chapter 13 cbse ncert presentation

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4. • Ecology: Ecologyis the branch of science that studies the
relationship between organisms and their physical & biological
environment.
• Levelof Organization inecology:
1. Organisms: living organism of environment atindividual level.
2. Species: Group of individuals which resembles each otherand
interbreed among themselves.
3. Population: Sumtotal of all individuals of aspecies inaspecific
geographical area.
4. Community: Group of population of speciespresentin
geographical area interacting with themselves.
5. Ecosystem: Ecosystem is afunctional unit of nature, whereliving
organisms interact among themselves and also with the
surrounding physical environment.
6. Environment: Sumtotal of biotic and abioticfactors.
7. Biome: The large unit of environment consisting of major type of
flora or vegetation and associated fauna( animals) in specific
climatic zone is called biome.

5. Annual variations in the intensity and duration
of temperature and precipitation are responsiblefor
the formation of majorbiomes.
• Themajor biomesare:
1. Arctic & alpinetundra
2. Coniferous forest
3. Temperateforest
4. Grasslands
5. Tropical Forest
6. Desert.

6. • Abiotic factors :Themost important abiotic factors of the environmentare
temperature, water, light andsoil.
• Biotic factors: Biotic factors are pathogens, parasites, predators,
competitors etc.
• Temperature: Thephysiological functions and geographical distribution of
organisms is governed by temperature.
• Temperature affects the kinetics of enzymes, BMR(BasicMetabolic Rate)
and other physiological actions inorganisms.
• Eurythermal: Afew organisms which cantolerate wide range of
temperatures are called eurythermal organisms.
• Stenothermal: Many organisms which cantolerate narrow rangeof
temperatures are called stenothermal organisms.
• Water: Important factor influence the life oforganisms.
• Theproductivity and distribution depends onwater.
• For aquatic organisms, chemical composition , pH, salinity andtemperature
of water areimportant.
• Euryhaline: Theorganisms which cantolerate wide range of salinityare
called euryhaline organisms.
• Stenohaline: Theorganisms which cantolerate narrow range of salinity
stenohaline organisms.

7. • Light: light is important abiotic factor bcoztheautotrophs
prepares its food byphotosynthesis.
• sciophytes : Small herbaceous plants and some shrubs live
under the canopy forest trees are adapted to photosynthesis
under very low light intensities.Theseare called sciophytes
• Animal use the seasonal variations in the light intensity and
photoperiod as cues for timing of forage, reproduction and
migration.
• Thedistribution ofred, green and brown algaeat difference
depths of water depends on the light, red algaecanlive in
very deepwater.
• Soil: Nature and properties of soil depends on climate,
weathering process.
• Thephysical and chemical properties of soil determinethe
type of plants that can grow in a particular habitat.
• Thecharacteristics of the bottom sediments of aquatic
environment determine type of benthic animals that can live
there.

8. • Organisms responses toenvironment:
• Regulation: Organismsmaintain homeostasis in
constant body temperature and osmoticconcentration.
• Conformation: Majority (99%)of animals and plants
cannot maintain aconstant internal environment.Such
animals and plants are simply called asconformers.
• Their body temperature varies according to ambient
temperature.
• In aquatic animals the osmotic concentration of body
fluid varies withambient water osmotic concentration.
• Thermoregulation is energy-expensive process. Heat
loss or gain is afunction of surface area. therefore
small animals are not found in polarregion.

9. • Migration: Organisms canmove away temporarily from
stressful conditions to another habitatis called migration.
• Suspension: Organisms that cannot migrate , suspendtheir
metabolic functions duringstressful period. It is called
suspension.
• E.g.Hibernation, aestivation, Diapuse.
• Hibernation: Hibernation is aprocess by which the animals
avoid the stressand become inactive duringwinter.
• Ex: Polar bear, Frogs, Lizards
• Aestivation: Aestivation is aprocess by which the animals
avoid the stressand summer related problems andbecome
inactive during summer.
• Ex:snails and fishes
• Diapause: It is astageof suspended development seenin
many zooplanktons to avoid unfavorableconditions.

10. • Adaptation: Adaptation is any changesof the organism
(morphological, physiological, and behavioral) that enablesto
survive and reproduce in itshabitat.
• Adaptations have evolved over along period of time andare
genetically controlled
• Examples:
• Desert Plants: have thick cuticle on leafsurface.
• Sunken stomata.
• leaves modified into spines.
• Dueto CAMpathway photosynthesis the stomata remainclosed
during the day.
• Ex:Opuntia, cactus etc.

11. • Aquatic Plants: Haveevolved aerenchyma for buoyancy
and floating. leaveshavewaxycovering.
• Desert animal: Kangaroorat living in the desert of
North America never drink water. Thewater
requirement is by internal fatoxidation (in which water
is the byproduct).
• It is also able to concentrate its urine so that the
minimal volume of wateris lost during excretion

12. • Allen’s rule: Allen’s rule states that, animalsfrom
colder climates generally haveShorter ears and
limbs to minimize the heatloss.
• In Polar sealshaveathick layer of fat below theskin
that acts asinsulator.
• It reduces loss of body heat. Shortears and limbs
minimize heat loss.

13. • Desert Lizardskeep their body temperature
constant by behavioral adaptation. Theybaskin the
sun and absorb the heat when their body
temperature decreasesbelow the comfortzone.
• Burrowing habit also helps to protectdesert
animals from high temperature

14. • Population attributes: Population is agroup of
individual living in aperticular geographicalarea.
• It hascertain attributes, theyare:
• Birth rate.
• Death Rate.
• SexRatio.
• Population density.
• Apopulation at any given time is composedof
individuals of different agegroup.As,
• Pre-reproductive, Reproductive and Post-reproductive.
• Age pyramid: If the agedistribution is plotted for the
population, the resulting structure is called asage
pyramid.
• For human population, the agepyramids show theage
distribution of males and females in acombined
diagram.

15. • Theshape of pyramids reflects the growth status of the
population i.e. an expanding/ growing population, a
stable population, adeclining population.
• Population Growth: Thesizeof population keeps
changeswith the time, depending on the factors like:
1. Food available;
2. weather,
3. predator pressure and
4. Competition.
• Thedensity of apopulation in agiven habitat duringa
given period changesdue to fourbasic
• Natality (N), Mortality (M), Immigration(I) and
Emigration (E).

16. • Thenatality and immigration contribute to increase
in the sizeand density of apopulation.
• Mortality and emigration contribute to adecrease
in population
• Sothe equation for the population growthis;
• Nt =N0+[(B+I)- (D+E)]
• Nt =Population density attime.
• N0=Population in beginning.
• B=Birth rate.
• I =Immigration.
• D=deathrate.
• E= emigration.

17. dN/dt= rN
N=population density at time
r= intrinsic rate of naturalincreas
• Population Growth Models:
• There are two models of populationgrowth:
• Exponential Growth Model: When the resources
availability is unlimited in the habitat, the population
grows in an exponential or geometricfashion,
• Theequation is: dN/dt= (b-d)*N
• Let (b-d)= r,
• then the equationis,
•
•
• e
• When apopulation shows exponential growth, the
curve plotted with Nin relation to time assume Jshape.

18. • Logistic growth Model: No population can
continue to grow exponentially, asthe resource
availability become limiting at certain point of time.
• It is described by theequation:
• dN/dt =rN(K-N/K)
• N=population density at time
• r= intrinsic rate of naturalincrease
• K=carryingcapacity

19. • LifeHistory Variations: Evolution of populations
aims at improving the reproductive fitness tothe
maximum in their habitats.
• Most birds and mammals breed many timesduring
their life time.
• According to ecologists life history traits of an
organism haveevolved in relation to theconstraints
imposed by the biotic and abiotic factors in their
habitats.

20. • Population Interactions:
• Living organisms interact in various waysto formbiological communities.
• Interspecific interactions: It is the interactions of population oftwo
different species.
• Interaspecific interactions: : It is the interactions of individuals of the same
species.
• Theinteractions are following types:
Interaction Species A Species B
Predation + -
Competition - -
Parasitism + -
Commensalism + 0
Ammensalism. - 0
Mutualism. + +

21. • Predation: It is an interspecific interaction in which
predator(strong animal) kills and consumesprey (weak
animal). Therefore one species is benefit and other isharmed.
• Predation is away to transfer theenergy from lower trophic
levels to higher trophiclevels.
• Predator keep the prey population under control. Otherwise
prey reach very high population density and causeimbalance
in the ecosystem.

22. • Sometimes predators are used asbiological control
for pests.
• Example:
• TheLadybird are useful to control aphids and
Dragonflies for mosquitoes.

23. • Preyspecies haveevolved various defence
mechanisms to reduce the impact ofpredation.
• Example:
• Certain insect species and frogs havecamouflage
(Cryptic coloration).

24. • Monarch Butterfly is very distasteful toits prey bird.
It hasaspecial chemical in its body. This chemical is
produced during its caterpillar stageby feeding on
poisonous weeds.

25. • Herbivores are the predators forplants.
• Theproblem of predation is more severeforplants
than animals asthey cannot move.
• About 25%of the known insects arethe
Phytophagus and feed on the plantsap.

26. • Plants havedeveloped certain morphologicaland
chemical defence mechanism againstherbivores.
E.g.Thorns in Bougainvillea and Spinesin Acacia

27. • Certain chemicals produced by the plants actfor
defense.
• Calotropis produces ahighly poisonous Glycoside
that is acardiacpoison.
• Nicotine, Caffeine, Quinine, Strychnine, Opiumetc
are the chemicals produced by the plants against
herbivores.

28. • Competition:
• Competition is an interaction among the individuals of
same species (Intraspecific ) or between individuals of
different species(Interspecific).
• Competition between the individuals ofsamespeciesis
for sameresources that arelimited.
• In some case,resources need not be limiting for
competition to occur, the feeding efficiency of one
speciesmight be reduced due to the interfering of the
other species.
• E.g.Abingdon tortoise in GalapagosIsland became
extinct within adecade after goats wereintroduced
into the island.
• It was due to the fact that the goats had greater
browsing efficiency than thetortoise.

29. • Unrelated speciesalso compete for sameresources.
• Ex:-flamingo & fish compete forzooplankton

30. • Competitive release:
• "A species,whose distribution is restricted to asmall
geographical area becauseof the presence ofacompetitively
superior species is called competitiverelease.
• Thesespecies is found to expand its distributional range
dramatically when the competing species isexperimentally
removed
• Gause’s Competitive Exclusion Principle :It states, ‘thattwo
closely related species competing for the sameresources
cannot exist together and the competitively inferior will be
eliminated bysuperior’.
• Resource Partitioning: It is the mechanism meant for co-
existence of species to face competition.
• According to this, if two species compete for the same
resource, they could avoid competition by choosingdifferent
times for feeding or different foraging patterns.

31. • E.g.
• MacArthur showed that five closely relatedspecies
of Warbles living on the sametree were able to
coexist and avoid competition by havingbehavioral
differences in their foraging( hunting)activities.

32. • Parasitism:
• Parasitism is the interspecific interaction where oneof
the species(Parasite) depends the other species
(Host)for food andshelter.
• Host gets harmed and parasite getsbenefitted.
• Parasitesare host-specific and parasite and itshost
tend to co-evolve.
• Co-evolve: It meansthat if the host evolves aspecial
mechanism to reject or resist the parasite, the parasite
hasto evolve the mechanisms toneutralize them.
• Parasites adaptations:
• Parasite tends to co-evolve.
• It may loss of senseorgans.
• Presenceof suckersor hooks.
• Lossof digestive system.
• High reproductive capacity.

33. • Someparasites havecomplex life cycle andgenerally
haveone or two intermediatehost.
• Intermediate hosts act asvectors which facilitates
parasitisation of host.
• Human liver fluke hastwo intermediate hosts: asnail
and afish
• Malaria Parasite hasone intermediate host(mosquito)
to spread to otherhost.

34. • Human lice and ticks areectoparasites
• Copepodsare the ectoparasites on some marinefish.
• Cuscutais aparasitic plant that grows on the treesor
shrubs.
• It lost itschlorophyll and leavesduring evolution.
• It gets its nutrition from the host plants by haustoria.

35. • Commensalism:
• Itis the interspecific interaction in which one speciesbenefits and the other
is neither harmed nor benefitted.
• Ex:Epiphytes i.e Orchids growing on atree branch.
• Barnaclesgrowing on the back of whales.
• Association between Egret and grazing cattle. Egretsalways forage close to
cattle are grazing becausethey easily get insects.
• TheClown fish living along with seaanemones. Clown fish get protection
from predators.
• Suckerfish on the back of shark

36. • Mutualism: It is the interspecific interaction in which Both the species
interact getsbenefit.
• E.g.Lichensare relationship between FungusandAlgae/ Cyanobacteria
• Mycorrhiza – an association of Funguswith roots of higher plants. Fungi
help toabsorb nutrients from the rocks and plants provide energy yielding
carbohydrates to fungi.
• Plants depend on insects for pollination and in return they give them
nectar or pollens to eat.
• Animals help the plants in seed dispersal and in return they give fruits to
animals asfood.

37. • figtree and pollinator species of wasp. Fig
specie
s canbe pollinated by its partner wasponly.

38. • Amensalism: It is the interspecific interaction in which one is
harmed and the other is neither benefited nor harmed.
• E.g:Penicillium secretes chemical penicillin killsbacteria.
Name the interaction in each of thefollowing:
• a) Cuscutagrowing on ashoe flower plant.
• b) Mycorrhizaa living on the roots of higher plants.
• c) Clown fish living among the tentacles ofseaanemone.
• d) Koel laying her eggsin crow'snest.
• e) Five closely related species of warblers living on the same
tree
• a. Parasitism
• b. Mutualism
• c. Commensalism
• d. Brood parasitism
• e).Competition with resourcepartitioning.