BiologyQ&A by dot point

Monosaccharides are the monomers from which larger carbohydrates are made. Glucose, galactose and fructose are common monosaccharides. A condensation reaction joins two monosaccharides to form a disaccharide and forms a glycosidic bond. Polysaccharides are formed by the condensation of many glucose units. The relationship between the structure of glycogen, starch and cellulose and their functions, plus biochemical tests for reducing sugars, non-reducing sugars and starch.

Enzymes as catalysts lowering activation energy through formation of enzyme-substrate complexes. The induced-fit model of enzyme action. The effects of temperature, pH, enzyme and substrate concentration, and competitive and non-competitive inhibitors on the rate of enzyme-controlled reactions.

Triglycerides are formed by the condensation of one molecule of glycerol and three molecules of fatty acid. A condensation reaction between glycerol and a fatty acid forms an ester bond. The R group of a fatty acid may be saturated or unsaturated. In phospholipids, one of the fatty acids of a triglyceride is substituted by a phosphate-containing group. The different structures of triglycerides and phospholipids relate to their different roles in living organisms. The emulsion test for lipids.

The structure of DNA and RNA as polymers of nucleotides joined by phosphodiester bonds. Semi-conservative replication of DNA. The structure of ATP and its hydrolysis to release energy.

Amino acids are the monomers from which proteins are made. The general structure of an amino acid as RCH(NH2)COOH. A condensation reaction between two amino acids forms a peptide bond. The relationship between primary, secondary, tertiary and quaternary structure, and protein function. The biuret test for proteins.

Water as a polar molecule with hydrogen bonding, and its importance as a metabolite, solvent and in its high heat capacity, latent heat of vaporisation and cohesion. The roles of inorganic ions including hydrogen ions, iron ions, sodium ions and phosphate ions.

Cell recognition by antigens, including self and non-self; the cellular and humoral immune responses involving phagocytes, T lymphocytes and B lymphocytes; the structure and function of antibodies; the primary and secondary responses and immunological memory; active and passive, natural and artificial immunity, vaccines and herd immunity; antigenic variation; and the use of monoclonal antibodies and the ELISA test.

The structure of eukaryotic cells, including the structure and function of the cell-surface membrane, nucleus, mitochondria, chloroplasts, Golgi apparatus and Golgi vesicles, lysosomes, ribosomes, rough and smooth endoplasmic reticulum, cell wall and cell vacuole, and the role of these organelles in producing and secreting proteins; the importance of the cytoskeleton.

Methods of studying cells, including the principles and limitations of optical, transmission electron and scanning electron microscopes; magnification and resolution; measurement and calibration using an eyepiece graticule and stage micrometer; cell fractionation and ultracentrifugation to separate organelles.

The cell cycle, including interphase (DNA replication) and mitosis as a controlled process producing two genetically identical daughter cells; the stages of mitosis (prophase, metaphase, anaphase, telophase) and cytokinesis; the calculation of a mitotic index; the role of mitosis in growth and repair, and how uncontrolled cell division can lead to the formation of tumours and cancer.

The structure of prokaryotic cells, including the cell wall, cell-surface membrane, capsule, circular DNA, flagella and plasmids, and how prokaryotic cells differ from eukaryotic cells; the structure of viruses as acellular, non-living particles including the genetic material, capsid and attachment proteins.

The fluid-mosaic model of membrane structure and how substances cross membranes by simple diffusion, facilitated diffusion, osmosis, active transport and co-transport; the role of carrier and channel proteins; the factors affecting the rate of transport across membranes.

Digestion in mammals: the action of carbohydrases, lipases and proteases (including membrane-bound disaccharidases and dipeptidases); the role of bile salts in lipid digestion; absorption of the products across the ileum epithelium, including co-transport of glucose and amino acids and the absorption of monoglycerides and fatty acids.

Gas exchange in single-celled organisms and across the body surface of insects, gills of fish, and the leaves of dicotyledonous plants; structural and functional adaptations for efficient gas exchange; the limitation of water loss and how it is overcome.

Mass transport in animals: the role of haemoglobin in oxygen transport, the oxygen dissociation curve and the Bohr effect; the structure of the heart and the cardiac cycle; the structure of arteries, veins and capillaries in relation to function.

Mass transport in plants: transport of water in the xylem by the cohesion-tension theory and transpiration; transport of organic substances in the phloem by mass flow (the source-to-sink translocation model) and supporting evidence.

The relationship between the size of an organism or structure and its surface area to volume ratio, and the consequences for exchange of substances and heat with the environment, including the role of Fick's law.

The genetic code is universal, non-overlapping and degenerate. Transcription produces mRNA from DNA, in eukaryotes pre-mRNA is spliced to remove introns, and translation at ribosomes uses tRNA and the genetic code to assemble a polypeptide from amino acids.

In prokaryotic cells DNA molecules are short, circular and not associated with proteins. In the nucleus of eukaryotic cells DNA molecules are very long, linear and associated with proteins called histones. A gene is a base sequence of DNA that codes for the amino acid sequence of a polypeptide or a functional RNA. The genome is the complete set of genes in a cell and the proteome is the full range of proteins a cell can produce.

Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include base substitution and base deletion. Because the genetic code is degenerate, not all mutations result in a change to the amino acid sequence. Mutagens increase the rate of mutation, and mutations are one source of genetic diversity within a gene pool.

Genetic diversity within a population, expressed as the number of different alleles in a gene pool, is acted on by natural selection. Random mutation produces new alleles, and selection results in changes in allele frequency. Directional and stabilising selection produce different effects, and selection leads to anatomical, physiological and behavioural adaptations that increase the chance of survival and reproduction.

Meiosis produces haploid daughter cells from a diploid parent cell, halving the number of chromosomes so that fertilisation restores the diploid number. Genetic variation arises from independent segregation of homologous chromosomes and from crossing over between homologous chromosomes during meiosis, and the number of possible combinations can be calculated.

A species is a group of similar organisms able to reproduce to give fertile offspring. Each species is given a binomial name. Courtship behaviour helps members of a species to recognise each other and is used in classification. Phylogenetic classification arranges species into a hierarchy of groups that share a common ancestor, and the taxa from domain to species reflect evolutionary relationships.

The transfer of biomass and energy through trophic levels in food chains and food webs; producers, primary, secondary and tertiary consumers, decomposers and saprobionts; the reasons why biomass and energy decrease at successive trophic levels; the calculation of the efficiency of energy transfer between trophic levels.

The nitrogen cycle and the roles of saprobionts, nitrogen-fixing, nitrifying and denitrifying bacteria; the phosphorus cycle and the role of mycorrhizae in phosphorus uptake; the role of microorganisms in recycling nutrients; the use of natural and artificial fertilisers and the environmental consequences of using nitrogen-containing and phosphorus-containing fertilisers, including leaching and eutrophication.

Photosynthesis as a two-stage process: the light-dependent reactions in the thylakoid membranes (photoionisation of chlorophyll, photolysis of water, the production of ATP by photophosphorylation, the production of reduced NADP, and the role of the electron transport chain); the light-independent reactions in the stroma (the Calvin cycle: fixation of carbon dioxide by RuBP to form GP, reduction of GP to TP using reduced NADP and ATP, and regeneration of RuBP); the effect of light intensity, carbon dioxide concentration and temperature as limiting factors.

Biomass as the mass of living material, measured as dry mass or as the chemical energy stored in dry biomass using calorimetry; gross primary production (GPP) as the chemical energy store in plant biomass; net primary production (NPP) as GPP minus respiratory losses; the calculation and units of GPP, NPP and net production of consumers; the ways in which farming practices increase the efficiency of energy transfer in food production.

Aerobic respiration as four stages: glycolysis in the cytoplasm (phosphorylation of glucose, oxidation to pyruvate, net yield of ATP and reduced NAD); the link reaction and the Krebs cycle in the mitochondrial matrix (decarboxylation, dehydrogenation, production of reduced NAD, reduced FAD, ATP and carbon dioxide); oxidative phosphorylation on the inner mitochondrial membrane (the electron transport chain, chemiosmosis, ATP synthase and the role of oxygen as the final electron acceptor); anaerobic respiration in animals (lactate) and in microorganisms and plants (ethanol).

The role of the kidney in osmoregulation and in the excretion of metabolic waste. The detailed structure of a nephron and its associated blood vessels. The processes of ultrafiltration and selective reabsorption, the role of the loop of Henle in producing concentrated urine, and the control of blood water potential by antidiuretic hormone (ADH) through negative feedback.

The principles of homeostasis and negative feedback in maintaining a constant internal environment. The control of blood glucose concentration by insulin and glucagon, including the roles of the liver in glycogenesis, glycogenolysis and gluconeogenesis, the action of insulin through the second messenger model involving adenylate cyclase and cyclic AMP, and the causes and control of types 1 and 2 diabetes mellitus.

The structure and function of myelinated motor neurones. The establishment of a resting potential in terms of differential membrane permeability, electrochemical gradients and the movement of sodium and potassium ions. Changes in membrane permeability that lead to depolarisation and the generation of an action potential, the all-or-nothing principle, the passage of a wave of depolarisation along a neurone, saltatory conduction in myelinated neurones, and the nature and importance of the refractory period.

Receptors are specific to a single type of stimulus and produce a generator potential when stimulated. The Pacinian corpuscle as a receptor that responds to changes in mechanical pressure. The role of rod and cone cells in the retina, the differences in sensitivity and visual acuity, and the distribution of rods and cones across the retina.

The gross and microscopic structure of skeletal muscle, including the ultrastructure of a myofibril and the sarcomere. The sliding filament theory of muscle contraction, including the roles of actin, myosin, calcium ions and ATP. The structure, location and general properties of slow and fast skeletal muscle fibres.

A stimulus is a detectable change in the internal or external environment of an organism that produces a response. Taxes and kineses as simple responses that maintain a mobile organism in a favourable environment; tropisms as growth responses controlled by indoleacetic acid (IAA); the role of a simple reflex arc in protecting the body from harm.

The detailed structure of a synapse and of a neuromuscular junction. The sequence of events involved in transmission across a cholinergic synapse. The roles of summation, both spatial and temporal, and the importance of synapses in ensuring unidirectional transmission. Predicting and explaining the effects of specific drugs on synaptic transmission.

Individuals within a population of a species may show a wide range of variation in phenotype. This variation may be the result of genetic factors, environmental factors or a combination of both. Differential reproductive success and its effect on the allele frequency within a gene pool. Directional selection, for example antibiotic resistance in bacteria, and stabilising selection, for example human birth weights. The role of geographic isolation (allopatric speciation) and reproductive isolation (sympatric speciation) in the production of new species, and the importance of genetic drift in causing changes in allele frequency in small populations, including the founder effect.

Genotype is the genetic constitution of an organism. Phenotype is the expression of this genetic constitution and its interaction with the environment. Most phenotypes are affected by more than one gene. The genotype, phenotype and ratio of offspring can be predicted for monohybrid and dihybrid crosses involving dominant, recessive, codominant and multiple alleles, sex-linkage, autosomal linkage and epistasis. The chi-squared (X2) test can be used to test the significance of the difference between observed and expected results.

A population is a group of organisms of the same species occupying a particular space at a particular time that can potentially interbreed. The individuals in a population of a species may show a wide range of variation in phenotype. This is the result of genetic and environmental factors. A gene pool is all the alleles of all the genes in a population. The frequency of an allele in a population is the proportion of organisms carrying that allele. The Hardy-Weinberg principle provides a mathematical model, which predicts that allele frequencies will not change from one generation to the next, given that no mutation, migration, selection or genetic drift occurs and that there is random mating in a large population. Since allele frequencies do change, the conditions required to maintain a Hardy-Weinberg equilibrium are rarely met. Students should be able to use the Hardy-Weinberg principle (p + q = 1 and p2 + 2pq + q2 = 1) to calculate allele, genotype and phenotype frequencies in populations and changes in these frequencies.

An ecosystem includes all the living organisms and all the abiotic conditions in a particular area. Within an ecosystem, populations of different species form a community. The population size of any species is limited by the effect of abiotic factors and biotic factors, such as interspecific and intraspecific competition and predation. Population size may vary as a result of the effect of abiotic factors and interactions between organisms; the carrying capacity is the maximum stable population size that an ecosystem can support over a long period. Students should be able to use given data to describe and interpret predator-prey relationships and to investigate populations and estimate the size of a population using randomly placed quadrats, transects and the mark-release-recapture method, including the assumptions made when using this method.

Succession from pioneer species to climax community. At each stage in succession, certain species may be recognised which change the environment so that it becomes more suitable for other species with different adaptations. The changes in the abiotic environment result in a less hostile environment and changing diversity. Conservation of habitats frequently involves management of succession. Students should be able to evaluate evidence and data concerning issues relating to the conservation of species and habitats and consider conflicting evidence; and use the concept of succession to explain the management of an ecosystem.

Epigenetic control of gene expression in eukaryotes. Epigenetics involves heritable changes in gene function, without changes to the base sequence of DNA. These changes are caused by changes in the environment that inhibit transcription by increased methylation of DNA or decreased acetylation of associated histones. The increased methylation of DNA and decreased acetylation of histones can inhibit transcription. Epigenetic changes can be inherited and have a role in the development of disease.

The role of the increased and decreased expression of genes in the development of tumours. The roles of tumour suppressor genes and oncogenes in the development of tumours. The role of abnormal methylation of tumour suppressor genes and oncogenes in the development of tumours. The increased exposure to oestrogen can increase the chances of developing some breast cancers. Benign and malignant tumours can be distinguished by their characteristics.

The use of labelled DNA probes that can be used to locate specific genes by complementary base pairing (DNA hybridisation). The use of these techniques in medical diagnosis. The principles of DNA sequencing and the development of high-throughput sequencing. Genetic fingerprinting and its use in determining genetic relationships and the genetic variability within a population, based on variable number tandem repeats (VNTRs), separated by size using gel electrophoresis.

Gene mutations involve a change in the base sequence of chromosomes. They can arise spontaneously during DNA replication and include addition, deletion, substitution, inversion, duplication and translocation of bases. The degenerate nature of the genetic code means that some substitutions do not change the amino acid coded for. Some gene mutations change only one triplet code; the position of a deletion or addition mutation within a gene is important. Mutagenic agents increase the rate of mutation. Stem cells are unspecialised cells capable of dividing and differentiating, and are described as totipotent, pluripotent, multipotent or unipotent.

Recombinant DNA technology involves transferring fragments of DNA from one organism, or species, to another. Because the genetic code is universal, the transferred DNA can be translated in the recipient. Fragments of DNA can be produced by conversion of mRNA to complementary DNA using reverse transcriptase, by using restriction endonucleases to cut a fragment containing the desired gene, and by creating the gene in a gene machine. DNA fragments can be amplified using in vivo techniques involving vectors and the use of the polymerase chain reaction (PCR) in vitro. The use of recombinant DNA technology to produce transformed organisms that benefit humans, and the use of gene therapy.

The control of transcription by specific transcription factors which move from the cytoplasm to the nucleus. In eukaryotes, transcription of target genes can be stimulated or inhibited when specific transcription factors bind to DNA. The effect of oestrogen on gene transcription. The control of translation of mRNA by RNA interference using small interfering RNA (siRNA), which can lead to the breakdown of mRNA or block its translation.