M6 C24: populations and sustainability PMT QP 1

Question 1

The grey wolf, Canis lupus, is a large predator whose diet includes elk. By 1926, grey wolves had been hunted to extinction in Yellowstone Park. However, this
species could still be found in other parts of the world.
In 1995, a population of grey wolves was introduced to Yellowstone Park and their numbers increased.

discuss the factors that may have affected the size of the elk population:
• before 1995
• after 1995.

Answer 1

• population size is determined by limiting factors

before 1995 pop. increases as there is plenty of food available

before 1995 pop. levels off as it reaches carrying capacity

before 1995 pop. becomes limited due to intraspecific completion for a mate and interspecific competition for food

pop. can decrease at anytime due to severe weather
decrease after 1995 due to wolves

Question 2

Explain why the introduction of wolves to Yellowstone Park in 1995 is an example of conservation.

Answer 2

• restoring ecosystem
• actively maintaining the biodiversity
• helps wolf population
• controls elk population which prevents over-grazing

Question 3

suggest how an ancestral species might have evolved into the two species, B. pratorum and B. terrestris.

Answer 3

• isolation
• seasonal difference
• behavioural difference
• different flower locations
• gene flow restricted
• different adaptations

Question 4

what type of behaviour is this example

The time taken for a worker bee to collect food from a flower decreases with practice.

Answer 4

operant conditioning/learning

Question 5

Name the enzyme that can be used to convert mRNA to single-stranded DNA.

Answer 5

reverse transcriptase

Question 6

In a colony of bees, about 5% of the workers are more adventurous than other workers. These bees are known as scout bees. They actively seek out new food sources and, if necessary, new nest sites.
Researchers investigated how gene expression differed in the brains of the scout bees compared to the normal worker bees.

• The researchers extracted mRNA from the brain cells of normal worker bees.

• This mRNA was used to produce lengths of single-stranded DNA, which were then
attached to a fluorescent dye.

• These lengths of single-stranded DNA were used as gene probes fixed onto a device known as a ‘microarray DNA chip’.
• mRNA extracted from the brain cells of scout bees would only bind to the gene probes that matched it, causing these probes to fluoresce.
• The locations of the brightest fluorescent spots on the DNA chip revealed which genes were most active.

Explain how the locations of the fluorescent spots on the DNA chip reveal which genes are most active.

Answer 6

• mRNA binds to probe by complementary base pairing
• the more active the gene the more mRNA produced
• during transcription more fluorescence indicates more mRNA is bound

Question 7

The researchers found many differences in gene activity in the scout bees compared to the normal worker bees. One of these differences in activity was in a gene used to make the neurotransmitter, dopamine.

In a follow-up experiment, scout bees became less adventurous if dopamine signalling was prevented.

Use your knowledge of the DRD4 dopamine receptor in humans to comment on the findings of this research into scout bee behaviour.

Answer 7

• dopamine is linked to ADHD in humans
• humans and bees do share some common mechanisms
• however they are different organisms and therefor the mechanisms may not be comparable despite being similar

Question 8

what is the difference between a pioneer community and climax community

Answer 8

• pioneers arrive before climax
• pioneer communities subject to more change
• pioneer community is usually less stable and has less biodiversity
• pioneer community has lower biomass

Question 9

what is the difference between decomposition and denitrification

Answer 9

• decomposition is the break down of dead matter/ converting organic matter to inorganic
• denitrification is the conversion of nitrates to nitrogen

Question 10

what is the difference between conservation and preservation

Answer 10

• conservation active maintains an ecosystem

- preservation leaves and ecosystem undisturbed

Question 11

what is the difference between nitrification and nitrogen fixation

Answer 11

• nitrogen fixation converts nitrogen (from atmosphere) into ammonia
• nitrification changes ammonia to to nitrate

Question 12

Explain, using scientific terms, why a collection of small islands remote from the mainland provides optimal conditions for speciation.

Answer 12

• geographical isolation
• reproductive isolation, less interbreeding between populations/species
• different selection pressures on different islands
• small gene pools
• resulting in founder effect
• resulting in greater genetic drift

Question 13

Outline the main ways in which increased human presence and activity have put endemic species on the Galapagos Islands, and in the sea around them, at risk of extinction.

In your answer you should link the ecological pressures imposed by human activity to examples of Galapagos Island species that have been affected.

[7 marks]

Answer 13

1 habitat / ecosystem , disturbance / destruction ;
2 (land used for) (named) building / roads ;
3 (land used for) agriculture / farming ;
4 deforestation ;
5 effect of (tourist) , boats / divers, described ;
6 more / increased , pollution ;
7 sewage / eutrophication , in sea / water
8 oil/fuel, spill in sea;
9 (humans) hunting / collecting / (over-) fishing ;
10 competition from introduced species ;
11 predation / overgrazing , by introduced species ;
12 (new / named) , diseases / pathogens, introduced ;