NEET Biology – Organisms and Populations – Study Notes

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Organisms and Populations

Table of Content

Organism and its Environment

  • Sun’s rotation and the tilt of its pivot cause yearly variations in the force and span of temperature, bringing forth the various seasons.
  • These variations alongside yearly variations in precipitation, frames significant biomes, for example, tundra, rainforest, and desert.
  • Temperature, soil, light, and water are the key components that prompt to such a great amount of variation in the physical and synthetic states of living spaces.
  • Both abiotic (physic-synthetic) and biotic parts (competitions, pathogen, predators, parasites) describe the environment of a life form.

Fig: Abiotic and Biotic factors that influence ecosystems

Major Abiotic Components


  • Temperature diminishes dynamically from equator moving towards the pole and high heights to > 50° C during summer in the tropical desert
  • Thermal springs and remote ocean hydrothermal vents are exceptional with >100° C
  • Temperature influences the BMR, the kinetics of enzymes, and other physiological activities
  • Eurythermals: creatures which can endure an extensive variety of temperatures
  • Stenothermals: creatures which can endure limited scope of temperatures

Fig: Steno-species exhibit a narrow tolerance zone while Eury- species exhibit a wide tolerance zone.


  • Water is additionally a vital component that impacts the life of a living being
  • The efficiency and conveyance of plants likewise rely on water
  • The saltiness fluctuates in the oceanic environment:
    • 5% in inland waters (new water)
    • 30-35 percent in ocean water
    • More than 100 percent in hyper saline tidal ponds
  • Euryhaline: life forms which can endure extensive variety of saltiness
  • Stenohaline: life forms which can endure limited scope of saltiness

Fig: A euryhaline fish

Fig: Yellow fin Tuna: A Stenohaline species


  • Plants deliver sustenance by photosynthesis, which is conceivable only in light. Consequently, it is imperative for autotrophs.
  • Plant species (bushes and herbs) adjusted for photosynthesis under shade.
  • Sunlight is required for a photoperiodic reaction like blooming.
  • Animals utilize diurnal and regular variations in light force and photoperiod as prompts for timing their migration, reproduction, and foraging.


  • Properties of soil change as per the atmosphere, the weathering procedure.
  • Aggregation, grain size, and soil composition decide the permeation and water holding limit of the soil.
  • These trademarks alongside pH, mineral organization and geography decide to a huge degree the vegetation in any range.
  • The silt trademark frequently decides the kind of benthic creature in oceanic environment.

Response to Abiotic Factors

Homeostasis; the procedure by which the creature keeps up a steady inner environment in regard to changing outside environment.

Fig: Homeostasis

How does organism cope with the changing Environment?


  • Some life forms can keep up homeostasis physiological (occasionally behavioral too) meaning which guarantees steady body temperature, consistent osmotic focus.
  • All mammals and birds and few lower spineless creatures are prepared to do such regulation i.e. osmoregulation and thermoregulation.
  • Success of warm-blooded creatures is because of thermoregulation.
  • We keep up a consistent body temperature of 37oC.
  • When outside temperature is high we sweat abundantly and evaporative cooling happens to cut the body temperature down.
  • In winter, because of low temperature outside our body, temperature falls underneath 37oC, we begin to shudder to create warmth to raise body temperature.

Fig: Regulators


  • Majority (99%) of creatures and plants can’t keep up a steady interior environment; their body temperature differs as indicated by surrounding temperature.
  • In sea-going creatures the osmotic convergence of body liquid differs with surrounding water osmotic focus.
  • All the above creatures and plants are just called as conformer.

Fig: Conformers

Why the conformers are not evolved to become regulators?

  • Thermoregulation is vigorously costly for some creatures.
  • Humming birds and small creature like shrews can’t bear the cost of such a great amount of vitality for thermoregulation.
  • Heat gain or heat loss is a component of surface range.
  • Small creatures have bigger surface range with respect to their volume, they have a tendency to lose body warmth quickly when it is chilly outside; they then need to use much vitality to produce body warmth through digestion system.
  • This is the reason little creatures are seldom found in Polar Regions.

Alternate response for difficult conditions is limited or stays for brief term.


  • The creatures move away briefly from the distressing territory to a more affable zone and return when the unpleasant condition is over
  • Birds move from the colder locale to hotter area


  • Spores with thick walls are shaped in organisms to defeat unpleasant outside environment. Spores sprout in ideal condition.
  • In higher plants, seeds and other vegetative conceptive structures are intended to hold over the stress. They diminish their metabolic movement and going into a condition of ‘dormancy’.
  • Hibernation: amid winter creatures like bears escape in time
  • Aestivation: creatures like snail and fish keep away from summer related issue like warmth and parching.
  • Diapauses: numerous zooplanktons experience a phase of suspended advancement in unpleasant conditions.


  • Adaptation: is any quality of the living being (behavioral, morphological, and physiological) that empowers the living being to survive and replicate in its living space.

Adaptation of animal in desert

  • Kangaroo rat meets their water prerequisite from oxidation of fat
  • Excrete extremely concentrated urine to save water

Fig: Adaptations of Kangaroo rat

Adaptation of plant in desert (xerophytes)

  • Leaf surfaces having thick cuticle
  • Sunken stomata, both to decrease transpiration
  • Have exceptional photosynthetic pathway (CAM), stomata shut amid daytime and stayed open amid night
  • Opuntia has no leaf- they are diminished to spines
  • Photosynthesis happens in flattened green stems

Fig: Desert Ground Plants

Adaptation of animal in cold climate

  • Allen’s Rule: warm-blooded creatures from colder atmospheres, for the most part, have shorter ears and appendages to minimize warmth loss.
  • Seals of polar oceanic oceans have blubber, a thick layer of fat underneath their skin that goes about as an insulator and decreases loss of body warmth.

Fig: Adaptations of Polar Bear in cold region

Adaptation in high altitude

  • An individual moving to high height (>3,500 meter), suffers from altitude sickness
  • Symptoms created are heart palpitations, fatigue and nausea
  • This is because of low air weight of high heights; the body is not able to get enough oxygen

How our bodies respond to the problem?

  • The body repays low oxygen accessibility by expanding the production of red blood cells
  • The body repays by diminishing binding capacity of hemoglobin to oxygen by expanding rate of respiration

Behavioral Adaptation

  • Desert reptiles are conformers thus they adapt to the distressing environment by their behavioral adjustments:
    • They lounge in the sun and assimilate warmth when their body temperature drops beneath the safe place in winter
    • Move towards shade when the surrounding temperature increases
    • Some species tunnel into the soil to conceal and escape from over the ground warmth


Population Attributes

  • Population: a gathering of individual living in a very much characterized topographical range, share or go after comparable assets, possibly interbreed.
  • Birth rate refers to per capita births and death rate alludes to per deaths.
  • Another property is sex proportion. The proportion between the male- female in a population.
  • If the age conveyance is plotted for a population the subsequent structure is called age pyramid.
  • The state of the pyramids mirrors the development status of the population like developing, stable or declining.
  • The population size is all the more in fact called as population density.

Fig: Diagram depicts the stage of Growth

Methods for measurement of population density

  • Percent cover
  • Counting the number
  • Pug marks and fecal pellets for tiger census
  • Biomass

Population Growth

  • The population size changes relying upon food accessibility, predation force and lessen climate.
  • Population estimate vacillated because of changes in four fundamental procedures, two of which (Natality and immigration) contribute an expansion in population density and two (mortality and emigration) to a diminishing.
  • Natality: number of birth in given period in the population.
  • Mortality: number of deaths in the population in a given timeframe.
  • Immigration is the quantity of people of same species that have come into the territory from somewhere else amid a given timeframe.
  • Emigration: number of people of the population who left the territory and gone somewhere else amid a given timeframe and age.
  • If “N” is the population density at time ‘t’, then its density at time t + 1 is:

N1+t = Nt + [( B+1) – (D + E)]

Fig: Verhulst Pearl Logistic Growth

dN/dt = rN [(K – N)/K]
Where B = the number of births

D = the number of deaths

I = the number of immigrants

E = the number of Emigrants

K = Carrying capacity (The maximum population size that an environment can sustain)

N = Population Density

t = Time period

r = Intrinsic rate of natural increase

Exponential Growth

  • The Exponential growth equation is Nt = N0ert
  • N0 = Population density at time zero
  • Nt = Population density after time t
  • e = the base of natural logarithms (2.71828)
  • r = intrinsic rate of natural increase
  • Exponential growth (‘J’ shape curve is obtained)
    At the point when assets are not constraining the development
  • Any species development exponentially under boundless assets conditions can achieve gigantic population densities in a brief span
  • Growth is not all that sensible and realistic

Logistic growth model

  • Verhulst-Pearl Logistic Growth is described by the following equation

dN/dt = rN (K–N / N)

  • WhereK = Carrying capacity
  • r = Intrinsic rate of natural increase
  • N = Population density at time t

Fig: Exponential vs Logistic Growth

Logistic Growth (Sigmoid curve is obtained)

  • When reactions are restricting the Growth.
  • Resources for development for most creature populations are limited and get to be distinctly restricting.
  • The logistic growth model is a more practical one.

Fig: Logistic Growth Curve

Population Interactions


  • Higher trophic level organisms (predator) sustains on the creature of lower trophic level (prey) is known as the predation
  • Even the herbivores are not altogether different from the predator
  • Predator goes about as a section for the exchange of vitality crosswise over the trophic level
  • Predators monitor prey populations
  • Exotic species have no normal predator subsequently they grow quickly. (thorny pear prickly plant presented in Australia made issue)
  • Predators additionally help in keeping up species assorted qualities in a group, by lessening the force of rivalry among contending prey species. (Pisaster starfish field experiment)

Defense developed by prey against predators


  • Insects and frogs are obscurely shaded (camouflaged) to abstain from being recognized by the predator
  • Some are noxious and in this way maintained a strategic distance from by the predators
  • Monarch butterfly is exceptionally disagreeable to its predator (flying creature) because of the nearness of unique concoction in its body. The substance procured by nourishing a harmful weed amid caterpillar stage.


  • Thorns in Cactus and Acacia are a morphological method for protection
  • Many plants create and store some substance which makes the herbivore wiped out if eaten, distress reproduction, digestion, and interferes feeding even slaughter the predators
  • Calotropis produces noxious cardiovascular glycosides against herbivores
  • Nicotine, opium, caffeine, strychnine, quinine, and so on are created by plant as resistances against the nibblers and browsers


  • Interspecific rivalry is a powerful drive in natural development.
  • Competition, for the most part, happens when firmly related species go after similar assets that are restricting, yet this not by any stretch true or genuine:
  • Firstly: absolutely random species could likewise go after similar assets.
    • American lakes going by flamingoes and inhabitant angles have their normal food, zooplanktons.
  • Secondly: assets need not be restricting for a rivalry to happen.
    • Abingdon tortoise in Galapagos Islands got to be distinctly wiped out within 10 years after goats were presented on the island, because of more prominent perusing capacity.


  • Parasitic method of life guarantees free space and food
  • Some parasites are host-particular (one parasite has a solitary host) in a manner that both host and parasite tend to co-develop

Parasitic Adaptation

  • Loss of superfluous sense organs
  • Presence of sucker or organs to stick on to the host
  • Loss of stomach related framework
  • High reproductive limit
  • Parasites having at least one intermediate host or vectors to encourage parasitisation of its essential host
  • Liver fluke has two hosts (snail and a fish) to finish its life cycle

Effects on the host:

  • Parasite dependably harms the host
  • Reduce its population density
  • They diminish the survival, development and generation of the host
  • They make the host more defenseless against the predators, by making it physically frail

• Ectoparasite: sustains on the outer surface of the host.

  • Lice on human
  • Marine fish pervaded with copepods
  • Ticks on dogs
  • Cuscutaa parasitic plant develop on hedge plants

• Endoparasites: are those that live inside the host body at various locales:

  • Life cycle is much complex
  • Highly created reproductive framework
  • Morphological and anatomical components are extraordinarily disentangled

• Brood parasitism:

  • Special sort of parasitism found in birds
  • The egg of the parasite is fundamentally the same as with the egg of the host
  • The parasitic winged creatures lay its eggs in the home of its host and let the host hatch them
  • Cuckoo lays eggs in the nest of the crow

Fig: Parasitism versus Predation


  • This is the association in which one species benefits and the other is neither profited nor hurt
  • Clown fish living in the tentacles of the sea anemone
  • Orchids developing as an epiphyte on a mango branch
  • Cattle Egret and nibbling steers
  • Barnacles on the back of whales


communication between two living being, both are similarly profited, nobody is hurt.

  • Lichen: a mycobiont and a Phycobiont
  • Mycorrhiza: relationship amongst fungi and base of the higher plant
  • Fig trees and its pollinating specialist wasp
  • Pollinating bugs and blossoming plants

Fig: The most commonly known mutualistic relationship is the honey bee and the flower though there are many different types of mutualistic relationships.

Sexual Deceit

Sexual Deceit is a type of pseudo copulation. Pseudo copulation describes behaviors similar to copulation that serve a reproductive function for one or both participants but do not involve actual sexual union between the individuals.

  • Mediterranean orchid Ophrys utilizes ‘sexual deceit’
  • The male honey bee pulled into what it sees as a female, “pseudo copulates” with the bloom, however, does not get any advantages
  • Petal of the bloom looks like the female honey bee

Fig: Sexual Deception by Ophrys apifera

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