AQA As level Biology Revision notes section 1

Particular groups of chemicals which are found in living organisms.

FORMATION OF MOLECULES

COVALENT BONDING: atoms share a pair of electrons to fill outer shell which results in a more stable compound called a molecule

IONIC BONDING: ions with opposite charges attract and their electrostatic force of attraction is known as an ionic bond. WEAKER THAN COVALENT BONDS

HYDROGEN BONDING:a molecule with an uneven distribution of charge is said to be polarised. The -ive region of one polar molecule attracts the +ive region of another. A weak electrostatic bond is formed between the 2.

Monomers can be linked to form long chains called polymers = polymerisation

Monomers of a polymer are usually based on C.

Some are industrially produced (polythene) others are made naturally in living organisms (polypeptides)

In polymerisation every time a sub unit is attached a molecule of H20 is formed. (condensation reaction)

Therefore the formation of polypeptide from amino acids + polysaccharide starch from monosaccharide glucose are both condensation reactions

Polymers can be broken down through the addition of H20. the water molecule breaks the bonds that link the sub units of a polymer (hydrolysis reaction)

METABOLISM= ALL THE CHEMICAL PROCESSES THAT TAKE PLACE IN LIVING ORGANISMS

EVIDENCE FOR EVOLUTION

There is a huge variety of different organisms on earth but they all share the same biochemistry. They all contain the same groups of carbon-based compounds that interact in similar ways (same DNA & RNA as genetic material and the same amino acids to build proteins). These similarities suggest that animals + plants have a common ancestor.

SUGARS

All carbs contain the elements C,H and O. The monomers that they are made from are called monosaccharides (e.g. glucose, fructose and galactose)

GLUCOSE is a hexose sugar (6 C atoms) and there are two types; ALPHA and BETA (isomers)

Isomers: molecules with same molecular formula as each other but with the atoms connected in a different way.

DISACCHARIDES:

2 monosaccharides join together via a condensation reaction forming

a glycosidic bond.

GLUCOSE + GLUCOSE= MALTOSE

GLUCOSE + FRUCTOSE= SUCROSE

GLUCOSE + GALACTOSE= LACTOSE

BENEDICT’S TEST FOR SUGARS

Reducing sugars= all monosaccharides and some disaccharides e.g maltose and lactose

Add benedict's reagent (it's blue) to a sample and heat in a water bath that's been boiled. If a coloured (green,yellow,orange,brick red) precipitate forms a reducing sugar is present but if it stays blue there isn't. The higher the conc of reducing sugars the further the colour change (can be more accurate by using a colorimeter)

Non reducing sugars= e.g sucrose

You first have to break them down into monosaccharides. You do this by heating a fresh sample with dilute HCL then you neutralise it by adding sodium hydrogencarbonate the just carry out a benedict's test.

If it stays blue then no reducing sugar or reducing sugar is present but if the sample forms a green-yellow-orange-brick red precipitate then a non reducing sugar is present.

Functions of polysaccharides

STARCH:

Cells get energy from glucose. Plants store excess glucose as…