(a) Following are the attributes that a population has but an individual organism does not (write any 2): [1]
Birth rate - Per capita Births
Death rate - Per capita deaths
Sex ratio - Ratio of number of males to females in a population.
(b) Population density refers to the number of individuals present per unit area at a given time/period. [1]
Different ways to measure population density are:
(i) By numbers : In order to determine the number of bacteria growing in a petri dish, their colonies are counted. [1]
(ii) By biomass or percentage cover : Biomass of one huge banyan tree is larger than hundreds of Parthenium plants. [1]
(iii) By indirect estimation : Tiger census is based on pugmarks and faecal pellets. [1]