Organism and Population Class 12 Notes- Important Points

Organism and Population Class 12 Notes

A continuous biological system that exists in an environment and has the ability to adapt and keep certain structures and behavior is referred to as an organism. Fungi, bacteria, plants, animals, and people are all part of it.

A population is a group of organisms.

The population manages the ecology as a community.

The ecosystem comprises both biotic and abiotic elements.

Ecology is the study of the interactions between organisms and their physical (abiotic) environment.

organism and population class 12 notes

Ecology is primarily concerned with four layers of biological organization.
These are as follows:
a) The organism: Individual living component of the environment and base unit of ecological hierarchy
b) The population: The total number of individuals of a species in a given geographical region.
c) Communities: A grouping of all the populations of different species existing in a given region that interact with one another.
d) The biome: It is a huge unit composed of a primary flora type and accompanying animals in a specific climatic zone. India’s principal biomes include tropical rainforest, deciduous forest, sea coast, deserts, and so on.

Having a brief idea of what organisms, populations, and Ecology is, let us move on to important bullet points on Organism and population class 12 notes.

Bullet points on Organism and Population Class 12 Notes

Factors Affecting the Ecosystem

The population manages the ecology as a community. Biotic and abiotic elements form the whole Ecosystem. Temperature, light, water, and soil are major abiotic elements that influence the physical and chemical characteristics of diverse habitats.

Because of genetic differences, all species have the potential to adapt to diverse environmental situations. Their chances of survival improve as a result. The polar bear possesses a variety of characteristics that aid in their adaptation to the extremely cold temperature of Antarctica. Their thick fur coats keep them warm and safe from predators. The waxy covering repels moisture while also keeping the body warm.

All living creatures in an ecosystem are considered biotic factors, as are their interactions and waste products. Some species consume plants and animals, while others generate their own sustenance. In addition, there are a number of creatures that feed on decomposing materials.

Not only do these factors affect the ecosystem to a greater effect, but also there are some strategies and it is mentioned below:

  1. To Regulate – Many animals can regulate their body temperature, which aids in temperature adaptation. For example, in the summer, our bodies control temperature through sweating, but in the cold, we shiver because shivering generates heat.
  2. To Conform – Some animals are unable to control their body temperature in response to environmental temperatures. These creatures are known as conformers. These conformers have not developed; rather, they have become regulators due to the high energy cost of regulating.
  3. To Migrate– This is another way of adaptation in which organisms migrate from adverse to favorable settings. Birds, for example, frequently migrate from chilly locations to somewhat warmer areas and vice versa.
  4. To Suspend – Some organisms suspend their metabolic activity and enter a dormant state.

How to bring in the Adaptions?

Adaptation is a natural process that allows organisms to survive or reproduce in their environments. It has been noticed that organisms generally adapt to the environment in which they do well. Desert plants, for example, have thick cuticles, leaves that have been transformed into spines, and sunken stomata to minimize transpiration and allow photosynthesis to occur via the CAM pathway.

Humans have experienced altitude sickness at greater altitudes, such as mountains and hills, resulting in nausea, shortness of breath, exhaustion, heart palpitations, and other symptoms. However, after some time, they acclimate to their surroundings, which leads in a larger generation of red blood cells, allowing more oxygen to bind.

Population Attributes

Birth rate– the total number of people born in a certain time period.
Death rates– The total number of deaths during a certain time period.
Sex Ratio– the total number of females and males per 1000 people.
A plot of age distribution is known as an age pyramid.

  • The birth rate and the mortality rate are two characteristics of the population. The birth rate is the rise in population, whereas the mortality rate is the decline in population.
  • The sex ratio is another demographic feature, as is age distribution, which can be represented as an age pyramid. the population’s situation The population in the age pyramid is increasing, constant, and dropping. The increasing population is a feature of the growing population that contains more young people than old people. When the number of young and old people is equal, the age pyramid is considered to be stable; when the number of elderly people is more than the number of young people, the age pyramid is said to be dropping.

Population growth and the factors responsible for the overall growth are also important lessons to learn in the organism and population class 12 notes.

Population Growth & Growth Models

The population number of any species in a given place is never static; it varies over time based on the availability of food resources, meteorological conditions, and predator pressure. Changes in population density are caused by four major factors, which are as follows:
I Natality: The number of births in a given period.

(ii) Mortality: The number of deaths in a particular period of time.

(iii) Immigration is defined as the number of species in a population moving to a new environment at a specific period.

(iv) Emigration is defined as the number of species in a population going out to N, where N indicates population density, which is provided as:



N= population density at time t,

B+I= the birth rate

D+E= Death Rate.

Organism and population class 12 notes has two growth models with graphs that hold high weightage from the exam point of view. Let’s discuss them quickly. For those looking for slides on this topic, you can refer to a site named exam

I) Exponential Growth Model
When the amount of nutrients available is excessive, exponential growth occurs. If N is the population size, b is the birth rate (per capita births not total births), and d is the death rate (per capita births not total births), then the rise or decrease in N (dN/dt) throughout period t will be:

dN/dt=(b–d) (N)

If (b–d)=r, then dN/dt=rN.


Nt = Population density after time t 

N0 = Population density at time zero 

r = intrinsic rate of natural increase 

e = the base of natural logarithms.

As given in the organism and population class 12 notes, the geometric growth pattern resembles the J-shape curve.

Organism and Population Class 12 Notes

II) Logistic Growth Model

When nutrients and other resources are few, population expansion is referred to as logistic growth or Verhulst-Pearl Logistic Growth. This circumstance will increase competition between organisms. The availability of restricted resources will cause a lag phase, followed by exponential growth, slowing, and eventually asymptote.


N = Population density at time t 

r = Intrinsic rate of natural increase 

K = Carrying capacity.

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