T7 Genetics, Populations, Evolution and Ecosystems

Question 1

In fruit flies, males have the sex chromosomes XY and the females have XX. In fruit flies, a gene for eye colour is carried on the X chromosome. The allele for red eyes, R, is dominant to the allele for white eyes, r.
(a) Male fruit flies are more likely than female fruit flies to have white eyes.
Explain why. 2 marks

Answer 1

1. Males have one allele;
   Accept males only need one allele.
2. Females need two recessive alleles
   OR
   Females must be homozygous recessive
   OR
   Females could have dominant and recessive alleles
   OR
   Females could be heterozygous/carriers;
   Ignore references to X and Y chromosomes.
   Accept r as recessive allele and R as dominant allele.
   If no reference to allele, accept for one mark male needs one
   recessive gene whereas females need two recessive genes.

Question 2

What is meant by the term phenotype? 2 marks

Answer 2

1. (Expression / appearance / characteristic due to) genetic constitution / genotype /
   allele(s);
2. (Expression / appearance / characteristic due to) environment;
3. Accept: named characteristic.
4. Accept: homozygous / heterozygous / genes / DNA.
5. Ignore: chromosomes.

Question 3

What does the Hardy–Weinberg principle predict? 3 marks

Answer 3

The frequency / proportion of alleles (of a particular gene);
Will stay constant from one generation to the next / over
generations / no genetic change over time;
Providing no mutation / no selection / population large / population
genetically isolated / mating at random / no migration;
The three principles for marking are:
What feature
What happens to it
Providing . . .
Accept: genotype / explanation of genotype
Accept: alternative wording, e.g. there is no gene flow / genetic drift
for genetically isolated

Question 4

What is a gene pool? 1 mark

Answer 4

All the alleles in a population;
Accept: The number of alleles in a population.
Note: All or number of alleles in a species on its own is not enough
on its own.

Question 5

Lord Howe Island in the Tasman Sea possesses two species of palm tree which have arisen via sympatric speciation. The two species diverged from each other after the island was formed 6.5 million years ago. The flowering times of the two species are different.
Using this information, suggest how these two species of palm tree arose by sympatric speciation. 5 marks

Answer 5

1. Occurs in the same habitat / environment / population;
2. Mutation/s cause different flowering times;
3. Reproductive separation / isolation
   OR
   No gene flow
   OR
   Gene pools remain separate;
4. Different allele/s passed on / selected
   OR
   Change in frequency of allele/s
5. Disruptive (natural) selection;
6. Eventually different species cannot (inter)breed to produce fertile offspring;
7. Accept: are not geographically isolated / separated.
8. Accept: same place
9. Accept: no interbreeding but must be a separate idea from
   mark point 6 which relates to definition of a species.
   Note: Answers relating only to allopatric speciation = 3 max, mark
   points 3, 4 and 6.

Question 6

There are nine subspecies of giraffe. These subspecies evolved when populations of giraffe were separated for long time periods. Each subspecies has distinct coloured skin markings. Some biologists have suggested that up to six of these subspecies should be classified as different species.
(a) Explain how different subspecies of giraffe may have evolved from a common ancestor.
Use information from the passage in your answer. 5 marks

Answer 6

1. No interbreeding / gene pools are separate / geographic(al) isolation;
   Accept: reproductive isolation as an alternative to no interbreeding.
2. Mutation linked to (different) markings/colours;
3. Selection/survival linked to (different) markings/colours;
4. Adapted organisms breed / differential reproductive success;
   Note: ’passed on to offspring’ on its own is not sufficient for
   reproduction.
5. Change/increase in allele frequency/frequencies;

Question 7

Biologists compared the mitochondrial DNA of the different subspecies of giraffe. They used the results from comparing this DNA to conclude that six of the nine subspecies are separate species.
Suggest how they came to this conclusion. 2 marks

Answer 7

1. (Compare DNA) base sequence / base pairing / (DNA)
   hybridisation;
   Ignore: compare chromosomes / ‘genetic make-up’.
   Accept: (compare) genes / introns / exons.
   Note: reference to only comparing alleles is 1 max.
2. Different in six (species) /different in different species / similar in
   three (subspecies) /similar in same species/subspecies;
   Ignore: compare chromosomes / ‘genetic make-up’.
   Reject: ‘ same alleles/ same DNA bases in three
   species/subspecies’.
   Note: mark point 2 can be awarded without mark point 1.

Question 8

Lake Malawi in East Africa contains around 400 different species of cichlids which are small, brightly coloured fish. All these species have evolved from a common ancestor.
(a) Describe one way in which scientists could find out whether cichlids from two different
populations belong to the same species. 2 marks

Answer 8

breed together;
if fertile offspring, then same species;

Question 9

Lake Malawi in East Africa contains around 400 different species of cichlids which are small, brightly coloured fish. All these species have evolved from a common ancestor.
During the last 700 000 years there have been long periods when the water level was much lower and Lake Malawi split up into many smaller lakes. Explain how speciation of
the cichlids may have occurred following the formation of separate, smaller lakes.
4 marks

Answer 9

isolation of two populations;
variation already present due to mutations;
different environmental conditions / selection pressures leading to
selection of different features and hence different alleles;
different frequency of alleles;
separate gene pools / no interbreeding

Question 10

Many species of cichlids are similar in size and, apart from their colour, in appearance.
Suggest how the variety of colour patterns displayed by these cichlids may help to maintain the fish as separate species. 2 marks

Answer 10

selection of mate dependent on colour pattern;
prevents interbreeding / keeps gene pools separate;

Question 11

The stream eventually recovered to reach a climax community.
Give two features of a climax community. 2 marks

Answer 11

1. Same species present (over long time) / stable community (over long time);
2. Abiotic factors (more or less) constant (over time)
3. Populations stable (around carrying capacity)

Question 12

The student used the mark-release-recapture technique to estimate the size of the population of sand lizards on an area of moorland. She collected 17 lizards and marked them before releasing them back into the same area. Later, she collected 20 lizards, 10 of which were marked.
(i) Give two conditions for results from mark-release-recapture investigations to be
valid. 2 marks

Answer 12

1. Marking is not removed / marking does not affect survival / predation;
2. Limited / no immigration / emigration;
   Accept ‘migration’ and descriptions of immigration / emigration
3. and 4. Increase / decrease in population is not sufficient – there
   must be a reason
4. Sufficient time for (marked) individuals to mix (within the population);
   Accept – ‘For mixing to occur between samples’
5. No / little births / deaths / breeding;
6. Sampling method is the same;
   Ignore ‘random sampling’

Question 13

In northern India, there is a conflict of interests between farmers of livestock (eg cows) and people trying to conserve ibex (a type of wild goat).
When livestock are given extra food, their populations can grow too large and compete with ibex.
(a) Name the type of competition between livestock and ibex. 1 mark

Answer 13

Interspecific (competition);

Question 14

The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes. The
soil in bogs and marshes is acidic and has very low concentrations of some nutrients. The
sundew can trap and digest insects.
(a)  Describe how you could estimate the size of a population of sundews in a small marsh. 5 marks

Answer 14

  1.   Use a grid
OR
Divide area into squares/sections;
Accept use of tape measures/map/area with coordinates.
Accept Belt transect.
2.   Method of obtaining random coordinates/numbers e.g. calculator/computer
/random numbers table/generator;
If transect method used accept quadrats at regular intervals or current
mark point 2.
3.   Count number/frequency in a quadrat/section;
Accept % cover in quadrat/section.
Ignore amount/abundance.
4.Large sample and calculate mean/average number (per quadrat/section);
Accept large sample and calculate mean %.
Accept large sample and method of calculating mean.
Accept many/multiple for large sample but ignore several.
If a specific number is given it must be 10 or more.
5.Valid method of calculating total number of sundews, e.g. mean number of
plants per quadrat/section/m2
multiplied by number of quadrats/sections/m2
in marsh;
Do not allow ‘scale up’ without further qualification.
Do not award if % cover determined.

Question 15

The sundew is a small flowering plant, growing in wet habitats such as bogs and marshes. The soil in bogs and marshes is acidic and has very low concentrations of some nutrients. The
sundew can trap and digest insects.
Suggest and explain how digesting insects helps the sundew to grow in soil with very low
concentrations of some nutrients. 2 marks

Answer 15

Mark in pairs 1 and 2, or 3 and 4.
Ignore carbohydrates, lipids or named carbohydrate/ lipid.
1.   Digestion/breakdown of proteins;
2.   Provides amino acids
OR
(Sundew can) produce a named (organic) nitrogen-containing compound e.g.
proteins, amino acids, DNA, ATP;
Ignore if nitrate or ammonium ions given as products.
3.   Digestion/breakdown of named (organic) phosphate-containing compound e.g.
DNA, RNA;
4.   Provides named (organic) phosphate-containing product e.g. nucleotides
OR
(Sundew can) produce a named phosphate-containing compound e.g. ATP,
DNA;
Accept phosphate as a named product.

Question 16

Dengue is a serious disease that is caused by a virus. The virus is carried from one person to
another by a mosquito, Aedes aegypti. One method used to try to reduce transmission of this disease is the Sterile Insect Technique (SIT). This involves releasing large numbers of sterile (infertile) male A. aegypti into the habitat. These males have been made infertile by using radiation.
(a) Explain how using the SIT could reduce transmission of dengue. 2 marks

Answer 16

1. Compete (with fertile males) to mate / for food / resources
   OR
   intraspecific competition;
2. Do not reproduce / breed
   OR
   Reduces population (of mosquitoes);
3. Must convey idea of competition.
4. Accept: ‘fewer mosquitoes’ / ‘fewer offspring’.

Question 17

Describe how the mark-release-recapture method could be used to determine the
population of mosquitos at the start of an investigation. 3 marks

Answer 17

1. Capture / collect / sample, mark and release;
2. Leave time for mosquitoes / Aedes to disperse before second sampling /
   collection;
3. (Population =) number in first sample × number in second sample divided by
   number of marked in second sample / number recaptured;
4. Accept: correct equation.

Question 18

What is a species? 1 mark

Answer 18

(Organisms that) can breed together / interbreed and produce fertile offspring;
Need both aspects. Reject ‘inbreed’
Reject viable offspring

Question 19

What is meant by uniformly distributed?

Answer 19

Same number (of organisms) in each region / (organisms) equally spread;
Allow other ways of expressing ‘region’ or ‘equally spread’, eg not
clumped together, same number per unit area

Question 20

Genotype definiton 1 mark

Answer 20

Genetic makeup of an organism

Question 21

What is adaptive radiation? 1 mark

Answer 21

When a population evolves to adapt to its local environment due to selection pressure

Question 22

Definiton of a gene 1 mark

Answer 22

A section of DNA that codes for a polypeptide and a functioning mRNA

Question 23

Definition of an allele 1 mark

Answer 23

A different form of a gene

Question 23

What does Polygenetic mean? 1 mark

Answer 23

Two or more genes contribute to the phenotypic expression of a single characteristic e.g. skin colour

Question 24

What does Codominant mean? 1 mark

Answer 24

A condition in which both alleles for a gene are fully expressed as they are both dominant

Question 25

Name for chromosome that is not sex-linked. 1 mark

Answer 25

Autosome

Question 26

What is autosomal linkage? 1 mark

Answer 26

When two genes are located on the same autosome (chromosome) and are inherited by the offspring together, they do not segregate in accordance with Mendel’s Law of Independent assortment

Question 27

What are the five conditions for the Hardy-Weinberg Principle to hold true? 2 marks.

Answer 27

• No mutations
• The population is isolated
• There is no selection
• The population is large
• Mating is random within the population

2 marks for all correct. 1 mark for four correct. No mark for less than four correct.

Question 28

What is natural selection? 1 mark

Answer 28

A process in which individuals that have advantageous alleles tend to survive and reproduce at higher rates than other individuals as they are more suited to the environment

Question 29

What are selection pressures? 1 mark

Answer 29

The environmental factors that favour certain phenotypes

Question 30

Genetic drift meaning 1 mark

Answer 30

A change in the allele frequency of within a population between generations

Question 31

What is Allopatric speciation? 1 mark

Answer 31

The formation of new species in populations that are geographically isolated from one another

Question 32

What is Sympatric speciation? 1 mark

Answer 32

The formation of a new species as a result of a genetic change that produces a reproductive barrier between the changed population (mutants) and the parent population. No geographic barrier is present

Question 33

Ecology definition. 1 mark

Answer 33

Scientific study of interactions among organisms and between organisms and their environment

Question 34

Largest number of individuals of a population that an ecosystem can support is called? 1 mark

Answer 34

Carrying capacity

Question 35

Community definition. 1 mark

Answer 35

All the different populations that live together in an area

Question 36

An organism’s particular role in an ecosystem, or how it makes its living is called what? 1 mark

Answer 36

Niche

Question 37

Definition of Intraspecific competition. 1 mark

Answer 37

Competition among members of the same species

Question 38

Definition of Interspecific competition 1 mark

Answer 38

Competition between members of different species

Question 39

Climax community definition. 1 mark

Answer 39

A stable, mature community that undergoes little or no change in species over time

Question 40

Definition of Exsitu conservation. 1 mark

Answer 40

Conserving a species in artificially created habitat

Question 40

Definition of Insitu conservation. 1 mark

Answer 40

Conserving a species in its natural habitat

Question 41

Guppies are small fish. Female guppies are dull in colour. Male guppies can be bright or dull in colour. Scientists investigated the effect of female brain size on choosing a mate. They used
laboratory-bred female guppies with large brains and with small brains.
They set up a fish tank with the female in the middle, a brightly coloured male and a dull male on either side, separated by a transparent barrier.
They observed each female for 10 minutes and recorded which male they were attracted towards. They repeated this with 45 large-brained females and 45 small-brained females.
1.
(a) Suggest three possible limitations of this investigation. 3 marks

Answer 41

1. Laboratory-raised female (guppies) might not react/behave/choose in the same way
   (as wild guppies);
   Ignore answers relating to sample size
   Accept laboratory-raised female (guppies) might not be
   representative of wild females
2. (Transparent) barrier might not allow for normal (courtship) behaviour/interaction;
   Accept choice might involve chemical/ mechanical
   signals/interaction
   Accept colour might not be the only thing females are attracted to
3. Do not know if (guppies) have been used in previous experiments;
4. 10 minutes might not be long enough for females to make a (final) choice
   OR
   Not enough time for females to make a (final) choice;
   Accept descriptions of a choice eg ‘show attraction’

Question 42

Guppies are small fish. Female guppies are dull in colour. Male guppies can be bright or dull in colour. Scientists investigated the effect of female brain size on choosing a mate. They used
laboratory-bred female guppies with large brains and with small brains.
They set up a fish tank with the female in the middle, a brightly coloured male and a dull male on either side, separated by a transparent barrier.

Guppies with large brains are better at identifying predators.
The scientists found that only female guppies with large brains were attracted to male guppies bright in colour.

(b) Suggest and explain the advantage of this behaviour to the population of guppies. 3 marks

(c) Describe how the behaviour of female guppies could result in sympatric speciation. 3 marks

Answer 42

1. (Females with large brains) will mate with males bright in colour;
   Accept answers that include references to alleles
2. Their (male) offspring would be (more likely to be) bright in colour;
3. (Bright in colour male) offspring could attract larger brained females;
4. The population/offspring could (evolve to) have larger brains;
   Ignore answers relating to females only
5. The population/offspring are better at identifying/avoiding predators;
   Ignore answers relating to females only
6. Not geographically isolated;
   Accept are in the same area
7. (Leading to) reproductive isolation
   OR
   Gene pools kept separate;
   Accept large brained females will only mate with males bright in
   colour and small brained females will only mate with males dull in
   colour
8. Changes in allele frequencies;
   Reject gene frequencies
9. Cannot breed/mate to produce fertile offspring;
   Reject inbreeding

Question 43

Net primary production (NPP) definition. 1 mark

Answer 43

Net primary production (NPP) is the chemical energy stored in plant biomass after respiratory losses (R) to the environment have been taken into account.

Question 44

Equation for NPP (Net primary production). 1 mark.

Answer 44

NPP = GPP − R.
Gross primary productivity - Respiratory loss

Question 45

Describe and explain the process of succession. 4 marks

They can give you a graph but it all comes down to this

It’s like the main point of all succession questions.

Answer 45

1. Pioneer species increases then decreases;
   1 and 4. Growth / reproduces = increases. Dies = decrease
2. Principle of a species changing the conditions / a species makes the conditions
   less hostile;
3. Accept description of change in conditions eg
   soil / humus forms, nutrients increased
4. New / named species better competitor / previous / named / pioneer species
   outcompeted;
   Pioneer species grows, dies and forms humus = 2 marks
5. (Main) species increases and other / named species decreases;

The main species will be whatever the graph on the question says

This is like a template for those types of questions

Question 46

Describe how you would determine the mean percentage cover for beach grass on a sand dune. 3 marks

Answer 46

1. Method of randomly determining position (of quadrats) e.g. random numbers
   table/generator;
   Ignore line/belt transect
2. Large number/sample of quadrats;
   Accept many/multiple
   Ignore point quadrat
   If a specified number is given, it must be 20 or more
3. Divide total percentage by number of quadrats/samples/readings;