Cambridge CIE IGCSE Biology PDF

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Biology Your notes Biological Molecules Contents Chemicals & Life Food Tests DNA Structure...

Head to www.savemyexams.com for more awesome resources Cambridge (CIE) IGCSE Biology Your notes Biological Molecules Contents Chemicals & Life Food Tests DNA Structure Page 1 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Chemicals & Life Your notes Chemical Elements Most of the molecules in living organisms fall into three categories: carbohydrates, proteins and lipids These all contain carbon and so are described as organic molecules Chemical Elements Table Large Molecules are Made from Smaller Molecules Carbohydrates Long chains of simple sugars Glucose is a simple sugar ( a monosaccharide) When 2 glucose molecules join together maltose is formed (a disaccharide) When lots of glucose molecules join together starch, glycogen or cellulose can form (a polysaccharide) Page 2 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Glycogen, cellulose and starch are all made from glucose molecules Fats Most fats (lipids) in the body are made up of triglycerides Their basic unit is 1 glycerol molecule chemically bonded to 3 fatty acid chains The fatty acids vary in size and structure Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature) Page 3 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Structure of a triglyceride Proteins Long chains of amino acids There are about 20 different amino acids They all contain the same basic structure but the ‘R’ group is different for each one When amino acids are joined together a protein is formed The amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins Even a small difference in the order of the amino acids results in a different protein being formed Page 4 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes General amino acid structure Page 5 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Amino acids join together to form proteins Page 6 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Food Tests Your notes Food tests in biology Food test for glucose (a reducing sugar) Add Benedict's solution into sample solution in test tube Heat at 60 - 70 °c in water bath for 5 minutes Take test tube out of water bath and observe the colour A positive test will show a colour change from blue to orange or brick red Use this image Page 7 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Benedict's test for glucose Food test for starch Your notes We can use iodine to test for the presence or absence of starch in a food sample. Use this image The iodine test for starch Add drops of iodine solution to the food sample A positive test will show a colour change from orange-brown to blue-black Page 8 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Use this image Testing a potato to prove the presence of starch Food test for protein Add drops of Biuret solution to the food sample A positive test will show a colour change from blue to violet / purple Page 9 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Use this image The Biuret test for protein Food test for lipids Food sample is mixed with 2cm3 of ethanol and shaken The ethanol is added to an equal volume of cold water A positive test will show a cloudy emulsion forming Page 10 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Use this image The ethanol test for lipids Food test for vitamin C Add 1cm3 of DCPIP solution to a test tube Add a small amount of food sample (as a solution) A positive test will show the blue colour of the dye disappearing Page 11 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Use this image The DCPIP test for vitamin C Examiner Tips and Tricks When describing food tests in exam answers, make sure you give the starting colour of the solution and the colour it changes to for a positive result. Page 12 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources DNA Structure Your notes Structure of a DNA Molecule: Extended Extended Tier Only DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for the growth and development of all organisms It consists of two strands of DNA wound around each other in what is called a double helix DNA, chromosomes and the nucleus The individual units of DNA are called nucleotides Page 13 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A nucleotide All nucleotides contain the same phosphate and deoxyribose sugar, but differ from each other in the base attached There are four different bases, Adenine (A), Cytosine (C), Thymine (T) and Guanine (G) The bases on each strand pair up with each other, holding the two strands of DNA in the double helix The bases always pair up in the same way: Adenine always pairs with Thymine (A-T) Cytosine always pairs with Guanine (C-G) Page 14 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes DNA base pairs The phosphate and sugar section of the nucleotides form the ‘backbone’ of the DNA strand (like the sides of a ladder) and the base pairs of each strand connect to form the rungs of the ladder Page 15 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes The DNA helix is made from two strands of DNA held together by hydrogen bonds It is this sequence of bases that holds the code for the formation of proteins Examiner Tips and Tricks You do not need to learn the names of the bases, just their letter. Make sure you know which bonds with which, as this is the most commonly asked question about this topic. Page 16 of 16 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers