NCERT Solutions Class 12 Biology Chapter 13 Organisms and Populations

NCERT Solutions Class 12 Biology Chapter 13 Organisms and Populations. The NCERT solutions for Class 11 Mathematics have been made by Mathematics teacher of one of the best CBSE school in India. These NCERT solutions have been made to give detailed answers and expanations of the concepts as per NCERT which can be easily understood by the students. Refer to other links also to download mathematics NCERT solutions, worksheets, sample papers and Exemplar Solutions. 

Class 12 Biology

NCERT Solutions

Chapter 13 Organisms and Populations

Question 1: How is diapause different from hibernation?

Answer Diapause is a stage of suspended development to cope with unfavourable conditions. Many species of Zooplankton and insects exhibit diapause to tide over adverse climatic conditions during their development. Hibernation or winter sleep is a resting stage where in animals escape winters (cold) by hiding themselves in their shelters. They escape the winter season by entering a state of inactivity by slowing their metabolism. The phenomenon of hibernation is exhibited by bats, squirrels, and other rodents.

Question 2: If a marine fish is placed in a fresh water aquarium, will the fish be able to survive? Why or why not?

Answer If a marine fish is placed in a fresh water aquarium, then its chances of survival will diminish. This is because their bodies are adapted to high salt concentrations of the marine environment. In fresh water conditions, they are unable to regulate the water entering their body (through osmosis). Water enters their body due to the hypotonic environment outside. This results in the swelling up of the body, eventually leading to the death of the marine fish.

Question 3: Define phenotypic adaptation. Give one example.

Answer Phenotypic adaptation involves changes in the body of an organism in response to genetic mutation or certain environmental changes. These responsive adjustments occur in an organism in order to cope with environmental conditions present in their natural habitats. For example, desert plants have thick cuticles and sunken stomata on the surface of their leaves to prevent transpiration. Similarly, elephants have long ears that act as thermoregulators.

Question 4: Most living organisms cannot survive at temperature above 45°C°. How are some microbes able to live in habitats with temperatures exceeding 100°C?

Answer Archaebacteria (Thermophiles) are ancient forms of bacteria found in hot water springs and deep sea hydrothermal vents. They are able to survive in high temperatures (which far exceed 100°C) because their bodies have adapted to such environmental conditions. These organisms contain specialized thermo-resistant enzymes, which carry out metabolic functions that do not get destroyed at such high temperatures.

Question 5: List the attributes that populations but not individuals possess.

Answer A population can be defined as a group of individuals of the same species residing in a particular geographical area at a particular time and functioning as a unit. For example, a ll human beings living at a particular place at a particular time constitute the population of humans. The main attributes or characteristics of a population residing in a given area are:-

(a) Birth rate (Natality): It is the ratio of live births in an area to the population of an area. It is expressed as the number of individuals added to the population with respect to the members of the population.

(b) Death rate (Mortality): It is the ratio of deaths in an area to the population of an area. It is expressed as the loss of individuals with respect to the members of the population.

(c) Sex ratio: It is the number of males or females per thousand individuals.

(d) Age Distribution: It is the percentage of individuals of different ages in a given population. At any given time, the population is composed of individuals that are present in various age groups. The age distribution pattern is commonly represented through age pyramids.

(e) Population density: It is defined as the number of individuals of a population present per unit area at a given time.

Question 6: If a population growing exponentially double in size in 3 years, what is the intrinsic rate of increase (r) of the population?

Answer A population grows exponentially if sufficient amounts of food resources are available to the individual. Its exponential growth can be calculated by the following integral form of the exponential growth equation:

Nt = No ert


Nt= Population density after time t

NO= Population density at time zero

r = Intrinsic rate of natural increase

e = Base of natural logarithms (2.71828) 

From the above equation, we can calculate the intrinsic rate of increase (r) of a population.

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