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.

3.2.1

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

3.3.1

Outline DNA nucleotide structure in terms of sugar (deoxyribose), base and phosphate.

2

Chemical formulas and the purine/pyrimidine subdivision are not required. Simple shapes can be used to represent the component parts. Only the relative positions are required.

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 three-dimensional structure of DNA dependent on the use of data generated by Rosalind Franklin, which was shared without her knowledge or consent?

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 semi-conservative.

1

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.

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.

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

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.