Balbharati solutions for Biology 12th Standard HSC for Maharashtra State Board chapter 13 - Organisms and Populations [Latest edition]
![Chapter 13: Organisms and Populations [ Exercise,Solutions,Notes ]](https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEhZ5FIhWo-YZMFCj9f1IxGOow2KvFGU1bRy66W-nAS_HXVulQ9RMi9XAQG41LTyVBFxEOL8jK946Teyf7CTnuE4bx4w_BiBc2el2OCjPVltjSatgam4r7Dop7StEeqIxRIiAoAsLaAVXIP3VlV_LDuXMYWLBcZmcnSexadDoEpH_C58hhc5ZTHVP8qH/s500/Chapter%2013%20Organisms%20and%20Populations%20.webp "Chapter 13: Organisms and Populations [ Exercise,Solutions,Notes ]")
Multiple choice question
Exercise | Q 1.1 | Page 307
Which factor of an ecosystem includes plants, animals, and micro-organisms?
- Biotic factor
- Abiotic factor
- Direct factor
- Indirect factor
Solution:
Biotic factor
Exercise | Q 1.2 | Page 307
An assemblage of individuals of different species living in the same habitat and having functional interactions is _______________.
- Biotic community
- Ecological niche
- Population
- Ecosystem
Solution:
An assemblage of individuals of different species living in the same habitat and having functional interactions is a Biotic community.
Exercise | Q 1.3 | Page 307
Association between sea anemone and Hermit crab in gastropod shell is that of _______________.
- Mutualism
- Commensalism
- Parasitism
- Amensalism
Solution:
Association between the sea anemone and Hermit crab in gastropod shell is that of Commensalism.
Exercise | Q 1.4 | Page 307
Select the statement which explains the best parasitism.
- One species is benefited.
- Both the species are benefited.
- One species is benefited, other is not affected.
- One species is benefited, other is harmed.
Solution:
One species is benefited, other is harmed.
Exercise | Q 1.5 | Page 307
Growth of bacteria in a newly inoculated agar plate shows ____________.
- exponential growth
- logistic growth
- Verhulst-Pearl logistic growth
- zero growth
Solution:
Growth of bacteria in a newly inoculated agar plate shows exponential growth.
Define the following term and give one example for each
Exercise | Q 2.1 | Page 307
Commensalism
Solution:
Commensalism: Commensalism is an interaction between two species in which one species gets benefited while the other remains unaffected. An orchid growing on the branches of a mango tree and barnacles attached to the body of whales are examples of commensalisms.
Exercise | Q 2.1 | Page 307
Parasitism
Solution:
Parasitism is a kind of relationship between two species in which one species which is termed a parasite, derives its food from the other species which is termed as host. Parasitism also involves shelter, in addition to food obtained by a parasite. Parasites may be ectoparasites or endoparasites. Ectoparasites live on the surface of their host while endoparasites live inside the body of the host.
Examples of Parasitism
(i) Cuscuta growing on a shoe flower plant is a parasitic interaction, as Cuscuta derives nutrition from Hibiscus (shoe flower), as it lacks chlorophyll.
(ii) Head lice is an ectoparasite and suck human blood
(iii) Ascaris (roundworm), Taenia (tapeworm), Malaria (Plasmodium) causing diseases in humans
(iv) Koel laying its eggs in a crow’s nest is an example of brood parasitism. Birds lay eggs in the nest of their host and the host incubates it.
Define the following term
Exercise | Q 2.1 | Page 307
Camouflage
Solution:
Camouflage, also called cryptic coloration, is a defense mechanism or tactic that organisms use to disguise their appearance, usually to blend in with their surroundings. Organisms use camouflage to mask their location, identity, and movement.
Exercise | Q 2.2 | Page 307
Give one example for Interspecific competition
Solution:
Mutualism:
Example 1. A human requires oxygen for life and plants use carbon dioxide for photosynthesis. Here both humans and plants are mutually benefited. Humans use the oxygen given by the plants. In return, plants use carbon dioxide, which is exhaled by the Humans
Example 2. lichen is a mutualistic relationship between a fungus and algae. Algae provide food to fungus obtained from photosynthesis. The fungus provides anchoring and protection to the algae.
Exercise | Q 2.2 | Page 307
Give one example for Mutualism
Solution:
Interspecific competition:
Example 1. Imagine a cow and a horse on a piece of grassland. Both of them belong to different species but compete for the same grass (food). This type of interaction is called interspecific interaction.
Example 2. Competition between leopards and lions for the same prey,
Example 3. Resident fish competing with migratory birds Flamingos for common food i.e. zooplankton
Exercise | Q 2.3 | Page 307
Name the type of association: Clownfish and sea anemone
Solution:
Clownfish and sea anemone: The symbiotic interaction in which both partners benefit is referred to as mutualism.
The clownfish need protection from predators, so it requires sea anemone for protection. Sea anemone, on the other hand, requires food that is given by clownfish (faeces) to live. The two species derive benefits from each other. Their partnership is thus called a mutualistic relationship.
Exercise | Q 2.3 | Page 307
Name the type of association: Crow feeding the hatchling of Koel
Solution:
Crow feeding the hatchling of Koel: Brood parasitism
Exercise | Q 2.3 | Page 307
Name the type of association: Hummingbirds and host flowering plants
Solution:
Hummingbirds and host flowering plants: Mutualism
Exercise | Q 2.4 | Page 307
What is the ecological process behind the biological control method of managing pest insects?
Solution:
The ecological process behind the biological control method of managing pest insects is Predation. Predators regulate the population of prey in a habitat, thus helping in the management of pest insects.
Exercise | Q 3.1 | Page 307
How is the dormancy of seeds different from hibernation in animals?
Solution:
i. Seed dormancy a condition in which seeds are prevented from germinating even under suitable environmental conditions, The main reason behind these conditions is that they require a period of rest before being capable of germination. whereas hibernation in animals is a state of reduced activities to escape cold winter conditions.
ii. During seed dormancy, the growth, and development of an embryo are arrested temporarily, whereas in hibernation animals enter a state of inactivity by slowing their metabolism.
Exercise | Q 3.2 | Page 307
If a marine fish is placed in a freshwater aquarium, will it be able to survive? Give reason.
Solution:
i. If a marine fish is placed in a freshwater aquarium, fish would not be able to survive because marine fishes are adapted to high salt concentrations of the marine environment.
ii. Marine fishes have more osmotic concentration (more salt concentration) than marine water which prevents marine water to enter the body.
iii. When marine fish is placed in a freshwater aquarium, water enters into the body of marine fish due to osmosis, as freshwater creates a hypotonic environment outside the fish’s body.
iv. Entry of water into the body causes its body to swell leading to the death of the marine fish.
Exercise | Q 3.3 | Page 307
Name important defense mechanisms in plants against herbivores.
Solution:
Defense mechanisms in plants against herbivores can be morphological like thorns (in Acacia, Cactus) or chemicals like poisonous cardiac glycosides (produced by Calotropis), secondary metabolites (for e.g.nicotine, caffeine, quinine, strychnine, opium, etc.)
Exercise | Q 3.4 | Page 307
An orchid plant is growing on the branch of the mango tree. How do you describe this interaction between the orchid and the mango tree?
Solution:
An orchid is an epiphyte growing on the branch of a mango tree. Epiphytes are plants growing on other plants which, however, do not derive nutrition from them. Therefore, the relationship between a mango tree and an orchid is commensalism, where one species gets benefited while the other remains unaffected. In the above interaction, the orchid is benefited as it gets support while the mango tree remains unaffected.
Exercise | Q 3.5 | Page 307
Distinguish between the following: Hibernation and Aestivation.
Solution:
| Hibernation | Aestivation | |
| i. | It is also called winter sleep. | It is also called summer sleep. |
| ii. | It is a state of reduced activities in some organisms to escape cold winter conditions. | It is a state of reduced activities in some organisms to escape desiccation due to heat in summer. |
| iii. | Animals rest in warm places. | Animals rest in cool, shady, and moist places. |
| iv. | It is shown by bears inhabiting cold regions. | It is shown by some fish and snails. |
Exercise | Q 3.5 | Page 307
Distinguish between the following: Ectotherms and Endotherms.
Solution:
| Ectotherms | Endotherms | |
| i. | These are cold-blooded animals. | These are warm-blooded animals. |
| ii. | Ectotherms do not possess the ability to generate sufficient heat to keep them warm, thus their body temperature varies with their surroundings | Endotherms do possess the ability to generate heat and keep them warm, thus they can maintain constant body temperature. |
| iii. | They are also known as poikilothermic. | They are also known as homeothermic. |
| iv. | They are affected by changes in environmental temperature | They remain unaffected by changes in environmental temperature. |
| E.g. Most of the fishes, amphibians, reptiles | E.g. Birds, mammals |
Exercise | Q 3.5 | Page 307
Distinguish between the following: Parasitism and Mutualism
Solution:
| Parasitism | Mutualism | |
| i. | In parasitism, only one species (parasite) is benefited and the interaction is detrimental to other species (host). | In mutualism, both species are benefited. |
| ii. | The parasite needs a host, but the host does not need the parasite. | Both species need the presence of each other. |
| E.g. | Cuscuta, a parasitic plant commonly found growing on hedge plants. | Lichen represents the mutualistic relationship between a fungus and photosynthetic algae or cyanobacteria. |
Exercise | Q 3.6 | Page 307
Write a short note on Adaptations of plants to water scarcity
Solution:
Adaptations of plants to water scarcity:
- Plants found in deserts are well adapted to cope with water scarcity and the scorching heat of the desert.
- Plants have an extensive root system to tap underground water.
- They bear thick cuticles and sunken stomata on the surface of their leaves to reduce transpiration.
- In Opuntia, the leaves are modified into spines and the process of photosynthesis is carried out by green stems.
- Desert plants have special pathways to synthesize food, called CAM (C4 pathway). It enables their stomata to remain closed during the day to reduce water loss by transpiration.
Exercise | Q 3.6 | Page 307
Write a short note on Behavioural adaptations in animals
Solution:
- Behavioural adaptations in animals
- Certain organisms are affected by temperature variations. These organisms undergo adaptations such as hibernation, aestivation, migration, etc. to escape environmental stress to suit their natural habitat. These adaptations in the behaviour of an organism are called behavioural adaptations. For example, ectothermal animals and certain endotherms exhibit behavioral adaptations. Ectotherms are cold-blooded animals such as fish, amphibians, reptiles, etc.
- Their temperature varies with their surroundings. For example, the desert lizard basks in the sun during early hours when the temperature is quite low. However, as the temperature begins to rise, the lizard burrows itself inside the sand to escape the scorching sun. Similar burrowing strategies are exhibited by other desert animals.
- Certain endotherms (warm-blooded animals) such as birds and mammals escape cold and hot weather conditions by hibernating during winters and aestivating during summers.
- They hide in shelters such as caves, burrows, etc. to protect against temperature variations.
Short answer question
Exercise | Q 3.6 | Page 307
Write a short note on Adaptations of desert animals
Solution:
Adaptations of animals for desert habitats:
1. Desert animal-like Kangaroo rat inhabiting the Arizona deserts has the potential to concentrate its urine to conserve water. This animal never drinks water in its life.
2. Snakes and desert lizards bask in the sun early in the morning and burrow themselves in the sand in the afternoons to escape the heat of the day, to prevent water loss.
3. Camels can store fat in the hump which can be metabolised for energy. A camel can survive for many days without water. Long eyelashes, ears lined with hair, and slit-like nostrils help to keep out sand.
Exercise | Q 3.7 | Page 307
Define Population.
Solution:
Individuals live in groups in a well-defined geographical area, share or compete for similar resources, potentially interbreed and thus form a population.
Exercise | Q 3.7 | Page 307
Define Community.
Solution:
Community: Several populations of different species in a particular area constitute a community that interacts with one another in several ways.
Exercise | Q 4.1 | Page 307
With the help of a suitable diagram describe the logistic population growth curve.
Solution:
- Logistic growth curve of population
- Resources like food and space are not always unlimited. They may be plenty in the beginning; but as the population density increases, competition for those resources starts, resulting in a slowdown in the rate at which the original population was growing. This results in a logistic or sigmoid growth curve.
- Competition between individuals for limited resources will weed out the ‘weaker' ones. Only the ‘fittest’ individuals will survive and reproduce.
- A given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible. This limit can be called nature’s carrying capacity (K) for that species in that habitat.
- A population growing in a habitat with limited resources shows initially a lag phase, followed by phases of acceleration and deceleration, and finally an asymptote when the population density reaches the carrying capacity.
- A plot of population density (N) in relation to time (t) results in a sigmoid curve. This type of population growth is called VerhulstPearl Logistic Growth.
- Since resources for the growth of most animal populations, are finite and become limiting sooner or later, the logistic growth model is considered a more realistic one.
Exercise | Q 4.2 | Page 307
Enlist and explain the important characteristics of a population.
Solution:
- The important characteristics of a population are population size, population density, natality, mortality, sex ratio, immigration, emigration, age pyramids, expanding population, population growth forms, and biotic potential.
- Population density: Population density tells us the number of individuals present in per unit space, in a given time. OR The density of a population is the total number of individuals in that population present per unit area at a specific time.
- Natality: Natality is the birth rate of a population.
- Mortality: Mortality is the death rate of a population.
- Age distribution and Age pyramids: 1. A population consists of individuals of different ages. The entire population is divided into three age groups – pre-reproductive (0-14 years), reproductive (age 15-44 years), post-reproductive (45-85+years)The relative proportion of individuals of various age groups in the population is referred to as the age structure of the population. 2. If the age distribution (percent individuals of a given age or age group) is plotted for the population, the resulting structure is called as age pyramid.
- Sex Ratio: Sex ratio is the ratio of the number of individuals of one sex to that of the other sex.
organisms and populations class 12 notes
Natural world around us shows amazing
diversity of forms and complexity of relations.
To understand these, we have to study
levels of organization in the living world
viz. macromolecules, cells, tissues, organs,
individual organism, population, communities,
ecosystems and biomes.
You have already studied in school, that
ecology is a study of the interactions among
organisms and between the organisms and their
physical (abiotic) environment.
Term ecology
was first used by Reiter but E. Haeckel gave
substance to the term (introduced) ecology.
Ecological grouping of organisms is
nothing but ecological hierarchy. There are four
sequential levels with increasing complexity
of ecological (biological) organizations viz,
Organism, Populations, Communities and
Biomes. Individual organism is the basic
unit of ecological hierarchy. Organisms of
same kind inhabiting a geographical area
constitute population.
Several populations of
different species in a particular area constitute
community that interact with one another
in several ways. Biome constitutes a large
regional terrestrial unit delimited by a specific
climatic zone having major vegetation zone
(plant communities) and the associated fauna.
There are six major groups of terrestrial biomes.
We shall explore first two levels viz, organism
and populations.
Organisms and the environment
around:
Ecology at the level of organism is basically
the study of animal or plant physiology which
helps us to understand how the organisms are adapted to their environments, not only
for their survival but also for propagation
(multiplication).
You have studied in earlier classes about
the rotation of earth around the Sun and the tilt
of its axis, cause seasons. These seasons with
annual variation in precipitation in the form of
rain and snow, gives rise to formation of major
biomes of the earth like desert, rain forest,
grassland, tundra, etc.
Regional and local variations within each
biome lead to the formation of a variety of
habitats. Major biomes of earth are shown
in Fig. 13.1. On the Earth, life exists even in
extreme and harsh habitats like scorching
deserts of Rajasthan, perpetually rain-soaked
forests of North Eastern states and high
mountain tops of Himalayas.
Here, we must remember that it is not only
the physico-chemical (abiotic) components
that make up the habitat of an organism, but
the habitat also includes biotic components like plants, pathogens, parasites, and predators of
the organism. We assume that over a period
of time, the organism had through natural
selection, evolved adaptations to optimize its
survival and reproduction in its habitat
Habitat and Niche :
Habitatis a place or the set of environmental
conditions around the organism to which it must
adapt to survive and prosper. The term Niche is
used to denote the functional role played by an
organism in its environment (J. Grinnell 1917).
Niche includes various aspects of the life of an
organism like diet, shelter, etc.
A habitat defines the physical space of
an organism with the other living or nonliving factors, while niche describes how
that organism is linked with its physical and
biological environment. In colloquial language
habitat is a postal address while niche is the
profession of organism.
Definition of Habitat :
Place or area where a particular species
lives, is its habitat. Factors like the sunlight,
average rainfall, annual temperatures, type
of soil present and other abiotic (topographic)
factors, affect the presence of organisms. These
factors help in determining the presence of the
particular type of species in the environment.
Pond, river, ocean, etc. are the examples
of habitat as many organisms are found in
the same place or habitat. These habitats can
be arboreal, terrestrial, aerial, aquatic, etc.
The immediate surrounding of an organism,
sometimes also referred to as microhabitat,
is an important concept to remember when
working with sedentary or weakly motile
organisms
Definition of Niche :
The term niche was first time used by ‘J.
Grinnell’. The term ecological niche is still
not well understood and is sometimes even
misused.
Niche is described as a position of a species
in the environment like, what they do for their
survival? how they fulfill their needs of shelter,
food? etc. Niche deals with the flow of energy
from one organism to another and hence, it is
important to understand, what an organism
eats, how it interacts with other organisms,
etc. As soon as the niche is left vacant, other
organisms fill that position.
The niche is
specific to each species, which means no two
species can share the same niche.
If the species creates its own unique
niche in an ecosystem, it would be helpful in
reducing competition for resources among
species. By taking an example of a bird, it
can be understood that how these birds differ
in their eating habits, where some birds eat
only insects, some only fruits and some can eat
both and anything they come across. So here
we can conclude that these birds living in the
same habitat differ in their niches because of
different eating habits.
Major Abiotic Factors :
Temperature:
It is the most ecologically relevant
environmental factor. Average temperature
on land varies from subzero levels in polar
areas and high altitudes, upwards upto 50o
C in
tropical deserts in summer. Temperature also
varies seasonally. It decreases progressively
from the equator towards the poles and from
plains to the mountain tops.
There are some
unique habitats such as hot springs (80 to
1000
C) and deep-sea hydrothermal vents where
average temperatures usually 400o
C. Ambient
temperature affects the enzyme kinetics of the
cell and thus, the entire metabolism, activity
and other physiology of the organism.
Only few organisms can tolerate and thrive
in a wide range of temperatures (eurythermal),
but, a vast majority of them are restricted to a
narrow range of temperatures (stenothermal).
Water: Availability of water is an important
factor affecting the organisms. As we know,
life on earth originated in water, its availability
is so limited in deserts that only special
adaptations are required to survive there. The
productivity and distribution of plants are also
heavily dependent on water.
Organisms living in water bodies such as
oceans, lakes and rivers, have their own waterrelated problems. For aquatic organisms the
chemical composition and pH of water are
important.
The dissolved salt concentration (measured
as salinity in parts per thousand), is less than
5ppt in fresh waters of streams , lakes and
rivers, and 30-35ppt in the seas and oceans.
It may go up to 100ppt in some hypersaline
lagoons.
Some organisms are tolerant for a wide
range of salinities (euryhaline) but others are
restricted to a narrow range (stenohaline).
Many fresh water animals cannot live for long
in sea water and vice versa because of the
osmotic problems, they would face.
Light: Plants use light for photosynthesis,
which is only source of energy for the entire
ecosystem. Photosynthesis can occur only in
presence of sunlight. Many species of small
plants (herbs and shrubs) growing on forest
floor are adapted to perform photosynthesis
optimally under very low light conditions
because they are constantly overshadowed by
tall trees.
For animals too, diurnal and seasonal
variations in light intensity and duration
(photoperiod) are clues for timing their foraging,
reproductive and migratory activities. The
availability of light on land is closely linked
with that of temperature, since the sun is the
source for both.
Soil: The nature and properties of soil are
dependent on the climate, the weathering
process.
Various characteristics of the soil such
as soil composition, grain size, determine
the percolation and water holding capacity
of the soil. These characteristics along with
pH, mineral composition and topography,
determine the vegetation of an area. Vegetation
in turn dictates the type of animals.
The abiotic factors that determine the type
of habitat, also show considerable diurnal and
seasonal variations.
The plants and animals
must adapt to these changes in order to survive
and flourish in the habitat. During the course
of their evolution, many species have evolved
a relatively constant ‘internal’ environment
that permits all biochemical reactions and
physiological functions to proceed with
optimum rate, and allow the species to flourish.
The organisms try to maintain the constancy of
its internal environment (homeostasis) despite
variations in the external environmental
conditions. To survive and flourish in any
environment, organisms must adapt to the
changes in the environment for which there are
following possibilities :
i. Regulate: Some organisms are able to
maintain homeostasis by physiological
and behavioural changes which ensure
constant body temperature, constant
osmotic concentration, etc. All birds and
mammals are capable of such regulation
(thermoregulation and osmoregulation).
ii. Conform: Most of animals and plants
cannot maintain a constant internal
environment. Their body temperature
changes with the ambient temperature. In
aquatic animals, the osmotic concentration
of the body fluids changes with that of the
ambient water osmotic concentration. These
animals and plants are simply conformers.
Some species have evolved the ability
to regulate, within a limited range of
environmental conditions, beyond which
they simply conform. If the stressful
environment is localized or only for a short
period of time, the organism may migrate
or suspend its activities
iii. Migrate: The organism can move away
temporarily from the stressful habitat to
a more hospitable area and return when
stressful period is over. Many animals,
particularly birds, during winter undertake
long-distance migrations to more hospitable
areas.
iv. Suspend: In plants, seeds serve as means to
tide over periods of stress; they germinate to
form new plants under favourable moisture
and temperature conditions. They do so by
reducing their metabolic activity and going
into a state of ‘dormancy’. In animals, the
organism, if unable to migrate may go into
hibernation during winter e.g. polar bear.
Some snails and fish go into aestivation to
avoid summer heat.
organism (morphological, physiological, and
behavioural) that enables the organism to
survive and reproduce in its habitat.
Many desert plants have a thick cuticle
on their leaf surfaces and have their stomata
in deep pits to minimize loss of water through
transpiration. They also have a special
photosynthetic pathway (CAM - Crassulacean
acid metabolism) that enables their stomata
to remain closed during daytime.
Some desert
plants like Opuntia, have their leaves reduced
(modified) to spines and the photosynthetic
function is taken over by the flattened stems.
Mammals from colder climates generally
have shorter snout, ears, tail and limbs to
minimize the loss of body heat (Allen’s Rule.)
In the polar seas, aquatic mammals like seals
have a thick layer of fat (blubber) below their
skin acting as an insulator to reduce loss of
body heat.
Some organisms show behavioural
responses to cope with variations in their
environment. Desert lizards manage to keep
their body temperature fairly constant by
behavioural adaptations. They bask in the sun
and absorb heat, when their body temperature
drops below the comfort zone, but move into
shade, when the ambient temperature starts
increasing. Some species burrow into the sand
to hide and escape from the heat.
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