Organism and Population MCQs for NEET — Botany Questions with Answers

(d) Bacteria, fungi and lower plants survive in adverse conditions through formation of thick-walled spores. Algae form resting spore or akinetes which are thick-walled spores and store food material. In fungi, thick-walled perennating spores called chlamydospores are formed. Bacteria form endospores which is probably the most resistant living thing known. They may remain alive in boiling water for more than 2 hours.

(b) Monarch butterfly escapes from predators because of its bitter taste. Viceroy butterfly (Basilarchia archippus) mimics monarch butterfly to escape from predators.

(b) Immigration is the entry of individuals into a region for permanent or temporary settlement thereby increasing the population density of that particular region due to addition of individuals. Food shortage, disease and famine are the factors that would limit the growth of a population. 

(a) The population growth curve will be S-shaped or sigmoid or logistic. The growth cure has five phases - lag phase, positive acceleration phase, exponential phase, negative acceleration phase and stationary phase. Most of the organisms including human population shows S-shaped curve.

Population increases due to increase in birth rate and immigration while population decreases due to increase in death rate and emigration.

A. Population is stable when B+I = D+E

B. Population is increasing when B+I > D+E

C. Population is decreasing when B+I < D+E.

If the age distribution (per cent individuals of a given age or age group) is plotted for the population, the resulting structure is called an age pyramid.

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Timing of birth, timing of death and the rate of population growth determines the age distribution of a population.

The density of a population in a given habitat during a given period, fluctuates due to changes in four basic processes:-

1. Natality and immigration contribute an increase in population density
2. Mortality and emigration to a decrease in population density

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Exponential growth occurs when there are unlimited food resources and  each species has the ability to realise fully its innate potential to grow in number. When there is no inhibition from crowding, exponential growth occurs.

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In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. This limit is called as nature’s carrying capacity (K) for that species in that habitat.

Logistic growth:  No population of any species in nature has its disposal unlimited resources to permit exponential growth. This leads to competition between individuals for limited resources. Eventually, the ‘fittest’ individual will survive and reproduce.

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