NEETClass 11thClass 12thClass 12th PlusJEEClass 11thClass 12thClass 12th PlusClass 6-10Class 6thClass 7thClass 8thClass 9thClass 10thOnline CoursesDistance LearningInternational OlympiadNEETClass 11thClass 12thClass 12th PlusJEE (Main+Advanced)Class 11thClass 12thClass 12th PlusJEE MainClass 11thClass 12thClass 12th PlusClass 6-10Class 6thClass 7thClass 8thClass 9thClass 10thKCET/MHT-CETKCETMHT-CETNEET20262025202420232022JEE20262025202420232022Class 6-1020262025JEE MainPrevious Year PapersSample PapersMock TestResultAnalysisSyllabusExam DatePercentile PredictorAnswer KeyCounsellingEligibilityExam PatternJEE MathsJEE ChemistryJEE PhysicsJEE AdvancedPrevious Year PapersSample PapersMock TestResultAnalysisSyllabusExam DateAnswer KeyEligibilityExam PatternRank PredictorNEETPrevious Year PapersSample PapersMock TestResultAnalysisSyllabusExam DateCollege PredictorAnswer KeyRank PredictorCounsellingEligibilityExam PatternBiologyNCERT SolutionsClass 6Class 7Class 8Class 9Class 10Class 11Class 12TextbooksCBSEClass 12Class 11Class 10Class 9Class 8Class 7Class 6SubjectsSyllabusNotesSample PapersQuestion PapersICSEClass 10Class 9Class 8Class 7Class 6State BoardBiharKarnatakaMadhya PradeshMaharashtraTamilnaduWest BengalUttar PradeshOlympiadMathsScienceEnglishSocial ScienceNSOIMONMTCTALLENTEXASATInstant Online ScholarshipAIOT(NEET)ALLEN for SchoolsAbout ALLENBlogsNewsCareersRequest a call backBook a demo
NCERT Solutions Class 12 Biology Chapter 11 Organisms and Populations
In Class 12 Biology Chapter 11, Organisms and Populations, students learn about how living organisms interact with their environment and with each other. Factors like temperature, water, light, and soil that influence survival, as well as population attributes such as density, growth, and distribution, are also discussed in detail here. The chapter aims to help students understand how a balance is maintained in natural ecosystems.
To ensure a thorough grasp of these ecological concepts, ALLEN provides structured NCERT Solutions to help students master the theoretical and numerical side of ecology, such as calculating population density and interpreting age-structure diagrams. By practicing with ALLEN’s academic materials, students can build the conceptual clarity and speed necessary to handle both descriptive board questions and time-sensitive competitive exams like NEET.
1.0Key Concepts of Class 12 Biology Chapter 11 Organisms and Populations
Organisms live in close association with their surroundings and respond to changes in environmental conditions. This chapter explains how abiotic factors influence organisms, how populations grow and interact, and how living organisms adapt to their habitats. The major concepts include:
- Abiotic Factors: Understand how temperature, water, light, and soil influence the survival, growth, and distribution of organisms.
- Adaptations: Learn how organisms develop structural, physiological, and behavioural adaptations that help them survive in different habitats.
- Population Attributes: Study important population characteristics such as population density, birth rate, death rate, age distribution, and sex ratio.
- Population Growth Models: Understand exponential and logistic growth models and how population size changes under different environmental conditions.
- Population Interactions: Explore competition, predation, parasitism, commensalism, and mutualism, along with their effects on interacting species.
- Human Population Growth: Learn about patterns of human population growth and understand their effects on natural resources and the environment.
2.0NCERT Class 12 Biology Chapter 11 Organisms and Populations : Detailed Solutions
- List the attributes that populations possess but not individuals. Ans. The attributes that populations but not individuals possess are:
- Population density
- Mortality or death rate
- Population growth
- Natality or birth rate
- Age distribution
- Sex ratio
- If a population growing exponentially doubles in size in 3 years, what is the intrinsic rate of increase ( ) of the population?
Ans.
Since,
Intrinsic rate of increase of
- Name important defense mechanisms in plants against herbivory.
Ans.
- An orchid plant is growing on the branch of mango tree. How do you describe this interaction between the orchid and the mango tree?
Ans. The interaction between an orchid and the mango tree is commensalism, because orchid is benefited by getting shelter from mango tree whereas the mango tree is neither harmed nor benefited.
- What is the ecological principle behind the biological control method of managing with pest insects?
Ans. The ecological principle behind the biological control of pest insect is based on the ability of predator to regulate prey population in that habitat. For example : Gambusia fish prey upon the larve of mosquito and acts as biological controller of malaria.
- Define population and community.
Ans. Population: Groups of individuals of same species, which can reproduce among themselves and occupy a particular area in a given time. Community: Groups of organisms of different species that live in common area, which are interrelated and interdependent. It is a natural aggregation of plants and animals in the same environment.
- Define the following terms and give one example for each: [IMP.] (A) Commensalism (B) Parasitism (C) Camouflage (D) Mutualism (E) Interspecific competition
Ans.
(A) Commensalism : This is the interaction in which one species benefits and the other is neither harmed nor benefited. Example : Commensalism in the interaction between sea anemone that has stinging tentacles and the clown fish that lives among them. The fish get protection from predators which stay away from stinging tentacles. The anemone does not appear to derive any benefits by hosting the clown fish.
(B) Parasitism : It is an interaction between two organisms in which one is benefited and the other is harmed, i.e. one organism lives at the cost of other organism. Example : Cuscuta, a parasitic plant that is found growing on hedge plants, do not have chlorophyll and thus derives its nutrition from the host. (C) Camouflage : Some species of insects and frogs are cryptically coloured (Camouflage) to avoid being detected easily by the predator. Example : Common tree frog, Giant leaf insect. (D) Mutualism : This interaction confers benefits on both the interacting species. Example : Lichen (association between algae and fungi). Here, fungi helps in absorption of nutrients and water while the algal partner manufactures food. (E) Interspecific competition: It is the competition among the members of different species for limited natural resources. Example : The Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the Island, apparently due to the greater browsing efficiency of the goats.
- With the help of suitable diagram describe the logistic population growth curve. [IMP.]
Ans. Logistic growth :
- The resources become limited at certain point of time, so no population can grow exponentially.
- This growth is more realistic.
- Maximum number of individuals of a particular species in a habitat that is allowed by nature is called carrying capacity (K).
- When N is plotted in relation to time t, the logistic growth show sigmoid curve and also called Verhulst-Pearl logistic growth. It is given by the following equation:
Where
Graph show lag phase, followed by phases of acceleration and deceleration and finally an asymptote when population density reaches the carrying capacity.
- Select the statement which explains best parasitism. (a) One organism is benefited. (b) Both the organisms are benefited. (c) One organism is benefited, other is not affected. (d) One organism is benefited, other is affected. Ans. (d) One organism is benefited, other is affected.
- List any three important characteristics of a population and explain.
Ans. The three important characteristics of a population are as follows:
(i) Population density: Population density of a species is the number of individuals of a species per unit area or volume. Where Population density N = Number of individuals in a region. S = Number of unit area in a region. (ii) Birth rate: Birth rate is defined as total number of birth in a population with respect to total number of individual of the population in a year. (iii) Death rate: Death rate is defined as total number of death in a population with respect to total number of individual of the population in a year.
3.0NCERT Solutions for Class 12 Biology | Other Chapter-wise Links
Get complete Class 12 Biology NCERT Solutions chapter-wise, with clear explanations and detailed answers to textbook questions available through the links below.
4.0Key Features and Benefits of Class 12 Biology Chapter 11 Organisms and Populations
- Clear Understanding of Population Ecology: Learn important concepts related to populations, their characteristics, and interactions with the environment in simple language.
- Population Growth Made Easy: Understand exponential and logistic growth through clear explanations and population growth curves.
- Real-World Ecological Examples: Connect concepts such as population interactions, competition, predation, and adaptation with examples from natural ecosystems.
- Easy Revision of Key Concepts: Quickly revise important terms, ecological relationships, graphs, and biological principles before examinations.
- Strong Foundation for NEET: Build a clear understanding of ecology and population-based concepts that are important for NEET Biology.
- Simple and Student-Friendly Learning: Complex ecological relationships and population processes are explained clearly for better understanding and recall.