Paper 1 mistakes

What is a monoclonal antibody? (1)

an antibody produced from identical B cells/cloned plasma cells

Describe the pathway taken by an oxygen molecule from the atmosphere to the respiring tissues of an insect (4)

• oxygen enters through spiracles

• down trachea

• to tracheoles

• diffuses into respiring tissues

• down conc grad

Figure 4 shows the R group for the amino acid tyrosine.

Draw the amino acid tyrosine (3)

Suggest why clonal cuttings of a plant would be used for an experiment (2)

• control variable

• reduce impact of genetic variation

Explain what is meant by herd immunity and explain the advantages of it (5)

• herd immunity = majority of population vaccinated

• prevents transmission of pathogen in community

• reduces infection rate in population

• can lead to eradication of disease

• protects vulnerable populations

• prevents future pandemics

Asthma affects bronchioles and reduces flow of air in and out of the lungs. Fibrosis does not affect bronchioles.

Which group, B or C, was the one containing people with fibrosis of their lungs? Use the information provided and evidence form Figure 2 to explain your answer (3)

1. Group B because they breathe out as quickly as healthy

2. so bronchioles are not affected

3. FVC reduced/total volume breathed out reduced

Explain the results shown in Figure 4

1. Group A - initial uptake slower because by diffusion only

2. Group A - levels off because same concentrations inside cells and outside cells/reached equilibrium

3. Group B - uptake faster because by diffusion and active transport

4. Group B fails to level off because uptake against gradient/no equilibrium to reach

5. Group B - rate slower because few/fewer chloride ions in external solution

Luscinia must be capitalised!!

This test only detects the presence of HIV antibodies. Give two reasons why it cannot be used to find out if a person has AIDS (2)

(to diagnose AIDS, need to look for)

1. AIDS related symptoms

2. number of helper T cells

During replication, the two DNA strands separate and each acts as a template for the production of a new strand. As new DNA strands are produced, nucleotides can only be added in the 5’ to 3’ direction.

Use Figure 6 and your knowledge of enzyme action and DNA replication to explain why new nucleotides can only be added in a 5’ to 3’ direction. (4)

• reference to DNA polymerase

• which is specific

• only complementory with 5’ end

• shapes of 5’ end and 3’ end are different

Describe the mass flow hypothesis for the mechanism of translocation in plants (4)

1. in leaf/source sugars actively transported into phloem

2. by companion cells

3. lowers water potential of sieve cell/tube and water enters by osmosis

4. increase in pressure causes mass movement towards sink/root

5. sugars used in root for respiration for storage

Describe the role of micelles in the absorption of fats into the cells lining the ileum (3)

• Micelles include bile salts and fatty acids; Ignore other correct components of micelles.

• Make the fatty acids (more) soluble in water;

  For 'fatty acids' accept fats / lipids.

• Bring/release/carry fatty acids to cell/lining (of the ileum);

  For ‘fatty acids’ accept fats/lipids.

• Maintain high(er) concentration of fatty acids to cell/lining (of the ileum);

• Fatty acids (absorbed) by diffusion; Reject if absorbed by facilitated diffusion Ignore if micelles themselves are being absorbed. Ignore references to monoglycerides.

Name structure Q in the diagram above and suggest how it is involved in the absorption of lipids (4)

• Golgi (apparatus);

• Modifies / processes triglycerides

• Combines triglycerides with proteins;

• Packaged for release / exocytosis OR

• Forms vesicles;

  Ignore ‘processes and packages’ unqualified 2. Reject synthesises triglycerides 3. Accept ‘forms / are lipoproteins’

Describe the role of a ribosome in the production of a polypeptide. Do not include transcription in your answer (3)

• mRNA binds to ribosome

• idea of two codons/binding sites

• allows tRNA with anticodons to bind/associate

• catalyses formation of peptide bonds between amino acids

• moves along mRNA to next codon

Describe the cohesion-tension theory of water transport in the xylem (5)

• water lost from leaf in transpiration

• lowers water potential of leaf cells

• water pulled up xylem

• continuous column - cohesive due to hydrogen bonds between water molecules

• adhesion of water molecules to xylem

During vaccination, each animal is initially injected with a small volume of venom. Two weeks later, it is injected with a larger volume of venom.

Use your knowledge of the humoral immune response to explain this vaccination program (3)

• B cells specific to the venom reproduce by mitosis

• produce plasma cells and memory cells

• the second dose produces antibodies in higher concentration and quickly

Describe the structure of HIV (4)

• RNA as genetic material

• reverse transcriptase

• capsid

• attachment proteins

• phospholipid envelope

Use the data in Table 3 and your knowledge of the immune response to suggest why HIV controllers do not develop symptoms of AIDS (3)

• all have more T helper cells

• lower viral load to destroy helper T cells

• activation of B cells/cytotoxic T cells/phagocytes

• production of antibodies/ability to kill virus infected cells

• more able to destroy other pathogens

Mammals such as a mouse and a horse are able to maintain a constant body temperature.

Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse (3)

• mouse smaller so larger surface area to volume ratio

• faster heat loss

• respiration releases heat

Describe the biochemical tests you would use to confirm the presence of lipid, non-reducing sugar and amylase in a sample (5)

Lipid

• add ethanol then add water and shake

• milky white emulsion

Non-reducing sugar

• benedicts test and stays blue

• boil with acid then neutralise with alkali

• heat with benedicts and becomes red/orange

Amylase

• add biuret and becomes purple

• add starch, test for reducing sugar/absence of starch