The document explores ecology, focusing on the interactions between organisms and their abiotic environment, highlighting the importance of ecological investigations for resource conservation and environmental issues. It categorizes major biomes like rainforests, deserts, and tundras, explaining their distinct climates and ecosystems. Additionally, it discusses population dynamics, growth models, and types of ecological interactions such as predation and competition, underlining the significance of both biotic and abiotic factors in determining the survival and adaptation of species.

1. UNIT NO 13
ORGANISMS AND
POPULATION
12TH BIOLOGY (BOARD)
Presented by Miss Madhuri Yashwantrao Bhande
Msc zooloy ,persuing ph.D
Subject zoology
Rajarshi shahu Mahavidyalaya latur

2. INTRODUCTION
 The study of interactions between organisms and between them and their physical (abiotic) environment is known as ecology.Ecology investigations are
crucial for finding a balance between resource use and conservation, the growth and maintenance of biotic and natural environments, and the resolution
of local, regional, and global environmental issues.

3. Organism and its Environment
The environment is the culmination of all biotic and abiotic
elements, materials, and circumstances that surround and may have
an impact on organisms without really being a part of them.
Physiological ecology studies how various organisms are adapted to
their environments for survival and procreation at the organism
level.
The establishment of major biomes like the desert, rain forest, and
tundra is caused by differences in the intensity and duration of
temperature as well as annual variations in precipitation.

5. Enjoy the knowledge
 A biome is a large community of vegetation and wildlife adapted to a specific climate.
 biome, also called major life zone, the largest geographic biotic unit, a major community of plants and
animals with similar life forms and environmental conditions. It includes various communities and is named
for the dominant type of vegetation, such as grassland or coniferous forest. Several similar biomes constitute
a biome type—for example, the temperate deciduous forest biome type includes the deciduous forest biomes
of Asia, Europe, and North America. “Major life zone
 coniferous forest, vegetation composed primarily of cone-bearing needle-leaved or scale-leaved evergreen
trees, found in areas that have long winters and moderate to high annual precipitation
 A rainforest is an area of tall, mostly evergreen trees and a high amount of rainfall. Rainforests are Earth's
oldest living ecosystems, with some surviving in their present form for at least 70 million years.
 The tundra is the coldest of the biomes. It also receives low amounts of precipitation, making the tundra
similar to a desert. Tundra is found in the regions just below the ice caps of the Arctic, extending across North
America, to Europe, and Siberia in Asia.
 Temperate climates are generally defined as environments with moderate rainfall spread across the year or
portion of the year with sporadic drought, mild to warm summers and cool to cold winters
 grassland, area in which the vegetation is dominated by a nearly continuous cover of grasses. Grasslands
occur in environments conducive to the growth of this plant cover but not to that of taller plants, particularly
trees and shrubs.

6.  A tropical forest is a type of forest found in areas with high regular rainfall and no more than
two months of low rainfall, and consisting of a completely closed canopy of trees that prevents
penetration of sunlight to the ground and discourages ground-cover growth.
 landscape: a section or expanse of rural scenery, usually extensive, that can be seen from a
single viewpoint.
 The biosphere is made up of the parts of Earth where life exists—all ecosystems. The biosphere
extends from the deepest root systems of trees, to the dark environments of ocean trenches, to
lush rain forests, high mountaintops, and transition zones like this one, where ocean and
terrestrial ecosystems meet
 The word biosphere came from the Greek “bios” that refers to “Life” and “sphaira” that refers
to the Earth's shape

7. MAJOR ABIOTIC FACTORS
 Regional and local variations within each biome lead to the formation of different kinds of habitats like tropical rain forest, deciduous forest,
desert, sea coast etc.
 The habitat includes biotic components like pathogens, parasites, predators and competitors of the organism with which they interact
constantly.
 Major Abiotic Factors
 a) Temperature- The most crucial biological aspect in determining a location's biomass is its temperature.
 The average land temperature fluctuates periodically and gradually drops from plains to the summits of mountains and from the equator to the
poles. The physiological processes of the organisms as well as the kinetics of enzymes and basal metabolism are impacted by temperature.
 Eurythermal organisms include cats, dogs, tigers, and other creatures that can withstand a broad variety of temperatures.
 Stenothermal organisms are those that can only withstand a limited range of temperatures; examples of these include fish, crocodiles, penguins,
and so on.

8. • .b) Water-Without water, life on Earth could not exist. Water has an enormous effect on plant dispersion and productivity. The
pH and chemical makeup of the water become crucial for aquatic life. In inland waters, the salinity (measured in parts per
thousand) is less than 5, in the sea, it is between 30 and 35, and in some hypersaline lagoons, it is greater than 100.
• The organisms that can tolerate wide range of salinities are called euryhaline ,for example salmon , hierring etc.
• The organism which have the ability to tolerate only a narrow range of salinities are called stenohaline, for example goldfish ( freshwater )
and haddock ( marine water )etc
• The organism which have the ability to tolerate only a narrow range of salinities are called stenohaline, for example goldfish ( freshwater ) and
haddock ( marine water )etc.

9.  c) Light- In the presence of sunlight, plants use photosynthesis to make food.
 Because they are shaded by large canopied trees, certain plants have adapted to low light levels. Certain plants only flower when they get
photoperiodism, or critical daylight.
 Since the sun is the source of both, the availability of light and land is strongly related to that of temperature. Sunlight's UV rays are toxic to both
plants and animals.

10.  d) Soil- The weathering process, climate, sedimentary or transported soil, and the process of soil development all affect the types of soil.
 Along with pH, mineral content, composition, and topography, soil composition, grain size, and aggregation determine the soils' ability to
percolate and hold water. These factors also determine the vegetation in any given area.
 Reactions to Abiotic Elements: Over the course of evolution, many species have developed a stable internal environment that enables all
physiological processes and biochemical reactions to function as efficiently as possible in order to enhance overall species fitness.
 Despite changing external conditions, organisms strive to maintain homeostasis, or consistency within their internal environment. Hemostasis
can be established in a number of ways:

11.  Regulate-
 All animals, including birds, are able to sustain homeostasis through physiological processes, which guarantees steady body temperature, steady
osmotic concentration, and so forth.
 Mammals thrive in a variety of environmental circumstances due to their ability to regulate their body temperature and osmoregulation.
 We sweat a lot in the summer because the outside temperature is higher than our body temperature. This causes evaporative cooling, which lowers
body temperature.
 We begin to shiver in the winter, which is a type of exercise that generates heat and increases body temperature.
 Conform-
 The majority of animals and plants experience temperature changes in response to their surroundings. In aquatic animals osmotic
concentration of the body fluid change with that of the ambient water osmotic concentration.
 These animals are called conformer. Conformer are not able to bear the energetic expenses to maintain the constant body
temperature.Heat loss or heat gain is a function of surface area.
 Small animals lose body heat more quickly in cold weather because their surface area is larger than their volume; therefore, they must
use more energy to produce body heat through metabolism. This is the primary cause of the rarity of very small animals in polar regions.
 Migrate- The organism temporarily relocates to a more suited habitat from the stressful unfavourable habitat and returns when the stressful period
is over. Many birds migrate over great distances in search of warmer climates. Birds from Siberia migrate to India's Keolado National Park in Bharatpur.
 Suspend: Thick-walled spores are produced by microorganisms such as fungi, bacteria, and lower plants to help them withstand adverse environments.
 When favourable conditions are restored, these spores begin to sprout.
 Higher plants use their seeds and other vegetative reproductive organs to help them disperse as well as survive stressful times.
 This dormant phase is characterised by minimal metabolic activity.
 a)Hibernation – the condition or period of an animal or plant spending the winter in a dormant state e.g bear
 b)Aestivation – the condition or period of an animal or plant spending the summer to avoid heat and dessication in a dormant
state e.g snails .

13. habitat and niche
Habitat Niche
A habitat is a particular place where organisms
live, i.e. address.
A niche defines a specific role played by
organisms in an ecosystem, i.e. profession.
Habitat is not species-specific, and many species
can occupy the same habitat.
Niche is species-specific, and it supports only a
single species.
Habitat consists of several niches.
Niche is specific to a particular species, which
may overlap with a similar niche but must have
distinct differences.
Habitat is a superset of niche. Niche is a subset of habitat.
Examples: desert, ocean, mountains, grassland,
forest, etc.
Examples: different trophic positions occupied
by Darwin’s finches.

16. What is a Habitat? –
Definition of Habitat
 Temperature, sunlight, rainfall, types of soil, etc. and other abiotic factors
determine the presence of organisms in an area. These factors prevailing in an
area determine the best-suited species for that environment.
 Habitat is the best-suited condition for a species and provides ideal conditions for
a species to grow, adapt, reproduce and flourish.
 It is the energy or nutrient-providing area for an organism. The habitat of a
species describes the totality of abiotic factors to which the species is exposed in
the area.
 Examples of habitats include deserts, ponds, freshwater lakes, oceans, mountains,
grassland, forest, etc.

17.  What is a Niche? – Definition of Niche
 “Niche is defined as a functional role played by an organism in its ecosystem.”
 Joseph Grinnel coined the term “Niche”. He described a niche as the distributional unit specific
to each species. He emphasised that no two species living in the same territory can occupy the
same ecological niche for long.
 The ecological niche not only involves the physical space occupied by an organism but also
describes the functional role or place of a species in its community structure. This includes
everything related to how it influences a community, i.e. what it eats, where it lives, what it
does, the trophic position occupied, etc. Niche describes how a species contributes to the
system’s energy flow and how it gains energy and supplies it further in an ecosystem.

18.  There are three aspects of an ecological niche:
 Spatial or habitat niche: It accounts for the physical space occupied by an organism. This
explains the different microhabitats owned by several species having similar general habitats.
E.g. seven species of millipedes reside in the same general habitat of the forest floor of a maple
oak forest, and all are decomposers, i.e. occupy the same trophic level but predominate in their
specific microhabitat that is created by several gradients in the decomposition stage.
 Trophic Niche: It tells about the functional role or trophic position occupied by a species. It
explains how different species share the same habitat but occupy different trophic niches. E.g.
Darwin’s finches of the Galapagos islands. These birds belong to the same genera and live in the
same general habitat but differ in their eating habits, i.e. trophic position. One species is
vegetarian, feeding on buds and fruits, and, others are insect eaters, feeding on insects of
different sizes. There is a woodpecker finch, which has a wood-pecking beak.
 Hypervolume or multidimensional niche: It represents the position of a species in the
environmental gradient. There are a large number of environmental factors, both abiotic and
biotic, that affect the population. This is the fundamental niche of the species and refers to the
totality of abiotic and biotic factors to which a given species is uniquely adapted.

19. Adaptation Definition “Adaptation is the physical or behavioural characteristic of an
organism that helps an organism to survive better in the surrounding environment.”
 All living things have evolved to fit their natural environments. This is a result of unique characteristics that aid in
their survival. These unique characteristics evolved as a result of gene mutation during evolution. These mutations
are passed down from generation to generation and help with survival and reproduction.
Structural Adaptations
These include an organism's physical characteristics that aid in its survival in the environment, such as the various
kinds of terrestrial habitat. The alterations in the physical surroundings are connected to the changes in the body.
Consider the protective colouring that aids in an organism's ability to blend in with its surroundings—camouflage. They
are better protected from predators and have a higher chance of surviving as a result. Also Read: Bergmann’s Rule
Behavioural Adaptations
This is the alteration that has an impact on an organism's behaviour. This may be brought on by alterations in the
immediate environment or by the activities of other animals. For instance, if the rabbit senses that a predator is
watching it, it freezes. Some examples of behavioural adaptations include modifications to feeding patterns,
hibernation, migration patterns, reproductive strategies, and communication techniques.
Physiological Adaptations
 Similar to structural adaptations, physiological adaptations entail morphological modifications within the species.
But an organism's appearance does not always reflect physiological adaptations. This kind of adaptation may result
from alterations in the surrounding environment or from the actions of other animals.
 For example, a fish must change its body chemistry to adapt when its water suddenly becomes more acidic.

20. Populations:
Every species' members reside in groups within clearly defined geographic areas, share
resources or engage in competition for them, may interbreed, and eventually form
populations.
 Population Attributes: Individual organisms may have births and deaths, but populations also have birth rates and death rates. These are some of the
characteristics that distinguish a population from an individual organism.
 Per capita births and deaths, which increase and decrease in relation to population members, are the terms used to describe the birth and death rates,
respectively.
 The population's sex ratio is another characteristic. Although a person can identify as male or female, the population has a sex ratio.
 a population made up of various individuals at various ages at a given time. Age pyramids are the structures created when the population's age
distribution is plotted. Pyramids' shapes are indicative of the population's growth status.
 Which may be
 (i) Expending
 (ii) Stable
 (iii) Declining

21.  § Population size or population density (N) is measured in terms of number but it may sometime not
appropriate.
 Population Growth : The size of population is not static. It keeps changing with time, depending
upon food availability, predation pressure and reduces weather. The main factors that determine
the population growth are-
 Mortality ( number of death during a given period in the population)
 o Immigration (individual of same species that have come into the habitat)
 o Emigration ( individual of population that have left the habitat )

22.  If ‘N’ is the population density at a time‘t’, then its density at time t+1 is Nt + 1 Nt + [(B + I) – (D + E)]
.Population density will increase if the number of births plus the number of immigrants (B + I) is more than the number of
deaths plus the number of emigrants (D + E), otherwise it will decrease.
Growth model
Growth of population takes place according to availability of food, habit condition and presence of other biotic and abiotic
factors. There are two main types of models-
i. Exponential Growth- in this kinds of growth occurs when food and space is available in sufficient amount. When resources
in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number .The
population grows in an exponential or geometric fashion. If in a population of size N, the birth rates as represented as ‘b’
and death rate as ‘d’. Then increase and decrease in N during unit period time ‘t’ will be
dN / dt = (b – d) × N
Let (b – d) = r, then
dN / dt = rN
Then, the r in this equation is called ‘intrinsic rate of natural increase’.

23.  ii. Logistic Growth- there is a competition between the individuals of a population for food
and space. The fittest organism survives and reproduces. In this types of growth initially
shows a leg phase followed by phases of acceleration and de-acceleration.
 Organisms and Populations class 12 Notes Biology
 Where N = Population density at time t
 R = Intrinsic rate of natural increase
 K = Carrying capacity
 Since resources for growth for populations are finite and become limiting , the logistic growth
model is considered a more realistic one.

25. Population interaction
All animals, plants and microbes in a biological community interact with each other. These
interactions may be beneficial, detrimental or neutral to one of species or both. Following types of
interaction is seen-
a. Predation
b. Competition
c. Parasitism
d. Commensalism
e. Mutualism

26. PREDATION : It is an Interspecific Interaction where one animal kills and
consumes the other weaker animal.
Roles of Predators
Transfer energy from plants to higher trophic levels (position of organism in
food chain)
Control Prey population – Prickly pear cactus- moth
Biological control of Agricultural pest
Maintain species diversity by reducing intensity of competition among
competing prey species
Over exploitation of prey by the predators results in extinction of prey and
predator.
Defense to lessen impact of predation
a)Insects and frog – camouflage
b)Monarch butterfly – poisonous
PLANTS MORPHOLOGICAL AND CHEMICAL DEFENCES
Thorns- cactus and Acacia
Produce and store chemical – Calotropis
Nicotine, Caffeine, Quinin, Strychnine, opium – against grazers & browsers

27. COMPETITION
Interaction either among individuals of same species or between individuals of different species.
Occurs among closely related species but not always true
1. Unrelated species also compete- flamingo & fish compete for zooplankton
2. Feeding efficiency of a species reduce due to other species even if resources are plenty – Abingdon
tortoise.
Evidence for competition
Competitive release – species distribution restricted to small areas due to competitively superior
species.
GAUSE’S COMPETITION EXCLUSION PRINCIPLE
“Two closely related species competing for same resources cannot coexist as the competitively
inferior one will be eliminated.”
Resource partition– Two competing species avoid competition by diff. feeding and foraging patterns-
Mc Arthur (warblers foraging activities)

29.  PARASITISM
 It is an interaction in which the host is harmed and one species (the parasite) depends on the other species (the host) for food and shelter.
 Insects and their hosts self-improve.
 Parasite adaptations
 Elimination of superfluous sense organs - Hooks and sucker
 - Digestive system loss - High reproductive potential
 Parasites-
 (i) Decrease the host's chances of survival;
 (ii) Slow down the rate of growth and reproduction; and
 (iii) Make the host weaker so that it is more susceptible to predators

30.  Types of parasite
 ECTOPARASITES–depend on external surface of host
 Example – head lice on humans, ticks on dogs
 ENDOPARASITES–take shelter within the body of the host organism
 Example – Liverfluke, Plasmodium
 MUTUALISM
 It is interaction in which both the interacting species are benefited
 Examples
 1. Lichen – fungi and algae
 2. Mycorrhizae – fungi and roots of higher plants
 3. Pollination of plants by insects
 4. Mediterranean orchid- sexual deceit for pollination- appears as female bee

31.  AMENSALISM:
 interaction between two distinct species wherein one suffers while the other is neither negatively or positively affected. For instance.
 In a few days, fungi such as Pencillium will grow on the bacterial culture, and its chemical secretions will kill the bacteria without helping the
fungi.
https://www.google.com/imgre
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32. REFERANCE
 https://mycbseguide.com/blog/organisms-populations-class-12-notes-biology/
 https://www.google.com/search?q=AMENSALISM%3A+&tbm=isch&ved=2ahUKEwi1kJr2sPuCAxX0R2
 https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwjlgb6isvuCAxV3TWwGHfbRA9QQFnoECCcQAQ&url=
https%3A%2F%2Fbyjus.com%2Fquestion-answer%2Fthe-get-cross-pollinated-by-a-species-of-bees-the-mediterranean-orchid-ophrys-employs-a-diapause-b-
camouflage-c-sexual-deceit-d-pseudocopulation%2F&usg=AOvVaw2kuIXEa0RKl-IOrgS_g9Yn&opi=89978449
 https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&cad=rja&uact=8&ved=2ahUKEwiLwK-
4svuCAxWV4TgGHfVdA1QQFnoECBcQAQ&url=https%3A%2F%2Fbyjus.com%2Fncert-solutions-class-12-biology%2Fchapter-13-organisms-
populations%2F&usg=AOvVaw2HP2SNHBer16rUTAKRd7LV&opi=89978449

33. Thank you