Organisms and Populations: questions with answers

(a) Exponential growth occurs under effectively unlimited resources with dN/dt = rN, while logistic growth slows near carrying capacity K through density dependence.

(d) The logistic model explicitly includes carrying capacity.

(b) Temperature, water, light and soil affect organism performance and distribution through physiological tolerance and resource availability; responses depend on both species traits and life stage.

(d) Multiple interacting abiotic and biotic factors shape distributions.

(b) Desert plants lose less water because of a thick cuticle, sunken stomata, CAM and changed leaves. Desert animals save water through behaviour and body changes. Adaptation is heritable, not acclimatisation that happens on purpose.

(b) CAM plants open stomata mainly at night to reduce water loss.

(a) Births, deaths, immigration and emigration change population size. Resource limitation, competition, disease and predation often create density-dependent feedback around a variable carrying capacity.

(b) Immigration adds individuals; emigration removes them.

(c) Population density, natality, mortality, age structure and sex ratio describe populations rather than single organisms. Density may be measured as numbers, biomass or another appropriate index.

(c) Birth rate is defined for a population over time.

(b) Natural selection shapes the timing of reproduction, offspring number, size and parental investment; trade-offs mean no single strategy maximises every component in every environment.

(a) Competition reduces access to shared limiting resources, while predation transfers energy and can regulate prey or maintain diversity; interaction outcomes depend on ecological context.

(c) Parasites gain resources from hosts and often evolve attachment, ways to escape the host's immune system, reduced unnecessary organs and high reproduction. Hosts evolve defences, producing reciprocal selection.

(b) In mutualism both partners benefit. In commensalism one benefits while the other shows no measurable effect. Outcomes can shift with environmental conditions.

(a) Organisms may regulate internal conditions, conform physiologically, migrate temporarily or suspend activity through dormancy, diapause or spores. These strategies have different costs and limits.