AQA A level Biology Revision Questions

AQA A level Biology Revision Questions A molecule has a better chance of passing through the phospholipid bilayer if... - It is a small molecule, is not a charged molecule, it is not an ion. Those that pass through best are lipid soluble and hydrophobic molecules. A protein molecule contains 150 amino acids. What is the total number of peptide bonds in this molecule? [1] - 149 An enzyme catalyses only one reaction. Explain why [2] - (Enzyme has) active site; Only substrate fits (the active site); Calculate the possible number of different combinations of chromosomes following meiosis (without crossing over) if parent cell contains 22 chromosomes (1 mark) - 211 = 2048 formula 2n Compare DNA Vs RNA (6/ 10marks) - Similarities: Contain phosphate Made up of nucleotides Contains organic bases (A, C and G) (not T as it is replaced by U in RNA) Pentose sugar (3 max) Differences RNA single stranded RNA has non-coding strands (introns) removed Ribose sugar in RNA deoxyribose in DNA U in ribose replaces the T 3 types of RNA, only one DNA Smaller than DNA (3 max) Define active immunity. - Resistance to disease resulting from the activities of an individual's own immune system whereby an antigen induces plasma cells to produce antibodies Define active transport. - Movement of a substance from a region where it is in low concentration to a region of high concentration. Requires energy. Define allele - one of a number of alternative forms of a gene. Define biodiversity? - The range and variety of genes, species and habitats within a particular region. Define diffusion. - The net movement of molecules or ions from high concentration region to a lower concentration region. Define Mass Flow - Mass flow is the bulk movement of liquids (and gases) due to a pressure difference. Define osmosis. - The passage of water from a region where it has a higher water potential to a region where it has a lower water potential through a selectively permeable membrane. Define the term antigen - An antigen is a