Upper secondaryCode 9700
Biology
44 topics and 259 objectives, each one something you should be able to do.
Written by Kindred in its own plain words. Your syllabus is still the official list, so check it for anything exact.
What this subject asks you to be able to do
1.1The microscope in cell studies5 objectives
- make temporary preparations from cell material so that it can be looked at under a light microscope
- draw what cells look like on microscope slides and in photomicrographs
- work out how much images are magnified, and the actual sizes of specimens, using drawings, photomicrographs and electron micrographs (scanning and transmission)
- apply an eyepiece graticule together with a stage micrometer scale when taking measurements, choosing the right units from millimetre (mm), micrometre (µm) and nanometre (nm)
- define resolution and magnification, and account for how these terms differ, referring to both light and electron microscopy
1.2Cells as the basic units of living organisms7 objectives
- recognise the organelles and other structures that eukaryotic cells contain, and outline the structure and job of each, limited to: nucleus, nucleolus and nuclear envelope, cell surface membrane, smooth endoplasmic reticulum, rough endoplasmic reticulum, ribosomes (80S ones in the cytoplasm, 70S ones in mitochondria and chloroplasts), Golgi body (also called the Golgi apparatus or Golgi complex), mitochondria (including the small circular DNA they hold), lysosomes, microtubules and centrioles, microvilli, cilia, chloroplasts (including the small circular DNA they hold), cell wall, plasmodesmata, and the tonoplast and large permanent vacuole of plant cells
- describe and interpret, for typical plant and animal cells, photomicrographs, electron micrographs and drawings
- compare how typical plant and animal cells are built
- state that cells power energy-demanding processes using ATP made by respiration
- outline the main structural features of a prokaryotic cell, taking a typical bacterium as the model, including: it is unicellular, is usually 1–5 µm across, has cell walls made of peptidoglycan, has circular DNA and 70S ribosomes, and has no organelles enclosed by a double membrane
- compare how a prokaryotic cell, as seen in a typical bacterium, is built against typical plant and animal eukaryotic cells
- state that every virus is a non-cellular entity whose core is nucleic acid, either DNA or RNA, enclosed by a protein capsid, and that certain viruses carry an outer envelope built from phospholipids
2.1Testing for biological molecules3 objectives
- describe and carry out each of these tests: Benedict’s test, which detects reducing sugars; the iodine test, which detects starch; the emulsion test, which detects lipids; the biuret test, which detects proteins
- describe and carry out a semi-quantitative version of Benedict’s test on a solution of a reducing sugar, standardising the method and then using the results (the time taken for the first colour change, or a match against colour standards) to estimate how concentrated the solution is
- describe and carry out a test, using acid hydrolysis and then Benedict’s solution, that shows whether non-reducing sugars are present
2.2Carbohydrates and lipids11 objectives
- describe and draw α-glucose and β-glucose in their ring forms
- define what is meant by a monosaccharide, a disaccharide and a polysaccharide, and by a monomer, a polymer and a macromolecule
- state the part played by covalent bonds when smaller molecules link together to make polymers
- state that sucrose is non-reducing, whereas glucose, fructose and maltose are reducing sugars
- describe how a glycosidic bond forms through condensation, referring to disaccharides (including sucrose) and polysaccharides
- describe how hydrolysis breaks glycosidic bonds in polysaccharides and disaccharides, making reference to the non-reducing sugar test
- outline the molecular structure of starch (amylose and amylopectin) and of glycogen, two polysaccharides, and connect these structures to the functions they serve in living organisms
- describe the molecular structure of cellulose, a polysaccharide, and outline how the way cellulose molecules are arranged helps plant cell walls to carry out their function
- state that triglycerides are hydrophobic, non-polar molecules, and describe how a triglyceride molecule is built, referring to glycerol, fatty acids (saturated and unsaturated) and how ester bonds are formed
- relate what triglycerides do in living organisms to their molecular structure
- describe how a phospholipid molecule is built, referring to its hydrophobic (non-polar) tails made of fatty acids and its hydrophilic (polar) head made of phosphate
2.3Proteins8 objectives
- describe and draw the general structure that every amino acid shares, and how a peptide bond is formed and broken
- explain what is meant by the terms primary structure, secondary structure, tertiary structure and quaternary structure as applied to proteins
- describe the kinds of interaction that keep a protein molecule in its shape, namely ionic bonding, hydrogen bonding, hydrophobic interactions and covalent bonding, including disulfide bonds
- state that, in general, globular proteins are soluble with physiological roles, while fibrous proteins are insoluble with structural roles
- describe how a haemoglobin molecule is built, taking it as one example of a globular protein, including how its quaternary structure is put together from a haem group, two beta (β) chains (β–globin) and two alpha (α) chains (α–globin)
- relate what haemoglobin does to the way it is built, including why the iron in the haem group matters
- describe how a collagen molecule is built, collagen being one example of a fibrous protein, and how collagen molecules are laid out to form collagen fibres
- relate the function of collagen to the way collagen molecules and collagen fibres are built
2.4Water1 objective
- account for the formation of hydrogen bonds between water molecules, and connect water's characteristics with the functions it performs in living things, limited to solvent action, the high specific heat capacity, and the latent heat of vaporisation
3.1Mode of action of enzymes4 objectives
- state that enzymes are globular proteins acting as catalysts, and that some (intracellular enzymes) work within cells while others (extracellular enzymes) are secreted and work outside cells
- explain how enzymes act (their mode of action), referring to the active site, formation of an enzyme–substrate complex, the way activation energy is lowered and why enzymes are specific, including both the lock-and-key and the induced-fit hypotheses
- investigate how far enzyme-catalysed reactions have progressed by measuring the rates at which products form when using catalase and the rates at which substrate disappears when using amylase
- outline how a colorimeter can be employed to track enzyme-catalysed reactions which involve changes in colour
3.2Factors that affect enzyme action4 objectives
- investigate and explain how the rate of enzyme-catalysed reactions is affected by temperature, pH (using buffer solutions), and the concentrations of enzyme, substrate and inhibitor
- explain that the Michaelis–Menten constant (Km) is worked out from the maximum rate of reaction (Vmax), and that Km is then used to compare how great an affinity different enzymes have for their substrates
- account for the influence that reversible inhibitors exert on enzyme activity, covering both competitive and non-competitive types
- investigate how an enzyme's activity differs when it is immobilised in alginate compared with when it is free in solution, and state the benefits of using immobilised enzymes
4.1Fluid mosaic membranes4 objectives
- describe the fluid mosaic model, showing how membrane structure arises from hydrophobic and hydrophilic interactions that form the phospholipid bilayer, and how proteins are positioned within it
- describe where glycoproteins, glycolipids and cholesterol are found and how they are arranged in cell surface membranes
- describe the roles that cholesterol, phospholipids, proteins, glycoproteins and glycolipids play in cell surface membranes, in terms of fluidity, stability and permeability, transport (through channel proteins and carrier proteins), cell recognition (through cell surface antigens – see 11.1.2) and cell signalling (through cell surface receptors)
- outline the main steps of cell signalling that lead to specific responses: cells secrete specific chemicals (ligands), the ligands are transported to target cells, and the ligands bind to cell surface receptors on those target cells
4.2Movement into and out of cells6 objectives
- describe and explain these processes: osmosis, simple and facilitated diffusion, active transport, exocytosis and endocytosis
- investigate osmosis and simple diffusion with plant tissue and with non-living materials, including agar and dialysis (Visking) tubing
- illustrate, by working out the volume and surface area of simple 3-D shapes, the principle that the surface area to volume ratio gets smaller as size increases (see the Mathematical requirements)
- investigate, using agar blocks of several sizes, how diffusion is affected when the surface area to volume ratio changes
- investigate what happens when plant tissue is placed into solutions with varying water potentials, and use the findings to estimate the water potential inside the tissue
- account for how water travels between cells and solutions using water potential, and account for the contrasting outcomes of this water movement in plant cells versus animal cells (a grasp of solute potential or pressure potential is not required)
5.1Replication and division of nuclei and cells6 objectives
- describe how a chromosome is built, limited to: its centromere and telomeres, its sister chromatids, and its DNA and histone proteins
- account for why mitosis matters in producing genetically identical daughter cells when: multicellular organisms grow, damaged or dead cells are swapped for new ones, tissues are mended by replacing cells, asexual reproduction takes place
- outline the course of the mitotic cell cycle, including: interphase (growth across the G1 and G2 phases, and copying of DNA in the S phase), mitosis, cytokinesis
- outline how telomeres help stop genes being lost from the tips of chromosomes during DNA replication
- outline what stem cells contribute to replacing cells and mending tissue through mitosis
- account for the way that cell division running out of control can lead to a tumour forming
5.2Chromosome behaviour in mitosis2 objectives
- describe how chromosomes behave in plant and animal cells through the mitotic cell cycle, along with the related behaviour of the nuclear envelope, cell surface membrane and spindle (students are expected to name the main stages of mitosis: prophase, metaphase, anaphase and telophase)
- interpret microscope slides, photomicrographs and diagrams that show cells at various points in the mitotic cell cycle, and identify which main stage of mitosis each cell is in
6.1Structure of nucleic acids and replication of DNA5 objectives
- describe how nucleotides are built, including ATP as a phosphorylated nucleotide (structural formulae are not required)
- state that adenine and guanine are purines, whose molecules have two fused rings, whereas cytosine, thymine and uracil are pyrimidines, which have one ring (the bases' structural formulae are not expected)
- describe the form a DNA molecule takes as a double helix, including: why complementary base pairing matters where one strand runs 5′ to 3′ and its partner runs 3′ to 5′ (antiparallel), how hydrogen bonds differ between C–G and A–T pairs, and how nucleotides are joined through phosphodiester bonds
- describe semi-conservative DNA replication, as it happens in the S phase of the cell cycle, including: the jobs done by DNA ligase and DNA polymerase (you are not expected to know other enzymes of DNA replication in cells, or the different types of DNA polymerase), and why the lagging strand is replicated differently from the leading strand, given that DNA polymerase can add nucleotides only in a 5′ to 3′ direction
- describe how an RNA molecule is structured, taking messenger RNA (mRNA) as an illustration
6.2Protein synthesis7 objectives
- state that a gene, a stretch of nucleotides lying within a DNA molecule, directs the making of a polypeptide
- describe the principle behind the universal genetic code: each triplet of DNA bases either codes for a specific amino acid or stands for a start or stop codon
- describe how polypeptides are built from the information held in DNA through transcription and translation, including what each of these does: ribosomes, codons and anticodons, RNA polymerase, messenger RNA (mRNA), transfer RNA (tRNA)
- state that the DNA strand serving as the template in transcription is termed the transcribed or template strand, while its partner is termed the non-transcribed strand
- account for how, in eukaryotes, the primary transcript, the RNA produced after transcription, is altered: non-coding introns are cut out and coding exons are spliced together to yield mRNA
- state that a gene mutation is an alteration to the sequence of base pairs found in DNA, which may lead to a polypeptide that has changed
- explain that a gene mutation results from the insertion, deletion or substitution of nucleotides in DNA, and outline the possible effect of each type on the polypeptide that is made
7.1Structure of transport tissues4 objectives
- draw plan diagrams showing transverse sections cut from herbaceous dicotyledonous plants' stems, roots and leaves, working from microscope slides and photomicrographs
- describe where xylem and phloem are found in transverse sections of the stem, root and leaf of a herbaceous dicotyledonous plant
- draw and label companion cells, phloem sieve tube elements and xylem vessel elements as seen in electron micrographs, photomicrographs and microscope slides
- relate what companion cells, phloem sieve tube elements and xylem vessel elements do to the way each is built
7.2Transport mechanisms8 objectives
- state that some organic compounds and mineral ions may be transported through plants in solution in water
- describe how water moves from the soil into the xylem by the apoplast pathway, including mention of lignin and cellulose; and by the symplast pathway, including mention of the endodermis, Casparian strip and suberin
- explain that transpiration involves water evaporating off the internal surfaces of leaves, with the resulting vapour then diffusing into the atmosphere
- account for the part played by hydrogen bonds between water molecules in water's upward journey through the xylem, through cohesion-tension and the transpiration pull, and through adhesion to the cellulose of cell walls
- make annotated drawings of transverse sections through the leaves of xerophytic plants, and use them to explain how these leaves are adapted to lose less water by transpiration
- state that assimilates such as sucrose and amino acids are moved in solution in water along phloem sieve tubes, from sources to sinks
- account for how companion cells move assimilates into phloem sieve tubes, drawing on proton pumps and cotransporter proteins
- account for mass flow inside phloem sieve tubes as it proceeds down a hydrostatic pressure gradient that runs from the source end to the sink end
8.1The circulatory system7 objectives
- state that mammals have a closed double circulation made up of blood, a heart and blood vessels, including veins, venules, capillaries, arterioles and arteries
- describe what the main blood vessels of the systemic and pulmonary circulations do, limited to the aorta, vena cava, pulmonary artery and pulmonary vein
- recognise capillaries, arteries and veins in electron micrographs, photomicrographs and microscope slides, and draw plan diagrams of the structure of veins and arteries as seen in longitudinal section (LS) and in transverse section (TS)
- account for the connection, in each case, between the structure of muscular arteries, elastic arteries, veins and capillaries and their functions
- recognise and draw lymphocytes, neutrophils, monocytes and red blood cells as seen in electron micrographs, photomicrographs and microscope slides
- state that blood and tissue fluid are mostly water, and link water's properties to the part it plays in transport in mammals, limited to its action as a solvent and its high specific heat capacity
- state the functions of tissue fluid, and describe how it forms across a capillary network
8.2Transport of oxygen and carbon dioxide6 objectives
- describe how red blood cells help to transport oxygen and carbon dioxide, referring to the formation of carbaminohaemoglobin, the formation of haemoglobinic acid, and the roles of carbonic anhydrase and haemoglobin
- outline the chloride shift, then account for why it is significant
- describe the role that plasma plays in transporting carbon dioxide
- outline and account for the oxygen dissociation curve shown by adult haemoglobin
- account for why the oxygen dissociation curve matters at the partial pressures of oxygen found in lungs and in tissues that respire
- outline the Bohr shift and account for its significance
8.3The heart4 objectives
- describe the structure of the mammalian heart, both on the outside and on the inside
- account for the variation in wall thickness between the atria and ventricles, and between the left ventricle and right ventricle
- describe the cardiac cycle, linking changes in blood pressure during systole and diastole to when the valves open and shut
- explain how the sinoatrial node, atrioventricular node and Purkyne tissue each contribute to the cardiac cycle (you are not expected to know how it is controlled by nerves and hormones)
9.1The gas exchange system7 objectives
- describe how the human gas exchange system is built, limited to: the trachea, bronchi, bronchioles and alveoli, the capillary network and the lungs
- describe where cartilage, ciliated epithelium, goblet cells, squamous epithelium of alveoli, smooth muscle and capillaries are found within the gas exchange system
- recognise, on microscope slides, photomicrographs and electron micrographs, cartilage, ciliated epithelium, goblet cells, squamous epithelium of alveoli, smooth muscle and capillaries
- recognise alveoli, bronchioles, bronchi and trachea in electron micrographs, photomicrographs and microscope slides, and draw plan diagrams of the trachea wall and the bronchus wall as seen in transverse section
- describe how mucous glands, goblet cells and ciliated epithelial cells keep the gas exchange system healthy
- describe the functions of squamous epithelium, elastic fibres, smooth muscle and cartilage within the gas exchange system
- describe how gas exchange takes place between the blood in the capillaries and the air in the alveoli
10.1Infectious diseases4 objectives
- state that infectious diseases arise from pathogens and can be passed between organisms
- state the name and type of the pathogen that causes each disease: Vibrio cholerae, a bacterium, causes cholera; the protoctists Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale and Plasmodium vivax cause malaria; the bacteria Mycobacterium tuberculosis and Mycobacterium bovis cause tuberculosis (TB); the human immunodeficiency virus (HIV) causes HIV/AIDS
- explain the ways in which HIV, TB, malaria and cholera are transmitted
- discuss the biological, social and economic considerations that must be taken into account when preventing and controlling cholera, malaria, TB and HIV
10.2Antibiotics2 objectives
- outline how penicillin works against bacteria, and the reasons viruses are not impacted by antibiotics
- discuss what follows from antibiotic resistance, and the measures that can be used to lessen its effects
11.1The immune system4 objectives
- describe, for phagocytes (neutrophils and macrophages), their mode of action
- explain the meaning of the word antigen (see 4.1.3), and state how self antigens differ from non-self antigens
- describe what happens, step by step, in a primary immune response, referring to the parts played by: macrophages; B-lymphocytes, including plasma cells; T-lymphocytes, limited to T-helper cells and T-killer cells
- explain what memory cells do that makes a secondary immune response possible and gives long-term immunity
11.2Antibodies and vaccination6 objectives
- relate how antibody molecules are structured to the functions they carry out
- outline how monoclonal antibodies can be made by means of the hybridoma method
- outline the core principles underlying the use of monoclonal antibodies for diagnosing disease and for treating disease
- outline how active immunity differs from passive immunity, and how natural immunity differs from artificial immunity
- explain that vaccines hold antigens that prompt the immune system to respond, conferring immunity over the long term
- explain in what ways vaccination programmes help bring the spread of infectious diseases under control
12.1Energy7 objectives
- outline why living organisms require energy, with reference to active transport, movement and anabolic reactions such as those taking place in DNA replication and protein synthesis
- describe why ATP is well suited to be the universal energy currency, in terms of its features
- state the two ways ATP is synthesised: chemiosmosis across chloroplast and mitochondrial membranes, and phosphate transfer in substrate-linked reactions
- explain how carbohydrates, lipids and proteins compare with one another for the energy values they provide as respiratory substrates
- state that the respiratory quotient (RQ) gives the ratio between carbon dioxide molecules produced and oxygen molecules taken in, during respiration
- work out, from respiration equations, the RQ value of each of several respiratory substrates
- describe and carry out experiments with simple respirometers to find the RQ of small invertebrates (e.g. blowfly larvae) or of seeds that are germinating
12.2Respiration14 objectives
- State where in a eukaryotic cell each of the four stages of aerobic respiration happens: oxidative phosphorylation takes place on the inner mitochondrial membrane, the link reaction and the Krebs cycle both take place in the mitochondrial matrix, and glycolysis takes place in the cytoplasm
- outline glycolysis: glucose is phosphorylated, then fructose 1,6-bisphosphate (6C) is split into two triose phosphate molecules (3C), each of which is oxidised further to form pyruvate (3C), producing ATP and reduced NAD along the way
- explain that, if oxygen is present, pyruvate is transported into mitochondria where it participates in the link reaction
- describe the link reaction, including what coenzyme A does in moving acetyl (2C) groups
- outline the Krebs cycle, explaining that oxaloacetate (4C) accepts the 2C fragment carried by acetyl coenzyme A, giving citrate (6C), and that a series of small steps then turns citrate back into oxaloacetate
- explain that reactions of the Krebs cycle involve decarboxylation and dehydrogenation, and that NAD and FAD coenzymes are reduced
- describe what NAD and FAD do when they pass hydrogen on to carriers located in the inner mitochondrial membrane
- explain that, in oxidative phosphorylation: hydrogen atoms are separated into energetic electrons and protons; as the energetic electrons move along the electron transport chain they give out energy; this energy is used to drive protons across the inner membrane of the mitochondrion; the protons diffuse back into the mitochondrial matrix through ATP synthase (facilitated diffusion), which supplies the energy to make ATP; and oxygen is the final electron acceptor, forming water
- describe how mitochondrial structure relates to what mitochondria do, using diagrams and electron micrographs
- outline anaerobic respiration both in yeast, where it is ethanol fermentation, and in mammals, where it is lactate fermentation
- explain why aerobic conditions give a far larger energy yield from respiration than anaerobic conditions do (a thorough breakdown of how much ATP glucose yields when respired aerobically is not expected)
- explain the ways in which rice is suited to growing with its roots immersed in water, limited to aerenchyma formation in the roots, ethanol fermentation in the roots and quicker stem growth
- describe and perform experiments with redox indicators, including DCPIP and methylene blue, to determine how temperature and substrate concentration influence the rate of respiration in yeast
- describe and carry out investigations in which simple respirometers are used to find out how the rate of respiration depends on temperature
13.1Photosynthesis as an energy transfer process12 objectives
- describe the link between chloroplast structure, as depicted in diagrams and electron micrographs, and the job it performs
- account for the way ATP and reduced NADP carry energy from the light-dependent stage into the light-independent stage (Calvin cycle) of photosynthesis, where that energy is used to build complex organic molecules
- state that, inside a chloroplast, the light-dependent stage takes place in the thylakoids (the thylakoid membranes and thylakoid spaces), stacked together as grana, while the light-independent stage takes place in the stroma
- describe what chloroplast pigments (chlorophyll a, chlorophyll b, carotene and xanthophyll) do when they absorb light inside thylakoids
- interpret the absorption spectra of chloroplast pigments plus the action spectra linked to photosynthesis
- describe and employ chromatography, which allows chloroplast pigments to be separated and identified, citing Rf values when identifying them
- state that the light-dependent stage of photosynthesis involves both cyclic and non-cyclic photophosphorylation
- account for the following in cyclic photophosphorylation: only photosystem I (PSI) takes part, chlorophyll undergoes photoactivation, and ATP is synthesised
- explain that non-cyclic photophosphorylation involves both photosystem I (PSI) and photosystem II (PSII), that chlorophyll is photoactivated, that the photolysis of water is catalysed by the oxygen-evolving complex, and that ATP and reduced NADP are both synthesised
- explain that, in photophosphorylation: energetic electrons give out energy as they move along the electron transport chain (the carriers' details are not expected); this energy is used to move protons across the thylakoid membrane; and the protons flow back out of the thylakoid space into the stroma by facilitated diffusion through ATP synthase, which provides energy to make ATP (ATP synthase need not be known in detail)
- outline the Calvin cycle's three main stages: carbon dioxide is fixed by rubisco, which catalyses its joining to ribulose bisphosphate (RuBP), a 5C compound, yielding two molecules of the 3C compound glycerate 3-phosphate (GP); GP is then reduced, in reactions needing ATP and reduced NADP, to triose phosphate (TP); and TP is used to regenerate RuBP, a step that also needs ATP
- state that intermediates of the Calvin cycle are used to make other molecules, limited to GP, from which some amino acids are made, and TP, from which carbohydrates, lipids and amino acids are made
13.2Investigation of limiting factors4 objectives
- name light intensity, carbon dioxide concentration and temperature as instances of limiting factors in photosynthesis
- explain how altering light intensity, carbon dioxide concentration and temperature affects how quickly photosynthesis proceeds
- describe and conduct investigations that employ redox indicators, including DCPIP and methylene blue, along with a chloroplast suspension, to determine how light intensity and light wavelength influence the rate of photosynthesis
- describe and carry out experiments on whole plants, including aquatic plants, to find out how the rate of photosynthesis is affected by temperature, carbon dioxide concentration and light intensity
14.1Homeostasis in mammals11 objectives
- explain the meaning of homeostasis and why it matters in mammals
- explain the principles of homeostasis using these ideas: negative feedback; internal and external stimuli; receptors; effectors (glands and muscles); and coordination systems (the endocrine system and the nervous system)
- state that the liver makes urea by deaminating surplus amino acids
- describe how the human kidney is built, limited to: the cortex and medulla, the fibrous capsule, the renal pelvis and ureter, and the branches of the renal vein and renal artery
- Identify the parts of a nephron along with its associated blood vessels and structures as shown in diagrams, photomicrographs and electron micrographs, limited to: glomerulus, Bowman’s capsule, proximal convoluted tubule, loop of Henle, distal convoluted tubule, collecting duct
- describe and account for how urine is produced in the nephron, limited to: glomerular filtrate arising through ultrafiltration within the Bowman’s capsule, and selective reabsorption occurring in the proximal convoluted tubule
- relate the functions of the Bowman’s capsule and of the proximal convoluted tubule in urine formation to their detailed structure
- describe the roles in osmoregulation of the collecting ducts, aquaporins, antidiuretic hormone (ADH), the posterior pituitary gland and the hypothalamus
- describe the principles of cell signalling, using as the example how glucagon controls blood glucose concentration, limited to: the hormone binding to a cell surface receptor, which causes a conformational change; activation of a G-protein, which stimulates adenylyl cyclase; formation of cyclic AMP (cAMP), the second messenger; cAMP activating protein kinase A, which starts an enzyme cascade; the signal being amplified along the cascade as more and more enzymes are activated by phosphorylation; and a cellular response in which the last enzyme of the pathway is activated and catalyses the breakdown of glycogen
- explain how blood glucose concentration is regulated by negative feedback control mechanisms, referring to how insulin affects liver cells and muscle cells and how glucagon affects liver cells
- account for how test strips and biosensors work when measuring glucose concentration in blood and urine, referring to the enzymes glucose oxidase and peroxidase
14.2Homeostasis in plants4 objectives
- explain that stomata open and close in response to changing environmental conditions, and that regulating the stomatal aperture strikes a balance between taking up carbon dioxide by diffusion and keeping water loss by transpiration as low as possible
- explain that stomata open and close in a daily rhythm
- describe how guard cells are built and what they do, and explain the mechanism they use to open and close stomata
- describe the part abscisic acid plays in making stomata close when water is scarce (water stress), including how calcium ions act as a second messenger
15.1Control and coordination in mammals12 objectives
- describe the traits of the endocrine system, using the hormones ADH, glucagon and insulin as reference points (see 14.1.8, 14.1.9 and 14.1.10)
- compare the characteristics of the nervous and endocrine systems
- describe how a motor neurone and a sensory neurone are built and what each does, and state that motor neurones and sensory neurones are linked by intermediate neurones
- outline what sensory receptor cells do when they pick up stimuli, and how they prompt impulses to pass along sensory neurones
- describe the order of events by which a sensory neurone comes to produce an action potential, taking as the example a chemoreceptor cell found in a human taste bud
- describe and explain how the membrane potential of a neurone changes, including: the way the resting potential is kept up, what happens during an action potential, and how, during the refractory period, the resting potential is brought back
- describe and explain how an impulse travels quickly along a myelinated neurone, referring to saltatory conduction
- explain why the refractory period matters for how often impulses can be sent
- describe how a cholinergic synapse is built and explain how it works, including what calcium ions do
- describe the part played in setting off contraction of striated muscle by the sarcoplasmic reticulum, the T-tubule system and neuromuscular junctions
- describe, from diagrams and electron micrographs, the ultrastructure of striated muscle, paying attention to how a sarcomere is built
- explain how muscles contract according to the sliding filament model, including what ATP, calcium ions, tropomyosin and troponin each do
15.2Control and coordination in plants3 objectives
- describe how the Venus fly trap gives a rapid response when hairs on the lobes of its modified leaves receive stimulation, and explain how the trap's closure is brought about
- explain the part auxin plays in elongation growth, namely by encouraging proton pumping which acidifies cell walls
- describe gibberellin's function in barley seed germination (see 16.3.4)
16.1Passage of information from parents to offspring7 objectives
- explain what is meant by diploid (2n) and by haploid (n)
- explain what it means for chromosomes to be in homologous pairs
- explain why a reduction division is required in meiosis when gametes are made
- describe what chromosomes do in animal and plant cells during meiosis, and what the spindle, the nuclear envelope and the cell surface membrane do alongside them (the main stages of meiosis should be named, though not the sub-divisions of prophase I: prophase I, metaphase I, anaphase I, telophase I, prophase II, metaphase II, anaphase II and telophase II)
- interpret photomicrographs and diagrams showing cells at varied points in meiosis, then pick out its principal stages
- account for how crossing over, plus the random orientation (independent assortment) of homologous chromosome pairs and sister chromatids during meiosis, gives rise to genetically different gametes
- account for how gametes joining at random during fertilisation results in genetically different individuals
16.2The roles of genes in determining the phenotype7 objectives
- explain what each of these terms means: genotype and phenotype; homozygous and heterozygous; dominant, recessive and codominant; gene, allele and locus; linkage; test cross; F1 and F2
- interpret and build genetic diagrams, including Punnett squares, in order to account for and forecast the outcomes of monohybrid and dihybrid crosses involving dominance, codominance, multiple alleles and sex linkage
- interpret and draw up genetic diagrams, including Punnett squares, so as to account for and forecast the outcomes of dihybrid crosses involving autosomal linkage and epistasis
- interpret and produce genetic diagrams, including Punnett squares, to account for and forecast the outcomes of test crosses
- use the chi-squared test to find out whether the differences between expected and observed results are significant
- explain how genes, proteins and phenotype are related, using these examples: albinism, tyrosinase and the TYR gene; sickle cell anaemia, haemoglobin and the HBB gene; haemophilia, factor VIII and the F8 gene; Huntington’s disease, huntingtin and the HTT gene
- explain how gibberellin brings about stem elongation, including the roles of the dominant allele, Le, which codes for a functional enzyme of the pathway that makes gibberellin, and of the recessive allele, le, which codes for a non-functional enzyme
16.3Gene control4 objectives
- describe how structural genes and regulatory genes differ, and how repressible enzymes differ from inducible enzymes
- explain how protein production is genetically governed in a prokaryote, drawing on the lac operon
- state that, in eukaryotes, gene expression is controlled partly by transcription factors: proteins that bind to DNA and raise or lower the rate at which transcription happens
- explain how gibberellin activates genes: it causes DELLA protein repressors to be broken down, and these repressors would otherwise inhibit the factors that promote transcription
17.1Variation4 objectives
- account for, using examples, how phenotypic variation arises from genetic factors, environmental factors, or a mix of both
- explain the meaning of continuous variation and of discontinuous variation
- account for the genetic underpinnings of both discontinuous and continuous variation
- use the t-test as a way of comparing two samples' means
17.2Natural and artificial selection7 objectives
- explain that natural selection happens because populations are able to produce large numbers of offspring, which then compete for resources; during the ‘struggle for existence’, the best-adapted individuals are the ones most likely to survive, breed and pass their alleles on to the next generation
- explain the ways in which environmental factors may act as directional, disruptive and stabilising forces of natural selection
- explain in what ways selection, the founder effect and genetic drift, including the bottleneck effect, may change the frequency of alleles in populations
- outline the process by which bacteria acquire resistance to antibiotics, taken as a case of natural selection
- use the Hardy–Weinberg principle to work out the frequencies of alleles and genotypes in a population, and state the conditions that must be met for the principle to apply
- describe the principles behind artificial selection, also known as selective breeding
- outline these examples of selective breeding: dairy cattle bred to give a higher milk yield; maize varieties made vigorous and uniform through inbreeding and hybridisation; and wheat and rice varieties given resistance to disease
17.3Evolution3 objectives
- outline the theory of evolution, in which changes to gene pools from one generation to the next lead, over time, to new species forming from species that already exist
- discuss the ways in which evolutionary relationships between species can be revealed by DNA sequence data
- explain how genetic isolation can lead to speciation, either through geographical separation (allopatric speciation) or through separation by ecology and behaviour (sympatric speciation)
18.1Classification6 objectives
- discuss what the word species signifies, with the discussion limited to the biological species concept, the morphological species concept and the ecological species concept
- describe how organisms are classified as belonging to one of three domains: Archaea, Bacteria and Eukarya
- state that Archaea and Bacteria are prokaryotes which differ from one another, limited to membrane lipids, ribosomal RNA and the makeup of cell walls
- describe how organisms of the Eukarya domain are classified using the taxonomic hierarchy, from kingdom down through phylum, class, order, family and genus to species
- outline the features typical of each kingdom: Protoctista, Fungi, Plantae and Animalia
- outline the basis on which viruses are classified, limited to which nucleic acid they contain (DNA or RNA) and whether it is double stranded or single stranded
18.2Biodiversity6 objectives
- define what is meant by a niche and by an ecosystem
- explain that biodiversity can be measured at several levels, including: how many different ecosystems and habitats there are and how varied they are; how many species there are and their relative abundance; and the genetic variation found within each species
- account for why random sampling matters when establishing the biodiversity of a given area
- describe and use suitable methods for assessing how organisms are distributed in an area and how abundant they are, limited to belt transects, line transects, frame quadrats and mark-release-recapture with the Lincoln index (you will be given the formula for the Lincoln index; see the Mathematical requirements)
- use Pearson’s linear correlation and Spearman’s rank correlation to analyse how two variables are related, including the effect of biotic and abiotic factors on the distribution and abundance of species (these correlations' formulae are given; see the Mathematical requirements)
- use Simpson’s index of diversity (D) to work out how biodiverse an area is, and state what different values of D indicate (the formula is given; see the Mathematical requirements)
18.3Conservation6 objectives
- explain why climate change, competition, hunting by humans, and the degradation and loss of habitats can drive species and populations to extinction
- outline why it is necessary to preserve biodiversity
- outline how seed banks, 'frozen zoos', conserved areas (including national parks and marine parks), botanic gardens and zoos each contribute to the conservation of endangered species
- describe the assisted reproduction methods that are used to conserve endangered mammals, limited to surrogacy, embryo transfer and IVF
- account for why invasive alien species need to be kept in check
- outline how the IUCN (International Union for Conservation of Nature) and CITES (Convention on International Trade in Endangered Species of Wild Fauna and Flora) each contribute to conservation
19.1Principles of genetic technology11 objectives
- define what is meant by recombinant DNA
- explain that genetic engineering is the deliberate changing of genetic material to alter specific characteristics of an organism; this may involve moving a gene into an organism in a way that lets it be expressed
- explain that a gene for transfer into an organism can be: cut out of a donor organism's DNA, made from a donor organism's mRNA, or synthesised chemically from nucleotides
- explain what restriction endonucleases, DNA ligase, plasmids, DNA polymerase and reverse transcriptase each do when a gene is moved into an organism
- explain why, alongside the target gene, a promoter might also need to be introduced into an organism
- explain how fluorescent products, encoded by marker genes, can serve to confirm that gene expression has taken place
- explain that gene editing works by inserting, deleting or replacing DNA at specific sites within the genome, which makes it a form of genetic engineering
- describe and explain the stages of the polymerase chain reaction (PCR), a method for cloning and amplifying DNA, including the function of Taq polymerase
- describe and explain how gel electrophoresis separates DNA fragments according to their length
- outline the ways microarrays are employed to examine genomes and to detect mRNA in gene expression research
- outline the advantages of consulting databases holding data on nucleotide sequences for genes and for whole genomes, along with amino acid sequences in proteins and their structures
19.2Genetic technology applied to medicine4 objectives
- account for the benefits of employing recombinant human proteins in treating disease, taking as examples insulin, factor VIII and adenosine deaminase
- outline the benefits genetic screening brings, taking as examples breast cancer (BRCA1 and BRCA2), Huntington’s disease and cystic fibrosis
- outline how gene therapy can treat genetic diseases, with examples drawn from SCID (severe combined immunodeficiency) and inherited eye diseases
- discuss the ethical and social issues raised by the medical use of gene therapy and genetic screening
19.3Genetically modified organisms in agriculture2 objectives
- explain that genetic engineering could help to meet the global demand for food through making crop plants and farmed animals more productive and of higher quality, as shown by GM salmon, herbicide-resistant soybean and insect-resistant cotton
- discuss the social and ethical implications of producing food with genetically modified organisms (GMOs)
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