Science

How to get an A/A* in Science

UNIT	This is the content that can only appear on the Higher Tier and therefore fulfils the highest grade requirements
B1	antibiotics kill individual pathogens of the non-resistant strain individual resistant pathogens survive and reproduce, so the population of the resistant strain increases now, antibiotics are no longer used to treat non-serious infections, such as mild throat infections, so that the rate of development of resistant strains is slowed down.
C1	be able to balance symbol equations. Emulsifiers have hydrophilic and hydrophobic properties. Vegetable oils that are unsaturated can be hardened by reacting them with hydrogen in the presence of a nickel catalyst at about 60°C. Hydrogen adds to the carbon–carbon double bonds. The hydrogenated oils have higher melting points so they are solids at room temperature, making them useful as spreads and in cakes and pastries. describe why we do not know how life was first formed. One theory as to how life was formed involves the interaction between hydrocarbons, ammonia and lightning. Air is a mixture of gases with different boiling points and can be fractionally distilled to provide a source of raw materials used in a variety of industrial processes.
P1	All content can range up to A/A*
B2	As the breakdown of glucose is incomplete, much less energy is released than during aerobic respiration. Anaerobic respiration results in an oxygen debt that has to be repaid in order to oxidise lactic acid to carbon dioxide and water. construct genetic diagrams of monohybrid crosses and predict the outcomes of monohybrid crosses and be able to use the terms homozygous, heterozygous, phenotype and genotype When a cell divides to form gametes: ■ copies of the genetic information are made ■ then the cell divides twice to form four gametes, each with a single set of chromosomes. amino acids which makes a specific protein. genetic variation – each population has a wide range of alleles that control their characteristics natural selection – in each population, the alleles that control the characteristics which help the organism to survive are selected speciation – the populations become so different that successful interbreeding is no longer possible.
C2	The electrons in the highest occupied energy levels (outer shell) of metal atoms are delocalised and so free to move through the whole structure. This corresponds to a structure of positive ions with electrons between the ions holding them together by strong electrostatic attractions. Substances that consist of simple molecules have only weak forces between the molecules (intermolecular forces). It is these intermolecular forces that are overcome, not the covalent bonds, when the substance melts or boils. In graphite, one electron from each carbon atom is delocalised. These delocalised electrons allow graphite to conduct heat and electricity. Carbon can also form fullerenes with different numbers of carbon atoms. Fullerenes can be used for drug delivery into the body, in lubricants, as catalysts, and in nanotubes for reinforcing materials, eg in tennis rackets. Metals conduct heat and electricity because of the delocalised electrons in their structures The relative atomic mass of an element (Ar) compares the mass of atoms of the element with the 12C isotope. It is an average value for the isotopes of the element. the mass spectrometer can also give the relative molecular mass of each of the substances separated in the column. The empirical formula of a compound can be calculated from the masses or percentages of the elements in a compound. The masses of reactants and products can be calculated from balanced symbol equations. Reactions at electrodes can be represented by half equations, for example: 2Cl– ➞ Cl2 + 2e– or 2Cl – – 2e– ➞ Cl2
P2	Calculation of the speed of an object from the gradient of a distance–time graph. Calculation of the acceleration of an object from the gradient of a velocity–time graph. Candidates should be able to explain resistance change in terms of ions and electrons. candidates should be able to determine the period and hence the frequency of a supply from diagrams of oscilloscope traces. Energy transferred, potential difference and charge are related by the equation: E = V XQ Nuclear equations to show single alpha and beta decay.