Scientific article questions.
1. Toxoplasma gondii is identified as being a Protozoan. This means it is a eukaryotic organism.
Give three ways in which its cell structure will differ from a prokaryotic organism such as
Mycobacterium tuberculosis.
3 marks
TG has linear DNA, MT has circular/eq DNA;
TG has larger/80s ribosomes, accept converse/MT has 70s ribosomes;
TG has DNA contained in a nucleus, and MT has DNA free in cytoplasm/nucleoid;
TG has membrane bound organelles/any named membrane bound organelle;
MT has mesosome/plasmid/ slime capsule/pili which are absent in TG.
2. By locating in the brain of its host, Toxoplasma gondii is able to evade the hosts immune
system.
Describe the normal sequence of events which would allow a host to produce antibodies effective
against Toxoplasma gondii, following exposure to the pathogen.
5 marks
Pathogen is phagocytosed/eq by macrophage which displays antigen on cell surface;
T helper cell with complementary receptor binds to (displayed) antigen and is activated;
B lymphocyte specific to antigen on pathogen becomes an antigen presenting cell;
T helper cell releases cytokines to cause clonal expansion/mitosis/replication of B lymphocyte;
B lymphocyte produces B memory and B effector cells;
B effector cells differentiate into plasma cells;
Plasma cells secrete (specific) antibody;
3. Natural selection will have favoured alleles in rats and mice that increase the chances of
survival in their environment. Using examples from the text give two examples of genetically
controlled behaviour in mice which increase survival chances, and explain why each one will
increase the probability of survival.
4 marks.
Avoidance of open spaces; nocturnal activity; either reduces risk of predation;
Avoidance of unfamiliar sources of food; reduces risk of being poisoned;
4. A lack of dopamine in the brain is thought to cause the condition of Parkinson’s Disease, so
many treatments for Parkinson’s Disease aim to raise the level of dopamine in the brain.
Name three different drug therapies which reduce the symptoms of Parkinson’s Disease, and for
each one outline the mechanism by which it works.
6 marks.
L-dopa; (crosses blood brain barrier) and is converted into dopamine in the brain;
Enzyme inhibitors/seligiline; inhibit enzymes (such as MAOA) which break down dopamine;
Dopamine agonists; bind to dopamine receptors and mimic action of dopamine;
5. In paragraph 12 it describes how Toxoplasma gondii has been genetically modified to
provoke an effective immune response.
Describe the techniques used to alter the genome of the parasite. (QWC – needs to be presented in
a logical sequence)
6 marks.
Isolate and replicate gene of interest;
using appropriate technique gene cloning/PCR/ restriction enzymes;
Insert gene into plasmid;
with ref. to use of antibiotic resistance marker gene and promoter gene;
Description of appropriate technique to insert gene into parasite cells (gene gun/viral vector/heat
shock);
Explanation of process of selection of modified cells with antibiotic;
6. Discuss how the long term alteration of the brains of the mice after a brief exposure to the
pathogen might be similar to the development of the visual cortex in mammals.
2 marks
Alteration of the pattern of synapses in the brain or visual cortex;
Changes are ‘hard wired’/ there is a loss of plasticity;
Changes are result of changes in gene expression/production of transcription factors;
7. Evaluate the evidence that there is a causal relationship between Toxoplasma gondii
infection in humans and the development of schizophrenia.
3marks.
For – people with schizophrenia are more likely than the general population to have been infected
with Toxoplasma
Against – Toxoplasma infection rates vary by region, while schizophrenia rates are consistent (at 1%)
globally;
8. When the Emerald Cockroach Wasp injects its venom into the cockroaches brain it blocks a
neurotransmitter called octapamine. Suggest how the venom could block synaptic
transmission. (QWC – spelling and logical sequence)
5 marks
Possible target of octapamine identified, calcium ion channels in pre synaptic cell/ receptors on
post synaptic cell/ synaptic vesicle/ neurotransmitter itself;
Each stage in synaptic transmission correctly described, but presaged with ‘will not’
Calcium ion channels will not open;
Calcium ions will not enter pre-synaptic neurone;
Vesicles will not move and fuse with pre-synaptic neurone;
Neurotransmitter will not be released into synaptic cleft;
Neurotransmitter will not bind to receptors on post synaptic neurone;
No generation of EPSP;
No action potential generated in post synaptic neurone;
9. With reference to the ‘zombie ant fungus’ explain what is meant by the term ‘ecological
niche’, and describe the niche of the fungus.
3 marks
Functional status of an organism is its ecosystem;
An obligate; parasite; on a single species;
10. In paragraph 31 it refers to insect biomass. Describe a procedure for determining biomass of
a named organism that you have studied.
5 marks.
Appropriate named organism;
Use of quadrats;
Description of how to place quadrats randomly;
Collect all organisms within quadrat;
Determine mass of organisms;
Explanation of how to determine biomass – dividing mass by area to fins mass per m2;
Appropriate ref. to replication;
11. The fungus causes atrophy of the muscles of the ant by destroying mitochondria and the
sarcoplasmic reticulum in the ant muscles. Explain in detail how the loss of these organelles
in muscle cells is likely to impair muscle contraction in the ant.
5 marks
Mitochondria - less ATP produced; less chemiosmosis; less operation of electron transport chain;
myosin heads cannot release from actin by attachment of ATP; myosin heads cannot be ‘recocked’
Sarcoplasmic reticulum – fewer calcium ions released into muscle fibre; less binding of calcium ions
to troponin; less removal of tropomyosin from binding sites on actin; fewer cross bridges form;
12. Alfred Russell Wallace published his findings on the ant fungus in the scientific literature of
his day. Describe the ways that scientists today circulate their finding to the scientific
community.
3 marks.
Internet;
Scientific journals;
Which are peer reviewed;
Scientific conferences;
13. There is apparently a great diversity of ‘zombie ant fungi’. There are three levels of
biodiversity. Name each of these levels and give a definition of each.
6 marks.
Species richness; number of different species in an area; genetic diversity; number or variety of
alleles in a species/population; ecosystem diversity; degree of diversity of ecosystems on earth;
14. In paragraph 47 it suggests that the climate in Germany 48 million years ago would have
been similar to that of present day Thailand. Describe how researchers might have been able
to arrive at such a conclusion.
2 marks
Use of some appropriate technique to establish plant communities in the past eg analysis of fossil
pollen;
Find somewhere on earth similar plant communities are found today;
Match climate of that area today with past climate of region under study;