: A Level Past Papers

Biology A Level Example Paper 1

Biology A Level Example Paper 1

  1. Cholera is a form of bacteria.
    1. Give the name of two structures which are found in an epithelial cell located in the small intestine but not in a cholera bacterium.
    2. It is possible to see cholera bacteria by using a transmission electron microscope (TEM) or a scanning electron microscope (SEM).
      1. Give one benefit of using TEM is rather than a SEM.
      2. Give one benefit of using a SEM is rather than a TEM.
      1. Bacteria is a pathogen. Name another type of pathogen.
      2. Provide two ways in which a pathogen might cause disease within the human body.
  1. Below is a diagram of a haemoglobin molecule.

SIMPLE DIAGRAM OF QUATERNARY STRUCTURE OF A HAEMOGLOBIN

    1. What evidence is shown in the diagram that haemoglobin is a quaternary structure?
      1. A gene codes for a -polypeptide chain. There are 321 bases in this gene that code for amino acids. How many amino acids are in the -polypeptide chain?
      2. There are more than 321 bases in the DNA of the -polypeptide chain. Provide two reasons why there are more than 321 bases.
    2. Haemoglobin can differ in chemical structure from one organism to another. Explain how.
    3. The dissociation curve for a mountain goat is shifted more to the left than the dissociation curve for a goat living at sea level. Explain how that makes mountain goats better at living high in the mountains than normal goats.
      1. What is meant by a dominant allele?
      2. What is meant by co-dominant alleles?
    1. Certain cardiovascular diseases can be inherited by children from their parents. One example is atherosclerosis. This is the narrowing of the arteries due to a build up of cholesterol and plaque formation. This then leads to coronary heart disease.
      1. Name two other risk factors associated with coronary heart disease.
      2. Atherosclerosis can lead to an aneurysm. Describe what an aneurysm is.
  1. Residual food intake (RFI) is the difference between the actual amount of food an animal consumes and how much food it is expected it will eat based on it’s size and growth rate.
      1. Pigs are selectively bred with a low RFI. Why are pigs with a low RFI advantageous to farmers?
      2. Low values when RFI is calculated are negative. Explain why.
    1. Scientists want to compare the RFI in pigs. They control two factors in order to do this: the type of food eaten and the environmental temperature. Why do these factors need to be under control?
      1. Type of food
      2. Environmental temperature
    2. Some people are against selective breeding. Give one advantage and one disadvantage of selective breeding.
    1. In natural ecosystems succession is a natural occurrence. Explain how it occurs.
    2. Ecosystems which are managed are more prone to pests. These can be managed using biological agents. Outline the advantages and disadvantages of using biological agents in this way.
    3. A change in an ecosystem can lead to speciation. Explain how speciation can occur.

ANSWERS

    1. Answers include:
        • nucleus, nuclear envelope, nuclear membrane or nucleolus
        • mitochondrion
        • endoplasmic reticulum (ER) smooth or rough
        • lysosome
        • microvillus
        • Golgi
        • non-circular DNA or linear DNA
        • larger (80S) ribosomes
      1. Answers include:
        • higher resolution or higher magnification
        • allows internal structures within the cells to be seen

Answers not accepted:

      • longer wavelength
      • can be used for living specimens
      • provides a clearer image
    1. Answers include:
      • thin sections don’t need to be prepared or can use thicker specimens
      • provides an image of the surface of a specimen
      • provides a 3D image

Answers not accepted:

      • can be used on living specimens
    1. Answers include:
      • virus
      • protozoan
      • fungus
    2. Answers include:
      • produces toxins
      • damages cells or tissues
    1. Correct: it contains more than one polypeptide chain

Incorrect: any mention to haem groups or any other kind of group

    1. 107
    2. Answers include:
      • stop or start sequences
      • there’s a non-coding strand
      • introns or junk DNA
      • addition of base by mutation

Answers not accepted:

        • some bases are repeated
    1. Correct: they have a different primary structure/amino acids/number of polypeptide chains

Incorrect: any mention of DNA

    1. Don’t forget to relate the answer to mountain goats. Points to include:
        • there’s a low partial pressure of oxygen in the lungs
        • a mountain goat can load more oxygen or a mountain goat’s haemoglobin is saturated at a low partial pressure of oxygen
        • a mountain goat’s haemoglobin has a higher affinity for oxygen
      1. It’s only expressed in the phenotype when homogenous alleles are present.
      2. Both alleles are expressed in the phenotype.
      1. Answers include:
        • blood cholesterol
        • diet
        • tobacco smoking
        • high blood pressure
      2. This is where the artery wall is weakened so much that the blood pressure causes it to deform or even burst.

    1. Answers include:
        • reduced cost or cost effective
        • less feed required
        • less land used
        • more growth rate with the same amount of food
    1. The amount of food taken is less than was expected.
      1. You need to provide a food compound that shows that these factors are affected by the food type e.g. The food may vary in the amount of fat/protein/fibre/carbohydrate/minerals/vitamins it contains and this could affect the energy value/absorption/growth of the animal/digestibility.
      2. Answers include:
        • will affect the amount of heat lost or gained
        • will affect respiration rate
        • will affect the metabolic rate
        • the animal needs to regulate its body temperature
        • more food/energy can then be used for growth
    2. Advantages include:
        • can produce fitter/stronger animals
        • can produce a higher yield of produce
        • can create animals better suited to their environment
        • can get rid of hereditary diseases

Disadvantages include:

        • inherent diseases can be amplified
        • variety is decreased
    1. Your answer should include:
      • colonisation by a pioneer species
      • a change in the environment occurs due to the organisms present
      • this change allows other species to colonise the area
      • this changes the biodiversity
      • stability increases and environment becomes less hostile
      • the climax community is reached

Advantages include:

      • it’s specific to one pesticides
      • only requires one application
      • it maintains a low population
      • pests don’t develop resistance to it
      • it doesn’t lead to bioaccumulation
      • it can be used on organic farms

Disadvantages include:

      • it doesn’t get rid of the pest completely
      • it’s possible that it will become a pest itself
      • it’s slow acting

No marks for references to:

      • leaching
      • eutrophication
      • cost
    1. Your answer should include:
      • geographical isolation
      • separate gene pools occur which means they can’t interbreed
      • variation can occur due to mutation
      • different environments therefore different selection pressures to contend with
      • differential reproductive success
      • this leads to a change in allele frequency
      • happens over a long period of time