Mutations are the ultimate source of genetic variation and are essential to evolution.
Lice are wingless insects that belong to the phylum arthropoda.
State one type of environmental factor that may increase the mutation rate of a gene.
Identify one type of gene mutation.
State two characteristics that identify lice as members of the arthropoda.
Some lice live in human hair and feed on blood. Shampoos that kill lice have been available for many years but some lice are now resistant to those shampoos. Two possible hypotheses are:
Discuss which hypothesis is a better explanation of the theory of evolution by natural selection.
b. chemical mutagens/carcinogens/papilloma virus/cigarette smoke
a. jointed appendages
b. «chitinous» exoskeleton
c. segmented body
mouth AND anus
a. «scientists would accept» hypothesis A as the better one as mutations are random
b. scientists would reject hypothesis B because characteristics acquired during the lifetime of the individual being inherited is Lamarckian/not part of the evolution by natural selection theory/not all mutations are heritable
c. «the resistance» mutation would be present in the population initially and not caused by the shampoo «as hypothesis B states»
d. both hypotheses include variation in the population of lice «resistant and non-resistant»
e. variation is necessary for natural selection to occur
f. frequency of the best adapted increases and these individuals reproduce/pass on resistance to their offspring, so the resistant population increases «so hypothesis A is better»
OWTTE can be used for any of the answers in this part.
Native oyster populations are decreasing where rivers meet the ocean along the northwest coast of North America. These oyster populations are being attacked by a gastropod.
It is known that oysters and gastropods have hard parts composed of calcium carbonate and that ocean acidification is increasing. Studies were carried out using juvenile oysters and gastropods to investigate the effects of acidification on the decrease in the population of oysters.
The first step was to raise oysters in two different mesocosms. One had seawater at a normal concentration of CO2 and the other had sea water with a high concentration of CO2. Gastropods were raised in two further mesocosms with normal and high CO2 concentrations respectively.
A juvenile gastropod will attack a juvenile oyster by using its tongue-like structure (radula) to drill a hole through the oyster shell. Once the hole has been drilled, the gastropod sucks out the soft flesh. Researchers investigated the shell thickness at the site of the drill hole in relation to the size of the oyster. The results are seen in this graph.
Equal numbers of oysters raised in seawater with a normal CO2 concentration and in seawater with a high CO2 concentration were then presented together to the gastropod predators in seawater with a normal CO2 concentration. The same numbers of oysters from the two groups were also presented together to the gastropods in seawater with a high CO2 concentration. The bar charts show how many of the oysters were drilled by the gastropods and the mean size of drilled oysters.
Outline how acidified sea water could affect the shells of the oyster.
Outline the trends shown in the data in the graph.
Estimate how much smaller drilled oysters raised in seawater at a high CO2 concentration were than drilled oysters raised in seawater at a normal CO2 concentration.
Deduce from the data in the bar charts which factors were and were not correlated significantly with the number of oysters drilled by the gastropods.
Suggest reasons for the differences in the numbers of oysters drilled, as shown in the bar charts.
The radula in a gastropod is hard but not made of calcium carbonate. Outline how this statement is supported by the drilling success of the gastropods in seawater with normal or high CO2 concentrations.
Using all the data, evaluate how CO2 concentrations affect the development of oysters and their predation by gastropods.
Shells might dissolve/deteriorate / become smaller/thinner/weaker / OWTTE
shell formation reduced / more difficult
a. positive correlation between shell thickness and shell size
as shell thickness increases, shell size «also» increases
b. (positive correlation) occurs at two different CO2 concentrations / both high and normal concentrations
c. trend for thickness is «slightly» lower with high CO2
«approximately» 0.2 mm2
«approximately» 40 % «smaller»
a. significant factor: concentration of CO2 in which oysters were raised
b. insignificant factor: concentration of CO2 at which oysters were presented to gastropods
a. (because) shells are thinner/smaller when the oyster is raised in high CO2/lower pH
«because» lower pH/higher acidity prevents/reduces deposition of calcium carbonate
b. gastropods target smaller/thinner-shelled oysters more
c. gastropods can eat/drill thin-shelled/smaller oysters at a faster rate (and move onto another)
d. eating smaller oysters «from high CO2 environments» means given population of gastropods require more oysters for same food intake
a. data shows that similar numbers are drilled regardless of conditions
b. since radulas are not affected by acidification
radulas not made of calcium carbonate so (remain) strong/successful at drilling
a. the data/trend lines indicate that a higher CO2 concentration diminishes the shell thickness, making gastropod predation more successful
the bar graphs suggest that oysters raised in a higher CO2 concentration are smaller, making gastropod predation more successful
b. CO2 concentrations «during feeding» do not change the occurrence of drilling/predation «by gastropods»
c. «limitation» no information about how exaggerated the CO2 concentrations were
«limitation» no information about numbers of gastropods used «in each setting»
Malaria is a mosquito-borne disease caused by a unicellular organism, Plasmodium. Plasmodium is a parasite that spends part of its life in a mosquito and part in a human. The mosquito transmits the Plasmodium to a human when it feeds on human blood. Mosquitoes hatch in water and are flying insects as adults. In the country of Belize, where malaria is a serious problem, studies have been made to determine what environmental factors affect the incidence of the disease. 156 villages were studied over a ten-year period.
Each of the six districts of Belize was studied from 1989 to 1999. The graph shows the mean number of people in each district to be affected by malaria per year per 1000 people.
The country of Belize has many different ecosystems. These ecosystems are shown in the bar chart. The white bars indicate the total area within each ecosystem with the lowest incidence of malaria. The dark grey bars indicate the total area within each ecosystem with the highest incidence of malaria. The total area with an intermediate incidence of malaria is not shown.
State the district where there is the highest number of villages with the highest incidence of malaria.
Analyse the data in the map to find whether there is an association between rivers and the incidence of malaria.
Compare the trends in incidence of malaria for Toledo and Corozal.
Suggest a reason for the decreases in the incidence of malaria from 1995 to 1999.
Suggest a reason why the incidence of malaria is so low in the Belize District.
Besides farmland, identify which two ecosystems have the greatest total area with a high incidence of malaria.
Predict with a reason, using the data, which district has most farmland.
Discuss whether malaria could be reduced by replacing farmland with natural ecosystems and replacing broadleaf hill forest with mixed hill forest.
a. in Cayo and/or Toledo the high incidence seems to be associated with rivers;
b. however, along one river in Toledo there is no high incidence;
c. in Belize District there is low incidence along the river / high incidence away from the river;
d. Orange Walk/Stan Creek there is no clear association;
e. (consequently) association of rivers with high incidence of malaria is inconclusive OWTTE;
a. both are stable from 1989 to 1992;
b. both see upward spike in 1992;
c. Corozal reaches its peak (one year) earlier / vice versa;
d. Toledo rises after 1998 but Corozal continues to decline / Corozal at the end decreases almost to 0, while Toledo still have incidence at the end of the decade;
e. Toledo has a higher incidence (throughout the decade) / vice versa;
f. Toledo changes more rapidly than Corozal / vice versa;
Do not award numerical comparisons.
insecticides used to kill mosquitoes / more anti malarial drugs / drought/less water for mosquito breeding / increased drainage / improved education / more mosquito nets / other reasonable change in conditions
Do not accept vaccines as they do not exist.
drier climate/less rainfall / more predators / vegetation/ecology not favourable to mosquitoes / higher rainfall so faster flowing rivers/more educated inhabitants so more aware of dangers.
lowland broadleaf forest and broadleaf hill forests (both required)
Toledo because it has the highest incidence of malaria in map/graph (and farmland has highest correlation to incidence of malaria in the table).
a. if farming provides habitat for mosquitoes, then reducing it could reduce malaria / OWTTE;
b. natural habitats provide predators, but farmland does not;
c. changing native vegetation is not practical since plants are adapted to their environment/organisms have specific adaptations to their environments;
d. might work to change broadleaf forest into mixed hill forest as much of broadleaf forest has high incidence of malaria and no part of mixed hill forest has high incidence of malaria / OWTTE;
e. loss of habitat/loss of biodiversity results in less stable environment;
f. the value of maintaining natural habitat must be balanced with the value of reduced malaria;
g. farmland feeds the population, so cannot be replaced / OWTTE
The graph shows a sigmoid population growth curve.
The table summarizes the genome size of several organisms.
The figure shows a pedigree chart for the blood groups of three generations.
Identify the phases labelled X and Y.
Outline how fossil records can provide evidence for evolution.
Distinguish between the terms genotype and phenotype.
Outline a structural difference between the chromosomes of Helicobacter pylori and Homo sapiens.
Deduce the percentage of adenine in Oryza sativa if the proportion of guanine in that organism is 30 %.
Deduce the possible phenotypes of individual X.
Describe ABO blood groups as an example of codominance.
X: plateau phase
Y: exponential growth / log phase
a. the sequence in which fossils appear matches the expected sequence of evolution;
b. comparisons with fossils and living organisms (morphology) shows change in characteristics from an ancestral form / OWTTE;
Vestigial organs and homologous structures are acceptable answers.
c. fossils of extinct species show that (evolutionary) change has occurred;
d. fossils can be dated with radioisotopes / geological depth/strata indicates (relative) age/date of organism;
e. can yield DNA for molecular clock analysis;
f. example of any of the above can earn one mark (eg: reptiles follow amphibians);
genotype is the genetic make-up/set of alleles (of an organism) while phenotype is the characteristics (expressed/shown in an organism)
chromosome from bacteria has no protein associated/naked DNA / bacteria is circular, H. sapiens is linear / (chromosomes of) H. sapiens are much bigger/have many more base pairs than bacteria
N.B.: Answer must refer to “chromosomes” not genomes of the two organisms.
A, B, AB and O
All four phenotypes must be shown to award the mark.
allele IA and the allele IB are (co)dominant as they are both expressed in the heterozygote/AB type blood / OWTTE
State the property of stem cells that makes them useful in medical treatment.
Explain how multicellular organisms develop specialized tissues.
Outline some of the outcomes of the sequencing of the human genome.
has the ability to differentiate (into specialized tissue)
only some genes are expressed in each cell type/tissue;
tissues therefore develop differently/become differentiated;
example of differentiated cell and the function of tissues;
knowledge of location of human genes / position of human genes on chromosomes;
knowledge of number of genes/interaction of genes / understanding the mechanism of mutations;
evolutionary relationships between humans and other animals;
discovery of proteins / understanding protein function / detection of genetic disease;
leads to the development of medical treatment/enhanced research techniques;
knowledge of the base sequence of genes/study of variation within genome;
Describe how natural selection leads to evolution.
Explain the consequences of altering a DNA base in the genome of an organism.
populations produce more offspring than can survive;
individuals show variation;
create a struggle for survival/competition;
survival of the fittest / some are better suited to the environment and survive;
variation/characteristic must be heritable;
best fitted individuals survive to reproduce;
advantageous variation/characteristic/allele passed on;
over time advantageous variation/characteristic/allele increases in the population;
altering a base (in DNA) is a (point) mutation;
only has an effect if base is in a gene;
when mRNA is produced by transcription one mRNA base is different;
one codon in mRNA is different;
one amino acid is different in the polypeptide;
polypeptide produced by translation of mRNA;
some base changes do not change the amino acid coded for;
structure of polypeptide /protein may be altered;
usually the polypeptide/protein does not function as well;
disease: sickle cell anemia;
mutation: GAG to GTG;
consequence in translation: glutamic acid to valine;
consequence for protein: hemoglobin altered so sickle cell formed;
consequence for individual: less oxygen can be carried;
Define the term allele as used in genetics.
List the possible genotypes for blood group B.
allele: one specific form of a gene (occupying the same gene locus as other alleles of the same gene)
IBIB and IBi
Sickle-cell anemia is a disease caused by a base substitution mutation, where GAG has changed to GTG. The distribution of the sickle-cell allele is correlated with the incidence of malaria in many places, as shown by the map of Africa.
The correlation shown in the data above can be explained by natural selection. Outline how the process of natural selection can lead to evolution.
Explain how a base substitution mutation, such as GAG to GTG, can lead to a disease like sickle-cell anemia.
Using a Punnett grid, determine the possible genotypes and phenotypes of a cross between a man and a woman who are both carriers of the sickle-cell allele. Use the symbol HbS for the sickle-cell allele and HbA for the normal allele.
offspring compete/environment cannot support all offspring;
(genetic) variation in the offspring;
natural selection /survival of better adapted/fittest organisms;
reproduction passes characteristics to other generations;
allele frequencies change;
malaria causes selection pressure (in Africa/worldwide);
different hemoglobin/sickle-cell genotypes exist / normal hemoglobin and sicklecell alleles exist;
natural selection/resistance to malaria of sickle-cell heterozygotes/allele;
survivors pass on sickle-cell allele to offspring; (do not accept sickle-cell anemia)
frequency of sickle-cell allele highest in areas of high malaria incidence;
change in the codon (of the mRNA);
tRNA with a different anticodon attaches;
(if codon changed) wrong/different amino acid is joined to peptide/glutamic acid replaced by valine;
distorted hemoglobin molecule alters red blood cell shape/reduces ability to carry oxygen;
(genotypes shown in a Punnett grid eg)
(HbA HbA) normal and (HbA HbS) normal carrier/intermediate/sickle-cell trait and (HbS HbS) sickle-cell anemia/diseased / (HbA HbA and HbA HbS) normal /symptomless and (HbS HbS) sickle-cell anemia/diseased;
To award the mark all phenotypes must be mentioned.
The image shows part of a cladogram.
Label the parts of two paired nucleotides in the polynucleotide of DNA.
Using the cladogram, identify one diagnostic feature that characterizes the given groups of vertebrates at A, B and C.
State the name of the domain to which these organisms belong.
I: nitrogenous base
A: gills or fins or scales or no limbs or external fertilization
B: homeothermic or endothermic or warm-blooded or lungs or tetrapod or four limbs or pentadactyl limbs or internal fertilization
C: hair or fur or mammary glands or milk