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Organisms and Populations — BIOLOGY STD 12 Science — Question

Rajasthan BoardEnglish MediumSTD 12 ScienceBIOLOGYOrganisms and Populations4 Marks
Question
Explain population attributes.
✓

Answer

→ A population has certain attributes whereas, an individual organism does not.
→ An individual may have births and deaths, but a population has birth rates and death rates.
→ In a population these rates refer to per capita births and deaths. The rates, hence, expressed are change in numbers (increase or decrease) with respect to members of the population
→ Birth rates : Refer to per capita births. E.g. In a pond, there are 20 lotus plants last year Through reproduction 8 new plants are added. Hence, the current population 28 The birth rate 8/20-0.4 offspring per lotus per year.
→ Death rates : Refer to per capita deaths.
E.g. 4 individuals in a laboratory population of 40 fruit flies died during a week. Hence, the death rate-4/40-0.1 individuals per fruit fly per week.
→ Sex ratio : A population has a sex ratio.
E.g. 60% of the population is females and 40% males
→ Age pyramid : It is the structure obtained when the age distribution (% individuals of a given age or age group) is plotted for the population.
→ For human population, age pyramids generally show age distribution of males and females in a combined diagram.
Image
→ Population size or population density (N) : It is the number of individuals of a species per unit area or volume.
→ E.g. population density of Siberian cranes at Bharatpur wetlands in any year is <10. It is millions for Chlamydomonas in a pond.
Growth status Expanding (growing) Representation of age pyramids for human population, population size is also measured in % cover or biomass.
→ E.g. In an area, 200 Parthenium plants and a huge banyan tree are seen. In such cases, measuring % cover or biomass is meaningful to show importance of banyan tree.
Total number is a difficult measure for a huge population. In such cases, relative population density (without knowing absolute population density) is used.
→ E.g. Number of fish caught per trap indicates its total population density in the lake.
→ In some cases, indirect estimation of population sizes is performed. E.g. Tiger census in national parks & tiger reserves based on pug marks & fecal pellets.

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