Outline the processes that occur in a cell during interphase, including those

needed to prepare for mitosis.

4 marks

DNA replication

DNA transcription

enzyme/ protein synthesis

biochemical reactions/ example of a biochemical reaction

cell respiration

growth

organelles replicated

Outline the thermal, cohesive and solvent properties of water.

5 marks

water has a high specific heat capacity;

a large amount of heat causes a small increase in temperature;

water has a high latent heat of vaporisation;

a large amount of heat energy is needed to vaporise/evaporate water;

hydrogen bonds between water molecules make them cohesive/stick together;

this gives water a high surface tension / explains how water rises up xylem;

water molecules are polar; this makes water a good solvent;

Describe the significance of water to living organisms.

5 marks

Each feature or property must be related to living organisms in order to receive a

mark.

Features may include:

surface tension - allows some organisms (e.g. insects) to move on water's surface

polarity / capillarity / adhesion - helps plants transport water

(excellent) solvent - capable of dissolving substances for transport in organisms

(excellent) thermal properties (high heat of vaporisation) - excellent coolant

ice floats - lakes / oceans do not freeze, allowing life under the ice

buoyancy - supports organisms

structure - turgor in plant cells / hydrostatic pressure

habitat - place for aquatic organisms to live

Describe the use of carbohydrates and lipids for energy storage in animals.

5 marks

Answers must discuss both carbohydrates and lipids to receive full marks

Carbohydrates

stored as glycogen (in liver)

short-term energy storage

more easily digested than lipids so energy can be released more quickly

Lipids

stored as fat in animals

long-term energy storage

more energy per gram than carbohydrates

lipids are insoluble in water so less osmotic effect

List three functions of lipids.

3 marks

energy storage / source of energy / respiration substrate

(heat) insulation

protection (of internal organs)

waterproofing / cuticle

buoyancy

(structural) component of cell membranes

electrical insulation by myelin sheath

(steroid) hormones

glycolipids acting as receptors

Describe the genetic code.

6 marks

composed of mRNA base triplets called codons

64 different codons

each codes for the addition of an amino acid to a growing polypeptide chain

the genetic code is degenerate

meaning more than one codon can code for a particular amino acid

the genetic code is universal

meaning it is the same in almost all organisms

(AUG is the) start codon

some (nonsense) codons code for the end of translation

Explain briefly the advantages and disadvantages of the universality of the

genetic code to humans.

4 marks

genetic material can be transferred between species

/ between humans

one species could use a useful gene from another species

transgenic crop plants/ livestock can be produced

bacteria/ yeasts can be genetically engineered to make a useful product

viruses can invade cells and take over their genetic apparatus

viruses cause disease

Compare how pyruvate is used in human cells when oxygen is available and when oxygen is not available.

5 marks

aerobic cell respiration if oxygen available and an aerobic if unavailable;

pyruvate enters mitochondria for aerobic respiration; whereas pyruvate stays in the cytoplasm for processing under anaerobic conditions;

pyruvate converted aerobically into carbon dioxide

and water; whereas pyruvate converted anaerobically to lactate

Large ATP yield when oxygen available/from aerobic

cell respiration; no (further) ATP yield without oxygen;

Explain the role of water in photosynthesis.

4 marks

water is a substrate / reactant / raw material / for photosynthesis / equation for photosynthesis

water is a source of electrons to replace those lost by chlorophyll / photosystem II

water is a source of H+ needed to produce NADPH + H

photolysis / splitting / breaking of water

water for non-cyclic photophosphorylation / ATP pro

duction

water is transparent so photosynthesis can take place underwater / light can

penetrate to chloroplasts

Define the terms gene and allele and explain how they differ.

4 marks

gene is a heritable factor / unit of inheritance

gene is composed of DNA

gene controls a specific characteristic / codes for a polypeptide / protein

allele is a form of a gene

alleles of a gene occupy the same gene locus / same position on chromosome

alleles differ (from each other) by one / a small number of bases(s)/ base pair(s)

Describe the consequences of a base substitution mutation with regards to sickle cell anaemia.

7 marks

the sequence of nucleotide bases in DNA codes for the sequence of amino acids in proteins

DNA is transcribed into mRNA, which is translated into amino acids of protein

normal (ß chain) haemoglobin gene / DNA produces normal (ß chain) haemoglobin protein / amino acids

substitution= the replacement of one (or more) nucleotide base with another caused by a copying mistake during DNA replication

As a result of a mutagen / X-rays / chemical / UV radiation / other mutagen mutation in normal (ß chain) haemoglobin gene alters the sequence of nucleotide bases

normal nucleotide sequence = CTC altered to CAC

resulting in altered mRNA (GAG to GUG) during transcription

resulting in altered sequence of amino acids in (ß chain) haemoglobin protein

(glutamic acid to valine) during translation

causing red blood cells to change shape / sickle under low oxygen conditions

causing sickle cells anaemia when two copies of the mutated gene are inherited

producing a sickle cell carrier when one copy of the mutated gene is inherited

sickle cells anaemia reduces oxygen flow to organs, leading to their deterioration

Compare the processes of mitosis and meiosis.

6 marks

Answers must be pairwise comparisons to receive any marks.

Mitosis: one cell division & Meiosis: two divisions 

Mitosis: chromosome number does not change & Meiosis: converts diploid to haploid cells

Mitosis: products genetically identical & Meiosis: products genetically diverse

Mitosis: separation of sister chromatids in anaphase & Meiosis: separation of homologous chromosomes in anaphase I and sister chromatids in anaphase II

Mitosis: no crossing over & Meiosis: crossing over

in prophase I

Mitosis: no formation of tetrads / no synapsis & Meiosis: formation of tetrads /synapsis

Mitosis: produce cells for growth/repair/asexual reproduction & Meiosis: produce sexual cells / gametes for sexual reproduction

Mitosis: two cells produced & Meiosis: four cells produced

Mitosis: daughter cells with both copies of chromosomes/random assortment does not occur & Meiosis: random assortment of maternal/

paternal chromosomes

Mitosis: replication of DNA in interphase & Meiosis replication of DNA in interphase

Mitosis: four phases: prophase, metaphase, anaphase and telophase & Meiosis: same

four phases twice