Organisms and Populations: Important Questions

CBSE Class 12 Biology Organisms and Populations Important Questions have been provided in this article along with detailed solutions. The important questions have been formulated as per the latest CBSE Board Curriculum that would help the students to cover essential topics in the chapter like Organisms, Organisms and Environment, Biotic and Abiotic Factors, Population Growth, Population Growth Models, Biomes, etc. 

Organisms and Populations all together play an essential role in maintaining the overall balance in the environment. Ecology is an important branch of Science which describes the relationship between various organisms and their environment. The four main components that makeup Ecology include Organisms, Populations, Communities and Biomes. It is essential to know that variations within nature affect the way organisms adapt and survive. Each of them adapts in their way and manages to stay in their environment. Moreover, the types of interaction between organisms also play a deciding factor in population growth.

Organisms and Populations

Read More: Organisms And Populations MCQs

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Very Short Answer Questions (1 Mark Questions) 

Ques. What are the four basic levels of biological organization within ecology?

Ans. Organisms, Population, Communities and Biomes.

Ques. What category of organisms do goldfish and haddock belong to? 

Ans. Stenohaline Species.

Ques. Name two main factors within the biome that leads to habitat formation. 

Ans. Regional and Local variations.

Ques. What are stenohaline organisms?

Ans. The organisms with the ability to tolerate only a narrow range of salinities. Eg. Goldfish and Haddock

Ques. What factors lead to variations in physical and chemical conditions of habitats? What are factors called?

Ans. Temperature, Water, Light, Soil. 

Ques. What is the process of homeostasis?

Ans. An organism trying to maintain the constancy of its internal environment is referred to as homeostasis.

Ques. How do many organisms cope with the state of homeostasis?

Ans. Through Regulate, Conform, Migrate or Suspend.

Ques. How does an organism check the uncontrolled growth of another organism within the biological system? 

Ans. An organism checks the uncontrolled growth of another organism within the biological system through Predation.

Ques. A process in which organisms succeed to blend with nature and their surroundings. What is it called?

Ans. Camouflage. 

Ques. Name two main microbes that survive within the human intestine. 

Ans. Lactobacillus and Escherichia Coli. 

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Short Answer Questions (2 Marks Questions) 

Ques. What are the main metabolic activities followed when organisms suspend as a part of homeostasis? Brief each of them.

Ans. Hibernation, Aestivation and Diapause are the main metabolic activities in the process when organisms suspend themselves. 

Read More: Difference Between Aestivation and Hibernation

Hibernation

Ques. Explain Darwinian fitness.

Ans. Populations tend to increase their reproductive fitness in the habitats they live in and this value is indicative of Darwinian fitness. 

Ques. Explain Brood Parasitism with an example.

Ans. It’s a state in which an organism lays its eggs in the nests of other birds and lets them incubate their eggs. One popular example is Cuckoo birds which lay their eggs in the crow’s nests.

Ques. State one similarity between parasitism and predation. 

Ans. In both parasitism and predation, one species is in benefit i.e. parasite and predator while the other is the target/victim i.e. host and prey.

Ques. Differentiate between commensalism and amensalism.

Ans. Commensalism is a process when one species is benefitted while another is neither benefited nor harmed i.e. unaffected. Amenalism is defined as the process when one species is harmed while the other remains unaffected.

Ques. Why cannot herbivores rely upon calotropis plants?

Ans. Herbivores cannot rely upon calotropis plants because these plants consist of highly poisonous “glycoside” which is harmful to their heart. 

Ques. Define adaptation.

Ans. Adaptation is a way in which organisms survive themselves and reproduce in their respective habitats. It could be morphological, physiological and behavioural. 

Ques. How do you differentiate between ectoparasites and endoparasites?

Ans. Ectoparasites rely and are more active upon outer/ external surfaces of the host. Eg. ticks over the dog’s body, head lice on the human’s head. 

Endoparasites actively dwell in the body of the host to target their organs such as lungs, kidneys and so on. Eg. tapeworms (within the gut), liver fluke, plasmodium.

Ques. How are heliophytes different from sciophytes?

Ans. Heliophytes are grown in sufficient bright sunlight. On the contrary, the sciophytes require very minimum sunlight to grow, hence growing well in shades.

Ques. What do you understand about thermoacidophiles?

Ans. Microbes that survive in high temperatures are known as thermoacidophiles. They manage to stay at such high temperatures due to a reduced amount of free water and occurring branched-chain lipids reducing the fluidity of cell membranes. 

Ques. What type of population interaction is the interspecific competition? Explain.

Ans. Interspecific competition is an interaction in which both the species involved are equally affected. Eg. The butterfly species, queen and monarch species are two interacting species equally affected. 

Ques. List a few abiotic factors and edaphic factors.

Ans. Abiotic Factors: Light, water, wind, temperature, humidity 

Edaphic Factors: Soil texture, minerals, topography, substratum (underlying layer within rock or soil) 

Read More: Characteristics Of Organisms

Ques. If a fish taken out from fresh water is put into a marine medium like an aquarium, will it be able to survive? 

Ans. No, the fishes are adapted to survive in the medium they are suited to. So, if fish is put from freshwater to saline medium, it could hardly survive in salinity and thus die. 

Ques. Briefly explain one unique feature of plants in arid regions. 

Ans. Plants in arid regions possess sunken stomata to minimize water loss during transpiration. Having sunken stomata allows them enough space to minimize their water loss and hence manage to cope with the climatic conditions.

Ques. An orchid plant growing on a mango tree. Explain this interaction classifying among mutualism, commensalism or predation. 

Ans. An orchid plant growing on a mango tree is a type of commensalism interaction. Here the orchid plant is growing so being benefited and the mango tree is neither Hermes nor benefitted. 

Predation

Read More: Population Interaction

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Long Answer Questions (3 Marks Questions)

Ques. State the Gause’s Competitive Exclusion Principle.

Ans. Gause’s Competitive Exclusion Principle states that two species which are very closely related to each other competitively survive for existence. The one which dominates to survive will survive leaving behind the inferior one to diminish especially when resources are limited.

This is indicative of an interspecific relationship where two species are related to each other and affect each other’s survival. For example, herbivores rely upon plants for their survival and hence win the competition to ensure their survival. 

Ques. What factors cause fluctuation in the density of population within a given period, in a given habitat? Explain each of them.

Ans. Natality, Mortality, Immigration and Emigration cause a notable increase or decrease in the density of the population. 

• Natality: Number of births within a given period that add up to the density of population.
• Mortality: Number of deaths within a given period that contribute to a decrease in density of population. 
• Immigration: Number of individuals belonging to the same species that have entered a place/ habitat during a noted time.
• Emigration: Number of individuals belonging to the same species that have left a habitat during a noted time. 

It is quite obvious that some of the factors contribute to adding up to density and others deduce the density of the overall population. Natality and Immigration lead to an increase while Mortality and Emigration lead to a decrease in the density of the population.

Read More: Difference Between Morbidity and Mortality

Ques. Explain the predator-prey relationship.

Ans. The predator-prey relationship is a perfect example which satisfies Gause’s Competitive Exclusion Principle. It states that no two species which are closely related to each other could survive within similar habitats or situations. One or the other has to diminish, preferably the one which is inferior to the other.

The predator-prey relationship involves two species interacting with each other in such a way that one species dominates and relies upon the other species. The dominating one is called the predator and the targeted one is called the prey. The predator species targets the prey and get to complete their food necessities.

For example herbivores (predators) like cows, and deer rely upon plants (prey) for fulfilling their basic requirements. Another example could be a lion eating a deer. This in turn forms a complex food web.

Food Web

Read More: Difference between Predation and Parasitism

Ques. Draw a line of distinction between diapause and hibernation.

Ans. Diapause and hibernation, are similar in the fact that both allow organisms to survive for their best, even in the worst environmental conditions. The line of distinction between diapause and hibernation is described as follows:-

Ques. Write four main attributes that contribute to the population growth census.

Ans. Population growth marks an important number as population census varies from region to region. Population growth census has four primary attributes:-

• Sex Ratio: The ratio of the number of males to the number of females within a particular region within a particular time interval. 
• Mortality and Natality: Mortality refers to the number of deaths seen within a given period and Natality refers to the number of births within a given period.
• Age Distribution: The proportionate number of persons in distinct age groups within a given population.
• Population Growth: The estimated increase in the population of a region during a noted time interval is referred to as population growth.

Read More: Difference Between Diapause and Hibernation

Very Long Answer Questions (5 Marks Questions)

Ques. Explain how desert plants manage the loss of water.

Ans. Desert plants need to manage the loss of water due to the scarcity of water and climatic conditions in the desert regions. This is done through Xeric adaptations brought into the process. Xeric adaptations include one or more of the following characteristic features:

• Developing succulent leaves, stems and roots. Eg. Asparagus, Begonia
• Inhibits small-sized leaves or no leaves at all to avoid transpiration.
• Developing an extensive root system.
• Thick cuticles on the stems and leaves surface to avoid transpiration and hence loss of water.
• Timely shedding of leaves to minimize water loss.
• Some xerophytes remain in a dormant state as seeds or roots and sprout up when it rains. These are called ephemerals.

Ques. Describe the Growth Model.

Ans. The growth Model highlights the status of growth of an individual or group of organisms in the biological system. The growth model is highly affected by varying habitat conditions, availability of food, and biotic and abiotic factors. The growth model consists of two submodels-

Exponential Model

Exponential growth states a change in the overall population and not population per individual growth rate that stays the same regardless of population size.

dN/dt= (b-d) * N 

Where,

• N = population size
• B and d are birth and death rates respectively.

Note: (b-d) is called the intrinsic rate of natural increase symbolized as ‘r’.

Logistic Model

In the logistic model, the population per individual growth rate gets smaller and smaller as population size approaches the maximum by limited resources in the environment (called carrying capacity). 

Where,

• N = population density at time t,
• K = carrying capacity
• r = intrinsic rate of natural increase 

Read More: Logistic Function: Graph, Equation & Derivation

Ques. Explain the types of population interaction.

Ans. Population interaction involves how the overall organisms within a population interact with each other. The types of population interaction include-

• Commensalism- It is an interaction where one species out of the two remains in benefit and the other is neither harmed nor benefited i.e. remains unaffected.
• Amensalism- It is an interaction in which one species is harmed while the other is neither way affected.
• Predation- An interaction where a superior species dominates by eating or killing the inferior species and targets it for its benefit. The dominating one is called the predator and the target species are called prey. 
• Parasitism- The interaction in which a species hosts another set of species for fulfilling its requirements. The species that are called parasites rely upon the species for using them for their good. The species which are being used are called hosts. Eg. ticks (parasites) on the dog’s body (host). 
• Mutualism- It is a mutual interaction between two species which helps in each other’s survival. They mutually exist ensuring that they contribute some benefits to each other and let them survive. 
• Competition- As the name suggests, competition allows species to compete for survival and let the right one survive. This is also related to the survival of the fittest, i.e. the one who has to survive has to compete. 

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