Biology AS

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Chapter 1

 

Biological Molecules

 

Bonding:

·      Covalent:  when atoms share electrons from their outer shell, to fill both outer shells

·      Ionic: ions with opposite charges attract. The electrostatic attraction is an ionic bond

·      Hydrogen: electrons within a molecule are not evenly distributed. A molecule with uneven distribution of charge is called a polar molecule. The negative region of one molecule attracts to the positively charged region of another forming a weak electrostatic bond.

 

Polymerisation:

·      Monomers can be linked to form long chains called polymers. They are formed through polymerisation

·      Monosaccharides join to form polysaccharides

·      Peptides joint to form polypeptides

 

Condensation and hydrolysis:

·      Polymerisation is a condensation reaction because a water molecule is formed

·      Polymers can be broken down using water in a reaction called hydrolysis.

 

Metabolism:

·      All the chemical processes that take place in living organisms

 

Mole and molar solutions:

·      The mole is the SI unit for measuring the amount of a substance (mol)

·      One mole has the same number of particles as in 12g of carbon-12 atoms.

·      A molar solution is a solution that contains one mole of solute in each litre of solution

Atoms:

·      Smallest unit of a chemical element.

·      Has a nucleus with protons and neutrons

·      Electrons orbit the nucleus

·      Protons – occur in the nucleus and have the same mass as neutrons with a positive charge

·      Neutrons – occur in the nucleus and have the same mass as protons with no charge

·      Electrons – orbit in shells around the nucleus. Tiny mass. They are negatively charged and the quantity determines the properties of an atom

·      Atomic number – the number of protons in an atom

·      Mass number – the number of protons and neutrons in an atom

·      Different types of atoms are called isotopes

·      If an atom loses or gains an electron it becomes an ion

 

Carbohydrates:

 

·      Carbon molecules combine with water

·      Readily form bonds with other carbon atoms

·      Large number of different types and sizes of molecules can be formed

·      The variety of life that exists on earth is a consequence of living organisms being based on the carbon atom

·      Monomers join to form polymers

·      Monosaccharides can be joined to form disaccharides (two) and polysaccharides

 

Monosaccharides

 

·      Sweet tasting soluble substances

·      Glucose, galactose and fructose

·      Glucose is a hexose (6 carbon sugar)

·      Alpha and beta glucose

 

Testing for reducing sugars

 

·      All monosaccharides and some disaccharides are reducing sugars

·      Reduction is a chemical reaction involving the gain of electrons or hydrogen.

·      Benedict’s test:

·      Alkaline solution – copper sulphate

·      Forms an insoluble

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