Curiosity is the foundation of learning, which is why Zigya follows a unique model of non-pedagogical approach to learning. Zigya's approach is designed to ensure that students remain curious to know more and build on self-reliance having timely answers to their questions.

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(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) Following are the attributes that a population has but an individual organism does not have:

Birth rate: per capita births. It represents the increase in number with respect to the population.
Death rate: per capita deaths. It represents the decrease in number with respect to the population.
Sex ratio: Ratio of number of males to females in a given population.
Age distribution: A population at any given time is composed of individuals of different ages.

(b) Population density means number of individuals present per unit area. Population density can be measured by determining the population size. The different methods to study population size are as follows:

(1) Indirect method: In this method the population density is measured without actually counting or seeing the organism. For examples – the tiger consensus in our national park and tiger reserves are often based on the pug marks and fecal pellets of the tiger.
Example: The number of Parthenium plants in a given area can be measured using the quadrat method.

(2) Direct observation: It involves the counting of organisms in the given area.
Example: In order to determine the number of bacteria growing in a Petri dish, their colonies are counted.

(3)Relative densities: When the population is too large to be counted then relative density is taken into account . For example: The number of fishes caught per trap gives the measure of their total density in a given water body.

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.

List any three important characteristics of a population and explain.

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) 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.

(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.