacity.
• The specific heat capacity of water is the number of calories required to raise the temperature of 1g water through 1ºC.
• The thermal stability plays an important role in water based protoplasm of individual’s metabolic activities.
(3) HIGH HEAT OF VAPORIZATION
• Liquid water requires higher amount of heat energy to change into vapours due to hydrogen bonding which holds the water molecules together.
• It provides cooling effect to plants when water is transpired, or to animals when water is respired.
(4) ACT AS AMPHOTERIC MOLECULE
• Water molecule acts both as acid and a base. As acid, it gives up electron to form H+ ion, while as a base, it gains electron to form OH ions.
H2O ? H+ + OH-
• It acts as buffer and prevents changes in the pH of living body.
(5) PROTECTION
• Water is an effective lubricant that provides protection against damage resulting from friction.
• It also forms a fluid cushion around organs that helps to protect them from trauma.
(6) AS REAGENT /TURGIDITY
• Water acts as a reagent in many processes such as photosynthesis and hydrolysis reactions.
• It also provides turgidity to the cells.

ORGANIC COMPOUNDS
Those compounds containing carbon (other than carbonates) are called organic compounds. E.g: carbohydrates, Proteins, Lipids and Nucleic acid.

INORGANIC COMPOUNDS
Those compounds, which are without carbon, are called inorganic compounds. E.g: water, carbondioxide, acids , bases and salts.

MACROMOLECULES
Huge and highly organized molecules which form the structure and carry out the activities of cells are called “Macromolecules” Macromolecules can be divided into four major groups.
• Proteins
• Carbohydrates
• Lipids
• Nucleic acids.

MONOMERS
Macromolecules are composed of large number of low molecular weight building blocks or subunits called “Monomers” E.g: Amino-acids (Protein).

CONDENSATION
The process by which two monomers are joined is called “Condensation”.
In this process two monomers join together when a hydroxyl(OH) group is removed from one monomer and a hydrogen (-H) is removed from other monomer.
This type of condensation is called “Dehydration Synthesis” because water is removed (dehydration ) and a bond is made (synthesis).

HYDROLYSIS
A process during which polymers are broken dawn into their subunits (monomers) by the addition of H2O called “Hydrolysis “. It is just reverse of the condensation.

FUNCTIONAL GROUPS
These are particular group of atoms that behave as a unit and give organic molecules their physical, chemical properties and solubility in aqueous solution. E.g
• Methyl group (CH3-)
• Hydroxyl or Alcohol group (OH-)
• Carboxylic acid or Organic-acid group (COOH-)
• Amino or Amine group (NH2-)
• Carbonyl group (CO=)
• Sulfhydryl group (SH-)

PROTEINS
These are the complex organic compounds having C, H,O and N as elements but sometimes they contain P and S also. Due the presence of N they are called “Nitrogenous Compounds” Proteins constitute more than 50% of dry weight of cell. They are present in all types of cells and in all parts of the cell.


CHEMICAL COMPOSITION OF PROTEINS
• Proteins are polymers of amino-acids and number of amino-acids varies from a few to 3000 or even more in different proteins.
• These amino-acids are linked together by specialized bond or linkage called “peptide linkage”
• Each proteins has a unique sequence of amino-acids that gives the unique properties to molecules.

AMINO ACID
It is the basic structural unit of proteins and all amino-acids have an “Amino group (NH2-) and a “Carboxyl group (COOH-)” attached to the same carbon atom, also known as “Alpha carbon”. The have the general formula as:
1. A hydrogen atom.
2. An amino (NH2) group.
3. A carboxyl group (COOH)
4. “Something else” this is the “R” group.
R
¦
H2N -C - COOH
(Amino group) ¦ (Carboxylic group)
H
“R” may be a “H” as in glycine, or CH3 as in alanine, or any other group. So amino acids mainly differ in the R-group.

POLYPEPTIDES
Amino Acids are linked together to from polypeptides of proteins. The amino group of one amino acids may react with the carboxyl group of another releasing a molecule of water. E.g: Glycine and analine may combine to form a dipeptiede

PEPTIDE LINKAGE/ BOND
The linkage between the hydroxyle group of carboxyl group of one amino-acid and the hydrogen of amino-group of another amino-acid release H2O and C-N link to form a bond called “Peptide bond”.


TYPES OF PROTEINS ON THE BASIS OF STRUCTURE
There are four basic structural levels of proteins.

(A) PRIMARY STRUCTURE
• A polypeptide chain having a linear sequence of amino-acids.
• Disulphide (S-S) bond is other important characteristic of the primary protein.
E.g: Insulin Polypeptide chain.

(B) SECONDARY STRUCTURE
• In this type polypeptide chain of amino-acids become spirally coiled.
• This coiling results in the formation of a rigid and tubular structure called “Helix”

(C) TERTIARY STRUCTURE
• Polypeptide chain bends and folds upon it self forming a globular shape.
• It is maintained by three types of bonds. Namely ionic, hydrogen and disulfide (S-S).

(D) QUATERNARY STRUCTURE
• This type is usually present in highly complex proteins in which polypeptide tertiary chains are aggregated and held together by hydrophobic interactions, hydrogen and ionic bonds.
E.g: Haemoglobin molecule.


FUNCTIONS OF PROTEIN
• They Build many Structures of the cell E.G: Plasma Membrane.
• All enzymes are proteins and in this way they control the whole metabolism of the cell.
• Skin, nails, hair, feather, horn etc. contain portion called keratin.
• Casein is the milk portion and ovalbumin is the egg white protein.
• Collagen present in bones, cartilage, etc. is the most abundant protein in higher vertebrates.
• Protein acts as antibodies, antigens and fibrin etc.


CARBOHYDRATES
It is a group of organic compounds having carbon, oxygen and hydrogen, in which hydrogen and oxygen are mostly found in the same ratio as in water i.e. 2:1 and thus called “Hydrated carbons” They are found about 1% by weight and generally called Sugars or saccharides” due to their sweet taste except polysaccharides.


CLASSIFICATION OF CARBOHYDRATES
The carbohydrates can be classified into following groups on the basis of number of monomers.
1. Monosaccharide
2. Oligosaccharides
3. Polysaccharides.

(1) MONOSACCHARIDES
• These are called “Simple Sugars”, because they can not be hydrolysed further into simple sugars.
• Their general formula is “Cn H2n On
• They are white crystalline solids with sweet taste and soluble in water.
• They are present in various fruits and vegetables.
E.g: Glucose, Galactose, Fructose and Ribose etc. Monosaccharide can be sub-classified according to umber of carbon atom present in each molecule. They may be triose, (Glycerose), tetrose (erythrose), pentose, (ribose), hexone (glucose) or heptose (Glucoheptose) having 3,4,5 ,6 and 7 carbon atoms respectively.

(2) OLIGOSACCHARIDES
• These carbohydrates yield 2to 10 monosaccharides mnolecules on hydrolysis
• Disaccharides are the most common and abundant carbohydrates of oligosaccharides.
• These sugars are comparatively less sweet in taste, and less soluble in water.
E.g: Maltose, Sucrose and lactose etc.

(3) POLYSACCHARIDES
• These are the most complex and most abundant carbohydrates in nature.
• They are of high molecular weight carbohydrate which on hydrolysis yield mainly monosaccarides or products related to monosaccharide.
• These sugars are formed by the condensation of hundreds of thousands of monosaccharide units.
• They are tasteless and only sparingly souble in H2O.
E.g: Strach, cellulose Glycogen , Dextrin Agar, pectin and Chitin etc.


FUNCTIONS OF CARBOHYDRATES
• Carbohydrates are the potential source of energy.
• They act as storage food molecules and also work as an excellent building, protective and supporting structure.
• They also form complex conjugated molecules.
• They are needed to synthesize lubricants and are also needed to prepare the nectar in some flowers.


LIPIDS
These are naturally occurring compounds, which are insoluble in water but soluble in organic solvents. They contain carbon, hydrogen and oxygen like carbohydrates rate but in much lesser ratio of oxygen than carbohydrates. These biomolecules are widely distributed among plants and animals.


CLASSIFICATION OF LIPIDS
Following are the important groups of lipids.
1. Acylglycerol (fats and oil)
2. Waxes
3. Phospholipids.
4. Terpenoids.

(1) ACYLGLYCEROL (FATS AND OIL)
• These are found in animals and plants, provide energy for different metabolic activates and are very rich in chemical energy.
• They are composed of glycerol and fatty acids. The most widely spread acylglycerol is triacyl glycerol, also called triglycerides or natural lipids.
• There are two types of acylgycerol

(A) SATURATED ACYLGLYCEROL
• They contain no double bond.
• They melt at higher temperature than unsatured acylglycerols.
• Lipids containing saturated acylgycerol are solid and known as Saturated lipids.
E.g: Butter and Animal fat. etc.

(B) UNSATURATED ACYLGLYCEROL
• They contain unsaturated fatty acids i.e they contain one or more than one double bond between carbon atom(C=C-).
• They are liquid at ordinary temperature .
• They are found in plant also called “Oil”
E.g: linolin found in cotton seeds etc.

(2) WAXES
Chemically waxes are mixtures of long chain alkanes and alcohols. Ketones and esters of long chain fathy acids
• Waxes are widespread as protective coatings of fruits and leaves some insects also secrete wax.
• Waxes protect plants form water loss and abrasive damage.
• They also provide water barrier for insects, birds and animals etc.

(3) PHOSPHOLIPIDS
• It is most important class of lipids from biological point of view and is similar to riacylglycerol or an oil except that one fatty acid is replaced by phosphate group.
• The molecule of phospholipids consist of two ends, which are called hydrophilic (water loving end (head) and hydrophobic (water fearing)end (Tail).
• These are frequently associated with membranes and are related to vital functions such as regulation of cell permeability and transport process.

(4) TERPENOIDS
• It is large and important class of lipids containing “Isoprenoid “ unit (C5H8).
• They help in oxidation reduction process, act as components of essential oils of plants and also found in cell membrances as “cholesterol

SUB-CLASSES OF LIPIDS
1. Terpenes
2. Steroids.
3. Carotenoids.

(1) TERPENES
• This group based only on “Isoprenoid” unit and they are usually volatile in nature produce special fragrance.
• Derivatives of this group are found in vitamin A and are also important constituents of chlorophyll and cholesterol biosynthesis.
• They are utilized in synthesis of “Rubber” and “Latex”, and some of these are used in perfumes.

(2) STEROIDS
This group of Terpenoids contains 17 carbon atoms ring called “steroid nucleus”.

(3) CAROTENOIDS
They consist of fatty acid like carbon chain and usually found in plants, for example carotene, xanthophylls etc.

NUCLEIC ACIDS
Nucleic Acids Were First Isolated In 1870 By an Austrian Physician Fridrich Micscher from the nuclei of pus cells. These bio molecules are acidic in nature and present in the nucleus.

TYPES OF NUCLEIC ACIDS
Nucleic acids are of two types.
1. Deoxyribonucleic acid or DNA
2. Ribonucleic acid or RNA

CHEMICAL NATURE OF NUCLEIC ACID
Nucleic acids are complex substances. They are polymers of units called nucleotides. DNA is made up of deoxyribonucleotides, while RNA is composed of ribo nucleotides.

STRUCTURE OF NUCLEOTIDE
Each nucleotide is made of three subunits
(a) 5-carbon monosaccharide (a pentose sugar)
(b) Nitrogen containing base.
(c) Phosphoric acid.

(A) PENTOSE SUGAR
Pentose sugar in RNA is ribose, while in DNA it is deoxyribose.

(B) NITROGENOUS BASE
Nitrogenous bases are of two types
(i) PYRIMIDINES (SINGLE RINGED): These are cytosine (abbreviated as C), thymine (abbreviated as T), and uracil (abbreviated as U).

(ii) PURINES (DOUBLE RINGED): These are adenine (abbreviated as A) and guanine(abbreviated as G).

C) PHOSPHORIC ACID
Phosphoric acid (H3PO4) has the ability to develop ester linkage with OH group of pentose sugar.

FORMATION OF NUCLEOTIDE
Formation of nucleotide takes place in two steps. First the mitrogenous base combines with pentose sugar at its first carbon to form a “Nucleoside”. In second step the phosphoric acid combines with the 5th carbon of pentose sugar to form a “Nucleotide”.


(A) MONONUCLEOTIDES
• They exist singly in the cell or as a part of other molecules.
• These are not the part of DNA or RNA and some of these have extra phosphate groups e.g ATP.

(B) DINCULEOTIDES
These nucleotides are covalently bounded together and usually act as co-enzymes
E.g NAD (Nicotinamide dinucleotide ).

(C) POLYNUCLEOTIDES
• Nucleotides are found in the nucleic acid as “Polynucleotide” and they have a variety of role in living organisms.
• They usually perform the function of transmitters of genetic information.
CONJUGATED MOLECULES
• Two different molecules, belonging to different categories, usually combine together to form “Conjugated molecules”.
• These conjugated molecules are not only of structural, but also are of functional significance.
• They play an important role in regulation of gene expression.

(A) GLYCOPROTEIN AND GLYCOLIPIDS
Carbolydrates may combine with proteins to form glycoprotein or with lipids to form glycolipid.

FUNCTIONS
(a) Most of cellular secretions are glycoprotein’s in nature.
(b) Both glycoproteins and glycolipids are integral structural components of plasma membranes.

(B) LIPOPROTEINS
Combination of lipids and proteins form lipoproteins.
FUNCTION
They are basic structural framework of all types of membranes in the cells.

(C) NUCLEOPROTEINS
Nucleic acids have special affinity for basic proteins . they are combined together to form nucleoproteins.
FUNCTIONS
The nucleoproteins (Histone) are present in chromosomes.

THINGS TO BE REMEMBER
• Proteins-Berzelius and G.J murlder.
• Lipids-Bloor in 1943.
• DNA –Hereditary material.
• RNA- carrier of genetic information.
• rRNA – (Ribosomal RNA)- Double stranded.
• Transcription- Formation of mRNA.
• Translation –Formation of Proteins by ribosmes.

1styear BIOLOGY Notes Chapter-1

Chapter-1
INTRODUCTION

DEFINITION OF BIOLOGY
Biology is the study of living organisms. It is derived from Greek words. Bios – life Logos – study.


CLASSIFICATION OF LIVING ORGANIZATION
According to the modern classification given by R.H.Whittaker in 1969, living organisms are divided into five major kingdoms, which are:

KINGDOM MONERA
It includes all prokaryotes, unicellular organisms. For example Bacteria and Cyan bacteria.

KINGDOM PROTOCTISTA(PROTISTA)
It includes unicellular Eukaryotic organisms, which are in between plants and animals. e.g. Chlamydomonas, Euglena, Paramecium. etc.

1. KINGDOM FUNGI
It includes non-chlorophyllus multi-cellular, thallophytic organisms having cell wall. For example all types of fungi, unicellular to multi-cellular like Mushrooms and Yeast etc.

2. KINGDOM PLANTAE
It includes all chlorophyllus multi-cellular Eukaryotic living organisms having cellulose cell wall. For example apple, red wood etc.

3. KINGDOM ANIMALIA
It includes all Eukaryotic multi-cellular, non-chlorophyllus organisms having no cell wall. For example Hydra, Earthworm, Human Beings etc.

EUKARYOTIC ORGANISMS
Those organisms, which have true membranous structure in their cells, like mitochondria, golgi bodies, endoplasmic reticulum. e.g. All plants, Higher animals.

PROKARYOTES
Those living organisms, which do not have true membranous structure in their cells. e.g. Bacteria, Blue green algae.

PHYLETIC LINEAGE
All living organisms of today belong to a common ancestor and each specie of organism arranged no ancestor to descendent order with rest of the group evolved from one that immediately preceded.

BRANCHES OF BIOLOGY
1. MOLECULAR BIOLOGY
It is a recent branch of biological science that deals with the structure and function of the molecules that form structure of cell and organelles that take part in the biological processes of a living organism (Nucleic acid – Protein molecule)

2. MICRO BIOLOGY
It deals with the study of micro-organisms (viruses, bacteria, protozoan etc)

3. ENVIRONMENTAL BIOLOGY
It deals with the study of environment and its effect on organisms.

4. MARINE BIOLOGY
It deals with the study of organisms inhabiting the sea an ocean, and the physical and chemical characteristics of their environment.

5. FRESH WATER BIOLOGY
It deals with the life dwelling in fresh waters, physical and chemical characteristics of fresh water bodies affecting it.

6. PARASITOLOGY
It deals with the study of parasitic organisms, their life cycles, mode of transmission and interaction with their hosts.

7. HUMAN BIOLOGY
The branch of biology deals with all biological aspects of man regarding evolution, anatomy physiology, health, inheritance etc.

8. SOCIAL BIOLOGY
Social biology is concerned with the social interactions with in a population of a given species, especially in human beings focuses on such issue as whether certain behavior are inherited or culturally induced.

9. BIOTECHNOLOGY
This is a very recent branch introduce in biological sciences. It deals with the use of data and techniques of engineering and technology for the study and solution of problems concerning living organisms particularly the human beings.

BIOLOGICAL METHOD
In order to solve the biological problems (any animal or plant disease or environmental hazard), following steps are necessary.

1. HYPOTHESIS
An educated guess or fact regarding the biological problem.

INDUCTIVE REASONING
Isolated facts to reach a general idea that explain the biological problem.

DEDUCTIVE REASONING
Accurate experimentation, true conclusions or results regarding the biological problems.

2. OBSERVATION/EXPERIMENTS
The given hypothesis is checked with the help of observation and experiments and then on the basis of it a theory or rule is established.

3. THEORY
If observations and experiments come true then hypothesis is taken true, other wise it is rejected. Only on the basis of true hypothesis a theory is established.

4. LAW/PRINCIPLE
When theory is proved to be true under all tested circumstances then it is accepted as a law.

MALARIA
• Malaria means disease cause by bad air.
• Actual Causative agent is plasmodium (Vector Female, Anopheles Mosquito)
• Leveran first discover plasmodium in human R.B.C.
• Ronald Ross discovered plasmodium in the stomach of female Anopheles Mosquito.
• Grassi discover the complete life cycle of Plasmodium in human being and mosquito.

ANTIBIOTICS
Substances or chemicals, which are required in small quantity to inhibit the growth of Microorganisms. The first antibiotic was penicillin discovered by Fleming. Other examples are: Erythocin, Rythocin, Gentamycin, Ampicillin etc.

CHEMOTHERAPY
Treatment with drug or chemical.

RADIOTHERAPY
Treatment with radiations, like a, ß, ? or X-rays.

HYDROPONICS
It is the science of terrestrial plants growing in aerated solutions (add CO2 under pressure, in any liquid also known as aerated water). This technique is also known as soil less or water culture.
ADVANTAGES
1. Control weeds and soil disease problems.
2. Area required for cultivation is minimum.
3. Can be applied on any part of the world.
4. Main purpose is to fulfill the food requirements of rapidly increasing world population.

CLONING
Production of duplicate copies of genetic material, cells or entire multicellular living organisms, occurring naturally in plants or animals. Duplicate copies are known as clones.

NATURAL CLONING
• Identical twin, triplet in humans.
• A***ual reproduction in plants and animal.
• Regeneration and wound healing.
• Growth of tumor cells or cancers.

ARTIFICIAL CLONING
• Cloning of human cells such as liver cells, skin cells, blood cells are quite helpful to develop human organs in laboratories.
• There are also enormous advantages of cloning in the field of medicine and agriculture. Examples are vegetative reproduction of fruits and nuts by grafting.
• Artificial cloning is also used for treating disease, production of medically significant substances such as Insulin, growth hormones, interferon and anti-thrombin etc.

LEVEL OF BIOLOGICAL ORGANIZATION
Life is built on chemical foundation and the life of all living organisms emerges on the level of cell. The foundation of cell is based on elements. Atoms of different elements unite to form molecules. Living organism usually form extremely large and complex molecules by living matter which is present in their bodies. The molecules of living organisms are mostly composed of carbon and provide building blocks of living matter. Mostly living matter of an organism is composed of organic molecules along with inorganic compounds (minerals) are also associated for e.g. Human blood. Simple organic molecules present in living organisms are sugar, glycerol and fatty acids, amino acids, purine and pyramidines. Similar types of cells form-tissues, similar tissues form organs, different organs coordinating with each other form system and different systems combine to form a living organism.
Cell →Tissues → organs →System → An Individual
Biological organization can be divided into the following levels:

SUB-ATOMIC PARTICLES
“Particles that make up an atom are called sub-atomic particles”.
For e.g. electron, proton and Neutron.

ATOM
“The smallest particle of an element that retains the property of that element”.
For example: Hydrogen, carbon and oxygen etc.

MOLECULE
“The combination of similar and different atoms are called molecules”.
For example Hydrogen and oxygen combines to form water molecules.

ORGANELLE
“A structure with in a cell that performs a specific function”.
For example: Mitochondria, chloroplast etc.

CELL
“The smallest structural and functional unit of life”.
For example: A nerve cell

TISSUE
“A group of similar cells that performs a specific function”.
For example: Nervous tissue.

ORGAN
"A structure with in an organism usually compose of several tissue types that forms a functional unit”.
For example: The brain

ORGAN SYSTEM
“Two or more organs working together in the execution of a specific bodily function”.
For example: The nervous system.

MULTICELLULAR ORGANISM
“An individual living thing composed of many cells are called Multicellular organisms”.
For example: Pronghom antelope.

SPECIE
“A group of very similar inter breeding organisms constitutes a species”.
For example Herd of pronghom antelope.

POPULATION
"Members of same species inhabiting the same area are considered as population”.
For example: Herd of pronghom antelope.

COMMUNITY
“Population of several species living and interacting in the same area form a community”.
For example: Snake, antelope and hawk.

ECO-SYSTEM
“A community with its environment including land, water and atmosphere, constitute an eco-system”.

BIOSPHERE
“The part of earth inhibited by living organisms, both living and non-living components."

How to Block Websites

Block a Website on Your PC

1. Open Windows Explorer and navigate to C:\Windows\System32\drivers\etc. If Windows is not installed on C:, substitute the appropriate drive letter.

2. Double-click hosts, and select Notepad when Windows prompts you to choose a program. If you don't get the prompt, or if the hosts file opens in another program, open Notepad (Start, All Programs, Accessories, Notepad), and then navigate to hosts by clicking File, Open within Notepad.

3. Place the cursor at the end of the last line, which will say something such as '127.0.0.1 localhost' or '::1 localhost'. Press Enter to create a new line.

4. Type 127.0.0.1, tap the spacebar once, and then type the address of a website you want to block. For example, to block all traffic from YouTube, type127.0.0.1 www.youtube.com on this line.

5. Continue to add the websites you wish to block, each prefaced with 127.0.0.1 and a space.

6. Click File, Save to commit to your changes. Dismiss any warnings from antimalware software, which may be triggered by your editing of the hosts file.

7. Close any open browser windows, and then reopen a browser to test your edits. The blocked sites should not display in any browser.

Selectively Block a Website Based on User or Time of Day

If blocking a site from all users at all times is overkill for your situation and you want more control, try using your router’s Web interface to block a website selectively.

1. Open a browser and enter your router’s IP address into the address bar. Refer to your router’s documentation for the IP address, or, if you don’t immediately know it, try a common address such as http://192.168.1.1, http://192.168.0.1, or http://192.168.2.1.

2. Enter your username and password. If you haven’t changed the username and password, and you don’t know the defaults, visit Port Forward’s Default Router Passwords page to find them.

3. Browse to the section where you can block websites, computers, and access during certain times of day. Router interfaces vary, but look for a section with a name such as 'Access Restrictions'.

4. Enter the details of the content and the users you’d like to restrict, and save your changes. Your router’s paper or electronic documentation should provide full instructions.

Remember to exercise caution when editing your hosts text file, and always make sure to back up files before you edit them.

Blocking a website on a router

Most home networks today have a network routerfor sharing an Internet connection between multiple devices. In addition to routing the network information between devices, the router can also block websites. We recommend blocking a website through a router because it can be password protected to prevent the block from being bypassed and because it will block a website on all devices. This means if you were trying to block Facebook from your children it will be blocked on the computer as well as any cell phone or tablet connected to your home network.

To block a website on a router connect to the home network router, typically this is done by opening a browser and visiting the default router address: http://192.168.1.1

If this address does not work or you're having trouble accessing your router setup visit the link below.

• How do I connect to my home router?

After connecting to the router, block a website through one of the below features. Unfortunately, every router setup is different so you'll need to find one of the below settings for your manufacturer of the router. Generally one of these options will be available under a "Security", "Parental control", "Firewall" tab or button.

• URL Filter - Some routers may have a URL filter section, which allows you to enter the URL for each website you want to block.
• Parental controls - New and more advanced routers have a section dedicated to parental controls, which gives you not only the option to block websites but also specify the times the Internet can be accessed.
• Firewall - Finally, if neither of the above options is available the router should offer some type of filtering through the Firewall router settings.

Block a website using Family safety

Note: Blocking a site using these steps only blocks the website on one computer. Any other computer, phone, or tablet connected to your computer will be able to access the site you're blocking.

The new versions of Windows include a new Windows Family Safety feature that allows parents to setup computer usage rules and includes the ability to only allow certain websites or block websites. If you're running Windows 7 or Windows 8, open Family Safety from either the Windows Start Menu or Start Screen by typing "family" and then clicking on the Family Safety shortcut that should appear.

When open you'll have a screen that resembles the example below which gives you access to web filtering, time limits, logs, as well as the type of games that can be played.

Blocking a website in Windows

Note: Blocking a site using these steps only blocks the website on one computer. Any other computer, phone, or tablet connected to your computer will be able to access the site you're blocking.

A website can be blocked on any Windows computer by editing the hosts file, in Windows this file is referred to as the lmhost file.

Locate the hosts file in Windows Explorer. For Windows XP and up, it will be located in the directory C:\WINDOWS\system32\drivers\etc\. In Windows 2000/NT, C:\WINNT\system32\drivers\etc\. In Windows 98 and ME, C:\WINDOWS\.

Navigate to the proper directory using Windows Explorer. Double-click the hosts file. Choose Notepad from the list of programs to open the file and edit it in Notepad.

Find the line below:

127.0.0.1 localhost

Right underneath it, add the following lines (replacing badsite.com with the site you want to block):

127.0.0.1 badsite.com
127.0.0.1 www.badsite.com

Click on the File menu and click Save. Close the file. The site should be blocked in all web browsers and now instead of trying to access that site the computer will redirect you to the localhost.

• Additional information with viewing, editing, and modifying the lmhost file.

Blocking a website using software

Note: Blocking a site using these steps only blocks the website on one computer. Any other computer, phone, or tablet connected to your computer will be able to access the site you're blocking.

You can also block websites using a software firewall or a filter (such as a parent control Internet filter). Also, most anti-virus software will come with a firewall or have an option to obtain one from them. Filtering software may also be available through the same companies or could be obtained separately. To configure these pieces of software to block websites, you need to follow the instructions provided by the software vendor.

Blocking a website in a browser

Note: Blocking a site in a browser only blocks the site in one browser. Any other browser, computer, phone, or tablet connected to your computer will be able to access the site you're blocking.

Blocking a website in Firefox
Blocking a website in Internet Explorer
Blocking a website in Chrome

Blocking in Firefox

Although not available with the default install of Firefox, there are plenty of add-ons that allow you to block sites in Firefox. Below are the steps on how to install BlockSite, a great add-on to block websites.

1. Click on the Tools menu and click Add-ons. If you don't see Tools press the Alt key.
2. In the top-right corner of the Add-ons Manager page, there is a search bar. Perform a search for BlockSite. The first result should be the add-on called BlockSite. Click the Install button to install the add-on.
3. Restart Firefox to complete the installation.
4. Click on the Tools menu and click Add-ons. This takes you to the Add-ons Manager page. Click the Extensions tab.
5. In the listing for BlockSite, click the Options button. The screen below will be shown.

In the BlockSite Preferences click the Add button. In the window asking for the Web address to block enter the address of the website to block and click the OK button. Click the OK button to exit BlockSite and continue browsing

Blocking in Internet Explorer

Note: If you're running Windows 7 or Windows 8, Windows now handles all the below settings through Family Safety.

1. Click Tools in the File menu and click Internet Options. If Tools is not visible press the Alt key.
2. In the Internet Options window click on the Content tab.
3. Under the Content Advisor heading, click Enable if it has not yet been enabled, or click Settings, enter your supervisor password and click the OK button.
4. In the Content Advisor window click the Approved Sites tab to show a screen similar to the example below.

Enter the Web address to block and click the Never button. Click the OK button to exit the Content Advisor window, then click OK again to exit the Internet Options window and continue browsing. Blocking in Google Chrome and other browsers

Blocking a website in Chrome

Chrome does not come included with any type of website blocking tool or feature. However, there are plenty of Chrome Extensions that can be added that allow you to block a website. Visit the Chrome web store and search for "blocksite" to pull up a listing of available extensions that will block websites.