Xam Idea Class 12 Biology Chapter 13 Solutions: Organisms And Populations

Xam Idea Class 12 Biology Solutions for Chapter 13 ‘Organisms And Populations’ is an excellent preparation guide that will help you to clear your entrance tests like NEET along with CBSE Class 12 exams. These solutions will assist you to revise the chapter quite efficiently. You will be solving questions related to hibernation, amensalism, habitats, and ecosystems, stenothermal, and eurythermal. The descriptions provided in our solutions would give you a better understanding of organisms and populations.

In total, there are 137 questions throughout this Xam Idea Solutions for chapter 13 Organisms And Populations. These questions are categorized into four separate sections which are very short answer questions, short answer questions (type I and II), and long answer questions respectively. The questionnaires in these segments will make you aware of different aspects such as photoperiod-dependent processes, how organisms effectively deal with global warming as well as Gause’s principle of competitive exclusion.

Instasolv’s solutions for Xam Idea Class 12 Biology Chapter 13 help you plan for your CBSE Class 12 board exams thoroughly. Refer to our solutions and all your doubts will be solved in minutes. Our Xam Idea solutions are a very trustworthy source for removing all your doubts. Our subject matter experts have created simple and comprehensive solutions in a very easy to understand language. All our solutions follow the latest CBSE guidelines.

Important topics of Xam Idea Class 12 Biology Solutions Chapter 13: Organisms And Populations

Ecology: It is the study of relationships between species as well as between organisms and it’s external (abiotic) climate. There are 3 stages of biological organization:

  • organisms
  • populations
  • communities
  • biomes

The Ecosystem at the organism level is a biological ecosystem, which aims to explain how various species get adjusted to their environment concerning their survival rate and breeding.  

Biome: It is the community of animals and plants that have common characteristics for the environment in which it operates.

The creation of a biome relies on:

  • Annual fluctuations in temperature intensity or length.
  • Annual precipitation variation.
  • Life occurs not only in desirable environments but also in extreme and harsh environments.

 Ecosystem Components: 


  • Physio-chemical (abiotic) components: Approximate temperature, water, light or soil



  • Biotic Components: Pathogens, parasites, predators, or competitors



  • Abiotic Major Factor:



  • Temperature of air 


The surface temperature of the soil changes throughout seasons   

This slowly declines from the equator to the poles and from the mountains to the mountain tops.

  • Water

Productivity or distribution of plants inside a geographical area is heavily dependent on groundwater. 

pH: The quality of the water depends on the chemical composition of the water.

The Light:

It plays a key role in physiology allowing the sustainability of autographs by helping them to manufacture food through photosynthesis.

The Soil:   

The soil quality (penetration or water-holding capability) is characterized by the following components: Soil composition, size of the grain, or Aggregation.

Homeostasis: The species can keep a steady body temperature despite different external conditions.

Different ways in which humans can deal with the growing environment: Regulate, Conform, Migrate and Suspend


  • Regulation:


  • Organisms store energy by physiological means, which ensures that homeostasis is maintained.
  • A constant temperature of the body (Thermoregulation)
  • Osmotic strength (Osmoregulation) Conform to:
  • Conform:   It involves organisms that cannot keep a consistent temperature of the body.
  • Their body temperature varies with the temperature.
  • Displayed by: 99 per cent of animals and almost all plant species.
  • Adaptation would be any trait of an organism (morphological, physiological, and behavioural) that allows the organism to survive and thrive in its environment.

Attributes to Population:

  • The population is the organisms residing in communities within a very well-defined geographical area, exchanging or struggling to compete for similar resources as well as potentially selective breeding.
  • Population biology ties biodiversity to human genetics and evolution.
  • Age Pyramids describes the structure of the demographic age distribution.

Population Density

  • Individuals within species per unit area:   Designated as ‘N.’


  • Representing the Density of Population:


Nt+1=N+ [(B+I) – (D+E)]

Nt is Population density (time t)

        Nt+t is Population density (time t+1)

        B is a Birth rate

        I signify Immigration

        D is a Death rate

        E is Emigration

Population Growth Models

  • Growth models can be used to anticipate population growth over time.
  • There are two development models:

The Exponential growth

The Logistic Growth

Exponential Growth

  • Shown in habitat with an unlimited resource for individual people.
  • The formula of exponential growth:

dN/dt = (b–d) × N

      Suppose, (b–d) = r, then

dN/dt = rN


N is the Population size

B represents Birth Rate

d is the Death rate

r is an intrinsic rate of natural increase

  • So if N is graphed regarding time in the graph, it tends to result in a J-shaped curve.
  • Could also be supported as:

Nt = N0 ert


Nt is Population density after time t

N0 is Population density at time zero

r is an intrinsic rate of natural increase

‘e’ is base natural logarithms (2.71828).

Logistic Growth

Neither of the population has limitless resources at its disposal to promote exponential growth. Logistic growth can indeed be calculated using the following formula:

dN/dt = rN [(K-N)/K]


N is Population density at time” t”

r is the Intrinsic rate for natural increase

K is Carrying capacity

Interspecific Relations

Interspecific relations are the association between organisms with two distinct types.

These relationships could be:

 Beneficial (expressed by + sign)

 Detrimental (expressed by – sign), Neutral (expressed by 0)

Economic Exclusion Theory of Gause:    

Two related species trying to compete for the same resources will not coexist indefinitely and the highly competitive inferior species will eventually be eliminated.

Resource Segmenting:

  • When two species remain competitive for the same resource, they may avoid competition by selecting. Different times for nourishing or distinct foraging trends.
  • Five highly associated warbler species can live on the very same tree and be able to ignore the competition and occur concurrently due to behavioural distinctions in their forage for food activities.

Discussion of exercises of Xam Idea Class 12 Biology Solutions Chapter 13: Organisms And Populations

Xam Idea Class 12 Biology Solutions Chapter 13 contains 137 questions in total which are divided into four categories containing PYQ (past years questions) and OIQ (objective inventory questionnaires). 

Very Short Answer Question

  • It encompasses a total of 50 problems out of which 24 problems placed under the PYQ segment and the rest 26 problems placed under the OIQ segment. 
  • These questions are normally straightforward and simple to answer. This section is based on population sigmoid growth curve, types of interactions, and the primary requirement of parasites.

Short Answer Question (type I)

  • This section contains 45 questions that are segmented into 30 PYQ and rest 15 problems within the OIQ segment.  
  • You are supposed to apply the formula of Gause’s principle of competitive exclusion.

Short Answer Question (type II):

  • This section essentially contains 25 questions only within the categorized PYQ segment.  
  • Here you need to analyze the density of population per unit area in a habitat. Few questions are based on the differentiation of ecological terms.

Long Answer Questions:

  • This section contains 17 questions that are segmented into 11 questions in PYQ and 6 problems in the OIQ segment. 
  • This section covers the diagrammatic representation of population graphs and the age pyramid of different populations.

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  • Utilizing Xam Idea Class 12 Biology Solutions for organisms and populations will stand as a huge advantage to you. 
  • If you have any doubts about writing about any explanation, you can use this practice book.
  • This book will be a trustworthy source of information to score higher in exams.
  • All implicit questions and answers can be found in Xam Idea Class 12 Biology Solutions Chapter 13 by instasolv.
  • Our subject matter experts have planned approaches, bearing in mind the problems that you face more frequently than otherwise.