Chapter 13

Organism And Population

An ecosystem is the group of food supply, predation, and competition. The chapter Organisms And Populations NCERT highlights the fitness of individuals, measured by their survival, growth rate, and reproductive success. Therefore, the population of a species in a given ecosystem or habitat depends on several factors such as climate, food supply, and predators. A species' population can increase or decrease depending on the aforementioned factors. The population that increases is known as the "expanding population," while the one that decreases is called "contracting population." Organisms And Populations Class 12 NCERT explains how food and energy availability affects the populations of organisms in an ecosystem. The population grows when food and energy are abundant in the environment. On the other hand, it decreases when these resources are scarce within the ecosystem.

Organisms And Populations Class 12 NCERT highlights that habitat includes all biotic and abiotic elements having a specific role in supporting the species present there. It determines where a particular organism lives or spends most of its time during its life cycle. Organisms And Populations NCERT states that population growth can be measured using birth rate, survival rate, age structure, density, and population stability. Population ecology stands for the population dynamics (the changes in the size of the population) of an individual species, population, or community. The study of population dynamics is known as Demography, while ecology is known for its Population Biology. Organisms And Populations Class 12 NCERT is about the Population Dynamics of a natural population for one year.

What are organisms, and how many types of organisms are there?

Organisms are living beings. An individual organism is called a cell or molecule. All organisms go through the same basic life steps: start with a single cell and divide into two cells. There are different organisms, including bacteria, plants, animals, and humans. Some organisms may be unicellular (one cell), while others may be multicellular (many cells). Organisms can grow from a single cell to an enormous size. 

Organisms can be broadly categorised into two – macroscopic and microscopic. Macroscopic organisms are readily observable by the naked eye, such as people, trees, and animals. Though some unicellular organisms fall under this category, most microscopic organisms are multicellular and large (turtles and crocodiles). Microscopic organisms include single-celled organisms such as bacteria, algae, protozoa, and fungi.

 

The environment is defined as a surrounding medium that contains all the resources organisms need. Without an environment, organisms cannot survive. The environment includes air, water, soil, and sunlight. Every organism has its specific environment depending on its type. For example, germs and bacteria live in the soil, and humans live on the earth's surface. The environment is affected by natural factors such as climate and altitude. Food supply is also a significant factor. In addition, other factors affect the environment, such as predators, competitors, and pathogens. 

 

Biotic factors and abiotic factors both influence the environment. Biotic factors are living organisms like bacteria, plants, predators, and vertebrates. Abiotic factors are non-living things that affect or regulate the environment, such as daylight, temperature, precipitation, and solar radiation. Abiotic Factors are nonliving things in the environment such as air, soil and water. Vertebrates are animals that have a backbone. These include large mammals such as humans and other mammals such as dogs or cats. Vertebrates may be terrestrial (living on land), like reptiles or birds, or aquatic (living in water) like fish or whales. They may also be amphibians (usually living in water but living on land). These factors affect the environment in the following ways:

  1. Biotic factors regulate the amount of light in the environment - Plants and trees are important as they provide shade and shelter to animals, preventing them from burning in the sun. Animals also help regulate their environment by eating plants, controlling pests or helping to aerate the soil. These effects can be summarised as "carrying capacity".
  2. Some Biotic Factors increase or decrease light levels.
  3. Abiotic Factors affect water levels in an environment.
  4. Abiotic factors also affect temperature.
  5. Abiotic Factors also affect soil moisture.
  6. The stability of an ecosystem is determined by increasing or decreasing abiotic factors such as CO2 levels and temperature.

 

The growth or decay of an organism depends on three basic ecological processes: Birth, Mortality, & Immigration. Birth refers to the production of new individuals – it can vary from vegetative (growing into plants or animals) to sexual (producing offspring that are sexually mature). Mortality is caused by death – affected by predation or disease. Finally, the term immigration refers to the arrival of new individuals into a population.

The size and structure of a population are unique in their way. The population is the number of organisms present in a community (local or non-local) or area. The size of a population can be determined by counting the number of individuals living in a particular area at a given time. Population size may be changing over time due to births and deaths. A population structure is based on the age, sex, and density of individuals in an area. A dynamic structure is dependent on several factors, including dispersal and migration. Migrating birds or fish use wind or water to disperse themselves to other areas and avoid overcrowding in areas that cannot support their present numbers. The environment, in turn, affects the population's growth rate through the availability of resources (food, water, shelter). For example, if the temperature is lowered or there is not enough water available for a plant to grow, it will not reproduce further. Therefore, an organism's genetic material may mutate or die off completely. There will be a change in gene frequency among generations if this occurs since only specific alleles will survive. This will repeatedly happen in the population and change its gene pool.

The study of population ecology is called demography and is concerned with how populations change over time. Demographers are interested in measuring how a population changes over time and space. From a social science perspective, demography is concerned with:

  • Census data, population trends
  • Sex ratios in different countries
  • Migration patterns
  • Family size and distribution
  • Births and deaths

The study of ecology is called population biology, which is concerned with how organisms interrelate within a population or community. Population biology questions include: 

  1. A given species' size, age structure, sex ratio, and reproductive success? 
  2. What are their life histories? 
  3. What are the causes of change in population size? 
  4. How does an organism establish and maintain a stable population within its habitat?

Population ecology studies the influence of biotic factors on populations. The biotic factors are determinants or components that are essential in the life cycle of the population. Population ecologists classify species based on how these components affect the population, such as how much food they require, what they eat, and how their habitat is affected by changes in their environment. A standard system for classifying organisms is by reproductive strategy. Some organisms reproduce more rapidly than others, and therefore, their populations grow in size more quickly. This is important because it signals to the ecologist that the population increases. Other organisms reproduce more slowly, and therefore, their populations increase more slowly or decrease over time. This is called a stable population. The reproductive strategy of the population also determines the number of offspring per individual, which can vary from a few (low fecundity) to many offspring (high fecundity).

Organisms are also classified by the location where they live. For example, terrestrial organisms live on land, aquatic organisms live in water, and certain algae live in both environments. Organisms also display many different types of social relationships with each other such as cooperative (e.g., ants or termites), predatory (e.g., lions), or commensalistic relationships (e.g., bats living in caves).

 

The environment can either provide more food or place more predation. Apart from this, several other factors affect the population of organisms. For example, a forest can support larger wild populations than a desert because they provide more food. This is because different types of trees, shrubs, and other plants (fungi, bacteria, and algae) are used as food sources by the organism. However, when there is less food, it becomes necessary for populations to compete for resources. Competition can result in a population change such that some die off while others reproduce more rapidly for the population to remain stable.

Ecology is the study of how organisms interact with their environments. This interaction can lead to changes in the organism's size, structure, and genetic makeup. For example, an ecosystem can alter the characteristics of the organisms in a community. This results in different populations within an ecosystem being more or less stable over time. Chapter 13 Biology Class 12 NCERT Solutions answers all your queries related to Organisms and Population Class 12 NCERT. The environment constantly changes due to biotic and abiotic factors that organisms often cannot respond to. Knowing these interactions can help us better understand the effects of population ecology on an organism's population size. You can download the MSVgo app to assist with Organisms and Population Class 12 NCERT and clarify your doubts related to the chapter.

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