ATS COACHING CLASSES
REVISION CLASSES
ORGANISMS AND POPULATION
Our living world is fascinating diverse and amazingly
complex, we can try to understand its complexity by
investigating processes at various levels of biological
organisation –macromolecules, cells, tissues, organs,
individual organism and population, communities’
ecosystems and biomes.
Ecology: The biology that explores the interactions
between organisms and their physical (abiotic)
environments is called ecology.
It is vital for maintaining a balance between the growth and
preservation of natural environments and biotic ecosystems,
the use and protection of resources, and the resolution of
local, regional, and global environmental problems. it is
basically concerned with four levels of biological
organisation:
1. Organisms
2. Populations
3. Communities
4. Biomes
Here, we shall look at the organisms and population levels
one by one:
Organisms and its Environment
Environment:
The environment is the sum total of all biotic
and abiotic stimuli, substances, and situations that surround
and possibly impact organisms without becoming a
component part of them. Regional and local variations within
each biome lead to the formation of a wide variety of habitats.
Physiological ecology: At this level, one seeks to understand
how various organisms adapt to their environment in terms
of survival and reproduction at the organism level.
On planet Earth, life exists not just in a few favourable
habitats but even in extreme and harsh habitats – scorching
Rajasthan desert, rain-soaked Meghalaya forests, deep ocean
trenches, torrential streams, permafrost (snow laden) polar
regions, high mountain tops, thermal springs, and stinking
compost pits, to name a few. Even our intestine is a unique
habitat for hundreds of species of microbes. The factors that
lead to their establishment are temperature (intensity,
duration) and changes in rainfall patterns.
Biotic components: these components make the habitat and
include bacteria, parasites, predators and competitors,
interaction among which continuously takes place.
Each organism has an invariably defined range of conditions
that it can tolerate, diversity in the resources it utilises and a
distinct functional role in the ecological system, all these
together comprise its niche.
Abiotic components: the abiotic components are.
Temperature: it helps in determining a location's bio-mass.
The average temperature on the land change frequently from
the equator to the poles, as well as from plains to mountain
peaks. Enzyme kinetics and basal metabolism, as well as
physiological activities in organisms, get influenced by
changes in temperature. It ranges from subzero levels in
polar areas and high altitudes to >500C in tropical deserts in
summer. There are, however, unique habitats such as thermal
springs and deep-sea hydrothermal vents where average
temperatures exceed 1000 C. It is general knowledge that
mango trees do not and cannot grow in temperate countries.
Eurythermal: organisms that can tolerate a wide range of
temperatures are called eurythermal. e.g. tigers, cats
Stenothermal: organisms that can tolerate a narrow range of
temperature are called stenothermal. E.g. fish, crocodiles
Euryhaline: organisms that can tolerate a wide range of
salinity are called euryhaline. e.g. salmon.
Stenohaline: organisms that can tolerate a narrow range of
salinity are called stenohaline. E.g. goldfish
Light: it is another abiotic factor that is very important for
photosynthesis in plants.
Photoperiodism: when a plant flower in the presence of
sunlight then it is called as photoperiodism.
Because the sun is the source of both light and land, their
availability is inextricably intertwined. The ultraviolet (UV)
component of sunlight is detrimental to plants and animals.
Soil: Temperature, weathering processes affects whether the
soil is transported or sedimentary, and how the soil has
developed. The percolation and water retention capacity of
soils are determined by soil composition, grain size, and
aggregation, as well as pH, mineral content, and topography.
Soil characteristics along with parameters such as pH,
mineral composition and topography determine to a large
extent the vegetation in any area. This in turn dictates the
type of animals that can be supported. Similarly, in the
aquatic environment, the sediment-characteristics often
determine the type of benthic animals that can thrive there.
Responses to the abiotic factors: Many animals have
developed a consistent interior environment to allow all
biochemical activities and physiological functions to perform
as efficiently as possible in order to maximise species’ fitness.
Despite a changing external environment, organisms strive to
preserve the consistency of their internal environment, this
is called homeostasis. There are several methods of
maintaining the internal consistency of the internal environment. Such animals perform the following for
homeostasis:
Regulate: Thermoregulation and osmoregulation are the
sources of mammalian success in all environmental
situations. Birds and animals are capable of maintaining
homeostasis by physiological mechanisms, such as keeping a
consistent body temperature and osmotic concentration. In
summers, we sweat a lot, this lowers our body temperature.
In the winter, we begin to shudder, which is a type of exercise
that generates heat and elevates the body temperature.
Note: Evolutionary biologists believe that the ‘success’ of
mammals is largely due to their ability to maintain a constant
body temperature and thrive whether they live in Antarctica
or in the Sahara desert.
Conform: The osmotic concentration of bodily fluid in
aquatic animals varies with the osmotic concentration of
ambient water. These creatures are known as
conformers. They are unable to withstand the metabolic
costs associated with maintaining a steady body temperature.
Heatloss or gain is proportionalto surface area. Because tiny
animals have a bigger surface area compared to their
volume, they lose body heat quickly when it is cold
outside, requiring them to expend a lot of energy to
create body heat through metabolism. This is the
primary reason why extremely tiny creatures are
uncommon in the polar areas.
Migrate: The creature moves away from the stressful adverse
environment for a period of time and then returns after the
stressful phase is ended. E.g. Every winter the famous
Keolado National Park (Bharatpur) in Rajasthan host
thousands of migratory birds coming from Siberia and other
extremely cold northern regions.
Suspend: Microorganisms such as bacteria, fungus, and lower
have thick-walled spores that enable them to survive in harsh
settings. When favorable conditions resume, these spores
germinate. Higher plants use seeds and other vegetative
reproductive structures to tide them over during times of
stress and to aid in dissemination. During this latent time,
metabolic activity is reduced to a bare minimum. In animals,
the organism, if unable to migrate, might avoid the stress by
escaping in time. E.g
Hibernation: in such cases, organisms avoid stress by
escaping in time. E.g. bears go for rest during winters.
Aestivation: organisms go into rest period to avoid summerrelated problems like heat and desiccation. E.g. snails and
fish.
Diapause: it is a stage of suspended development. E.g. many
zooplankton species.
Adaptations: these are morphological, behavioural
and physiological changes that make organisms
capable of surviving and reproducing. These
adaptations include.
(i) In the absence of water, kangaroo rats in North
American deserts meet their water requirements
through internal fat oxidation. It can also concentrate
its urine, requiring only a small amount of water to
eliminate excretory materials.
(ii) Many plants have a thick cuticle that resists water loss.
CAM plants widen their stomata at night to prevent
water loss during photosynthesis. Some desert plants
like Opuntia, have no leaves – they are reduced to
spines– and the photosynthetic function is taken over
by the flattened stems.
(iii) Colder environment mammals have shorter ears and
limbs that help them in reducing heat loss. This is
known as Allen's Rule.
iv) Aquatic mammals such as seals in the polar regions
have a thick layer of fat beneath their skin called
blubber, which acts as an insulator and decreases heat
loss.
(v) An example is altitude sickness, it is a condition that
occurs at higher altitudes and involves symptoms such
as nausea, exhaustion, and heart palpitations caused by
a lack of oxygen and atmospheric pressure. When an
individual progressively adapts to it, he/she stops
feeling altitude sickness.
(vi) A variety of marine invertebrates and fish exist in
temperatures that are always less than zero, and some
live at tremendous depths in the ocean where pressure
is extremely, this is biochemical adaptation.
(vii) Some creatures, such as desert lizards, lack
physiological competence yet cope with extreme
temperatures in their environment by behavioural
means. They bask in the sun and absorb heat when
their body temperature falls below a comfortable level,
but they seek cover when the temperature rises.
• Sex ratio: number of males and females in a population
• Age of a population: individuals of different ages are
found in a population.
Age Pyramid: When the population's age distribution is
plotted, the resulting structure is known as age pyramids. The
form of pyramids represents the shape of population growth
status. The pyramid can be:
(a) Expanding
(b) Stable and
(c) Declining
• Population size: it is generally measured in terms of
number. Population size, technically called population
density (designated as N), need not necessarily be
measured in numbers only. Although total number is
generally the most appropriate measure of population
density, it is in some cases either meaningless or difficult
to determine.
• Population growth: The size of a population for any
species is not a static parameter. It keeps changing with
time, depending on various factors including food
availability, predation pressure and adverse weather.
The changes throughout time and this depends on food
supply, predation pressure, and meteorological
conditions, some of the factors that impact population
are:
(a) Natality: it refers to the number of births during a given
period to the population that are added to the initial
density
(b) Mortality: it is the number of deaths in the population
during a given period of time
(c) Immigration: it is a number of individuals of the same
species that have come into the habitat from elsewhere
during the time period under consideration
(d) Emigration: what is the number of individuals of the
population to left the habitat and gone during the time
period under consideration.
So, if N is the population density at time t then its
density at time t +1 will be:
Nt+1 = Nt + [ (B + I)] – [ (D +E)]
Where: (B + I) is the number of births plus the number
of immigrants.
(D + E) is the number of deaths plus number of
emigrants.
Growth Models: they are of two types:
1. Exponential growth: When enough food and room are
available, this type of growth takes place. When
resources in the ecosystem are abundant, each species
has the capacity to fully realise its natural potential for
population growth. The population increases in an
exponential or geometric manner.
If in a population of size N, the birth rates (not total
number but per capita births) are
represented as b and death rates (again, per capita
death rates) as d, then the increase or decrease in N
during a unit time period t (dN/dt) will be.
dN/dt = (b-d) x N
If we consider (b-d) as r, then
dN/dt = rn
The above equation describes the exponential or
geometric growth pattern of a population which
when plotted on a graph comes out to be J-shaped.
Here, r: intrinsic rate of natural increase, it is very
important in analyzing the effects of biotic or
abiotic factors on population growth.
2. Logistic growth: There is a rivalry for food and space
among individuals in a population. The organism that
is the most fit lives and reproduces. This form of
development begins with a leg phase, followed by
acceleration and de-acceleration phases.
dN/dt = Rn (K-N/K)
Where: N is the population density at time t
r: intrinsic rate of natural increase
K: carrying capacity.
Population Interaction: In a biological community
animal, plants, and bacteria all interact with one
another some are helpful, harmful, or neutral to one or
both species. Various interaction that are commonly
seen are:
o Mutualism: in this type of interaction both the species
are benefitted. The most spectacular and
evolutionarily fascinating examples of mutualism are
found in plant-animal relationships. In many species of
fig trees, there is a tight one-to-one relationship with
the pollinator species of wasp. It means that a given fig
species can be pollinated only by its ‘partner’ wasp
species and no other species. The female wasp uses the
fruit not only as an oviposition (egg-laying) site but
uses the developing seeds within the fruit for
nourishing its larvae. The wasp pollinates the fig
inflorescence while searching for suitable egglaying sites. In return for the favour of pollination the
fig offers the wasp some ofits developing seeds, as food
for the developing wasp larvae. Orchids show a
bewildering diversity of floral patterns many of which
have evolved to attract the right pollinator insect (bees
and bumblebees) and ensure guaranteed pollination
by it (Figure 13.8). Not all orchids offer rewards. The
Mediterranean orchid Ophrys employs ‘sexual
deceit’ to get pollination done by a species of bee.
One petal of its flower bears an uncanny resemblance
to the female of the bee in size, colour and markings.
The male bee is attracted to what it perceives as a
female, ‘pseudocopulates’ with the flower, and during
that process is dusted with pollen from the flower.
When this same bee ‘pseudocopulates’ with another
flower, it transfers pollen to it and thus, pollinates the
flower. Other eaxmples include, Lichen (fungi and
algae), Mycorrhizae ( fungi and the roots of higher
plants).
o Amensalism: an interaction in which one species is
harmed and the other one has no effect. E.g. when we
culture bacteria, colonies appear on it, and after some
time we can also see fungal colonies growing on it,
these fungal colonies secrete some chemical that
destroys bacterial colonies while fungus has no effect.
o Commensalism: This is the interaction in which one
species benefits and the other is neither harmed nor
benefited. E.g An orchid growing as an epiphyte on a
mango branch, and barnacles growing on the back of a
whale benefit while neither the mango tree nor the
whale derives any apparent benefit. The cattle egret
and grazing cattle in close association, a sight you are
most likely to catch if you live in farmed rural areas, is
a classic example of commensalism. Another example
is an the interaction between sea anemone that has
stinging tentacles and the clown fish that lives among
them. The fish gets protection from predators which
stay away from the stinging tentacles. The anemone
does not appear to derive any benefit by hosting the
clown fish.
o Predation: here an animal kills another weak animal,
it is an interspecific type of interaction. Predators help
in the transfer of energy from plants to higher trophic
levels, they help in controlling the Prey population,
they also help in biological control of Agricultural
pests, they maintain species diversity by reducing the
intensity of competition among species that are in
competition. Besides acting as ‘conduits’ for energy
transfer across trophic levels, predators play other
important roles. They keep prey populations under
control. Some plants have developed chemical
defences to protect themselves from predation
like, the presence of thorns in Cactus and Acacia,
Calotropis produces chemicals and some plants
produce nicotine, caffeine, quinine and opium to
protectthemselves from grazing animals. Predators
also help in maintaining species diversity in a
community, by reducing the intensity of competition
among competing prey species. In the rocky
intertidal communities of the American Pacific
Coast the starfish Pisaster is an important
predator.
o Parasitism: here, one species depends on the other for
food, and shelter and in such cases the host that is
providing food and shelter is harmed. In accordance
with their life styles, parasites evolved special
adaptations such as the loss of unnecessary sense
organs, presence of adhesive organs or suckers to cling on to the host, loss of digestive system and high
reproductive capacity. The life cycles of parasites are
often complex, involving one or two intermediate hosts
or vectors to facilitate the parasitisation of its primary
host. The human liver fluke (a trematode parasite)
depends on two intermediate hosts (a snail and a fish)
to complete its life cycle. The malarial parasite needs a
vector (mosquito) to spread to other hosts. Majority of
the parasites harm the host; they may reduce the
survival, growth and reproduction of the host and
reduce its population density
A parasite can be an ectoparasite (lice in human
head, ticks on dogs) and endoparasite (
Plasmodium and liver fluke).
o Competition: it may occur between organisms of same
species or unrelated species also. E.g competition
between flamingo and fish for zooplanktons.
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12th CLASS NOTES