Question
a. Distinguish between fundamental niche and realized niche.[1]
b. Outline the impact of competition on the niche of an organism.[2]
c. Outline the characteristics of keystone species in an ecosystem.[1]
▶️Answer/Explanation
Ans:
a. fundamental is the potential (niche) and realized is the actual (niche)
OWTTE.
b. a. competition can limit the niche
b. competition can limit resources
c. when competition is removed the niche can expand
d. can result in exclusion or removal of a species from a niche / only one species can occupy a niche
c. a. keystone species has a strong/disproportionate effect on a community/food web/ecosystem
b. absence of keystone species would completely alter the ecosystem
Question
Gersmehl diagrams for two ecosystems are shown.
a. Identify the processes represented by the arrows labelled A and B in both diagrams.[2]
b. Deduce, with a reason, which ecosystem is representative of a tropical rainforest.[2]
▶️Answer/Explanation
Ans:
a. a. Process A: decomposition/decay
b. Process B: leaching/erosion/run-off/weathering
b. a. ecosystem I
b. low levels of litter due to high rates of decomposition OR high amounts of biomass related to high rates of productivity OR weathering/leaching due to high rates of precipitation
Question
The diploid number of chromosomes in horses (Equus ferus) is 64 and the diploid number in donkeys (Equus africanus) is 62. When a male donkey and a female horse are mated, the result is a mule which has 63 chromosomes.
State the haploid number for horses.
Explain reasons that mules cannot reproduce.
Discuss whether or not horses and donkeys should be placed in the same species.
A mule was born at the University of Idaho in the USA with 64 chromosomes. Suggest a mechanism by which this could happen.
▶️Answer/Explanation
Markscheme
32
a. because the chromosome number is not an even number/63
b. (so) cannot divide by two during meiosis/cannot perform meiosis/chromosomes cannot pair up during meiosis
c. one chromosome has no homologue/WTTE
d. because unlikely to/cannot produce viable gametes/sperm/egg cells
a. to be in same species two organisms must have the same genes arranged on the same chromosomes
OR
must have the same number of chromosomes
b. members of same species produce fertile offspring and a mule is not fertile
non-disjunction
Accept description of non-disjunction.