Topic 7 Exam questions Flashcards
(10 cards)
Mutation is one cause of genetic variation in organisms.
Give two other causes of genetic variation. (2)
- Crossing over;
- Independent segregation/assortment (of homologous chromosomes);
Accept independent assortment of alleles.
Accept meiosis as an alternative for 1 or 2 if neither
of these marks is awarded. - Random fusion of gametes
OR
Random fertilisation;
In genetic crosses, the observed phenotypic ratios obtained in the offspring
are often not the same as the expected ratios.
Suggest two reasons why. (2)
- Small sample size;
- Fusion/fertilisation of gametes is random;
- Linked Genes;
Accept crossing over / sex linkage - Epistasis;
- Lethal genotypes;
What is meant by the term phenotype? (2)
- (Expression / appearance / characteristic due to) genetic constitution
/ genotype / allele(s); - (Expression / appearance / characteristic due to) environment;
Suggest two reasons why observed ratios are often not the same as
expected ratios. (2)
Fertilisation is random
OR
Fusion of gametes is random;
2. Small / not large population / sample;
3. Selection advantage / disadvantage / lethal alleles;
What is meant by codominant alleles?
(1)
Both alleles expressed in the phenotype (if both are present);
What is a gene pool? (1)
All the alleles in a population;
The mark-release-recapture method can be used to estimate the size of a
fish population (lines 13–14).
Explain how. (4)
- Capture/collect sample, mark and release;
- Ensure marking is not harmful (to fish)
OR
Ensure marking does not affect survival (of fish);
Accept examples e.g., marking should not be toxic. - Allow (time for) fish to (randomly) distribute before
collecting a second sample; - (Population =) number in first sample × number in second
sample divided by number of marked fish in second
sample/number recaptured;
Succession occurs in natural ecosystems. Describe and explain how
succession occurs. (4)
- (Colonisation by) pioneer species;
- Pioneers/species/organisms change the
environment/habitat/conditions/factors;
Accept example of change e.g. forms soil/humus/organic
matter/nutrients.
Must convey idea of change being caused by
pioneers/species/organisms - (Environment becomes) less hostile for other/new species
OR
(Environment becomes) more suitable for other/new species
OR
(Environment becomes) less suitable for previous species;
Accept previous species out-competed. - Change/increase in diversity/biodiversity;
- (To) climax community;
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)
- Use a grid
OR
Divide area into squares/sections;
Accept use of tape measures/map/area with coordinates.
Accept Belt transect. - 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. - Count number/frequency in a quadrat/section;
Accept % cover in quadrat/section.
Ignore amount/abundance. - 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. - 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;
Give two features of a climax community (2)
- Same species present (over long time) / stable community (over long
time); - Abiotic factors (more or less) constant (over time)
- Populations stable (around carrying capacity)
