CBSE Solutions for Class 12 Biology Chapter 11 Organisms and Populations

*As per the revised curriculum of CBSE Syllabus 2023-24, this chapter, previously known as Chapter 13, has now been renumbered as Chapter 11. Stay updated with the latest changes in the curriculum.

Organism and Populations Class 12 NCERT Solution is all about the basics of organisms, populations, and different methods to calculate population. These NCERT Solutions are prepared by our Top Biology Experts in order to take care of all Important Topics that might be asked in the upcoming examination 2023. So, Students can also refer to these solutions for their final Examination preparation.

This Class 12 Biology Chapter 11 Organism and Populations NCERT Solutions are carefully developed using easy-to-understand language while adhering to the guidelines for solving NCERT Solutions for Class 12. Working through these solutions can be highly beneficial for students in their board exams, as well as in preparing for future competitive Exams.

Organism and Population CBSE Class12 Questions and Answers

NCERT Solution for Class 12 Organisms and Population describe the brief organism, population, population growth models, adaptation, and interspecies relationship. To solve the textbook questions, students can go through NCERT Solutions class 12 biology. Revise the basic concepts of Organism and Population for quick revision and class notes.

Q1: List the attributes that populations possess but not individuals.

Answer:

Groups of individuals from the same species that share or compete for similar resources and live together in a defined geographical area constitute a population. The following are the attributes that the population possesses:

• Birth rate: The birth rate in a place is the number of babies born there for every 1000 people during a particular period of time.
• Death rate: The death rate is the number of people per thousand who die in a particular area during a particular period of time.
• Sex Ratio: It is the number of females per 1000 males. It compares the number of females and males in a population group.
• Age distribution: In a given population it can be defined as the percentage of individuals of various ages. When the percentage of individuals of a certain age or age group is graphed for the population, it produces an age pyramid. The shape of the pyramids is an indicator of the population’s growth status, which can be (a) increasing, (b) stable, or (c) decreasing.
• Size of a population: It indicates the status of the population in the habitat. It is measured in the form of population density.

Q2: If a population growing exponentially doubles in size in 3 years, what is the intrinsic rate of increase (r) of the population?

Answer:

When an adequate quantity of food resources is available in an area, the population grows exponentially. To estimate the exponential growth, an integral form of the exponential growth equation can be used, that is

   N_t = N_oe^rt

• N_t  is the population density after time t.
• N_o is the population density at time Zero.
• r is the intrinsic rate of natural increase.
• e is the base of natural logarithm is 2.71828

Assuming,

Let the current population density be x 

   Population density after 2 years will be 2x.  

   Time ‘t’ given is 3 years.

Using equation N_t =N_oe^rt 

2x = xe^3r

x = e^3r

Applying log on both sides

      Log 2 = 3r log e

          r = log² /3 log e

          r = 0.301/ 3×0.434

          r = 0.2311

Hence, the intrinsic rate of increase (r) of the population is 0.2311.

Q3: Name important defense mechanisms in plants against herbivory.

Answer:

Plants have evolved a variety of morphological and chemical defenses against their predators like herbivores and  Insects (known to feed on plant sap and other parts of plants). The following are a few examples of  the defense mechanisms:

Morphological defense mechanisms 

• The thorns or spines on cactus(Acacia).
• Impenetrable defenses, such as bark and waxy cuticles.
• Some plants have sharp margins that prevent herbivores to feed on them.

 Chemical defense mechanisms

• Several plants contain substances that can make animals that eat them feel ill, and inhibit feeding or digestion.
• Calotropis weed produces highly poisonous cardiac glycosides.
• Nicotine, caffeine, quinine, strychnine, opium, etc are produced by plants as defenses against grazers and browsers.

Q4: An orchid plant is growing on the branch of the mango tree. How do you describe this interaction between the orchid and the mango tree?

Answer:

An orchid growing on the branch of a mango tree is an epiphyte. An epiphyte grows on the plant’s surface and derives its nutrition from air, water, rain, and debris around them. Therefore, the relationship between the mango tree and orchid plant is an example of Commensalism where one species receives its benefits, and the other stays unaffected. In this case, the orchid benefits because it uses the mango tree for physical support. It attaches itself to the tree and grows with the help of its structure. On the other hand, the mango tree doesn’t experience any positive or negative effects from the orchid’s presence.

Q5: What is the ecological principle behind the biological control method of managing pest insects?

Answer:

The ecological principle behind the biological control method of managing pest insects is predation. Predation refers to ecological interaction, where one organism, known as a predator, kills and consumes the other organism known as prey. It plays a significant role in controlling and balancing the population of prey like the pest insects. For example, predation by the Heron(bird) helps regulate the population size of the fish in the pond.

Q6:Define population and community.

Answer:

• The population is defined as groups of individuals from the same species that share or compete for similar resources and live together in a defined geographical area. Characteristics of the population are birth rate, death rate, sex ratio, population density, and age distribution. Example: Population of Tiger in Forest.
• A community is defined as a group of interacting organisms of different species that live in the same habitat and interact with one another. Example: Forest ecosystem.

Q7: Define the following terms and give one example for each:

• (a) Commensalism
• (b) Parasitism
• (c) Camouflage
• (d) Mutualism
• (e) Interspecific competition

Answer:

(a) Commensalism

Commensalism is a type of ecological interaction between two species, where one benefits and the other is neither harmed nor benefits. For example, the interaction between sea anemones and clownfish. The fish gets protection from predators which stay away from the stinging tentacles. The anemone remains unaffected.

(b) Parasitism 

The ecological interaction between the two species, where one species benefits( positively affected) and the other is negatively affected. For example, ticks on dogs and licks on. The human liver fluke (a trematode parasite) depends on two intermediate hosts (a snail and a fish) to complete its life cycle. The malarial parasite needs a vector (mosquito) to spread to other hosts.

(c) Camouflage

Camouflage refers to adaptation by an organism to blend in with its surrounding, concealing itself from predators. It’s a survival strategy used by the various organism to increase their chances of survival. Many species of insects and frogs
are cryptically colored (camouflaged) to protect themselves from the predator.

(d) Mutualism

Ecological interaction is in which both interacting species benefits from each other. For example Lichens, it’s a mutualistic relationship between fungi and algae. Fungi help the algae in the absorption of nutrients from the soil and in turn, algae provide food to the fungi.

(e) Interspecific competition

The interaction between the two species is where both are negatively affected. For example, visiting Flamingo and resident fish competing for the typical food, zooplankton in the South American lakes.

Q8: With the help of a Suitable diagram Describe the Logistic Population Growth Curve.

Answer:

The logistic growth model describes the population in an area having limited resources. It includes five phases, explained as follow:

1. Lag phase: In this phase, the population size remains relatively stable or shows minimal growth. As the individual is introduced to a new area, it takes time to adapt to a new environment.
2. Exponential phase: As an individual adapts to the environment, the condition improves, and resources become available, the population grows exponentially. The growth curve rises steeply.
3. Acceleration phase: The population grows slowly at the start of the phase.
4. Deceleration Phase: With the growth of the population, competition increases among the individuals of the same species for resources. Therefore, after the exponential growth phase, the growth rate starts to slow down. 
5. Stationary phase: As nature reaches its carrying capacity, the growth of the population slows down and becomes stable. The curve is represented graphically as a sigmoid shape. This type of population growth is also called Verhulst – Pearl Logistic Growth. This growth model is described as a more realistic one. 

Q9: 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, and another is affected.

Answer:

Option (d) best explains parasitism. Parasitism is the ecological interaction between two species where one species is benefited and other is affected—for example, Ticks on dogs and lice on humans.

Q10: List any three important characteristics of a population and explain.

Answer:

The population is defined as a group of individuals of a single species that can interbreed and live in the same area simultaneously. The three important characteristics of the population are as follows:

1. Birth rate: Birth rate refers to the number of live births per 1,000 people in a given population within a specific time period.
2. Death rate: The death rate is the number of people per thousand who die in a particular area during a particular period of time.
3. Age distribution: In a given population it can be defined as the percentage of individuals of various ages. When the percentage of individuals of a certain age or age group is graphed for the population, it produces an age pyramid.

Key Features of NCERT Solutions Class 12 Biology Chapter 11 Organisms and Populations

• They enhance the conceptual knowledge of the students.
• Clear and Comprehensible Content.
• Aid in Competitive Exam Preparation.
• The answers are provided by Top subject experts.
• Readily available and easily accessible.

FAQs on Human Reproduction Class 12 NCERT Solution

Q1: What is the name of chapter 11 of NCERT class 12 Biology?

Answer:

Class 12 Biology Chapter 11 name is Organism and Populations which is about organisms and populations.

Q2: Where can I find NCERT solutions for Class 12 Biology Chapter 11?

Answer:

NCERT solutions for Class 12 Biology Chapter 11 can be found on various online platforms such as the official NCERT website, GeeksForGeeks, and more.

Q3: Why are NCERT Solutions for Class 12 Biology Chapter 11 beneficial for the students??

Answer:

The benefits of using the NCERT Solutions for Class 12 Biology Chapter 11 are:

1. Completely solved answers for all the questions present in the NCERT textbook are available in PDF format.
2. Simple and easy-to-understand language is used to make learning fun for the students.
3. Top Subject matter experts prepare the solutions after conducting vast research on each concept.
4. The solutions not only help students with their board exam preparation but also for various competitive exams like JEE, NEET, etc.