G4 Conservation of biodiversity
G5 Population ecology
Format of the syllabus details
The structure is as follows.
Topics or options
Topics are numbered and options are indicated by a letter (for example, “Topic 5: Ecology and evolution”, or “Option D: Evolution”).
Sub-topics
Sub-topics are numbered and the estimated teaching time required to cover the material is indicated (for example, “7.1 DNA structure”).
Assessment statements (AS)
Assessment statements, which are numbered, are expressed in terms of the outcomes that are expected of students at the end of the course (for example, “5.1.2 Distinguish between autotroph and heterotroph”). These are intended to prescribe to examiners what can be assessed by means of the written examinations. Each one is classified as objective 1, 2 or 3 (see the “Objectives” section) according to the command terms used (see the “Command terms” section). The objective levels are relevant for the examinations and for
balance within the syllabus, while the command terms indicate the depth of treatment required for a given assessment statement. It is important that students are made aware of the meanings of the command
terms because these will be used in examination questions.
Teacher’s notes
Teacher’s notes, which are included alongside some assessment statements, provide further guidance to teachers.
They may also suggest ideas for the promotion of aim 7, aim 8, TOK and the international dimension (Int).
 |
Assessment statement |
Obj |
Teacher’s notes |
|
| 1.1.1 | State that error bars are a graphical representation of the variability of data. |
1 |
Error bars can be used to show either the range of the data or the standard deviation. |
| 1.1.2 | Calculate the mean and standard deviation of a set of values. |
2 |
Students should specify the standard deviation (s), not the population standard deviation. Students will not be expected to know the formulas for calculating these statistics. They will be expected to use the standard deviation function of a graphic display or scientific calculator. Aim 7: Students could also be taught how to calculate standard deviation using a spreadsheet computer program. |
| 1.1.3 | State that the term standard deviation is used to summarize the spread of values around the mean, and that 68% of the values fall within one standard deviation of the mean. |
1 |
For normally distributed data, about 68% of all values lie within ±1 standard deviation (s or σ) of the mean. This rises to about 95% for ±2 standard deviations. |
| 1.1.4 | Explain how the standard deviation is useful for comparing the means and the spread of data between two or more samples. |
3 |
A small standard deviation indicates that the data is clustered closely around the mean value. Conversely, a large standard deviation indicates a wider spread around the mean. |
| 1.1.5 | Deduce the significance of the difference between two sets of data using calculated values for t and the appropriate tables. |
3 |
For the t-test to be applied, the data must have a normal distribution and a sample size of at least 10. The t-test can be used to compare two sets of data and measure the amount of overlap. Students will not be expected to calculate values of t. Only a two-tailed, unpaired t-test is expected. Aim 7: While students are not expected to calculate a value for the t-test, students could be shown how to calculate such values using a spreadsheet program or the graphic display calculator. TOK: The scientific community defines an objective standard by which claims about data can be made. |
| 1.1.6 | Explain that the existence of a correlation does not establish that there is a causal relationship between two variables. |
3 |
Aim 7: While calculations of such values are not expected, students who want to use r and r2 values in their practical work could be shown how to determine such values using a spreadsheet program. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 2.1.1 | Outline the cell theory. | 2 | Include the following. • Living organisms are composed of cells. • Cells are the smallest unit of life. • Cells come from pre-existing cells. |
| 2.1.2 | Discuss the evidence for the cell theory. |
3 | TOK: The nature of scientific theories could be introduced here: the accumulation of evidence that allows a hypothesis to become a theory; whether a theory should be abandoned when there is evidence that it does not offer a full explanation; and what evidence is needed for a theory to be adopted or rejected. |
| 2.1.3 | State that unicellular organisms carry out all the functions of life. |
1 | Include metabolism, response, homeostasis, growth, reproduction and nutrition. |
| 2.1.4 | Compare the relative sizes of molecules, cell membrane thickness, viruses, bacteria, organelles and cells, using the appropriate SI unit. |
3 | Appreciation of relative size is required, such as molecules (1 nm), thickness of membranes (10 nm), viruses (100 nm), bacteria (1 μm), organelles (up to 10 μm), and most cells (up to 100 μm). The three-dimensional nature/shape of cells should be emphasized. TOK: All the biological entities in the above list are beyond our ability to perceive directly. They must be observed through the use of technology such as the light microscope and the electron microscope. Is there any distinction to be drawn between knowledge claims dependent upon observations made directly with the senses and knowledge claims dependent upon observations assisted by technology? |
| 2.1.5 | Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification. |
2 | Magnification could be stated (for example, ×250) or indicated by means of a scale bar, for example: 1 μm Aim 7: The size of objects in digital images of microscope fields could be analysed using graticule baselines and image-processing software. |
| 2.1.6 | Explain the importance of the surface area to volume ratio as a factor limiting cell size. |
3 | Mention the concept that the rate of heat production/waste production/resource consumption of a cell is a function of its volume, whereas the rate of exchange of materials and energy (heat) is a function of its surface area. Simple mathematical models involving cubes and the changes in the ratio that occur as the sides increase by one unit could be compared. Aim 7: Data logging could be carried out to measure changes in conductivity in distilled water as salt diffuses out of salt–agar cubes of different dimensions. |
| 2.1.7 | State that multicellular organisms show emergent properties. |
1 | Emergent properties arise from the interaction of component parts: the whole is greater than the sum of its parts. TOK: The concept of emergent properties has many implications in biology, and this is an opportunity to introduce them. Life itself can be viewed as an emergent property, and the nature of life could be discussed in the light of this, including differences between living and non-living things and problems about defining death in medical decisions. |
| 2.1.8 | Explain that cells in multicellular organisms differentiate to carry out specialized functions by expressing some of their genes but not others. |
3 | |
| 2.1.9 | State that stem cells retain the capacity to divide and have the ability to differentiate along different pathways. |
1 | |
| 2.1.10 | Outline one therapeutic use of stem cells. |
2 | This is an area of rapid development. In 2005, stem cells were used to restore the insulation tissue of neurons in laboratory rats, resulting in subsequent improvements in their mobility. Any example of the therapeutic use of stem cells in humans or other animals can be chosen. Aim 8: There are ethical issues involved in stem cell research, whether humans or other animals are used. Use of embryonic stem cells involves the death of early-stage embryos, but if therapeutic cloning is successfully developed the suffering of patients with a wide variety of conditions could be reduced. Int: Stem cell research has depended on the work of teams of scientists in many countries, who share results and so speed up the rate of progress. However, ethical concerns about the procedures have led to restrictions on research in some countries. National governments are influenced by local, cultural and religious traditions, which vary greatly, and these, therefore, have an impact on the work of scientists. TOK: This is an opportunity to discuss balancing the huge opportunities of therapeutic cloning against the considerable risks—for example, stem cells developing into tumours. Another issue is how the scientific community conveys information about its work to the wider community in such a way that informed decisions about research can be made. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 2.2.1 | Draw and label a diagram of the ultrastructure of Escherichia coli (E. coli) as an example of a prokaryote. |
1 | The diagram should show the cell wall, plasma membrane, cytoplasm, pili, flagella, ribosomes and nucleoid (region containing naked DNA). |
| 2.2.2 | Annotate the diagram from 2.2.1 with the functions of each named structure. |
2 | |
| 2.2.3 | Identify structures from 2.2.1 in electron micrographs of E. coli. |
2 | |
| 2.2.4 | State that prokaryotic cells divide by binary fission. |
1 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 2.3.1 | Draw and label a diagram of the ultrastructure of a liver cell as an example of an animal cell. |
1 | The diagram should show free ribosomes, rough endoplasmic reticulum (rER), lysosome, Golgi apparatus, mitochondrion and nucleus. The term Golgi apparatus will be used in place of Golgi body, Golgi complex or dictyosome. |
| 2.3.2 | Annotate the diagram from 2.3.1 with the functions of each named structure. |
2 | |
| 2.3.3 | Identify structures from 2.3.1 in electron micrographs of liver cells. |
2 | |
| 2.3.4 | Compare prokaryotic and eukaryotic cells. |
3 | Differences should include: • naked DNA versus DNA associated with proteins • DNA in cytoplasm versus DNA enclosed in a nuclear envelope • no mitochondria versus mitochondria • 70S versus 80S ribosomes • eukaryotic cells have internal membranes that compartmentalize their functions. |
| 2.3.5 | State three differences between plant and animal cells. |
1 | |
| 2.3.6 | Outline two roles of extracellular components. |
2 | The plant cell wall maintains cell shape, prevents excessive water uptake, and holds the whole plant up against the force of gravity. Animal cells secrete glycoproteins that form the extracellular matrix. This functions in support, adhesion and movement. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 2.4.1 | Draw and label a diagram to show the structure of membranes. |
1 | The diagram should show the phospholipid bilayer, cholesterol, glycoproteins, and integral and peripheral proteins. Use the term plasma membrane, not cell surface membrane, for the membrane surrounding the cytoplasm. Integral proteins are embedded in the phospholipid of the membrane, whereas peripheral proteins are attached to its surface. Variations in composition related to the type of membrane are not required. Aim 7: Data logging to measure the changes in membrane permeability using colorimeter probes can be used. |
| 2.4.2 | Explain how the hydrophobic and hydrophilic properties of phospholipids help to maintain the structure of cell membranes. |
3 | |
| 2.4.3 | List the functions of membrane proteins. |
1 | Include the following: hormone binding sites, immobilized enzymes, cell adhesion, cell-to-cell communication, channels for passive transport, and pumps for active transport. |
| 2.4.4 | Define diffusion and osmosis. | 1 | Diffusion is the passive movement of particles from a region of high concentration to a region of low concentration. Osmosis is the passive movement of water molecules, across a partially permeable membrane, from a region of lower solute concentration to a region of higher solute concentration. |
| 2.4.5 | Explain passive transport across membranes by simple diffusion and facilitated diffusion. |
3 | |
| 2.4.6 | Explain the role of protein pumps and ATP in active transport across membranes. |
3 | |
| 2.4.7 | Explain how vesicles are used to transport materials within a cell between the rough endoplasmic reticulum, Golgi apparatus and plasma membrane. |
3 | |
| 2.4.8 | Describe how the fluidity of the membrane allows it to change shape, break and re-form during endocytosis and exocytosis. |
2 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 2.5.1 | Outline the stages in the cell cycle, including interphase (G1, S, G2), mitosis and cytokinesis. |
2 | |
| 2.5.2 | State that tumours (cancers) are the result of uncontrolled cell division and that these can occur in any organ or tissue. |
1 | |
| 2.5.3 | State that interphase is an active period in the life of a cell when many metabolic reactions occur, including protein synthesis, DNA replication and an increase in the number of mitochondria and/or chloroplasts. |
1 | |
| 2.5.4 | Describe the events that occur in the four phases of mitosis (prophase, metaphase, anaphase and telophase). |
2 | Include supercoiling of chromosomes, attachment of spindle microtubules to centromeres, splitting of centromeres, movement of sister chromosomes to opposite poles, and breakage and re-formation of nuclear membranes. Textbooks vary in the use of the terms chromosome and chromatid. In this course, the two DNA molecules formed by DNA replication are considered to be sister chromatids until the splitting of the centromere at the start of anaphase; after this, they are individual chromosomes. The term kinetochore is not expected. Aim 7: Students could determine mitotic index and fraction of cells in each phase of mitosis. Individual groups could paste data into a database. Pie charts could be constructed with a graphing computer program. If a graphing computer program is used in DCP for internal assessment, it should be according to the IA and ICT clarifications. |
| 2.5.5 | Explain how mitosis produces two genetically identical nuclei. |
3 | |
| 2.5.6 | State that growth, embryonic development, tissue repair and asexual reproduction involve mitosis. |
1 |
Topic 3: The Chemistry of Life
3.1 Chemical elements and water
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 3.1.1 | State that the most frequently occurring chemical elements in living things are carbon, hydrogen, oxygen and nitrogen. |
1 | |
| 3.1.2 | State that a variety of other elements are needed by living organisms, including sulfur, calcium, phosphorus, iron and sodium. |
1 | |
| 3.1.3 | State one role for each of the elements mentioned in 3.1.2. |
1 | Refer to the roles in plants, animals and prokaryotes. |
| 3.1.4 | Draw and label a diagram showing the structure of water molecules to show their polarity and hydrogen bond formation. |
1 | |
| 3.1.5 | Outline the thermal, cohesive and solvent properties of water. |
2 | Aim 7: Data logging could be carried out to compare the thermal properties of water with those of other liquids. TOK: Claims about the “memory of water” have been categorized as pseudoscientific. By what criteria can a claim be judged to be pseudoscientific? |
| 3.1.6 | Explain the relationship between the properties of water and its uses in living organisms as a coolant, medium for metabolic reactions and transport medium. |
3 | Limit the properties to those outlined in 3.1.5. |
3.2 Carbohydrates, lipids and proteins
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 3.2.1 | Distinguish between organic and inorganic compounds. |
2 | Compounds containing carbon that are found in living organisms (except hydrogencarbonates, carbonates and oxides of carbon) are regarded as organic. |
| 3.2.2 | Identify amino acids, glucose, ribose and fatty acids from diagrams showing their structure. |
2 | Specific names of amino acids and fatty acids are not expected. |
| 3.2.3 | List three examples each of monosaccharides, disaccharides and polysaccharides. |
1 | The examples used should be: • glucose, galactose and fructose • maltose, lactose and sucrose • starch, glycogen and cellulose. |
| 3.2.4 | State one function of glucose, lactose and glycogen in animals, and of fructose, sucrose and cellulose in plants. |
1 | |
| 3.2.5 | Outline the role of condensation and hydrolysis in the relationships between monosaccharides, disaccharides and polysaccharides; between fatty acids, glycerol and triglycerides; and between amino acids and polypeptides. |
2 | This can be dealt with using equations with words or chemical formulas. |
| 3.2.6 | State three functions of lipids. | 1 | Include energy storage and thermal insulation. |
| 3.2.7 | Compare the use of carbohydrates and lipids in energy storage. |
3 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 3.3.1 | Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate. |
2 | Chemical formulas and the purine/pyrimidine
|
| 3.3.2 | State the names of the four bases in DNA. |
1 | |
| 3.3.3 | Outline how DNA nucleotides are linked together by covalent bonds into a single strand. |
2 | Only the relative positions are required.
|
| 3.3.4 | Explain how a DNA double helix is formed using complementary base pairing and hydrogen bonds. |
3 | |
| 3.3.5 | Draw and label a simple diagram of the molecular structure of DNA. |
1 | An extension of the diagram in 3.3.3 is sufficient to show the complementary base pairs of A–T and G–C, held together by hydrogen bonds and the sugar–phosphate backbones. The number of hydrogen bonds between pairs and details of purine/pyrimidines are not required. TOK: The story of the elucidation of the structure of DNA illustrates that cooperation and collaboration among scientists exists alongside competition between research groups. To what extent was Watson and Crick’s “discovery” of the threedimensional structure of DNA dependent on the use of data generated by Rosalind Franklin, which was shared without her knowledge or consent? |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 3.4.1 | Explain DNA replication in terms of unwinding the double helix and separation of the strands by helicase, followed by formation of the new complementary strands by DNA polymerase. |
3 | It is not necessary to mention that there is more than one DNA polymerase. |
| 3.4.2 | Explain the significance of complementary base pairing in the conservation of the base sequence of DNA. |
3 | |
| 3.4.3 | State that DNA replication is semiconservative. | 1 |
3.5 Transcription and translation
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 3.5.1 | Compare the structure of RNA and DNA. |
3 | Limit this to the names of sugars, bases and the number of strands. |
| 3.5.2 | Outline DNA transcription in terms of the formation of an RNA strand complementary to the DNA strand by RNA polymerase. |
2 | |
| 3.5.3 | Describe the genetic code in terms of codons composed of triplets of bases. |
2 | |
| 3.5.4 | Explain the process of translation, leading to polypeptide formation. |
3 | Include the roles of messenger RNA (mRNA), transfer RNA (tRNA), codons, anticodons, ribosomes and amino acids. |
| 3.5.5 | Discuss the relationship between one gene and one polypeptide. |
3 | Originally, it was assumed that one gene would invariably code for one polypeptide, but many exceptions have been discovered. TOK: The way in which theories are modified as related evidence accumulates could be discussed, and whether contrary evidence should cause a theory to be discarded immediately if there are exceptions to it. Where a theory is suddenly and totally abandoned, to be replaced by a different theory, this is known as a paradigm shift. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 3.6.1 | Define enzyme and active site. | 1 | |
| 3.6.2 | Explain enzyme–substrate specificity. | 3 | The lock-and-key model can be used as a basis for the explanation. Refer to the three-dimensional structure. The induced-fit model is not expected at SL. |
| 3.6.3 | Explain the effects of temperature, pH and substrate concentration on enzyme activity. |
3 | Aim 7: Enzyme activity could be measured using data loggers such as pressure sensors, pH sensors or colorimeters. Aim 8: The effects of environmental acid rain could be discussed. |
| 3.6.4 | Define denaturation. | 1 | Denaturation is a structural change in a protein that results in the loss (usually permanent) of its biological properties. Refer only to heat and pH as agents. |
| 3.6.5 | Explain the use of lactase in the production of lactose-free milk. |
3 | Aim 8: Production of lactose-free milk is an example of an industrial process depending on biological methods (biotechnology). These methods are of huge and increasing economic importance. Int/TOK: Development of some techniques benefits particular human populations and not others because of the natural variation in human characteristics. Lactose intolerance is found in a high proportion of the human population (for example, in Asia) but more rarely among those of European origin. Sometimes a transfer of biotechnology is needed when techniques are developed in one part of the world that are more applicable in another. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 3.7.1 | Define cell respiration. | 1 | Cell respiration is the controlled release of energy from organic compounds in cells to form ATP. |
| 3.7.2 | State that, in cell respiration, glucose in the cytoplasm is broken down by glycolysis into pyruvate, with a small yield of ATP. |
1 | |
| 3.7.3 | Explain that, during anaerobic cell respiration, pyruvate can be converted in the cytoplasm into lactate, or ethanol and carbon dioxide, with no further yield of ATP. |
3 | Mention that ethanol and carbon dioxide are produced in yeast, whereas lactate is produced in humans. Aim 7: Data logging using gas sensors, oxygen, carbon dioxide or pH probes could be used. |
| 3.7.4 | Explain that, during aerobic cell respiration, pyruvate can be broken down in the mitochondrion into carbon dioxide and water with a large yield of ATP. |
3 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 3.8.1 | State that photosynthesis involves the conversion of light energy into chemical energy. |
1 | |
| 3.8.2 | State that light from the Sun is composed of a range of wavelengths (colours). |
1 | Reference to actual wavelengths or frequencies is not expected. |
| 3.8.3 | State that chlorophyll is the main photosynthetic pigment. |
1 | |
| 3.8.4 | Outline the differences in absorption of red, blue and green light by chlorophyll. |
2 | Students should appreciate that pigments absorb certain colours of light. The remaining colours of light are reflected. It is not necessary to mention wavelengths or the structure responsible for the absorption. Aim 7: Data logging using colorimeters or light sensors could be used. |
| 3.8.5 | State that light energy is used to produce ATP, and to split water molecules (photolysis) to form oxygen and hydrogen. |
1 | |
| 3.8.6 | State that ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules. |
1 | |
| 3.8.7 | Explain that the rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by an increase in biomass. |
3 | The recall of details of specific experiments to indicate that photosynthesis has occurred or to measure the rate of photosynthesis is not expected. |
| 3.8.8 | Outline the effects of temperature, light intensity and carbon dioxide concentration on the rate of photosynthesis. |
2 | The shape of the graphs is required. The concept of limiting factors is not expected. Aim 7: Data logging using gas sensors, oxygen, carbon dioxide or pH probes could be used. |
4.1 Chromosomes, genes, alleles and mutations
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 4.1.1 | State that eukaryote chromosomes are made of DNA and proteins. |
1 | The names of the proteins (histones) are not required, nor is the structural relationship between DNA and the proteins. |
| 4.1.2 | Define gene, allele and genome. | 1 | Gene: a heritable factor that controls a specific characteristic. (The differences between structural genes, regulator genes and genes coding for tRNA and rRNA are not expected at SL). Allele: one specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene. Genome: the whole of the genetic information of an organism. |
| 4.1.3 | Define gene mutation. | 1 | The terms point mutation or frameshift mutation will not be used. |
| 4.1.4 | Explain the consequence of a base substitution mutation in relation to the processes of transcription and translation, using the example of sickle-cell anemia. |
3 | GAG has mutated to GTG causing glutamic acid to be replaced by valine, and hence sickle-cell anemia. Aim 8: There is a variety of social issues associated with sickle-cell anemia, including the suffering due to anemia, personal feelings if one has either inherited or passed on the sickle-cell allele, questions relating to the desirability of genetic screening for the sickle-cell allele before having children, and the genetic counselling of carriers of the allele. There are also ethical issues relating to screening of fetuses and abortion of those found to have a genetic disease. TOK: Where a correlation is found, a causal link may or may not be present. The frequency of the sickle-cell allele is correlated with the prevalence of malaria in many parts of the world. In this case, there is a clear causal link. Other cases where there is no causal link could be described as a contrast. There has clearly been natural selection in favour of the sickle-cell allele in malarial areas, despite it causing severe anemia in the homozygous condition. Natural selection has led to particular frequencies of the sickle-cell and the normal hemoglobin alleles, to balance the twin risks of anemia and malaria. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 4.2.1 | State that meiosis is a reduction division of a diploid nucleus to form haploid nuclei. |
1 | |
| 4.2.2 | Define homologous chromosomes. | 1 | |
| 4.2.3 | Outline the process of meiosis, including pairing of homologous chromosomes and crossing over, followed by two divisions, which results in four haploid cells. |
2 | Limit crossing over to the exchange of genetic material between non-sister chromatids during prophase I. Names of the stages are required. |
| 4.2.4 | Explain that non-disjunction can lead to changes in chromosome number, illustrated by reference to Down syndrome (trisomy 21). |
3 | The characteristics of Down syndrome are not required. |
| 4.2.5 | State that, in karyotyping, chromosomes are arranged in pairs according to their size and structure. |
1 | |
| 4.2.6 | State that karyotyping is performed using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities. |
1 | Aim 8: There are ethical and social issues associated with karyotyping of unborn fetuses because this procedure allows parents to abort fetuses with a chromosome abnormality. There is also evidence that, in some parts of the world, abortion on the basis of gender is carried out. TOK: Various questions relating to karyotyping could be raised, including balancing the risks of side-effects (for example, miscarriage) against the possibility of identifying and aborting a fetus with an abnormality. There are questions about decision-making: who should make the decision about whether to perform karyotyping and allow a subsequent abortion—parents or health-care professionals or both groups? There are also questions about whether or not national governments should interfere with personal freedoms, and whether or not they should be able to ban procedures within the country and possibly also ban citizens travelling to foreign countries where the procedures are permitted. |
| 4.2.7 | Analyse a human karyotype to determine gender and whether nondisjunction has occurred. |
3 | Karyotyping can be done by using enlarged photographs of chromosomes. Aim 7: Online simulations of karyotyping activities are available. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 4.3.1 | Define genotype, phenotype, dominant allele, recessive allele, codominant alleles, locus, homozygous, heterozygous, carrier and test cross. |
1 | Genotype: the alleles of an organism. Phenotype: the characteristics of an organism. Dominant allele: an allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state. Recessive allele: an allele that only has an effect on the phenotype when present in the homozygous state. Codominant alleles: pairs of alleles that both affect the phenotype when present in a heterozygote. (The terms incomplete and partial dominance are no longer used.) Locus: the particular position on homologous chromosomes of a gene. Homozygous: having two identical alleles of a gene. Heterozygous: having two different alleles of a gene. Carrier: an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele. Test cross: testing a suspected heterozygote by crossing it with a known homozygous recessive. (The term backcross is no longer used.) |
| 4.3.2 | Determine the genotypes and phenotypes of the offspring of a monohybrid cross using a Punnett grid. |
3 | The grid should be labelled to include parental genotypes, gametes, and both offspring genotype and phenotype. Aim 7: Genetics simulation software is available. |
| 4.3.3 | State that some genes have more than two alleles (multiple alleles). |
1 | |
| 4.3.4 | Describe ABO blood groups as an example of codominance and multiple alleles. |
2 | Phenotype Genotype O ii A IAIA or IAi B IBIB or IBi AB IAIB |
| 4.3.5 | Explain how the sex chromosomes control gender by referring to the inheritance of X and Y chromosomes in humans. |
3 | |
| 4.3.6 | State that some genes are present on the X chromosome and absent from the shorter Y chromosome in humans. |
1 | |
| 4.3.7 | Define sex linkage. | 1 | |
| 4.3.8 | Describe the inheritance of colour blindness and hemophilia as examples of sex linkage. |
2 | Both colour blindness and hemophilia are produced by a recessive sex-linked allele on the X chromosome. Xb and Xh is the notation for the alleles concerned. The corresponding dominant alleles are XB and XH. |
| 4.3.9 | State that a human female can be homozygous or heterozygous with respect to sex-linked genes. |
1 | |
| 4.3.10 | Explain that female carriers are heterozygous for X-linked recessive alleles. |
3 | |
| 4.3.11 | Predict the genotypic and phenotypic ratios of offspring of monohybrid crosses involving any of the above patterns of inheritance. |
3 | Aim 8: Statisticians are convinced that Mendel’s results are too close to exact ratios to be genuine. We shall never know how this came about, but it offers an opportunity to discuss the need for scientists to be truthful about their results, whether it is right to discard results that do not fit a theory as Louis Pasteur is known to have done, and the danger of publishing results only when they show statistically significant differences. TOK: Reasons for Mendel’s theories not being accepted by the scientific community for a long time could be considered. Other cases of paradigm shifts taking a long time to be accepted could be considered. Ways in which individual scientists are most likely to be able to convince the scientific community could be considered, and also the need always to consider the evidence rather than the views of individual scientists, however distinguished. |
| 4.3.12 | Deduce the genotypes and phenotypes of individuals in pedigree charts. |
3 | For dominant and recessive alleles, upper-case and lower-case letters, respectively, should be used. Letters representing alleles should be chosen with care to avoid confusion between upper and lower case. For codominance, the main letter should relate to the gene and the suffix to the allele, both upper case. For example, red and white codominant flower colours should be represented as CR and Cw, respectively. For sickle-cell anemia, HbA is normal and Hbs is sickle cell. Aim 8: There are many social issues in families in which there is a genetic disease, including decisions for carriers about whether to have children, personal feelings for those who have inherited or passed on alleles for the disease, and potential problems in finding partners, employment and health or life insurance. There are ethical questions about whether personal details about genes should be disclosed to insurance companies or employers. Decisions may have to be made about whether or not to have screening. These are particularly acute in the case of Huntington disease. |
4.4 Genetic engineering and biotechnology
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 4.4.1 | Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA. |
2 | Details of methods are not required. |
| 4.4.2 | State that, in gel electrophoresis, fragments of DNA move in an electric field and are separated according to their size. |
1 | |
| 4.4.3 | State that gel electrophoresis of DNA is used in DNA profiling. |
1 | |
| 4.4.4 | Describe the application of DNA profiling to determine paternity and also in forensic investigations. |
2 | Aim 8: There is a variety of social implications stemming from DNA profiling, such as identity issues for a child who learns unexpectedly who his or her biological father is, self-esteem problems for someone who learns he is not a father, problems in relationships where the male partner learns that he did not father a child, but also relief for crime victims when those responsible for the crime are identified and convicted, sometimes decades later. TOK: A comparison could be made between blood groups and DNA profiles in their potential for determining paternity. The difficulty in assessing the chance of two individuals having the same profile could be discussed, and also the success of DNA profiling in securing convictions in some of the high-profile legal cases of recent years. |
| 4.4.5 | Analyse DNA profiles to draw conclusions about paternity or forensic investigations. |
3 | The outcomes of this analysis could include knowledge of the number of human genes, the location of specific genes, discovery of proteins and their functions, and evolutionary relationships. Aim 7: Online bioinformatics simulations are available. Aim 8: We can either emphasize the large shared content of the human genome, which is common to all of us and should give us a sense of unity, or we can emphasize the small but significant allelic differences that create the biodiversity within our species, which should be treasured. Differences in the success of human races in coping with the modern world and the threat to some small human tribes could be mentioned. It is important to stress parity of esteem of all humans, whatever their genome. TOK: The Human Genome Project was an international endeavour, with laboratories throughout the world collaborating. However, there were also efforts in some parts of the world to gain commercial benefits from the outcomes of the project. The data from the Human Genome Project can be viewed in different ways: it could be seen as a complete account of what makes up a human, if one takes a reductionist view of life, or, alternatively, as merely the chemical instructions that have allowed a huge range of more significant human characteristics to develop. This could lead to a discussion about the essential nature of humanity. |
| 4.4.6 | Outline three outcomes of the sequencing of the complete human genome. |
2 | |
| 4.4.7 | State that, when genes are transferred between species, the amino acid sequence of polypeptides translated from them is unchanged because the genetic code is universal. |
1 | Aim 8: There is an ethical or moral question here: whether it is right to change the genetic integrity of a species by transferring genes to it from another species. The discussion could include the wider question of selective breeding of animals, and whether this is distinctively different and always acceptable. The possibility of animals suffering as a result of genetic modification could be considered. |
| 4.4.8 | Outline a basic technique used for gene transfer involving plasmids, a host cell (bacterium, yeast or other cell), restriction enzymes (endonucleases) and DNA ligase. |
2 | The use of E. coli in gene technology is well documented. Most of its DNA is in one circular chromosome, but it also has plasmids (smaller circles of DNA). These plasmids can be removed and cleaved by restriction enzymes at target sequences. DNA fragments from another organism can also be cleaved by the same restriction enzyme, and these pieces can be added to the open plasmid and spliced together by ligase. The recombinant plasmids formed can be inserted into new host cells and cloned. |
| 4.4.9 | State two examples of the current uses of genetically modified crops or animals. |
1 | Examples include salt tolerance in tomato plants, synthesis of beta-carotene (vitamin A precursor) in rice, herbicide resistance in crop plants and factor IX (human blood clotting) in sheep milk. Aim 8: The economic benefits of genetic modification to biotechnology companies that perform it could be considered. Also mention the possibility that harmful changes to local economies could result, and the danger that wealth could become more concentrated in a smaller percentage of the population if expensive but profitable new techniques are introduced. In this respect, inequalities in wealth may become greater. |
| 4.4.10 | Discuss the potential benefits and possible harmful effects of one example of genetic modification. |
3 | Aim 8: There are ethical questions here about how far it is acceptable for humans to change other species, as well as other ecosystems, in order to gain benefit for humans. TOK: This is an opportunity to discuss how we can assess whether risks are great enough to justify banning techniques and how the scientific community can inform communities generally about potential risks. Informed decisions need to be made but irrational fears should not be propagated. Consideration could be given to the paradox that careful research is needed to assess the risks, but performing this research in itself could be risky. Do protesters who destroy trials of GM crops make the world safer? |
| 4.4.11 | Define clone. | 1 | Clone: a group of genetically identical organisms or a group of cells derived from a single parent cell. |
| 4.4.12 | Outline a technique for cloning using differentiated animal cells. |
2 | Aim 8: Ethical questions about cloning should be separated into questions about reproductive cloning and therapeutic cloning. Some groups are vehemently opposed to both types. |
| 4.4.13 | Discuss the ethical issues of therapeutic cloning in humans. |
3 | Therapeutic cloning is the creation of an embryo to supply embryonic stem cells for medical use. |
Topic 5: Ecology and Evolution
5.1 Communities and ecosystems
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 5.1.1 | Define species, habitat, population, community, ecosystem and ecology. |
1 | Species: a group of organisms that can interbreed and produce fertile offspring. Habitat: the environment in which a species normally lives or the location of a living organism. Population: a group of organisms of the same species who live in the same area at the same time. Community: a group of populations living and interacting with each other in an area. Ecosystem: a community and its abiotic environment. Ecology: the study of relationships between living organisms and between organisms and their environment. |
| 5.1.2 | Distinguish between autotroph and heterotroph. |
2 | Autotroph: an organism that synthesizes its organic molecules from simple inorganic substances. Heterotroph: an organism that obtains organic molecules from other organisms. |
| 5.1.3 | Distinguish between consumers, detritivores and saprotrophs. |
2 | Consumer: an organism that ingests other organic matter that is living or recently killed. Detritivore: an organism that ingests non-living organic matter. Saprotroph: an organism that lives on or in nonliving organic matter, secreting digestive enzymes into it and absorbing the products of digestion. |
| 5.1.4 | Describe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms). |
2 | Only real examples should be used from natural ecosystems. A→ B indicates that A is being “eaten” by B (that is, the arrow indicates the direction of energy flow). Each food chain should include a producer and consumers, but not decomposers. Named organisms at either species or genus level should be used. Common species names can be used instead of binomial names. General names such as “tree” or “fish” should not be used. |
| 5.1.5 | Describe what is meant by a food web. |
2 | |
| 5.1.6 | Define trophic level. | 1 | |
| 5.1.7 |
Deduce the trophic level of organisms in a food chain and a food web. |
3 | Students should be able to place an organism at the level of producer, primary consumer, secondary consumer, and so on, as the terms herbivore and carnivore are not always applicable. |
| 5.1.8 | Construct a food web containing up to 10 organisms, using appropriate information. |
3 | |
| 5.1.9 | State that light is the initial energy source for almost all communities. |
1 | No reference to communities where food chains start with chemical energy is required. |
| 5.1.10 | Explain the energy flow in a food chain. |
3 | Energy losses between trophic levels include material not consumed or material not assimilated, and heat loss through cell respiration. |
| 5.1.11 | State that energy transformations are never 100% efficient. |
1 | Reference to the second law of thermodynamics is not expected. |
| 5.1.12 | Explain reasons for the shape of pyramids of energy. |
3 | A pyramid of energy shows the flow of energy from one trophic level to the next in a community. The units of pyramids of energy are, therefore, energy per unit area per unit time, for example, kJ m–2 yr–1. |
| 5.1.13 | Explain that energy enters and leaves ecosystems, but nutrients must be recycled. |
3 | |
| 5.1.14 | State that saprotrophic bacteria and fungi (decomposers) recycle nutrients. |
1 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 5.2.1 | Draw and label a diagram of the carbon cycle to show the processes involved. |
1 | The details of the carbon cycle should include the interaction of living organisms and the biosphere through the processes of photosynthesis, cell respiration, fossilization and combustion. Recall of specific quantitative data is not required. TOK: What difference might it make to scientific work if nature were to be regarded as a machine, for example, as a clockwork mechanism, or as an organism, that is, the Gaia hypothesis? How useful are these metaphors? |
| 5.2.2 | Analyse the changes in concentration of atmospheric carbon dioxide using historical records. |
3 | Data from the Mauna Loa, Hawaii, or Cape Grim, Tasmania, monitoring stations may be used. |
| 5.2.3 | Explain the relationship between rises in concentrations of atmospheric carbon dioxide, methane and oxides of nitrogen and the enhanced greenhouse effect. |
3 | Students should be aware that the greenhouse effect is a natural phenomenon. Reference should be made to transmission of incoming shorter-wave radiation and re-radiated longer-wave radiation. Knowledge that other gases, including methane and oxides of nitrogen, are greenhouse gases is expected. |
| 5.2.4 | Outline the precautionary principle. | 2 | The precautionary principle holds that, if the effects of a human-induced change would be very large, perhaps catastrophic, those responsible for the change must prove that it will not do harm before proceeding. This is the reverse of the normal situation, where those who are concerned about the change would have to prove that it will do harm in order to prevent such changes going ahead. TOK: Parallels could be drawn here between success in deterring crime by increasing the severity of the punishment or by increasing the chance of detection. If the possible consequences of rapid global warming are devastating enough, preventive measures are justified even if it is far from certain that rapid global warming will result from current human activities. |
| 5.2.5 | Evaluate the precautionary principle as a justification for strong action in response to the threats posed by the enhanced greenhouse effect. |
3 | Aim 8: Consider whether the economic harm of measures taken now to limit global warming could be balanced against the potentially much greater harm for future generations of taking no action now. There are also ethical questions about whether the health and wealth of future human generations should be jeopardized, and whether it is right to knowingly damage the habitat of, and possibly drive to extinction, species other than humans. The environmental angle here is that the issue of global warming is, by definition, a genuinely global one in terms of causes, consequences and remedies. Only through international cooperation will a solution be found. There is an inequality between those in the world who are contributing most to the problem and those who will be most harmed. |
| 5.2.6 | Outline the consequences of a global temperature rise on arctic ecosystems. |
2 | Effects include increased rates of decomposition of detritus previously trapped in permafrost, expansion of the range of habitats available to temperate species, loss of ice habitat, changes in distribution of prey species affecting higher trophic levels, and increased success of pest species, including pathogens. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 5.3.1 | Outline how population size is affected by natality, immigration, mortality and emigration. |
2 | Aim 7: Simulation exercises can be performed. |
| 5.3.2 | Draw and label a graph showing a sigmoid (S-shaped) population growth curve. |
1 | |
| 5.3.3 | Explain the reasons for the exponential growth phase, the plateau phase and the transitional phase between these two phases. |
3 | |
| 5.3.4 | List three factors that set limits to population increase. |
1 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 5.4.1 | Define evolution. | 1 | Evolution is the cumulative change in the heritable characteristics of a population. If we accept not only that species can evolve, but also that new species arise by evolution from preexisting ones, then the whole of life can be seen as unified by its common origins. Variation within our species is the result of different selection pressures operating in different parts of the world, yet this variation is not so vast to justify a construct such as race having a biological or scientific basis. |
| 5.4.2 | Outline the evidence for evolution provided by the fossil record, selective breeding of domesticated animals and homologous structures. |
2 | |
| 5.4.3 | State that populations tend to produce more offspring than the environment can support. |
1 | |
| 5.4.4 | Explain that the consequence of the potential overproduction of offspring is a struggle for survival. |
3 | |
| 5.4.5 | State that the members of a species show variation. |
1 | |
| 5.4.6 | Explain how sexual reproduction promotes variation in a species. |
3 | |
| 5.4.7 | Explain how natural selection leads to evolution. |
3 | Greater survival and reproductive success of individuals with favourable heritable variations can lead to change in the characteristics of a population. Aim 7: Computer simulations can be performed. |
| 5.4.8 | Explain two examples of evolution in response to environmental change; one must be antibiotic resistance in bacteria. |
3 | Other examples could include: the changes in size and shape of the beaks of Galapagos finches; pesticide resistance, industrial melanism or heavymetal tolerance in plants. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 5.5.1 | Outline the binomial system of nomenclature. |
2 | TOK: The adoption of a system of binomial nomenclature is largely due to Swedish botanist and physician Carolus Linnaeus (1707–1778). Linnaeus also defined four groups of humans, and the divisions were based on both physical and social traits. By 21st-century standards, his descriptions can be regarded as racist. How does the social context of scientific work affect the methods and findings of research? Is it necessary to consider the social context when evaluating ethical aspects of knowledge claims? |
| 5.5.2 | List seven levels in the hierarchy of taxa—kingdom, phylum, class, order, family, genus and species—using an example from two different kingdoms for each level. |
1 | |
| 5.5.3 | Distinguish between the following phyla of plants, using simple external recognition features: bryophyta, filicinophyta, coniferophyta and angiospermophyta. |
2 | |
| 5.5.4 | Distinguish between the following phyla of animals, using simple external recognition features: porifera, cnidaria, platyhelminthes, annelida, mollusca and arthropoda. |
2 | |
| 5.5.5 | Apply and design a key for a group of up to eight organisms. |
3 | A dichotomous key should be used. |
Topic 6: Human health and physiology
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 6.1.1 | Explain why digestion of large food molecules is essential. |
3 | |
| 6.1.2 | Explain the need for enzymes in digestion. |
3 | The need for increasing the rate of digestion at body temperature should be emphasized. |
| 6.1.3 | State the source, substrate, products and optimum pH conditions for one amylase, one protease and one lipase. |
1 | Any human enzymes can be selected. Details of structure or mechanisms of action are not required. Aim 7: Data logging with pH sensors and lipase, and data logging with colorimeters and amylase can be used. |
| 6.1.4 | Draw and label a diagram of the digestive system. |
1 | The diagram should show the mouth, esophagus, stomach, small intestine, large intestine, anus, liver, pancreas and gall bladder. The diagram should clearly show the interconnections between these structures. |
| 6.1.5 | Outline the function of the stomach, small intestine and large intestine. |
2 | |
| 6.1.6 | Distinguish between absorption and assimilation. |
2 | |
| 6.1.7 | Explain how the structure of the villus is related to its role in absorption and transport of the products of digestion. |
3 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 6.2.1 | Draw and label a diagram of the heart showing the four chambers, associated blood vessels, valves and the route of blood through the heart. |
1 | Care should be taken to show the relative wall thickness of the four chambers. Neither the coronary vessels nor the conductive system are required. |
| 6.2.2 | State that the coronary arteries supply heart muscle with oxygen and nutrients. |
1 | |
| 6.2.3 | Explain the action of the heart in terms of collecting blood, pumping blood, and opening and closing of valves. |
3 | A basic understanding is required, limited to the collection of blood by the atria, which is then pumped out by the ventricles into the arteries. The direction of flow is controlled by atrio-ventricular and semilunar valves. |
| 6.2.4 | Outline the control of the heartbeat in terms of myogenic muscle contraction, the role of the pacemaker, nerves, the medulla of the brain and epinephrine (adrenaline). |
2 | Histology of the heart muscle, names of nerves or transmitter substances are not required. Aim 7: Simulation and data logging involving heart rate monitors, or data logging involving an EKG sensor to measure electrical signals produced during muscle contractions, can be used. |
| 6.2.5 | Explain the relationship between the structure and function of arteries, capillaries and veins. |
3 | |
| 6.2.6 | State that blood is composed of plasma, erythrocytes, leucocytes (phagocytes and lymphocytes) and platelets. |
1 | |
| 6.2.7 | State that the following are transported by the blood: nutrients, oxygen, carbon dioxide, hormones, antibodies, urea and heat. |
1 | No chemical details are required. |
6.3 Defence against infectious disease
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 6.3.1 | Define pathogen. | 1 | Pathogen: an organism or virus that causes a disease. |
| 6.3.2 | Explain why antibiotics are effective against bacteria but not against viruses. |
3 | Antibiotics block specific metabolic pathways found in bacteria. Viruses reproduce using the host cell’s metabolic pathways, which are not affected by antibiotics. Aim 8: The great benefits to people throughout the world in the control of bacterial diseases using antibiotics should be stressed. Examples of diseases that often proved fatal before the advent of antibiotics could be named. |
| 6.3.3 | Outline the role of skin and mucous membranes in defence against pathogens. |
2 | A diagram of the skin is not required. |
| 6.3.4 | Outline how phagocytic leucocytes ingest pathogens in the blood and in body tissues. |
2 | Details of the subdivisions and classifications of phagocytes are not required. |
| 6.3.5 | Distinguish between antigens and antibodies. |
2 | |
| 6.3.6 | Explain antibody production. | 3 | Many different types of lymphocyte exist. Each type recognizes one specific antigen and responds by dividing to form a clone. This clone then secretes a specific antibody against the antigen. No other details are required. |
| 6.3.7 | Outline the effects of HIV on the immune system. |
2 | The effects of HIV should be limited to a reduction in the number of active lymphocytes and a loss of the ability to produce antibodies. |
| 6.3.8 | Discuss the cause, transmission and social implications of AIDS. |
3 | Aim 8: The social implications of AIDS are well known. Cases of AIDS are not evenly distributed in the world, and consideration could be given to the severe problems in southern Africa. Cultural and economic reasons for differences in the prevalence of AIDS could be considered. The moral obligation of those with the technology and the wealth to help others lacking these things could be discussed. TOK: The different methods of transmission of HIV each carry their own risk. The extent to which individuals in different societies can minimize or eliminate each of these risks could be considered. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 6.4.1 | Distinguish between ventilation, gas exchange and cell respiration. |
2 | |
| 6.4.2 | Explain the need for a ventilation system. |
3 | A ventilation system is needed to maintain high concentration gradients in the alveoli. |
| 6.4.3 | Describe the features of alveoli that adapt them to gas exchange. |
2 | This should include a large total surface area, a wall consisting of a single layer of flattened cells, a film of moisture and a dense network of capillaries. |
| 6.4.4 | Draw and label a diagram of the ventilation system, including trachea, lungs, bronchi, bronchioles and alveoli. |
1 | Students should draw the alveoli in an inset diagram at a higher magnification. |
| 6.4.5 | Explain the mechanism of ventilation of the lungs in terms of volume and pressure changes caused by the internal and external intercostal muscles, the diaphragm and abdominal muscles. |
3 | Aim 7: Data logging involving spirometers or ventilation rate monitors is possible here. |
6.5 Nerves, hormones and homeostasis
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 6.5.1 | State that the nervous system consists of the central nervous system (CNS) and peripheral nerves, and is composed of cells called neurons that can carry rapid electrical impulses. |
1 | No other structural or functional divisions of the nervous system are required. |
| 6.5.2 | Draw and label a diagram of the structure of a motor neuron. |
1 | Include dendrites, cell body with nucleus, axon, myelin sheath, nodes of Ranvier and motor end plates. |
| 6.5.3 | State that nerve impulses are conducted from receptors to the CNS by sensory neurons, within the CNS by relay neurons, and from the CNS to effectors by motor neurons. |
1 | |
| 6.5.4 | Define resting potential and action potential (depolarization and repolarization). |
1 | |
| 6.5.5 | Explain how a nerve impulse passes along a non-myelinated neuron. |
3 | Include the movement of Na+ and K+ ions to create a resting potential and an action potential. |
| 6.5.6 | Explain the principles of synaptic transmission. |
3 | Include the release, diffusion and binding of the neurotransmitter, initiation of an action potential in the post-synaptic membrane, and subsequent removal of the neurotransmitter. Aim 7: Data logging can be used to measure changes in conductivity in distilled water as Na+ and K+ diffuse out of salt–agar cubes or dialysing tubing. |
| 6.5.7 | State that the endocrine system consists of glands that release hormones that are transported in the blood. |
1 | The nature and action of hormones or direct comparisons between nerve and endocrine systems are not required. |
| 6.5.8 | State that homeostasis involves maintaining the internal environment between limits, including blood pH, carbon dioxide concentration, blood glucose concentration, body temperature and water balance. |
1 | The internal environment consists of blood and tissue fluid. |
| 6.5.9 | Explain that homeostasis involves monitoring levels of variables and correcting changes in levels by negative feedback mechanisms. |
3 | |
| 6.5.10 | Explain the control of body temperature, including the transfer of heat in blood, and the roles of the hypothalamus, sweat glands, skin arterioles and shivering. |
3 | Aim 7: Data logging using a surface temperature sensor to investigate the warming by nasal passages could be carried out here. |
| 6.5.11 | Explain the control of blood glucose concentration, including the roles of glucagon, insulin and α and β cells in the pancreatic islets. |
3 | The effects of adrenaline are not required here. |
| 6.5.12 | Distinguish between type I and type II diabetes. |
2 | Aim 8: Diabetes is having an increasing effect on human societies around the world, including personal suffering due to ill health from the diabetes directly but also from side-effects such as kidney failure. There are economic consequences relating to the health-care costs of treating diabetics. TOK: The causes of the variation in rates of type II diabetes in different human populations could be analysed. Rates can be particularly high when individuals consume a diet very different to the traditional one of their ancestors, for example, when having migrated to a new country. There are genetic differences in our capacity to cope with high levels of refined sugar and fat in the diet. Humans also vary considerably in how prone they are to become obese. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 6.6.1 | Draw and label diagrams of the adult male and female reproductive systems. |
1 | The relative positions of the organs is important. Do not include any histological details, but include the bladder and urethra. |
| 6.6.2 | Outline the role of hormones in the menstrual cycle, including FSH (follicle stimulating hormone), LH (luteinizing hormone), estrogen and progesterone. |
2 | |
| 6.6.3 | Annotate a graph showing hormone levels in the menstrual cycle, illustrating the relationship between changes in hormone levels and ovulation, menstruation and thickening of the endometrium. |
2 | |
| 6.6.4 | List three roles of testosterone in males. |
1 | Limit this to pre-natal development of male genitalia, development of secondary sexual characteristics and maintenance of sex drive. |
| 6.6.5 | Outline the process of in vitro fertilization (IVF). |
2 | |
| 6.6.6 | Discuss the ethical issues associated with IVF. |
3 | Aim 8: There is great variation between human societies around the world in the views held on IVF. This is the result of cultural and religious diversity. There is little evidence to suggest that children born as a result of standard IVF protocols are different in any way from children conceived naturally. It is important that there is parity of esteem for all children, however they were conceived. TOK: There are potential risks in the drug treatments that the woman is given, and there are concerns about the artificial selection of sperm and the injection of them into the eggs that occurs with some IVF protocols. The natural selection of sperm with consequent elimination of unhealthy ones is bypassed, and there is evidence that there are higher rates of abnormality in the offspring as a result. |
Syllabus details—AHL
Topic 7: Nucleic acids and proteins
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 7.1.1 | Describe the structure of DNA, including the antiparallel strands, 3’–5’ linkages and hydrogen bonding between purines and pyrimidines. |
2 | Major and minor grooves, direction of the “twist”, alternative B and Z forms, and details of the dimensions are not required. |
| 7.1.2 | Outline the structure of nucleosomes. | 2 | Limit this to the fact that a nucleosome consists of DNA wrapped around eight histone proteins and held together by another histone protein. |
| 7.1.3 | State that nucleosomes help to supercoil chromosomes and help to regulate transcription. |
1 | |
| 7.1.4 | Distinguish between unique or single-copy genes and highly repetitive sequences in nuclear DNA. |
2 | Highly repetitive sequences (satellite DNA) constitutes 5–45% of the genome. The sequences are typically between 5 and 300 base pairs per repeat, and may be duplicated as many as 105 times per genome. TOK: Highly repetitive sequences were once classified as “junk DNA”, showing a degree of confidence that it had no role. This addresses the question: To what extent do the labels and categories used in the pursuit of knowledge affect the knowledge we obtain? |
| 7.1.5 | State that eukaryotic genes can contain exons and introns. |
1 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 7.2.1 | State that DNA replication occurs in a 5’ --> 3’ direction. |
1 | The 5’ end of the free DNA nucleotide is added to the 3’ end of the chain of nucleotides that is already synthesized. |
| 7.2.2 | Explain the process of DNA replication in prokaryotes, including the role of enzymes (helicase, DNA polymerase, RNA primase and DNA ligase), Okazaki fragments and deoxynucleoside triphosphates. |
3 | The explanation of Okazaki fragments in relation to the direction of DNA polymerase III action is required. DNA polymerase III adds nucleotides in the 5’ --> 3’ direction. DNA polymerase I excises the RNA primers and replaces them with DNA. |
| 7.2.3 | State that DNA replication is initiated at many points in eukaryotic chromosomes. |
1 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 7.3.1 | State that transcription is carried out in a 5’ --> 3’ direction. |
1 | The 5’ end of the free RNA nucleotide is added to the 3’ end of the RNA molecule that is already synthesized. |
| 7.3.2 | Distinguish between the sense and antisense strands of DNA. |
2 | The sense strand (coding strand) has the same base sequence as mRNA with uracil instead of thymine. The antisense (template) strand is transcribed. |
| 7.3.3 | Explain the process of transcription in prokaryotes, including the role of the promoter region, RNA polymerase, nucleoside triphosphates and the terminator. |
3 | The following details are not required: there is more than one type of RNA polymerase; features of the promoter region; the need for transcription protein factors for RNA polymerase binding; TATA boxes (and other repetitive sequences); and the exact sequence of the bases that act as terminators. |
| 7.3.4 | State that eukaryotic RNA needs the
|
1 | Further details of the process of post-transcriptional modification of RNA are not required. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 7.4.1 | Explain that each tRNA molecule is recognized by a tRNA-activating enzyme that binds a specific amino acid to the tRNA, using ATP for energy. |
3 | Each amino acid has a specific tRNA-activating enzyme (the name aminoacyl-tRNA synthetase is not required). The shape of tRNA and CCA at the 3’ end should be included. |
| 7.4.2 | Outline the structure of ribosomes, including protein and RNA composition, large and small subunits, three tRNA binding sites and mRNA binding sites. |
2 | |
| 7.4.3 | State that translation consists of initiation, elongation, translocation and termination. |
1 | |
| 7.4.4 | State that translation occurs in a 5’ --> 3’ direction. |
1 | During translation, the ribosome moves along the mRNA towards the 3’ end. The start codon is nearer to the 5’ end. |
| 7.4.5 | Draw and label a diagram showing the structure of a peptide bond between two amino acids. |
1 | |
| 7.4.6 | Explain the process of translation, including ribosomes, polysomes, start codons and stop codons. |
3 | Use of methionine for initiation, details of the T factor and recall of actual stop codons are not required. |
| 7.4.7 | State that free ribosomes synthesize proteins for use primarily within the cell, and that bound ribosomes synthesize proteins primarily for secretion or for lysosomes. |
1 |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 7.5.1 | Explain the four levels of protein structure, indicating the significance of each level. |
3 | Quaternary structure may involve the binding of a prosthetic group to form a conjugated protein. Aim 7: Simulation exercises showing threedimensional molecular models of proteins are available. |
| 7.5.2 | Outline the difference between fibrous and globular proteins, with reference to two examples of each protein type. |
2 | |
| 7.5.3 | Explain the significance of polar and non-polar amino acids. |
3 | Limit this to controlling the position of proteins in membranes, creating hydrophilic channels through membranes, and the specificity of active sites in enzymes. |
| 7.5.4 | State four functions of proteins, giving a named example of each. |
1 | Membrane proteins should not be included. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 7.6.1 | State that metabolic pathways consist of chains and cycles of enzymecatalysed reactions. |
1 | |
| 7.6.2 | Describe the induced-fit model. | 2 | This is an extension of the lock-and-key model. Its importance in accounting for the ability of some enzymes to bind to several substrates should be mentioned. TOK: Scientific truths are often pragmatic. We accept them as true because they give us predictive power, that is, they work. The German scientist Emil Fischer introduced the lock-and-key model for enzymes and their substrates in 1890. It was not until 1958 that Daniel Koshland in the United States suggested that the binding of the substrate to the active site caused a conformational change, hence the induced-fit model. This is an example of one model or theory, accepted for many years, being superseded by another that offers a fuller explanation of a process. |
| 7.6.3 | Explain that enzymes lower the activation energy of the chemical reactions that they catalyse. |
3 | Only exothermic reactions should be considered. Specific energy values do not need to be recalled. |
| 7.6.4 | Explain the difference between competitive and non-competitive inhibition, with reference to one example of each. |
3 | Competitive inhibition is the situation when an inhibiting molecule that is structurally similar to the substrate molecule binds to the active site, preventing substrate binding. Limit non-competitive inhibition to an inhibitor binding to an enzyme (not to its active site) that causes a conformational change in its active site, resulting in a decrease in activity. Reversible inhibition, as compared to irreversible inhibition, is not required. |
| 7.6.5 | Explain the control of metabolic pathways by end-product inhibition, including the role of allosteric sites. |
3 |
Topic 8: Cell respiration and photosynthesis
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 8.1.1 | State that oxidation involves the loss of electrons from an element, whereas reduction involves a gain of electrons; and that oxidation frequently involves gaining oxygen or losing hydrogen, whereas reduction frequently involves losing oxygen or gaining hydrogen. |
1 | |
| 8.1.2 | Outline the process of glycolysis, including phosphorylation, lysis, oxidation and ATP formation. |
2 | In the cytoplasm, one hexose sugar is converted into two three-carbon atom compounds (pyruvate) with a net gain of two ATP and two NADH + H+. |
| 8.1.3 | Draw and label a diagram showing the structure of a mitochondrion as seen in electron micrographs. |
1 | |
| 8.1.4 | Explain aerobic respiration, including the link reaction, the Krebs cycle, the role of NADH + H+, the electron transport chain and the role of oxygen. |
3 | In aerobic respiration (in mitochondria in |
| 8.1.5 | Explain oxidative phosphorylation in terms of chemiosmosis. |
3 | |
| 8.1.6 | Explain the relationship between the structure of the mitochondrion and its function. |
3 | Limit this to cristae forming a large surface area for the electron transport chain, the small space between inner and outer membranes for accumulation of protons, and the fluid matrix containing enzymes of the Krebs cycle. |
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 8.2.1 | Draw and label a diagram showing the structure of a chloroplast as seen in electron micrographs. |
1 | |
| 8.2.2 | State that photosynthesis consists of light-dependent and lightindependent reactions. |
1 | These should not be called “light” and “dark” reactions. |
| 8.2.3 | Explain the light-dependent reactions. |
3 | Include the photoactivation of photosystem II, photolysis of water, electron transport, cyclic and non-cyclic photophosphorylation, photoactivation of photosystem I, and reduction of NADP+. |
| 8.2.4 | Explain photophosphorylation in terms of chemiosmosis. |
3 | |
| 8.2.5 | Explain the light-independent reactions. |
3 | Include the roles of ribulose bisphosphate (RuBP) carboxylase, reduction of glycerate 3-phosphate (GP) to triose phosphate (TP), NADPH + H+, ATP, regeneration of RuBP, and subsequent synthesis of more complex carbohydrates. TOK: The lollipop apparatus used to work out the biochemical details of the Calvin cycle shows considerable creativity. To what extent is the creation of an elegant protocol similar to the creation of a work of art? |
| 8.2.6 | Explain the relationship between the structure of the chloroplast and its function. |
3 | Limit this to the large surface area of thylakoids for light absorption, the small space inside thylakoids for accumulation of protons, and the fluid stroma for the enzymes of the Calvin cycle. |
| 8.2.7 | Explain the relationship between the action spectrum and the absorption spectrum of photosynthetic pigments in green plants. |
3 | A separate spectrum for each pigment (chlorophyll a, chlorophyll b, and so on) is not required. |
| 8.2.8 | Explain the concept of limiting factors in photosynthesis, with reference to light intensity, temperature and concentration of carbon dioxide. |
3 | TOK: This is an opportunity to discuss the need for very carefully controlled experiments. If we want to investigate the effect of one factor, all other factors that could have an influence must be controlled. In photosynthesis, the situation is relatively simple, and we can ensure that factors other than the one we are investigating are maintained at a constant and optimal level. In other areas, there are much greater problems. In the many investigations of human health, there are almost always complicating factors. For example, vegetarians have a longer life expectancy than meat eaters. We would be wrong to conclude that eating meat lowers life expectancy unless we could show that the only difference between the vegetarians and the meat eaters in our trial was the meat eating. |
9.1 Plant structure and growth
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 9.1.1 | Draw and label plan diagrams to show the distribution of tissues in the stem and leaf of a dicotyledonous plant. |
1 | Either sunflower, bean or another dicotyledonous plant with similar tissue distribution should be used. Note that plan diagrams show distribution of tissues (for example, xylem, phloem) and do not show individual cells. They are sometimes called “lowpower” diagrams. |
| 9.1.2 | Outline three differences between the structures of dicotyledonous and monocotyledonous plants. |
2 | Teachers should emphasize three differences between monocotyledonous and dicotyledonous plants (examples include: parallel versus net-like venation in leaves, distribution of vascular tissue in stems, number of cotyledons, floral organs in multiples of 3 in monocotyledonous versus 4 or 5 in dicotyledonous, fibrous adventitious roots in monocotyledonous versus tap root with lateral branches in dicotyledonous). |
| 9.1.3 | Explain the relationship between the distribution of tissues in the leaf and the functions of these tissues. |
3 | This should be restricted to dicotyledonous plants. The functions should include: absorption of light, gas exchange, support, water conservation, and the transport of water and products of photosynthesis. |
| 9.1.4 | Identify modifications of roots, stems and leaves for different functions: bulbs, stem tubers, storage roots and tendrils. |
2 | |
| 9.1.5 | State that dicotyledonous plants have apical and lateral meristems. |
1 | Apical meristems are sometimes referred to as primary meristems, and lateral meristems as cambium. Meristems generate new cells for growth of the plant. |
| 9.1.6 | Compare growth due to apical and lateral meristems in dicotyledonous plants. |
3 | |
| 9.1.7 | Explain the role of auxin in phototropism as an example of the control of plant growth. |
3 |
9.2 Transport in angiospermophytes
| Assessment statement | Obj | Teacher’s notes | |
|---|---|---|---|
| 9.2.1 | Outline how the root system provides a large surface area for mineral ion and water uptake by means of branching and root hairs. |
2 | |
| 9.2.2 | List ways in which mineral ions in the soil move to the root. |
1 | There are three processes: diffusion of mineral ions, fungal hyphae (mutualism), and mass flow of water in the soil carrying ions. |
| 9.2.3 | Explain the process of mineral ion absorption from the soil into roots by active transport. |
3 | |
| 9.2.4 | State that terrestrial plants support themselves by means of thickened cellulose, cell turgor and lignified xylem. |
1 | |
| 9.2.5 | Define transpiration. | 1 | Transpiration is the loss of water vapour from the leaves and stems of plants. Aim 7: Data logging with pressure sensors, humidity, light or |