Chapter 13: Organisms And Enviroment

Our living world is very diverse and amazingly complex. Biological organisation – Macromolecules, cells, tissues, organs, individual organism, population, communities and ecosystems and biomes. At any level of biological organisation we have two questions how ? and why?.

Question 1:Explain Homeostasis, Eurythermal, Stenothermal, Euryhaline and Stenohaline .

Answer :

  • Homeostasis: process of maintaining constant internal environment by living organism in terms of optimal temperature and optimal osmotic concentration of the body fluids is called homeostasis.
  • Eurythermal: organisms which can tolerate wide range of temperatures.
  • Stenothermal : organisms which are restricted to a narrow range of temperatures.
  • Euryhaline: organisms which can tolerate wide range of salinities.
  • Stenohaline: organisms which are restricted to a narrow range of salinities.

Question 2: Explain about the response of various organisms to abiotic stress or abiotic factors ?

Answer : Organisms response to various abiotic factors in following manner:

  1. Regulators :Some organisms are able to maintain homeostasis by physiological or behavioural means to ensure constant body temperature or osmotic concentration . Ex: all birds , all mammals ,but few lower vertebrates and invertebrates.
  2. Conformers : Organisms which cannot perform homeostasis, they change their body temperature or osmotic concentration according to external Enviroment to become conformer. Ex : 99% of animals and all plants.

Question 3 : Why humming birds or other small animals rarely found in polar region ?

Answer :Heat loss or heat gain is the function of surface area . Since small animals have larger surface area as compared to their volume. So they loose body heat very fast. When it is cold outside they expand much energy to generate body heat through metabolism , so small animals like shrews , humming bird are not found in polar region.

Question 4: What responses are produced when stressful external conditions are localized or remain for short duration ?

Answer :

  1. Migration : Organisms move away for short duration from stressful habitat to suitable area and return when stressful period is over. Ex: Siberian crane migrate to Bharatpur Rajasthan in winter season and return back.
  2. Suspension : In this , organisms become dormant for sometime and reduce metabolic activities . Examples :
    • Plants, fungi and bacteria make various kinds of thick walled spores which help them to survive in unfavourable conditions.
    • In higher plants seeds and other vegetative reproductive parts like eye buds in potato’s , runners in grasses help them to survive unfavourable condition and germinate during favourable conditions.
    • Diapause : Under unfavourable condition many zooplanktons in lakes and ponds enter a stage of suspended development called diapause.
    • Hibernation : It is winter sleep during which organism avoid stressful condition by escaping in time . Ex: frog , bear ,etc.
    • Aestivation : It is summer sleep during which organism avoiding the heat and desiccation. Ex: snails ,fish, etc

Question 4: What is adaptation ? give examples?

Answer :Physiological , behavioral or morphological adjustment of the organism that enable the organism to survive and reproduce in its habitat is called adaptation.

  • Physiological adaptation of Kangaroo rat :
    1. They are able to concentrate its urine , so less volume of water is removed during excretion.
    2. Kangaroo rat obtain water by internal fat oxidation in which water is a by product.
  • Adaptation in desert plants :
    1. Physiological adaptations: They have CAM(Crassulacean Acid Metabolism) photosynthetic pathway that enable their stomata to remain close at day time.
    2. Morphological adaptations :
      1. Thick cuticle and sunken stomata are present on leaves to minimize water loss through transpiration.
      2. Some desert plants like opuntia , euphorbia leaves or stipules are reduced to spines and photosynthesis is performed by flat stem.
      3. Desert plants usually have very long roots to absorb water.
  • Adaptation in polar region :
    1. Anatomical adaptations:In polar sea aquatic mammals like seals have thick layer of fat called blubber below their skin that acts as insulator.
    2. Morphological adaptations : Mammals of colder climate generally have shorter ears and limbs to minimise heat loss(Allens rule).

Question 4:Name the processes which fluctuates growth of the population ?

Answer :The processes which fluctuates the growth of the population are :

  1. Natality (B): It refers to the number of births during a given period in the population that added to the initial population density.
  2. Mortality (D) : Number of the deaths in the population during a given period.
  3. Immigration (I) : Number of the individuals of the same species that comes into habitat from elsewhere during time period under consideration.
  4. Emigration (E) : Number of the individuals of the population who left the habitat and gone elsewhere during the time under consideration.

If the population density at time “t” then its density at time “t+1” is

Nt+1 = Nt + [(B+I)-(D+E)] .

Question 5: Describe the attributes present in population but absent in an individual ?

Answer :The attributes present in population but absent in an individual are :

  1. Population density : Number of individuals of a species per unit area or volume.(population density = Number of individuals in a region (N)/Number of unit area in a region (S).Population density = N / S.
  2. Birth rate : Number of births per thousand individuals of a population per year.
  3. Death rate : Number of deaths per thousand individuals of a population per year.
  4. Age pyramid : If the age distribution is plotted for the population , the resulting structure is called an age pyramid.
  5. Sex ratio : An individual is either a male or female but the population has a sex ratio. It is the percent ratio of male and female in a population.

Question 6: Differentiate between logistic and exponential growth curve ?

Answer :When resources in the habitat are unlimited , each species has the ability to release fully its innate potential to grow in number and population grows in an exponential or geometric fashion was given by Thomas Robert Malthus . If in a population of size N ,the birth rates are represented as “B” and death rates by “D” , then the increases or decreases in N during a unit time period t (dN/dt) will be

dN / dt = (B-D)N

Let (B-D) = r , then

dN / dt =rN

r is “intrinsic rate of natural increase”.

Exponential growth results in J-shaped curve , when we plot N in relation to time . Integral form of the exponential growth equation is Nt = Noe rt

where , Nt = population density after time t

No = population density at time zero

r = intrinsic rate of natural increase

e = the base of natural logarithms

Question 7 : Explain logistic growth curve ?

Answer : According to logistic growth curve no population has unlimited resources to permit exponential growth , this leads to competition between individual’s for limited resources . Eventually the fittest will survive and reproduce.

A population growing in a habitat with limited resources show initially a lag phase , followed by phases of acceleration or deceleration and finally asymptote , when the population density reaches the carrying capacity (It is the limit of the habitat to support a maximum possible number beyond which no further growth is possible)

A plot of N in relation to time (t) results in sigmoid curve this type of population growth is called Verhulst Perl Logistic Growth curve , described by equation

dN / dt = rN(K-N/k)

where , N = population density at time t

r = intrinsic rate of natural increase

K = carrying capacity

It is more realistic curve.

Question 8 : Explain about various types of interspecific population interaction ? <

Answer : The following are the population interaction :

  1. Predation : Population interaction in which one species is benefitted(predator) and other is harmed(prey) is predation. Significance of predation in nature :
    • They keep the prey populations under control.
  2. They act as conduits for energy transfer across trophic levels
  3. Maintain species diversity in a community by reducing the intensity of competiton among competing prey species .
  4. They prevent exotic from becoming invasive.
  5. Protection measures for prey :
    1. Morphological : Thorns , pricks
    2. Chemicals : Cardiac glycosidase
    3. Camouflage : garden lizard.
  6. Competition : population interaction in which both species are harmed as they compete for the same resources food and shelter . “Intra specific competition is more harmful then interspecific competition they common needs ”
    “Herbivores and plants more adversely affected by competition then carnivores “.

    Gausses competitive exclusion principle : Two closely related species competing for same resources can not co-exist indefinitely and the competitively inferior one will be eradicated.

    Competitive Release : expansion in the distribution of one species in a small area when the competitively superior species is removed experimentally .

    Resource partioning : If two species competiting for the same resources can co-exist if they perform resource portioning by acquiring different time for feed or foraging .According to Mac Arthur 5 closely related species of warblers living on same tree can avoid competition and co-exist due to behavioural differences in their foraging patterns .

  7. Parasitism : Population interaction in which one species is benefitted and other is harmed . One organism (parasites) feeds and live on another organism (host).
    Parasites of are of two types :

    • Ectoparasites : parasites feed and live on the external surface of the host ex: lice ,cuscuta , copepods, etc.
    • Endoparasites : parasites live inside the host body ex: Ascaris , liver fluke ,etc .

    Brood parasitism : parasitic bird (cucukoo) lays its eggs in the nest of its host (crow) and lets the host take care of them .

  8. Commensalism : Population interaction in which one species is bennefitted and other is neither benefitted nor harmed .
  9. Mutulasim : Population interaction in which both the species are benefitted .Ex : plant and animals , Mycorizha , lichens
  10. Ammensalism : Population interaction in which one species is harmed and other is neither benefitted nor harmed .Ex: antibiotics released from fungi penicillium kills bacteria

Dharmendra Gaur

Dharmendra Gaur (Msc. Zoology) aka DRGP. I love to learn and teach biology. By this blog I want to increase my knowledge and share my knowledge with others. Feel free to ask what ever you want to ask related to biology, I try my best to help you.

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