AQA A-Level Biology Revision

Year 12

• Surface area to volume ratio
  • 1.1 The relationship between the size of an organism or structure and its surface area to volume ratio
  • 1.2 Changes to body shape and the development of systems in larger organisms as adaptations that facilitate exchange as this ratio reduces
  • 1.3 appreciate the relationship between surface area to volume ratio and metabolic rate
  • 1.4 PS 1.1
  • 1.5 Students could use agar blocks containing indicator to determine the effect of surface area to volume ratio and concentration gradient on the diffusion of an acid or alkali
  • 1.6 Students could be given the dimensions of cells with different shapes from which to calculate the surface area to volume ratios of these cells
• Gas exchange
  • 2.1 Adaptations of gas exchange surfaces, shown by gas exchange
  • 2.2 in the tracheal system of an insect (tracheae, tracheoles and spiracles)
  • 2.3 Structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss shown by terrestrial insects and xerophytic plants
  • 2.4 The essential features of the alveolar epithelium as a surface over which gas exchange takes place
  • 2.5 interpret information relating to the effects of lung disease on gas exchange and/or ventilation
  • 2.6 evaluate the way in which experimental data led to statutory restrictions on the sources of risk factors
  • 2.7 AT j
  • 2.8 AT d
  • 2.9 examine vertical sections through a dicotyledonous leaf
  • 2.10 Students could be given values of pulmonary ventilation rate (PVR) and one other measure, requiring them to change the subject of the equation
• Digestion and absorption
  • 3.1 During digestion, large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes
  • 3.2 Digestion in mammals of
  • 3.3 carbohydrates by amylases and membrane-bound disaccharidases
  • 3.4 proteins by endopeptidases, exopeptidases and membrane-bound dipeptidases
  • 3.5 Mechanisms for the absorption of the products of digestion by cells lining the ileum of mammals, to include
  • 3.6 co-transport mechanisms for the absorption of amino acids and of monosaccharides
  • 3.7 the role of micelles in the absorption of lipids
  • 3.8 Students could
  • 3.9 design and carry out investigations into the effect of a pH or bile salts on the rate of reaction catalysed by a digestive enzyme
  • 3.10 use Visking tubing models to investigate the absorption of the products of digestion
• Mass transport
  • 4.1 Over large distances, efficient movement of substance to and from exchange surfaces is provided by mass transport
  • 4.2 The role of haemoglobin and red blood cells in the transport of oxygen. The loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve. The cooperative nature of oxygen binding to show that the change in shape of haemoglobin caused by binding of the first oxygens makes the binding of further oxygens easier. The effects of carbon dioxide concentration on the dissociation of oxyhaemoglobin (the Bohr effect)
  • 4.3 The general pattern of blood circulation in a mammal. Names are required only of the coronary arteries and of the blood vessels entering and leaving the heart, lungs and kidneys
  • 4.4 The structure of capillaries and the importance of capillary beds as exchange surfaces. The formation of tissue fluid and its return to the circulatory system
  • 4.5 analyse and interpret data associated with specific risk factors and the incidence of cardiovascular disease
  • 4.6 AT h
  • 4.7 Students could be given values of cardiac output (CO) and one other measure, requiring them to change the subject of the equation
  • 4.8 Mass transport in plants
  • 4.9 Phloem as the tissue that transports organic substances in plants. The mass flow hypothesis for the mechanism of translocation in plants. The use of tracers and ringing experiments to investigate transport in plants
  • 4.10 Students could set up and use a potometer to investigate the effect of a named environmental variable on the rate of transpiration
• DNA, genes and chromosomes
  • 5.1 In prokaryotic cells, DNA molecules are short, circular and not associated with proteins
  • 5.2 In the nucleus of eukaryotic cells, DNA molecules are very long, linear and associated with proteins, called histones. Together a DNA molecule and its associated proteins form a chromosome
  • 5.3 The mitochondria and chloroplasts of eukaryotic cells also contain DNA which, like the DNA of prokaryotes, is short, circular and not associated with protein
  • 5.4 A gene is a base sequence of DNA that codes for
  • 5.5 the amino acid sequence of a polypeptide
  • 5.6 a functional RNA (including ribosomal RNA and tRNAs)
  • 5.7 A gene occupies a fixed position, called a locus, on a particular DNA molecule
  • 5.8 A sequence of three DNA bases, called a triplet, codes for a specific amino acid. The genetic code is universal, non-overlapping and degenerate
  • 5.9 In eukaryotes, much of the nuclear DNA does not code for polypeptides. There are, for example, non-coding multiple repeats of base sequences between genes. Even within a gene only some sequences, called exons, code for amino acid sequences. Within the gene, these exons are separated by one or more non-coding sequences, called introns
• DNA and protein synthesis
  • 6.1 The concept of the genome as the complete set of genes in a cell and of the proteome as the full range of proteins that a cell is able to produce
  • 6.2 The structure of molecules of messenger RNA (mRNA) and of transfer RNA (tRNA)
  • 6.3 Transcription as the production of mRNA from DNA. The role of RNA polymerase in joining mRNA nucleotides
  • 6.4 In prokaryotes, transcription results directly in the production of mRNA from DNA
  • 6.5 In eukaryotes, transcription results in the production of pre-mRNA
  • 6.6 this is then spliced to form mRNA
  • 6.7 Translation as the production of polypeptides from the sequence of codons carried by mRNA. The roles of ribosomes, tRNA and ATP
  • 6.8 relate the base sequence of nucleic acids to the amino acid sequence of polypeptides, when provided with suitable data about the genetic code
  • 6.9 interpret data from experimental work investigating the role of nucleic acids
  • 6.10 Students will not be required to recall in written papers specific codons and the amino acids for which they code
• Genetic diversity can arise as a result of mutation or during meiosis
  • 7.1 Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include base deletion and base substitution. Due to the degenerate nature of the genetic code, not all base substitutions cause a change in the sequence of encoded amino acids. Mutagenic agents can increase the rate of gene mutation
  • 7.2 Mutations in the number of chromosomes can arise spontaneously by chromosome non-disjunction during meiosis
  • 7.3 The process of meiosis only in sufficient detail to show how
  • 7.4 two nuclear divisions result usually in the formation of four haploid daughter cells from a single diploid parent cell
  • 7.5 genetically different daughter cells result from the independent segregation of homologous chromosomes
  • 7.6 complete diagrams showing the chromosome content of cells after the first and second meiotic division, when given the chromosome content of the parent cell
  • 7.7 explain the different outcome of mitosis and meiosis
  • 7.8 recognise where meiosis occurs when given information about an unfamiliar life cycle
  • 7.9 use the expression 2n to calculate the possible number of different combinations of chromosomes following meiosis, without crossing over
  • 7.10 derive a formula from this to calculate the possible number of different combinations of chromosomes following random fertilisation of two gametes,
• Genetic diversity and adaptation
  • 8.1 Genetic diversity as the number of different alleles of genes in a population
  • 8.2 Genetic diversity is a factor enabling natural selection to occur
  • 8.3 Random mutation can result in new alleles of a gene
  • 8.4 Many mutations are harmful but, in certain environments, the new allele of a gene might benefit its possessor, leading to increased reproductive success
  • 8.5 The advantageous allele is inherited by members of the next generation
  • 8.6 Directional selection, exemplified by antibiotic resistance in bacteria, and stabilising selection, exemplified by human birth weights
  • 8.7 Natural selection results in species that are better adapted to their environment. These adaptations may be anatomical, physiological or behavioural
  • 8.8 use unfamiliar information to explain how selection produces changes within a population of a species
  • 8.9 show understanding that adaptation and selection are major factors in evolution and contribute to the diversity of living organisms
  • 8.10 Students could use a logarithmic scale when dealing with data relating to large numbers of bacteria in a culture
• Species and taxonomy
  • 9.1 Two organisms belong to the same species if they are able to produce fertile offspring. Courtship behaviour as a necessary precursor to successful mating. The role of courtship in species recognition
  • 9.2 A phylogenetic classification system attempts to arrange species into groups based on their evolutionary origins and relationships. It uses a hierarchy in which smaller groups are placed within larger groups, with no overlap between groups. Each group is called a taxon (plural taxa)
  • 9.3 One hierarchy comprises the taxa: domain, kingdom, phylum, class, order, family, genus and species
  • 9.4 Each species is universally identified by a binomial consisting of the name of its genus and species, eg, Homo sapiens
  • 9.5 Recall of different taxonomic systems, such as the three domain or five kingdom systems, will not be required
  • 9.6 appreciate that advances in immunology and genome sequencing help to clarify evolutionary relationships between organisms
• Biodiversity within a community
  • 10.1 Biodiversity can relate to a range of habitats, from a small local habitat to the Earth
  • 10.2 Species richness is a measure of the number of different species in a community
  • 10.3 An index of diversity describes the relationship between the number of species in a community and the number of individuals in each species
  • 10.4 Calculation of an index of diversity (
  • 10.5 where
  • 10.6 Farming techniques reduce biodiversity. The balance between conservation and farming
  • 10.7 Students could be given data from which to calculate an index of diversity and interpret the significance of the calculated value of the index
• Investigating diversity
  • 11.1 the frequency of measurable or observable characteristics
  • 11.2 the base sequence of mRNA
  • 11.3 interpret data relating to similarities and differences in the base sequences of DNA and in the amino acid sequences of proteins to suggest relationships between different organisms within a species and between species
  • 11.4 inferring DNA differences from measurable or observable characteristics has been replaced by direct investigation of DNA sequences.Knowledge of gene technologies will not be tested
  • 11.5 collecting data from random samples
  • 11.6 interpreting mean values and their standard deviations
  • 11.7 AT k
  • 11.8 design appropriate methods to ensure random sampling
  • 11.9 use random samples to investigate the effect of position on the growth of leaves
  • 11.10 Students could calculate, and interpret the values of, the standard deviations of their mean values
• Cell structure
  • 12.1 The cell theory is a unifying concept in biology
  • 12.2 nucleus (containing chromosomes, consisting of protein-bound, linear DNA, and one or more nucleoli)
  • 12.3 lysosomes (a membrane-bound organelle that releases hydrolytic enzymes)
  • 12.4 cell wall (in plants, algae and fungi)
  • 12.5 Structure of prokaryotic cells and of viruses
  • 12.6 no nucleus
  • 12.7 one or more plasmids
  • 12.8 Details of these structural differences are not required
  • 12.9 Measuring the size of an object viewed with an optical microscope. The difference between magnification and resolution
  • 12.10 Students could use iodine in potassium iodide solution to identify starch grains in plant cells
• All cells arise from other cells
  • 13.1 Within multicellular organisms, not all cells retain the ability to divide
  • 13.2 DNA replication occurs during the interphase of the cell cycle
  • 13.3 The behaviour of chromosomes during interphase, prophase, metaphase, anaphase and telophase of mitosis. The role of spindle fibres attached to centromeres in the separation of chromatids
  • 13.4 Meiosis is covered in section 3.4.3
  • 13.5 explain the appearance of cells in each stage of mitosis
  • 13.6 Binary fission in prokaryotic cells involves
  • 13.7 division of the cytoplasm to produce two daughter cells, each with a single copy of the circular DNA and a variable number of copies of plasmids
  • 13.8 Required practical 2: Preparation of stained squashes of cells from plant root tips
  • 13.9 Students should measure the apparent size of cells in the root tip and calculate their actual size using the formula
  • 13.10 Calculation of a mitotic index
• Transport across cell membranes
  • 14.1 The basic structure of all cell membranes, including cell-surface membranes and the membranes around the cell organelles of eukaryotes, is the same
  • 14.2 Movement across membranes occurs by
  • 14.3 simple diffusion (involving limitations imposed by the nature of the phospholipid bilayer)
  • 14.4 osmosis (explained in terms of water potential)
  • 14.5 active transport (involving the role of carrier proteins and the importance of the hydrolysis of ATP)
  • 14.6 Cells may be adapted for rapid transport across their internal or external membranes by an increase in surface area of, or by an increase in the number of protein channels and carrier molecules in, their membranes
  • 14.7 explain the adaptations of specialised cells in relation to the rate of transport across their internal and external membranes
  • 14.8 Required practical 3: Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue
  • 14.9 Required practical 4: Investigation into the effect of a named variable on the permeability of cell-surface membranes
  • 14.10 Students could determine the water potential of plant tissues using the intercept of a graph of, eg, water potential of solution against gain/loss of mass
• Cell recognition and the immune system
  • 15.1 Each type of cell has specific molecules on its surface that identify it. These molecules include proteins and enable the immune system to identify
  • 15.2 abnormal body cells
  • 15.3 Phagocytosis of pathogens. The subsequent destruction of ingested pathogens by lysozymes
  • 15.4 The role of antigen-presenting cells in the cellular response
  • 15.5 Definition of antibody
  • 15.6 The roles of plasma cells and of memory cells in producing primary and secondary immune responses
  • 15.7 Structure of the human immunodeficiency virus (HIV) and its replication in helper T cells
  • 15.8 The use of monoclonal antibodies in
  • 15.9 Details of the commercial or scientific production of monoclonal antibodies are not required
  • 15.10 evaluate methodology, evidence and data relating to the use of vaccines and monoclonal antibodies
• Monomers and polymers
  • 16.1 The variety of life, both past and present, is extensive, but the biochemical basis of life is similar for all living things
  • 16.2 Monomers are the smaller units from which larger molecules are made
  • 16.3 Polymers are molecules made from a large number of monomers joined together
  • 16.4 Monosaccharides, amino acids and nucleotides are examples of monomers
  • 16.5 A condensation reaction joins two molecules together with the formation of a chemical bond and involves the elimination of a molecule of water
  • 16.6 A hydrolysis reaction breaks a chemical bond between two molecules and involves the use of a water molecule
• Carbohydrates
  • 17.1 Monosaccharides are the monomers from which larger carbohydrates are made. Glucose, galactose and fructose are common monosaccharides
  • 17.2 Disaccharides are formed by the condensation of two monosaccharides
  • 17.3 sucrose is a disaccharide formed by condensation of a glucose molecule and a fructose molecule
  • 17.4 lactose is a disaccharide formed by condensation of a glucose molecule and a galactose molecule
  • 17.5 Polysaccharides are formed by the condensation of many glucose units
  • 17.6 Cellulose is formed by the condensation of β-glucose
  • 17.7 Biochemical tests using Benedict's solution for reducing sugars and non-reducing sugars and iodine/potassium iodide for starch
  • 17.8 AT f
  • 17.9 Students could use chromatography, with known standard solutions, to separate a mixture of monosaccharides and identify their components
  • 17.10 Students could produce a dilution series of glucose solution and use colorimetric techniques to produce a calibration curve with which to identify the concentration of glucose in an unknown solution
• Lipids
  • 18.1 Triglycerides and phospholipids are two groups of lipid
  • 18.2 Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid
  • 18.3 A condensation reaction between glycerol and a fatty acid (RCOOH) forms an ester bond
  • 18.4 The R-group of a fatty acid may be saturated or unsaturated
  • 18.5 In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group
  • 18.6 The different properties of triglycerides and phospholipids related to their different structures
  • 18.7 The emulsion test for lipids
  • 18.8 recognise, from diagrams, saturated and unsaturated fatty acids
  • 18.9 explain the different properties of triglycerides and phospholipids
  • 18.10 AT f
• Proteins
  • 19.1 General properties of proteins
  • 19.2 Dipeptides are formed by the condensation of two amino acids
  • 19.3 The role of hydrogen bonds, ionic bonds and disulfide bridges in the structure of proteins
  • 19.4 AT f
  • 19.5 Students could use chromatography with known standard solutions, to separate a mixture of amino acids and identify their components
  • 19.6 The induced-fit model of enzyme action
  • 19.7 The effects of the following factors on the rate of enzyme-controlled reactions – enzyme concentration, substrate concentration, concentration of competitive and of non-competitive inhibitors, pH and temperature
  • 19.8 Required practical 1 : Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction
  • 19.9 PS 3.3
  • 19.10 Students could use a tangent to find the initial rate of an enzyme-controlled reaction
• Nucleic acids are important information-carrying molecules
  • 20.1 Structure of DNA and RNA
  • 20.2 Ribosomes are formed from RNA and proteins
  • 20.3 The components of a DNA nucleotide are deoxyribose, a phosphate group and one of the organic bases adenine, cytosine, guanine or thymine
  • 20.4 A condensation reaction between two nucleotides forms a phosphodiester bond
  • 20.5 An RNA molecule is a relatively short polynucleotide chain
  • 20.6 DNA replication
  • 20.7 The process of semi-conservative replication of DNA in terms of
  • 20.8 breakage of hydrogen bonds between complementary bases in the polynucleotide strands
  • 20.9 attraction of new DNA nucleotides to exposed bases on template strands and base pairing
  • 20.10 evaluate the work of scientists in validating the Watson–Crick model of DNA replication
• ATP
  • 21.1 A single molecule of adenosine triphosphate (ATP) is a nucleotide derivative and is formed from a molecule of ribose, a molecule of adenine and three phosphate groups
  • 21.2 Hydrolysis of ATP to adenosine diphosphate (ADP) and an inorganic phosphate group (Pi ) is catalysed by the enzyme ATP hydrolase
  • 21.3 The hydrolysis of ATP can be coupled to energy-requiring reactions within cells
  • 21.4 The inorganic phosphate released during the hydrolysis of ATP can be used to phosphorylate other compounds, often making them more reactive
  • 21.5 ATP is resynthesised by the condensation of ADP and Pi . This reaction is catalysed by the enzyme ATP synthase during photosynthesis, or during respiration
• Water
  • 22.1 Water is a major component of cells. It has several properties that are important in biology. In particular, water
  • 22.2 is a metabolite in many metabolic reactions, including condensation and hydrolysis reactions
  • 22.3 is an important solvent in which metabolic reactions occur
  • 22.4 has a relatively high heat capacity, buffering changes in temperature
  • 22.5 has a relatively large latent heat of vaporisation, providing a cooling effect with little loss of water through evaporation
  • 22.6 has strong cohesion between water molecules
  • 22.7 this supports columns of water in the tube-like transport cells of plants and produces surface tension where water meets air
• Inorganic ions
  • 23.1 Inorganic ions occur in solution in the cytoplasm and body fluids of organisms, some in high concentrations and others in very low concentrations
  • 23.2 Each type of ion has a specific role, depending on its properties
  • 23.3 recognise the role of ions in the following topics: hydrogen ions and pH
  • 23.4 iron ions as a component of haemoglobin
  • 23.5 sodium ions in the co-transport of glucose and amino acids
  • 23.6 and phosphate ions as components of DNA and of ATP

Year 13

• Photosynthesis
  • 1.1 The light-dependent reaction in such detail as to show that
  • 1.2 some of the energy from electrons released during photoionisation is conserved in the production of ATP and reduced NADP
  • 1.3 photolysis of water produces protons, electrons and oxygen
  • 1.4 The light-independent reaction uses reduced NADP from the light-dependent reaction to form a simple sugar. The hydrolysis of ATP, also from the light-dependent reaction, provides the additional energy for this reaction
  • 1.5 carbon dioxide reacts with ribulose bisphosphate (RuBP) to form two molecules of glycerate 3-phosphate (GP). This reaction is catalysed by the enzyme rubisco
  • 1.6 some of the triose phosphate is used to regenerate RuBP in the Calvin cycle
  • 1.7 identify environmental factors that limit the rate of photosynthesis
  • 1.8 evaluate data relating to common agricultural practices used to overcome the effect of these limiting factors
  • 1.9 Students could devise and carry out experiments to investigate the effect of named environmental variables on the rate of photosynthesis using aquatic plants, algae or immobilised algal beads
  • 1.10 Required practical 8: Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts
• Respiration
  • 2.1 Respiration produces ATP
  • 2.2 Glycolysis involves the following stages
  • 2.3 production of triose phosphate
  • 2.4 If respiration is only anaerobic, pyruvate can be converted to ethanol or lactate using reduced NAD. The oxidised NAD produced in this way can be used in further glycolysis
  • 2.5 Aerobic respiration in such detail as to show that
  • 2.6 acetate combines with coenzyme A in the link reaction to produce acetylcoenzyme A
  • 2.7 in a series of oxidation-reduction reactions, the Krebs cycle generates reduced coenzymes and ATP by substrate-level phosphorylation, and carbon dioxide is lost
  • 2.8 other respiratory substrates include the breakdown products of lipids and amino acids, which enter the Krebs cycle
  • 2.9 Students could use a redox indicator to investigate dehydrogenase activity
  • 2.10 AT b and i
• Energy and ecosystems
  • 3.1 In any ecosystem, plants synthesise organic compounds from atmospheric, or aquatic, carbon dioxide
  • 3.2 Biomass can be measured in terms of mass of carbon or dry mass of tissue per given area. The chemical energy store in dry biomass can be estimated using calorimetry
  • 3.3 Net primary production (
  • 3.4 This net primary production is available for plant growth and reproduction. It is also available to other trophic levels in the ecosystem, such as herbivores and decomposers
  • 3.5 Primary and secondary productivity is the rate of primary or secondary production, respectively. It is measured as biomass in a given area in a given time eg kJ ha–1 year–1
  • 3.6 appreciate the ways in which production is affected by farming practices designed to increase the efficiency of energy transfer by
  • 3.7 reducing respiratory losses within a human food chain
  • 3.8 AT a
  • 3.9 the net productivity of producers or consumers from given data
  • 3.10 Students could be given data from which to calculate percentage yields
• Nutrient cycles
  • 4.1 Nutrients are recycled within natural ecosystems, exemplified by the nitrogen cycle and the phosphorus cycle
  • 4.2 Microorganisms play a vital role in recycling chemical elements such as phosphorus and nitrogen
  • 4.3 The role of saprobionts in decomposition
  • 4.4 The role of mycorrhizae in facilitating the uptake of water and inorganic ions by plants
  • 4.5 The role of bacteria in the nitrogen cycle in sufficient detail to illustrate the processes of saprobiotic nutrition, ammonification, nitrification, nitrogen fixation and denitrification
  • 4.6 (The names of individual species of bacteria are not required)
  • 4.7 The use of natural and artificial fertilisers to replace the nitrates and phosphates lost by harvesting plants and removing livestock
  • 4.8 The environmental issues arising from the use of fertilisers including leaching and eutrophication
  • 4.9 Students could devise investigations into the effect of named minerals on plant growth
• Inheritance
  • 5.1 The genotype is the genetic constitution of an organism
  • 5.2 The phenotype is the expression of this genetic constitution and its interaction with the environment
  • 5.3 Alleles may be dominant, recessive or codominant
  • 5.4 In a diploid organism, the alleles at a specific locus may be either homozygous or heterozygous
  • 5.5 monohybrid and dihybrid crosses involving dominant, recessive and codominant alleles
  • 5.6 crosses involving sex-linkage, autosomal linkage, multiple alleles and epistasis
  • 5.7 AT h
  • 5.8 Students could investigate genetic ratios using crosses of Drosophila or Fast Plant®
  • 5.9 Students could show understanding of the probability associated with inheritance
  • 5.10 Students could use the
• Populations
  • 6.1 Species exist as one or more populations
  • 6.2 A population as a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed
  • 6.3 The concepts of gene pool and allele frequency
  • 6.4 The Hardy–Weinberg principle provides a mathematical model, which predicts that allele frequencies will not change from generation to generation. The conditions under which the principle applies
  • 6.5 The frequency of alleles, genotypes and phenotypes in a population can be calculated using the Hardy–Weinberg equation
  • 6.6 where
  • 6.7 AT k
  • 6.8 Students could collect data about the frequency of observable phenotypes within a single population
  • 6.9 Students could calculate allele, genotype and phenotype frequencies from appropriate data using the Hardy–Weinberg equation
• Evolution may lead to speciation
  • 7.1 Individuals within a population of a species may show a wide range of variation in phenotype. This is due to genetic and environmental factors. The primary source of genetic variation is mutation. Meiosis and the random fertilisation of gametes during sexual reproduction produce further genetic variation
  • 7.2 Those organisms with phenotypes providing selective advantages are likely to produce more offspring and pass on their favourable alleles to the next generation. The effect of this differential reproductive success on the allele frequencies within a gene pool
  • 7.3 The effects of stabilising, directional and disruptive selection
  • 7.4 Reproductive separation of two populations can result in the accumulation of difference in their gene pools. New species arise when these genetic differences lead to an inability of members of the populations to interbreed and produce fertile offspring. In this way, new species arise from existing species
  • 7.5 explain why individuals within a population of a species may show a wide range of variation in phenotype
  • 7.6 explain why genetic drift is important only in small populations
  • 7.7 explain how evolutionary change over a long period of time has resulted in a great diversity of species
  • 7.8 PS 1.2
  • 7.9 Students could devise an investigation to mimic the effects of random sampling on allele frequencies in a population
  • 7.10 Students could use computer programs to model the effects of natural selection and of genetic drift
• Populations in ecosystems
  • 8.1 Populations of different species form a community. A community and the non-living components of its environment together form an ecosystem. Ecosystems can range in size from the very small to the very large
  • 8.2 the effect of abiotic factors
  • 8.3 randomly placed quadrats, or quadrats along a belt transect, for slow-moving or non-motile organisms
  • 8.4 Ecosystems are dynamic systems
  • 8.5 Conservation of habitats frequently involves management of succession
  • 8.6 use given data to calculate the size of a population estimated using the mark-release-recapture method
  • 8.7 investigate the distribution of organisms in a named habitat using randomly placed frame quadrats, or a belt transect
  • 8.8 AT h
  • 8.9 Students could use turbidity measurements to investigate the growth rate of a broth culture of microorganisms
  • 8.10 AT a and k
• Stimuli, both internal and external, are detected and lead to a response
  • 9.1 Survival and response
  • 9.2 In flowering plants, specific growth factors move from growing regions to other tissues, where they regulate growth in response to directional stimuli
  • 9.3 The protective effect of a simple reflex, exemplified by a three-neurone simple reflex. Details of spinal cord and dorsal and ventral roots are not required
  • 9.4 Students could design and carry out investigations into the effects of indoleacetic acid on root growth in seedlings
  • 9.5 receptors respond only to specific stimuli
  • 9.6 The basic structure of a Pacinian corpuscle
  • 9.7 the sensitivity of temperature receptors in human skin
  • 9.8 resolution of touch receptors in human skin
  • 9.9 The roles and locations of chemoreceptors and pressure receptors and the roles of the autonomic nervous system and effectors in controlling heart rate
  • 9.10 Students could use values of heart rate ( R ) and stroke volume ( V ) to calculate cardiac output ( CO ), using the formula
• Nervous coordination
  • 10.1 Nerve impulses
  • 10.2 The establishment of a resting potential in terms of differential membrane permeability, electrochemical gradients and the movement of sodium ions and potassium ions
  • 10.3 The passage of an action potential along non-myelinated and myelinated axons, resulting in nerve impulses
  • 10.4 Factors affecting the speed of conductance: myelination and saltatory conduction
  • 10.5 temperature
  • 10.6 Synaptic transmission
  • 10.7 The sequence of events involved in transmission across a cholinergic synapse in sufficient detail to explain
  • 10.8 temporal and spatial summation
  • 10.9 A comparison of transmission across a cholinergic synapse and across a neuromuscular junction
  • 10.10 (Recall of the names and mode of action of individual drugs will not be required.)
• Skeletal muscles are stimulated to contract by nerves and act as effectors
  • 11.1 Muscles act in antagonistic pairs against an incompressible skeleton
  • 11.2 Gross and microscopic structure of skeletal muscle. The ultrastructure of a myofibril
  • 11.3 The roles of actin, myosin, calcium ions and ATP in myofibril contraction
  • 11.4 The roles of calcium ions and tropomyosin in the cycle of actinomyosin bridge formation. (The role of troponin is not required.)
  • 11.5 The roles of ATP and phosphocreatine in muscle contraction
  • 11.6 The structure, location and general properties of slow and fast skeletal muscle fibres
  • 11.7 AT d
  • 11.8 Students could examine prepared slides of skeletal muscle using an optical microscope
  • 11.9 AT h
  • 11.10 Students could investigate the effect of repeated muscular contraction on the rate of muscle fatigue in human vounteers
• Homeostasis is the maintenance of a stable internal environment
  • 12.1 Principles of homeostasis and negative feedback
  • 12.2 The importance of maintaining a stable blood glucose concentration in terms of availability of respiratory substrate and of the water potential of blood
  • 12.3 Control of blood glucose concentration
  • 12.4 The action of insulin by
  • 12.5 activating enzymes involved in the conversion of glucose to glycogen
  • 12.6 The role of adrenaline by
  • 12.7 evaluate the positions of health advisers and the food industry in relation to the increased incidence of type II diabetes
  • 12.8 Control of blood water potential
  • 12.9 the formation of glomerular filtrate
  • 12.10 reabsorption of water by the distal convoluted tubule and collecting ducts
• Alteration of the sequence of bases in DNA can alter the structure of proteins
  • 13.1 Gene mutations might arise during DNA replication. They include addition, deletion, substitution, inversion, duplication and translocation of bases
  • 13.2 Gene mutations occur spontaneously. The mutation rate is increased by mutagenic agents. Mutations can result in a different amino acid sequence in the encoded polypeptide
  • 13.3 Some gene mutations change only one triplet code. Due to the degenerate nature of the genetic code, not all such mutations result in a change to the encoded amino acid
  • 13.4 Some gene mutations change the nature of all base triplets downstream from the mutation, ie result in a frame shift
  • 13.5 relate the nature of a gene mutation to its effect on the encoded polypeptide
• Gene expression is controlled by a number of features
  • 14.1 Most of a cell’s DNA is not translated
  • 14.2 Totipotent cells occur only for a limited time in early mammalian embryos
  • 14.3 Pluripotent stem cells can divide in unlimited numbers and can be used in treating human disorders
  • 14.4 evaluate the use of stem cells in treating human disorders
  • 14.5 In eukaryotes, transcription of target genes can be stimulated or inhibited when specific transcriptional factors move from the cytoplasm into the nucleus. The role of the steroid hormone, oestrogen, in initiating transcription
  • 14.6 decreased acetylation of associated histones
  • 14.7 interpret data provided from investigations into gene expression
  • 14.8 The main characteristics of benign and malignant tumours
  • 14.9 abnormal methylation of tumour suppressor genes and oncogenes
  • 14.10 interpret information relating to the way in which an understanding of the roles of oncogenes and tumour suppressor genes could be used in the prevention, treatment and cure of cancer
• Using genome projects
  • 15.1 Sequencing projects have read the genomes of a wide range of organisms
  • 15.2 including humans
  • 15.3 Determining the genome of simpler organisms allows the sequences of the proteins that derive from the genetic code (the proteome) of the organism to be determined
  • 15.4 This may have many applications
  • 15.5 including the identification of potential antigens for use in vaccine production
  • 15.6 In more complex organisms
  • 15.7 the presence of non-coding DNA and of regulatory genes means that knowledge of the genome cannot easily be translated into the proteome
  • 15.8 Sequencing methods are continuously updated
  • 15.9 have become automated
• Gene technologies allow the study and alteration of gene function allowing a better understanding of organism function and the design of new industrial and medical processes
  • 16.1 Recombinant DNA technology
  • 16.2 conversion of mRNA to complementary DNA (cDNA), using reverse transcriptase
  • 16.3 The principles of the polymerase chain reaction (PCR) as an in vitro method to amplify DNA fragments
  • 16.4 The use of restriction endonucleases and ligases to insert fragments of DNA into vectors. Transformation of host cells using these vectors
  • 16.5 evaluate the ethical, financial and social issues associated with the use and ownership of recombinant DNA technology in agriculture, in industry and in medicine
  • 16.6 Students could investigate the specificity of restriction enzymes using extracted DNA and electrophoresis
  • 16.7 The use of labelled DNA probes that can be used to screen patients for heritable conditions, drug responses or health risks
  • 16.8 Genetic fingerprinting
  • 16.9 explain the biological principles that underpin genetic fingerprinting techniques
  • 16.10 Students could use gel electrophoresis to produce ‘fingerprints’ of food dyes