7. Genetics, populations, evolution and ecosystems Flashcards
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. Suggest and explain the advantage of this behaviour to the population of guppies. (3 marks)
- (Females with large brains) will mate with males bright in colour
- Their (male) offspring would be (more likely to be) bright in colour;
- (Bright in colour male) offspring could attract larger brained females;
- The offspring could (evolve to) have larger brains;
- The offspring are better at identifying predators;
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. Explain how different subspecies of giraffe may have evolved from a common ancestor.
Use information from the passage in your answer. (5 marks)
- No interbreeding
- Mutation linked to (different) markings
- Survival linked to (different) markings
- Adapted organisms breed
- Change in allele frequency
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)
- (Compare DNA) base sequence
- Different in six (species)
Lemmings often live in isolated populations. From time to time some lemmings move and
join other populations. Explain how this movement is important in maintaining genetic variability in lemming populations which have large fluctuations in size. (2 marks)
- smaller populations have fewer different alleles
- migrants bring in different alleles and increase gene pool
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.
Describe one way in which scientists could find out whether cichlids from two different populations belong to the same species. (2 marks)
- breed together;
- if fertile offspring, then same species
Suggest and explain how digesting insects helps the sundew to grow in soil with very low concentrations of some nutrients (2 marks)
1. Digestion/breakdown of proteins;
2. Provides amino acids
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.
Explain how using the SIT could reduce transmission of dengue. (2 marks)
- Compete (with fertile males) to mate / for food / resources
- Reduces population (of mosquitoes)
The release of radiation-sterilised A. aegypti has not been very successful in controlling the
transmission of dengue.
Suggest one reason why. (1 mark)
(Radiation) affects their ‘attractiveness’
The scientists used percentage cover rather than frequency to record the abundance of
algae present
Suggest why. (1 mark)
Difficult/too many to count
Apart from availability of water, describe and explain how two abiotic factors may have
caused differences in the species of algae growing at sites A and B. (2 marks)
- Light – (linked to) photosynthesis (at either site);
- Temperature – (linked to) photosynthesis/respiration (at either site);
The consumers were starved for 5 days before the investigation.
Explain why. (2 marks)
- hungry
- so allows comparison
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often box
not the same as the expected ratios.
Suggest two reasons why. (2 marks)
- Fusion/fertilisation of gametes is random;
- Linked genes
Succession occurs in natural ecosystems. Describe and explain how succession
occurs. (4 marks)
- (Colonisation by) pioneer species;
- Pioneers/species/organisms change the environment/habitat/conditions/factors;
- (Environment becomes) less hostile for other/new species
- Change/increase in diversity/biodiversity;
- (To) climax community;
Explain how succession results in a wide variety of fish living on coral reefs. (2 marks)
- Increase in variety/diversity of
species/plants/animals; - Provides more/different habitats/niches
Suggest why the mark-release-recapture method can produce unreliable results in
very large lakes (1 mark)
Less chance of recapturing fish
OR
Unlikely fish distribute randomly/evenly;
Suggest one precaution needed when marking the lemurs to make sure the estimate
of the number of lemurs is valid. (1 mark)
(Marking) does not affect
survival/predation/recapture;
Suggest two reasons for conserving rainforests. (2 marks)
- Conserve/protect
species/plants/animals/organisms - Conserve/protect habitats/niches
- Reduces climate change;
- Source of medicines/drugs/wood;
- Reduces erosion/eutrophication;
- (For) tourism;
- For (bio)diversity;
Describe how farming cattle as a source of milk could have led to an increase in lactase (4 marks)
- Lactase due to mutation
- Milk provides glucose
- Individuals with lactase more likely to survive and reproduce
- Directional selection;
- Frequency of allele increases in offspring
Explain why the number of people showing
lactase would rapidly increase once selection for this condition had been established. (2 marks)
- dominant allele
- always expressed
Suggest and explain two reasons why there is a high frequency of a mutation in an isolated island (2 marks)
- Isolated so inbreeding / low genetic diversity
- Allele inherited through generations from (common) ancestor
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 (3 marks)
- Initially one insect with favourable mutation
- Individuals with (favourable) mutation will have more
offspring; - Takes many generations for (favourable) mutation to
become the most common allele (of this gene).
Give two features of a climax community. (2 marks)
- Same species present (over long time)
- Abiotic factors constant (over time)
- Populations stable (around carrying capacity)
Suggest an explanation for the decrease in species diversity when non-native species were
introduced to communities. (2 marks)
- Non-native species out-competes native plants;
- Some (populations of) native species become extinct
Individuals in a population show phenotypic variation.
Give the two types of factor that cause this variation. (2 marks)
- mutations
- environment;
What is sympatric speciation? (2 marks)
- Formation of new species / reproductive isolation;
- Without geographical isolation;
Give two possible causes of this variation that result from meiosis during gamete
formation. (2 marks)
- crossing over
- random segregation
When comparing variation in size between two groups of organisms, it is often
considered more useful to compare standard deviations rather than ranges. Explain
why. (2 marks)
- S.D. shows spread about mean
- range only shows highest
and lowest values
What is the evidence for stabilising selection? (1 mark)
most survive from the middle of the range;
The percentage of white snow geese in snowy conditions has changed. Use your knowledge of climate change to suggest an
explanation. (2 marks)
- less snow;
- white geese decreasing as less well camouflaged
Explain why large geese can breed in colder conditions (2 marks)
- more fat;
- for insulation when they are sitting on eggs;
Suggest two factors that the scientists should have taken into account when
selecting the twins to be used in this study. (2 marks)
- age
- family’s medical history
Explain the increase in the diversity of birds as the woodland developed. (3 marks)
- Greater diversity of plants
- More food sources
- More habitats
