Question
a. Sketch the complementary strand to complete the section of a DNA diagram.
[3]
▶️Answer/Explanation
Markscheme
a. correct base sequence: T, G, A;
b. strand drawn anti-parallel;
c. correct shapes used;
Award [2 max] if bonds are not from the correct carbon or if the nucleotides are not joined.
change in genetic makeup/DNA/nucleotide/base sequence
a. mutations cause variation among organisms of same species/population;
b. some variations/mutations make individual more suited to its environment/way of life;
c. individuals that are better adapted survive and produce offspring;
d. individuals pass on genetic characteristics/mutation/variation to offspring;
e. natural selection increases frequency of characteristics/alleles that make individuals better adapted;
Question
Tuberculosis (TB) is an infectious disease caused by the bacterium Mycobacterium tuberculosis.
a. Outline the structures in M. tuberculosis that are not present in a human cell. [3]
b. Explain the production of antibodies when a patient is infected with the TB bacterium. [7]
c. Describe the risk to the human population of indiscriminate use of antibiotics.[5]
▶️Answer/Explanation
Markscheme
a. cell wall ✔
b. pili/flagella ✔
c. 70S ribosomes ✔
d. nucleoid / circular DNA
OR
naked DNA ✔
e. plasmids ✔
As candidates do not need to know the structure of Mycobacterium tuberculosis, all prokaryotic structures are accepted.
Ignore references to membrane bound organelles.
a. phagocytes/lymphocytes are white blood cells ✔
b. TB bacterium has a specific antigen ✔
c. this antigen is recognised by white blood cells ✔
d. a clone of lymphocytes/plasma cells/B cells are produced ✔
e. antibodies are produced by lymphocytes ✔
f. each lymphocyte produces just one type of antibody ✔
g. (this is) specific immunity ✔
h. (part of the) antibody/immunoglobulin binds to the antigen / specific antibody binds to the specific antigen ✔
i. antibodies are proteins/immunoglobulins ✔
j. (some) plasma cells become memory cells ✔
k. memory cells reproduce quickly ✔
l. memory cells prevent infection in the future ✔
Allow annotated diagrams to explain the process.
a. antibiotics block bacterial processes ✔
b. example of bacterial process ✔ e.g. cell wall formation
c. variations exist naturally in a population / some are naturally resistant to the antibiotic ✔
d. bacteria that are not resistant to this antibiotic will die / only resistant will survive (when antibiotic given) ✔
e. this characteristic could be passed to next generation ✔
f. (natural selection) leads to changes in the proportions/frequency in the population ✔
g. human population will be exposed to antibiotic resistant bacteria and will not have antibiotic to kill them ✔
h. (antibiotic resistant bacteria) may pass resistance to other bacteria species/types by means of plasmids (so other bacteria species turn resistant too) ✔