The Complete IB Biology Syllabus: SL and HL

• Nucleosomes help to supercoil the DNA.
• DNA structure suggested a mechanism for DNA replication.
• DNA polymerases can only add nucleotides to the 3' end of a primer.
• DNA replication is continuous on the leading strand and discontinuous on the lagging strand.
• DNA replication is carried out by a complex system of enzymes.
• Some regions of DNA do not code for proteins but have other important functions.

• Transcription occurs in a 5' to 3' direction.
• Nucleosomes help to regulate transcription in eukaryotes.
• Eukaryotic cells modify mRNA after transcription.
• Splicing of mRNA increases the number of different proteins an organism can produce.
• Gene expression is regulated by proteins that bind to specific base sequences in DNA.
• The environment of a cell and of an organism has an impact on gene expression.

• Initiation of translation involves assembly of the components that carry out the process.
• Synthesis of the polypeptide involves a repeated cycle of events.
• Disassembly of the components follows termination of translation.
• Free ribosomes synthesize proteins for use primarily within the cell.
• Bound ribosomes synthesize proteins primarily for secretion or for use in lysosomes.
• Translation can occur immediately after transcription in prokaryotes due to the absence of a nuclear membrane.
• The sequence and number of amino acids in the polypeptide is the primary structure.
• The secondary structure is the formation of alpha helices and beta pleated sheets stabilized by hydrogen bonding.
• The tertiary structure is the further folding of the polypeptide stabilized by interactions between R groups.
• The quaternary structure exists in proteins with more than one polypeptide chain.

• Metabolic pathways consist of chains and cycles of enzyme-catalysed reactions.
• Enzymes lower the activation energy of the chemical reactions that they catalyse.
• Enzyme inhibitors can be competitive or non-competitive.
• Metabolic pathways can be controlled by end-product inhibition.

• Cell respiration involves the oxidation and reduction of electron carriers.
• Phosphorylation of molecules makes them less stable.
• In glycolysis, glucose is converted to pyruvate in the cytoplasm.
• Glycolysis gives a small net gain of ATP without the use of oxygen.
• In aerobic cell respiration pyruvate is decarboxylated and oxidized, and converted into acetyl compound and attached to coenzyme A to form acetyl coenzyme A in the link reaction.
• In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers, liberating carbon dioxide.
• Energy released by oxidation reactions is carried to the cristae of the mitochondria by reduced NAD and FAD.
• Transfer of electrons between carriers in the electron transport chain in the membrane of the cristae is coupled to proton pumping.
• In chemiosmosis protons diffuse through ATP synthase to generate ATP.
• Oxygen is needed to bind with the free protons to maintain the hydrogen gradient, resulting in the formation of water.
• The structure of the mitochondrion is adapted to the function it performs.

• Light-dependent reactions take place in the intermembrane space of the thylakoids.
• Light-independent reactions take place in the stroma.
• Reduced NADP and ATP are produced in the light-dependent reactions.
• Absorption of light by photosystems generates excited electrons.
• Photolysis of water generates electrons for use in the light-dependent reactions.
• Transfer of excited electrons occurs between carriers in thylakoid membranes.
• Excited electrons from Photosystem II are used to contribute to generate a proton gradient.
• ATP synthase in thylakoids generates ATP using the proton gradient.
• Excited electrons from Photosystem I are used to reduce NADP.
• In the light-independent reactions a carboxylase catalyses the carboxylation of ribulose bisphosphate.
• Glycerate 3-phosphate is reduced to triose phosphate using reduced NADP and ATP.
• Triose phosphate is used to regenerate RuBP and produce carbohydrates.
• Ribulose bisphosphate is reformed using ATP.
• The structure of the chloroplast is adapted to its function in photosynthesis.

• Transpiration is the inevitable consequence of gas exchange in the leaf.
• Plants transport water from the roots to the leaves to replace losses from transpiration.
• The cohesive property of water and the structure of the xylem vessels allow transport under tension.
• The adhesive property of water and evaporation generate tension forces in leaf cell walls.
• Active uptake of mineral ions in the roots causes absorption of water by osmosis.

• Plants transport organic compounds from sources to sinks.
• Incompressibility of water allows transport along hydrostatic pressure gradients.
• Active transport is used to load organic compounds into phloem sieve tubes at the source.
• High concentrations of solutes in the phloem at the source lead to water uptake by osmosis.
• Raised hydrostatic pressure causes the contents of the phloem to flow towards sinks.

• Undifferentiated cells in the meristems of plants allow indeterminate growth.
• Mitosis and cell division in the shoot apex provide cells needed for extension of the stem and development of leaves.
• Plant hormones control growth in the shoot apex.
• Plant shoots respond to the environment by tropisms.
• Auxin efflux pumps can set up concentration gradients of auxin in plant tissue.
• Auxin influences cell growth rates by changing the pattern of gene expression.

• Flowering involves a change in gene expression in the shoot apex.
• The switch to flowering is a response to the length of light and dark periods in many plants.
• Success in plant reproduction depends on pollination, fertilization and seed dispersal.
• Most flowering plants use mutualistic relationships with pollinators in sexual reproduction.

10.1

• Chromosomes replicate in interphase before meiosis.
• Crossing over is the exchange of DNA material between non-sister homologous chromatids.
• Crossing over produces new combinations of alleles on the chromosomes of the haploid cells.
• Chiasmata formation between non-sister chromatids can result in an exchange of alleles.
• Homologous chromosomes separate in meiosis I.
• Sister chromatids separate in meiosis II.
• Independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I.

• Gene loci are said to be linked if on the same chromosome.
• Unlinked genes segregate independently as a result of meiosis.
• Variation can be discrete or continuous.
• The phenotypes of polygenic characteristics tend to show continuous variation.
• Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant.

• A gene pool consists of all the genes and their different alleles, present in an interbreeding population.
• Evolution requires that allele frequencies change with time in populations.
• Reproductive isolation of populations can be temporal, behavioural or geographic.
• Speciation due to divergence of isolated populations can be gradual.
• Speciation can occur abruptly.

• Every organism has unique molecules on the surface of its cells.
• Pathogens can be species-specific although others can cross species barriers.
• B lymphocytes are activated by T lymphocytes in mammals.
• Activated B cells multiply to form clones of plasma cells and memory cells.
• Plasma cells secrete antibodies.
• Antibodies aid the destruction of pathogens.
• White cells release histamine in response to allergens.
• Histamines cause allergic symptoms.
• Immunity depends upon the persistence of memory cells.
• Vaccines contain antigens that trigger immunity but do not cause the disease.
• Fusion of a tumour cell with an antibody-producing plasma cell creates a hybridoma cell.
• Monoclonal antibodies are produced by hybridoma cells.

• Bones and exoskeletons provide anchorage for muscles and act as levers.
• Synovial joints allow certain movements but not others.
• Movement of the body requires muscles to work in antagonistic pairs.
• Skeletal muscle fibres are multinucleate and contain specialized endoplasmic reticulum.
• Muscle fibres contain many myofibrils.
• Each myofibril is made up of contractile sarcomeres.
• The contraction of the skeletal muscle is achieved by the sliding of actin and myosin filaments.
• ATP hydrolysis and cross bridge formation are necessary for the filaments to slide.
• Calcium ions and the proteins tropomyosin and troponin control muscle contractions.

• Animals are either osmoregulators or osmoconformers.
• The Malpighian tubule system in insects and the kidney carry out osmoregulation and removal of nitrogenous wastes.
• The composition of blood in the renal artery is different from that in the renal vein.
• The ultrastructure of the glomerulus and Bowman's capsule facilitate ultrafiltration.
• The proximal convoluted tubule selectively reabsorbs useful substances by active transport.
• The loop of Henle maintains hypertonic conditions in the medulla.
• ADH controls reabsorption of water in the collecting duct.
• The length of the loop of Henle is positively correlated with the need for water conservation in animals.
• The type of nitrogenous waste in animals is correlated with evolutionary history and habitat.

• Spermatogenesis and oogenesis both involve mitosis, cell growth, two divisions of meiosis and differentiation.
• Processes in spermatogenesis and oogenesis result in different numbers of gametes with different amounts of cytoplasm.
• Fertilization in animals can be internal or external.
• Fertilization involves mechanisms that prevent polyspermy.
• Implantation of the blastocyst in the endometrium is essential for the continuation of pregnancy.
• HCG stimulates the ovary to secrete progesterone during early pregnancy.
• The placenta facilitates the exchange of materials between the mother and fetus.
• Estrogen and progesterone are secreted by the placenta once it has formed.
• Birth is mediated by positive feedback involving estrogen and oxytocin.

• The neural tube of embryonic chordates is formed by infolding of ectoderm followed by elongation of the tube.
• Neurons are initially produced by differentiation in the neural tube.
• Immature neurons migrate to a final location.
• An axon grows from each immature neuron in response to chemical stimuli.
• Some axons extend beyond the neural tube to reach other parts of the body.
• A developing neuron forms multiple synapses.
• Synapses that are not used do not persist.
• Neural pruning involves the loss of unused neurons.
• The plasticity of the nervous system allows it to change with experience.

• The anterior part of the neural tube expands to form the brain.
• Different parts of the brain have specific roles.
• The autonomic nervous system controls involuntary processes in the body using centres located mainly in the brain stem.
• The cerebral cortex forms a larger proportion of the brain and is more highly developed in humans than other animals.
• The human cerebral cortex has become enlarged principally by an increase in total area with extensive folding to accommodate it within the cranium.
• The cerebral hemispheres are responsible for higher order functions.
• The left cerebral hemisphere receives sensory input from sensory receptors in the right side of the body and the right side of the visual field in both eyes and vice versa for the right hemisphere.
• The left cerebral hemisphere controls muscle contraction in the right side of the body and vice versa for the right hemisphere.
• Brain metabolism requires large energy inputs.

• Receptors detect changes in the environment.
• Rods and cones are photoreceptors located in the retina.
• Rods and cones differ in their sensitivities to light intensities and wavelengths.
• Bipolar cells send the impulses from rods and cones to ganglion cells.
• Ganglion cells send messages to the brain via the optic nerve.
• The information from the right field of vision from both eyes is sent to the left part of the visual cortex and vice versa.
• Structures in the middle ear transmit and amplify sound.
• Sensory hairs of the cochlea detect sounds of specific wavelengths.
• Impulses caused by sound perception are transmitted to the brain via the auditory nerve.
• Hair cells in the semicircular canals detect movement of the head.

• Innate behaviour is inherited from parents and so develops independently of the environment.
• Autonomic and involuntary responses are referred to as reflexes.
• Reflex arcs comprise the neurons that mediate reflexes.
• Reflex conditioning involves forming new associations.
• Learned behaviour develops as a result of experience.
• Imprinting is learning occurring at a particular life stage and is independent of the consequences of behaviour.
• Operant conditioning is a form of learning that consists of trial and error experiences.
• Learning is the acquisition of skill or knowledge.
• Memory is the process of encoding, storing and accessing information.

• Some neurotransmitters excite nerve impulses in postsynaptic neurons and others inhibit them.
• Nerve impulses are initiated or inhibited in post-synaptic neurons as a result of summation of all excitatory and inhibitory neurotransmitters received from presynaptic neurones.
• Many different slow-acting neurotransmitters modulate fast synaptic transmission in the brain.
• Memory and learning involve changes in neurones caused by slow-acting neurotransmitters.
• Psychoactive drugs affect the brain by either increasing or decreasing postsynaptic transmission.
• Anesthetics act by interfering with neural transmission between areas of sensory perception and the CNS.
• Stimulant drugs mimic the stimulation provided by the sympathetic nervous system.
• Addiction can be affected by genetic predisposition, social environment and dopamine secretion.

• Ethology is the study of animal behaviour in natural conditions.
• Natural selection can change the frequency of observed animal behaviour.
• Behaviour that increases the chances of survival and reproduction will become more prevalent in a population.
• Learned behaviour can spread through a population or be lost from it more rapidly than innate behaviour.

• Microorganisms are metabolically diverse.
• Microorganisms are used in industry because they are small and have a fast growth rate.
• Pathway engineering optimizes genetic and regulatory processes within microorganisms.
• Pathway engineering is used industrially to produce metabolites of interest.
• Fermenters allow large-scale production of metabolites by microorganisms.
• Fermentation is carried out by batch or continuous culture.
• Microorganisms in fermenters become limited by their own waste products.
• Probes are used to monitor conditions within fermenters.
• Conditions are maintained at optimal levels for the growth of the microorganisms being cultured.

• Transgenic organisms produce proteins that were not previously part of their species' proteome.
• Genetic modification can be used to overcome environmental resistance to increase crop yields.
• Genetically modified crop plants can be used to produce novel products.
• Bioinformatics plays a role in identifying target genes.
• The target gene is linked to other sequences that control its expression.
• An open reading frame is a significant length of DNA from a start codon to a stop codon.
• Marker genes are used to indicate successful uptake.
• Recombinant DNA must be inserted into the plant cell and taken up by its chromosome or chloroplast DNA.
• Recombinant DNA can be introduced into whole plants, leaf discs or protoplasts.
• Recombinant DNA can be introduced by direct physical and chemical methods or indirectly by vectors.

• Responses to pollution incidents can involve bioremediation combined with physical and chemical procedures.
• Microorganisms are used in bioremediation.
• Some pollutants are metabolized by microorganisms.
• Cooperative aggregates of microorganisms can form biofilms.
• Biofilms possess emergent properties.
• Microorganisms growing in a biofilm are highly resistant to antimicrobial agents.
• Microorganisms in biofilms cooperate through quorum sensing.
• Bacteriophages are used in the disinfection of water systems.

• Infection by a pathogen can be detected by the presence of its genetic material or by its antigens.
• Predisposition to a genetic disease can be detected through the presence of markers.
• DNA microarrays can be used to test for genetic predisposition or to diagnose the disease.
• Metabolites that indicate disease can be detected in blood and urine.
• Tracking experiments are used to gain information about the localization and interaction of a desired protein.
• Biopharming uses genetically modified animals and plants to produce proteins for therapeutic use.
• Viral vectors can be used in gene therapy.

• Databases allow scientists easy access to information.
• The body of data stored in databases is increasing exponentially.
• BLAST searches can identify similar sequences in different organisms.
• Gene function can be studied using model organisms with similar sequences.
• Sequence alignment software allows comparison of sequences from different organisms.
• BLASTn allows nucleotide sequence alignment while BLASTp allows protein alignment.
• Databases can be searched to compare newly identified sequences with sequences of known function in other organisms.
• Multiple sequence alignment is used in the study of phylogenetics.
• EST is an expressed sequence tag that can be used to identify potential genes.

• The distribution of species is affected by limiting factors.
• Community structure can be strongly affected by keystone species.
• Each species plays a unique role within a community because of the unique combination of its spatial habitat and interactions with other species.
• Interactions between species in a community can be classified according to their effect.
• Two species cannot survive indefinitely in the same habitat if their niches are identical.

• Most species occupy different trophic levels in multiple food chains.
• A food web shows all the possible food chains in a community.
• The percentage of ingested energy converted to biomass is dependent on the respiration rate.
• The type of stable ecosystem that will emerge in an area is predictable based on climate.
• In closed ecosystems energy but not matter is exchanged with the surroundings.
• Disturbance influences the structure and rate of change within ecosystems.

• Introduced alien species can escape into local ecosystems and become invasive.
• Competitive exclusion and the absence of predators can lead to reduction in the numbers of endemic species when alien species become invasive.
• Pollutants become concentrated in the tissues of organisms at higher trophic levels by biomagnification.
• Macroplastic and microplastic debris has accumulated in marine environments.

• An indicator species is an organism used to assess a specific environmental condition.
• Relative numbers of indicator species can be used to calculate the value of a biotic index.
• In situ conservation may require active management of nature reserves or national parks.
• Ex situ conservation is the preservation of species outside their natural habitats.
• Biogeographic factors affect species diversity.
• Richness and evenness are components of biodiversity.

• Sampling techniques are used to estimate population size.
• The exponential growth pattern occurs in an ideal, unlimited environment.
• Population growth slows as a population reaches the carrying capacity of the environment.
• The phases shown in the sigmoid curve can be explained by relative rates of natality, mortality, immigration and emigration.
• Limiting factors can be top down or bottom up.

• Nitrogen-fixing bacteria convert atmospheric nitrogen to ammonia.
• Rhizobium associates with roots in a mutualistic relationship.
• In the absence of oxygen denitrifying bacteria reduce nitrate in the soil.
• Phosphorus can be added to the phosphorus cycle by application of fertilizer or removed by the harvesting of agricultural crops.
• The rate of turnover in the phosphorus cycle is much lower than the nitrogen cycle.
• Availability of phosphate may become limiting to agriculture in the future.
• Leaching of mineral nutrients from agricultural land into rivers causes eutrophication and leads to increased biochemical oxygen demand.

• Essential nutrients cannot be synthesized by the body, therefore they have to be included in the diet.
• Dietary minerals are essential chemical elements.
• Vitamins are chemically diverse carbon compounds that cannot be synthesized by the body.
• Some fatty acids and some amino acids are essential.
• Lack of essential amino acids affects the production of proteins.
• Malnutrition may be caused by a deficiency, imbalance or excess of nutrients in the diet.
• Appetite is controlled by a centre in the hypothalamus.
• Overweight individuals are more likely to suffer hypertension and type II diabetes.
• Starvation can lead to breakdown of body tissue.

• Nervous and hormonal mechanisms control the secretion of digestive juices.
• Exocrine glands secrete to the surface of the body or the lumen of the gut.
• The volume and content of gastric secretions are controlled by nervous and hormonal mechanisms.
• Acid conditions in the stomach favour some hydrolysis reactions and help to control pathogens in ingested food.
• The structure of cells of the epithelium of the villi is adapted to the absorption of food.
• The rate of transit of materials through the large intestine is positively correlated with their fibre content.
• Materials not absorbed are egested.

• The liver removes toxins from the blood and detoxifies them.
• Components of red blood cells are recycled by the liver.
• The breakdown of erythrocytes starts with phagocytosis of red blood cells by Kupffer cells.
• Iron is carried to the bone marrow to produce hemoglobin in new red blood cells.
• Surplus cholesterol is converted to bile salts.
• Endoplasmic reticulum and Golgi apparatus in hepatocytes produce plasma proteins.
• The liver intercepts blood from the gut to regulate nutrient levels.
• Some nutrients in excess can be stored in the liver.

• Structure of cardiac muscle cells allows propagation of stimuli through the heart wall.
• Signals from the sinoatrial node that cause contraction cannot pass directly from atria to ventricles.
• There is a delay between the arrival and passing on of a stimulus at the atrioventricular node.
• This delay allows time for atrial systole before the atrioventricular valves close.
• Conducting fibres ensure coordinated contraction of the entire ventricle wall.
• Normal heart sounds are caused by the atrioventricular valves and semilunar valves closing causing changes in blood flow.

• Endocrine glands secrete hormones directly into the bloodstream.
• Steroid hormones bind to receptor proteins in the cytoplasm of the target cell to form a receptor–hormone complex.
• The receptor–hormone complex promotes the transcription of specific genes.
• Peptide hormones bind to receptors in the plasma membrane of the target cell.
• Binding of hormones to membrane receptors activates a cascade mediated by a second messenger inside the cell.
• The hypothalamus controls hormone secretion by the anterior and posterior lobes of the pituitary gland.
• Hormones secreted by the pituitary control growth, developmental changes, reproduction and homeostasis.

• Oxygen dissociation curves show the affinity of hemoglobin for oxygen.
• Carbon dioxide is carried in solution and bound to hemoglobin in the blood.
• Carbon dioxide is transformed in red blood cells into hydrogencarbonate ions.
• The Bohr shift explains the increased release of oxygen by hemoglobin in respiring tissues.
• Chemoreceptors are sensitive to changes in blood pH.
• The rate of ventilation is controlled by the respiratory control centre in the medulla oblongata.
• During exercise the rate of ventilation changes in response to the amount of CO2 in the blood.
• Fetal hemoglobin is different from adult hemoglobin allowing the transfer of oxygen in the placenta onto the fetal hemoglobin.