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List any three important characteristics of a population and explain.

Three important characteristics of a population are :

(i) Population size and population density

(ii) Birth or natality rate

(iii) Death or mortality rate.

(i) Population size. The size of population keeps changing with time depending on the factors like :

(i) Food availability (ii) Weather

(iii) Predation pressure and (iv) Competition.

The population density in a given habitat during a given period, changes due to four basic processes namely (1) Natality, (2) Mortality, (3) Immigration and (4) Emigration.

While natality and immigration contribute to an increase in the size and density of a population, mortality and emigration contribute to a decrease in them.

So the equation for population growth is :

N_{t +1} = N_t + [(B + I) - (D + E)],

where N_t = population density at time t.

B = birth rate.

I = Immigration.

D = death rate.

E = emigration.

If B + I is more than D - E, the population density increases.

If B + I is less than D - E, the population density decreases.

(ii) Birth or Natality rate. It is generally expressed as number or births per 1,000 individuals of a population per year. It increases the population size (total number of individuals of a population) and population density.

(iii) Death or Mortality rate. It is opposite of natality rate. It is commonly expressed as the number of deaths per 1,000 individuals of a population per year.

List the attributes that populations possess but not the individuals.

If the population growing exponentially doubles in size in 3 years, what is the intrinsic rate of increase (r) of the population?

Name important defence mechanisms in plants against herhivory.

With the help of suitable diagram describe the logistic population growth curve.

Write short notes on :
(a) adaptations of desert plants and animals.

(b) adaptations of plants to water scarcity.

(c) behavioural adaptations in animals.

(d) importance of light to plants.

(e) Effect of temperature or water scarcity and the adaptations of animals.

Define the following terms and give one example for each:
(a) Commensalism
(b) Parasitism
(c) Camouflage
(d) Mutualism
(e) Interspecific competition

Select the statement which explains best parasitism.

How is diapause different from hibernation ?

List the various abiotic environmental factors factors.

If a marine fish is placed in a fresh water aquarium, will the fish be able to survive ? Why or why not ?

Define phenotypic adaptation. Give one example.

Most living organisms cannot survive at temperature at about 45°C. How are some microbes able to live in habitats with temperatures exceeding 100°C ?

An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree ?

What is the ecological principle behind the biological control method of managing with pest insect ?

Distinguish between the following :
(a) Hiberation and aestivation

(b) Ectotherms and endotherms.

Give an example for:
(a) An endothermic animal
(b) An ectothermic animal
(c) An organism of benthic zone

Define population and community

'Analysis of age-pyramids for human population can provide important inputs for long-term planning strategies.' Explain.

(a) List the different attributes that a population has and not an individual organism.

(b) What is population density ? Explain any three different ways the population density can be measured, with the help of an example each.

(a) Explain giving reasons why the tourists visiting Rohtang Pass or Mansarovar are advised to resume normal active life only after a few days of reaching there.

(b) It is impossible to find small animals in the polar regions. Give reasons.