: A Level Past Papers

Biology A Level Example Paper 2

Biology A Level Example Paper 2

  1. Pathogens are able to cause disease within a host.
    1. Provide two ways in which a pathogen can harm the body of their host.
    2. One way to protect the body against disease is through vaccination. Describe what a vaccine is.
    3. Scientists conducted a experiments on a vaccine, Vaccine A, on three groups of adult volunteers. They wanted to measure the increase of T memory cells if they used a booster vaccine after Vaccine A. They used three groups:

Group 1: injected with Vaccine A

Group 2: injected within the booster shot

Group 3: injected with Vaccine A followed 2 weeks later by the booster shot

    1. When selecting the adult volunteers suggest two factors the scientists should have considered.
    2. Group 3 had the largest increase of memory cells. What does this show about Vaccine A and the booster shot?
  1. Cholera is a rod-shaped bacteria. It has a single polar flagellum.
    1. Flagella is one structure that differs from a eukaryotic cell. Name two other features that are different between a prokaryotic and a eukaryotic cell.
    2. Cholera is a main cause of diarrhoea in developing countries. It’s usually transmitted through contaminated drinking water. A test has been developed which uses monoclonal antibodies to find out whether a person is infected with cholera. Monoclonal antibodies used against Cholera bacteria are attached to a test plate. A sample from the person is then added to the plate and any Cholera bacteria present will bind to the antibody antigens.
      1. Why is it important that monoclonal antibodies are used?
      2. Why does the Cholera bacteria bind to the antigen of the antibody?
      3. are is to treat cholera in developing countries. are made sugar and salt solutions. Explain why it is important that the solution contains both sugar and salt.
    1. Fish use gills to absorb oxygen from the water. Explain how fish gills are adapted to gaseous exchange.
    2. A number of fish live in the Antarctic, like the Antarctic cod. There are also a lot of creatures that live on the seabed, like the sea cucumber. The concentration of oxygen is higher in the surface water than that close to the seabed.
      1. Sketch the dissociation curve for the Antarctic cod and the sea cucumber.
      2. Explain your dissociation curves.
  1. Below is the sequence for part of a DNA molecule.

A G C A T T G G C A T C

T C G T A A C C G T A G

    1. What is the maximum number of amino acids this piece of DNA could code for?
    2. Scientists calculated the percentage of different bases in the DNA from a species of bacterium. They found that 14% of the bases were guanine.
      1. What percentage of bases in this bacterium was cytosine?
      2. What percentage of bases in this bacterium was adenine?
    3. Another species of bacterium was analysed. This bacterium contained 29% guanine bases. Explain the difference in the percentage of guanine bases between the two species.
    1. Describe and explain how enzymes of the digestive system completely breakdown starch.
    2. Describe what processes are involved in the absorption of the starch digestion products.

ANSWERS

    1. Correct:
        • Damage/destroy the cells/tissues
        • Produce toxins
    2. Correct:
        • A vaccine contains the antigens of the pathogen/virus/bacteria/micro-organism or a weakened form of it.
        • This then stimulates the production of antibodies/plasma cells/memory cells in the body.

Incorrect: You can’t simply say ‘immune response': you need to explain it further.

      1. Correct:
        • Age
        • Sex
        • That they’re healthy and not on any medication
        • Ethnicity
        • That they weren’t previously vaccinated or infected with TB

Incorrect: Sample size

    1. They contain the same antigens.
    1. The word ‘features‘ is used so you don’t have to stick to structural differences only.

Correct:

        • prokaryotic cells don’t have a nucleus
        • prokaryotic cells lack organelles
        • prokaryotic cells are not found in humans and eukaryotic cells are
        • prokaryotic cells are always unicellular and eukaryotic cells are usually multicellular
        • prokaryotic cells reproduce/divide by binary fission and eukaryotic cells divide by mitosis and meiosis
      1. Correct:
        • They all have the same shape
        • They only bind to a specific antigen
      2. Correct: It has a complimentary shape due to its specific tertiary structure/variable region

Incorrect: You can’t just say binds/fits unless you qualify this statement.

    1. For each correct example you give you’ll get one mark.
        • The lamellae/filaments provide a large surface area.
        • The water and blood are separated only by thin epithelium.
        • The water and blood are flowing countercurrently so a concentration gradient is maintained.
        • The water next to the blood is always at a lower concentration of oxygen.
        • The circulation replaces blood which is saturated with oxygen.
        • Ventilation replaces water.
      1. Make sure that the sea cucumber curve is higher and steeper than that of the Antarctic cod.
      2. There’s not as much oxygen near the seabed. The haemoglobin of the sea cucumber has a higher affinity for oxygen at a low partial pressure of oxygen. (You could also use the opposite explanation for the Antarctic cod).
    1. 4
      1. 14
      2. 36
    2. Correct:
        • Different proteins
        • Different genes
        • Difference base sequences
  1. This is a long answer question. Make sure you check the marks awarded to get an idea of how many points you need to make.
    1. Make sure you cover all of the following:
      1. Amylase
      2. Starch to maltose
      3. Malatse
      4. Maltase to glucose
      5. Hydrolysis of the glycosidic bonds
    2. Make sure you cover all of the following:
      1. Glucose moves into the epithelial cell with sodium via carrier/channel proteins.
      2. Sodium is removed from the epithelial cells by active transport/sodium-potassium pumps into the blood.
      3. This maintains: a low concentration of sodium in the epithelial cell/a sodium concentration gradient between the lumen and the epithelial cell.
      4. Glucose moves into the blood by facilitated diffusion.