Recall -

Question 1

Name the blood vessels that carry blood to the heart muscle.

Answer 1

Coronary arteries

Question 2

If most of the mitochondria in a cell are faulty, this prevents many important enzyme-catalysed reactions taking place or slows them down.

Suggest and explain one reason why.

Answer 2

1. Not enough / little ATP produced;

One reason asked for, so list rule applies

Ignore ref. to no ATP produced

2. ATP provides energy for (enzyme) reactions

OR

ATP phosphorylates substrates / enzymes, so making them (more) reactive

Question 3

Mitochondrial diseases are caused by faulty mitochondria. All of a person’s mitochondria are inherited from their mother via the egg cell. An egg cell contains approximately 3 × 105 mitochondria.

One proposed treatment to prevent passing on faulty mitochondria involves

• removing the nucleus from an egg cell donated by a woman with healthy mitochondria
• replacing this nucleus with the contents of the polar body from a woman whose egg cells are affected by mitochondrial disease.

Suggest how this treatment prevents inheritance of mitochondrial diseases.

Answer 3

1. Egg (created) has nucleus / DNA / genes of (affected) woman / mother;
2. It has mostly / many / lots of normal mitochondria (of unaffected woman)

OR

There are few faulty mitochondria;

Question 4

Describe the gross structure of the human gas exchange system and how we breathe in and out.

Answer 4

1. Named structures – trachea, bronchi, bronchioles, alveoli;
2. Above structures named in correct order
3. Breathing in – diaphragm contracts and external intercostal muscles contract;
4. (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric, resulting in air moving in);

For thoracic cavity accept ‘lungs’ or ‘thorax’.

Reference to ‘thoracic cavity’ only required once.

5. Breathing out - Diaphragm relaxes and internal intercostal muscles contract;

Accept diaphragm relaxes and (external) intercostal muscles relax and lung tissue elastic (so recoils).

6. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric, resulting in air moving out);

Question 5

Mucus produced by epithelial cells in the human gas exchange system contains triglycerides and phospholipids.

Compare and contrast the structure and properties of triglycerides and phospholipids.

Answer 5

1. Both contain ester bonds (between glycerol and fatty acid);

All statements must be clearly comparative or linked by the candidate, not inferred from separate statements.

Accept mark points shown on adjacent annotated diagrams.

2. Both contain glycerol;
3. Fatty acids on both may be saturated or unsaturated;
4. Both are insoluble in water;
5. Both contain C, H and O but phospholipids also contain P;

Must relate to element.

6. Triglyceride has three fatty acids and phospholipid has two fatty acids plus phosphate group;
7. Triglycerides are hydrophobic/non-polar and phospholipids have hydrophilic and hydrophobic region;

Accept ‘non-polar’ for hydrophobic and ‘polar’ for hydrophilic.

8. Phospholipids form monolayer (on surface)/micelle/bilayer (in water) but triglycerides don’t;

Question 6

Mucus also contains glycoproteins. One of these glycoproteins is a polypeptide with the sugar, lactose, attached.

Describe how lactose is formed and where in the cell it would be attached to a polypeptide to form a glycoprotein.

Answer 6

1. Glucose and galactose;

Ignore α or β for glucose

2. Joined by condensation (reaction);
3. Joined by glycosidic bond;
4. Added to polypeptide in Golgi (apparatus);;

Question 7

Figure 1 shows all the chromosomes present in one human cell during mitosis. A scientist stained and photographed the chromosomes. In Figure 2, the scientist has arranged the images of these chromosomes in homologous pairs.

(a) Give two pieces of evidence from Figure 1 that this cell was undergoing mitosis. Explain your answers.

Answer 7

1. The (individual) chromosomes are visible because they have condensed;
2. (Each) chromosome is made up of two chromatids because DNA has replicated;

Accept ‘sister chromatids’ for ‘two chromatids’.
.

3. The chromosomes are not arranged in homologous pairs, which they would be if it was meiosis;

Question 8

When preparing the cells for observation the scientist placed them in a solution that had a slightly higher (less negative) water potential than the cytoplasm. This did not cause the cells to burst but moved the chromosomes further apart in order to reduce the overlapping of the chromosomes when observed with an optical microscope.

Suggest how this procedure moved the chromosomes apart

Answer 8

1. Water moves into the cells/cytoplasm by osmosis;

Reject water moving into chromosomes/nucleus.

2. Cell/cytoplasm gets bigger;

Question 9

The dark stain used on the chromosomes binds more to some areas of the chromosomes than others, giving the chromosomes a striped appearance.

Suggest one way the structure of the chromosome could differ along its length to result in the stain binding more in some areas.

Answer 9

Differences in base sequences

OR

Differences in histones/interaction with histones

OR

Differences in condensation/(super)coiling

Question 10

What is a homologous pair of chromosomes?

Answer 10

(Two chromosomes that) carry the same genes;

Question 11

Give two ways in which the arrangement of prokaryotic DNA is different from the arrangement of the human DNA

Answer 11

(Prokaryotic DNA) is

1. Circular (as opposed to linear);
2. Not associated with proteins/histones ;
3. Only one molecule/piece of DNA

OR

present as plasmids;

Question 12

What is a monomer?

Answer 12

(a monomer is a smaller / repeating) unit / molecule from which larger molecules / polymers are made;

Question 13

Lactulose is a disaccharide formed from one molecule of galactose and one molecule of fructose.
Other than both being disaccharides, give one similarity and one difference between the structures of lactulose and lactose.

Answer 13

Similarity
1. Both contain galactose / a glycosidic bond;
Ignore references to hydrolysis and / or condensation
Difference
2. Lactulose contains fructose, whereas lactose contains glucose;

Question 14

Following digestion and absorption of food, the undigested remains are processed to form faeces in the parts of the intestine below the ileum.
The faeces of people with constipation are dry and hard. Constipation can be treated by drinking lactulose. Lactulose is soluble, but is not digested or absorbed in the human intestine.
Use your knowledge of water potential to suggest why lactulose can be used to help people suffering from constipation.

Answer 14

1. (Lactulose) lowers the water potential of faeces / intestine / contents of the intestine;
   Accept Ψ for water potential
2. Water retained / enters (due to osmosis) and softens the faeces;

Question 15

Give two features of DNA and explain how each one is important in the semi-conservative replication of DNA.

Answer 15

1. Weak / easily broken hydrogen bonds between bases allow two strands to separate / unzip;
   may appear in the same feature
2. Two strands, so both can act as templates;
   may appear in the same feature
3. Complementary base pairing allows accurate replication;

Question 16

Describe how you would test a liquid sample for the presence of lipid and how you would recognise a positive result.

Answer 16

1. (Mix / shake sample) with ethanol, then water;
   Sequence is important
2. White / milky (emulsion);

Question 17

Figure 1 shows a hierarchy. Explain how.

Answer 17

1. (It shows) smaller groups within larger groups / larger groups containing smaller groups;
   Accept groups within groups
2. With no overlap (between groups);

Question 18

What is the proteome of a cell?

Answer 18

(The proteome is the full) range of / number of different proteins that a cell is able to produce (at a given time);
OR
(The proteome is the full) range of / number of different proteins the genome / DNA is able to code for;

Question 19

Give two structural differences between a molecule of messenger RNA (mRNA) and a molecule of transfer RNA (tRNA).

Answer 19

1. mRNA does not have hydrogen bonds / base pairing, tRNA does;
   OR
   mRNA is linear / straight chain, tRNA is cloverleaf;
2. mRNA does not have an amino acid binding site, tRNA does;
   Accept mRNA cannot carry an amino acid, tRNA can
3. mRNA has more nucleotides;
   Accept mRNA is longer or converse
4. (Different) mRNAs have different lengths, all tRNAs are similar / same length;
5. mRNA has codons, tRNA has an anticodon;

Question 20

Starting with mRNA in the cytoplasm, describe how translation leads to the production of a polypeptide.
Do not include descriptions of transcription and splicing in your answer.

Answer 20

1. mRNA associates with a ribosome / ribosome attaches to mRNA;
   Idea of association is required
2. Ribosome moves to / finds the start codon / AUG;
3. tRNA brings / carries (appropriate / specific) amino acid;
   Must be explicitly stated and not inferred.
4. Anticodon (on tRNA complementary) to codon (on mRNA);
5. Ribosome moves along to next codon;
   OR
   Ribosome ‘fits’ around two codons / can fit two tRNAs;
6. (Process repeated and) amino acids join by peptide bonds / condensation reaction (to form polypeptide);
   OR
   (Process repeated and) amino acids joined using (energy from) ATP (to form polypeptide);

Question 21

State and explain the property of water that can help to buffer changes in temperature

Answer 21

1. (water has a relatively) high (specific) heat capacity;
   Ignore numbers relating to heat capacity
2. Can gain / lose a lot of heat / energy without changing temperature;
   OR
   Takes a lot of heat / energy to change temperature;

Question 22

Water is used to hydrolyse ATP.

Name the two products of ATP hydrolysis.

Answer 22

Adenosine diphosphate and (inorganic) phosphate

Question 23

Describe the pathway taken by an oxygen molecule from an alveolus to the blood.

Answer 23

1. (Across) alveolar epithelium;

2. Endothelium / epithelium of capillary;

Question 24

Explain how one feature of an alveolus allows efficient gas exchange to occur.

Answer 24

1. (The alveolar epithelium) is one cell thick;
   Reject thin membrane
2. Creating a short diffusion pathway / reduces the diffusion distance;

Question 25

Human breast milk is produced and secreted by gland cells. These gland cells have adaptations that include many mitochondria and many Golgi vesicles. The milk contains a high concentration of protein. Explain the role of these cell adaptations in the production and secretion of breast milk

Answer 25

(Many mitochondria) release energy / ATP for movement of vesicles / synthesis of protein / active transport; (Many Golgi) vesicles transport protein / glycoprotein / milk to cell membrane / out of cell;

Question 26

Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how.

Answer 26

1. Sodium ions actively transported from ileum cell to blood; 2. Maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose); 3. Glucose enters by facilitated diffusion with sodium ions;

Question 27

Water and inorganic ions have important biological functions within cells. (a) Give two properties of water that are important in the cytoplasm of cells. For each property of water, explain its importance in the cytoplasm.

Answer 27

1. Polar molecule; 2. Acts as a (universal) solvent; OR 3. (Universal) solvent; 4. (Metabolic) reactions occur faster in solution; OR 5. Reactive; 6. Takes place in hydrolysis / condensation / named reaction;

Question 28

Other than sodium, name one inorganic ion and give one example of its biological importance in a cell.

Answer 28

Name of ion; | Correct function within cell;

Question 29

Compare and contrast the processes by which water and inorganic ions enter cells.

Answer 29

1. Comparison: both move down concentration gradient; 2. Comparison: both move through (protein) channels in membrane; Accept aquaporins (for water) and ion channels 3. Contrast: ions can move against a concentration gradient by active transport

Question 30

The scientist used the reduction in total leaf area of the experimental plants as an indicator of plant growth. Outline a method by which you could find the area of a plant leaf.

Answer 30

Draw around leaf on graph paper and count squares;

Question 31

DNA and RNA can be found in bacteria. | Give two ways in which the nucleotides in DNA are different from the nucleotides in RNA.

Answer 31

1. DNA contains thymine and RNA contains uracil; | 2. DNA contains deoxyribose and RNA contains ribose.