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NCERT Solutions for Class 12 Biology Chapter 13
Organisms and Populations Class 12
Chapter 13 Organisms and Populations Exercise Solutions
Exercise : Solutions of Questions on Page Number : 239
Q1 :
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.
Q2 :
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.
Q3 :
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.
Q4 :
Most living organisms cannot survive at temperature above 45°C°. How are some microbes able to live in
habitats with temperatures exceeding 100°C?
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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.
Q5 :
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, all 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.
Q6 :
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
Where,
Nt= Population density after time t
NO= Population density at time zero
www.ncrtsolutions.in
NCERT Solutions for Class 12 Biology Chapter 13
Organisms and Populations Class 12
Chapter 13 Organisms and Populations Exercise Solutions
Exercise : Solutions of Questions on Page Number : 239
Q1 :
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.
Q2 :
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.
Q3 :
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.
Q4 :
Most living organisms cannot survive at temperature above 45°C°. How are some microbes able to live in
habitats with temperatures exceeding 100°C?
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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.
Q5 :
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, all 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.
Q6 :
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
Where,
Nt= Population density after time t
NO= Population density at time zero
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