population questions Flashcards
On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus Anolis. Scientists believe that these species evolved from two species found on mainland USA. Explain how the Caribbean species could have evolved. 6marks
- Geographic(al) isolation;
- Separate gene pools / no interbreeding / gene flow (between populations);
Accept: reproductive isolation
This mark should only be awarded in context of during the process of speciation. Do not credit if context is after speciation has occurred. - Variation due to mutation;
- Different selection pressures / different abiotic / biotic conditions /
environments / habitats;
Neutral: different conditions / climates if not qualified Accept: named abiotic / biotic conditions - Different(ial) reproductive success / selected organisms (survive and) reproduce;
Accept: pass on alleles - Leads to change / increase in allele frequency.
Anolis sagrei is a species of lizard that is found on some of the smallest Caribbean islands. Describe how you could use the mark-release-recapture method to estimate the number of Anolis sagrei on one of these islands.
1.capture and collect
2. Method of marking does not harm lizard / make it more visible to
Capture / collect sample, mark and release;
predators;
3. Leave sufficient time for lizards to (randomly) distribute (on island)
before collecting a second sample;
4. (Population =) number in first sample × number in second sample
divided by number of marked lizards in second sample / number recaptured.
Large areas of tropical forest are still found on some Caribbean islands. The concentration of carbon dioxide in the air of these forests changes over a period of 24 hours and at different heights above ground.
Use your knowledge of photosynthesis and respiration to describe and explain how the concentration of carbon dioxide in the air changes:
• over a period of 24 hours
• at different heights above ground.
- High concentration of / increase in carbon dioxide linked with respiration at night / in darkness;
- No photosynthesis in dark / night / photosynthesis only in light / day;
Neutral: less photosynthesis - In light net uptake of carbon dioxide / use more carbon dioxide than produced / (rate of) photosynthesis greater than rate of respiration;
- Decrease in carbon dioxide concentration with height;
More carbon dioxide absorbed higher up
(i) Explain why both types of twin were used in this investigation.
Identical twins show genetic influence / differences between them show environmental influence;
Neutral: allows a comparison
It must be clear which set of twins is being referred to
Non-identical twins (also) show an environmental / non-genetic influence;
It must be clear which set of twins is being referred to Do not credit repetition of bullet points in stem
(ii) What do these data suggest about the relative effects of genetic and environmental factors on the development of schizophrenia
Genes play a greater role / environment plays a lesser role;
Must be comparative
Neutral: genes are involved
Neutral: involves genes and the environment
(iii) Suggest two factors that the scientists should have taken into account when selecting the twins to be used in this study.
- Age;
- Sex (non-identical twins);
- Family / medical history (of mental illness);
- No use of recreational drugs;
- Ethnic origins;
(a)
Explain the advantage of presenting the results as a ratio
(a)
1. Allows (valid) comparison;
Number / sample size may vary;
What do these data show about the effect of red blood cell phenotypes on the chance of developing severe malaria rather than mild malaria
Increased chance of (severe malaria) with blood group A / decreased chance of (severe malaria) with sickle cell;
Accept: converse for mild malaria i.e. increased chance of mild malaria with sickle cell / decreased chance of mild malaria with blood group A.
Accept: if answer is comparative e.g. greatest risk of severe malaria with blood group A.
almost equal chance with blood group O / slightly greater chance of mild malaria with O / slightly lower chance of severe malaria with O / 2.5 x / 2.48 x / more than twice the chance of severe with blood group A / (almost) 50% / half the chance of severe malaria with sickle cell / twice the chance of mild malaria with sickle cell;
…………………………………………………………………………………………………………
The allele for normal haemoglobin in red blood cells is HbA. In some parts of Africa where malaria occurs there is a high frequency in the population of the allele HbC. Individuals possessing the HbC allele have a lower chance of developing severe malaria. Severe malaria causes a large number of deaths in Africa.
(c)
Explain the high frequency of the HbC allele in areas where malaria occurs.
Neutral: answers which only refer to or use ratios.
Individuals with the HbC (allele) reproduce;
Pass on HbC (allele) which increases in frequency;
HbA HbA individuals less likely to survive / reproduce / frequency of HbA (allele) decreases;
Can you conclude that the insect pest resistant to Bt toxin found in the years 2002 to 2005 was the same insect species?
Graph / bar chart only shows number of species, not the name of the species.
b)
One farmer stated that the increase in the use of Bt crop plants had caused a mutation in one of the insect species and that this mutation had spread to other species of insect. Was he correct? Explain your answer.
………………………………………………………………………………….
(No – no mark)
1. Mutations are spontaneous / random;
2. Only the rate of mutation is affected by environment;
3. Different species do not interbreed / do not produce fertile offspring; 4. So mutation / gene / allele cannot be passed from one species to
another.
Ignore references to correlation does not prove causation
There was a time lag between the introduction of Bt crops and the appearance of the first insect species that was resistant to the Bt toxin.
Explain why there was a time lag.
…………………………………………………
Initially one / few insects with favourable mutation / allele;
2. Individuals with (favourable) mutation / allele will have more offspring;
3. Takes many generations for (favourable) mutation / allele to become the
most common allele (of this gene).
Use the Hardy–Weinberg equation to calculate the frequency of mosquitoes
heterozygous for the KDR gene in this population in 2003.
Show your working.
Frequency of heterozygotes in population in 2003 ……………………………..
(b) Suggest an explanation for the results in the figure above. ……
Correct answer = 2 marks Accept 32% for 1 mark max
Incorrect answer but identifying 2pq as heterozygous = 1 mark
Mutation produced KDR minus / resistance allele;
DDT use provides selection pressure;
Mosquitoes with KDR minus allele more likely (to survive) to reproduce; Leading to increase in KDR minus allele in population
The KDR plus allele codes for the sodium ion channels found in neurones.
When DDT binds to a sodium ion channel, the channel remains open all the time.
Use this information to suggest how DDT kills insects.
Neurones remain depolarised;
So no action potentials / no impulse transmission.
…………………………………………………………………………………………………………
The KDR plus allele codes for the sodium ion channels found in neurones.
When DDT binds to a sodium ion channel, the channel remains open all the time.
Use this information to suggest how DDT kills insects. ………………………………………………………………………………..
Mutation) changes shape of sodium ion channel (protein) / of receptor (protein);
DDT no longer complementary / no longer able to bind.
