NEET Important Chapter - Organisms and Populations

This article contains Organisms and Populations chapter notes according to the NEET syllabus for biology. This article is useful for the students who are preparing for the NEET 2022 exam because it covers the important topics for last minute revision. Organisms and Populations NCERT PDF notes for NEET will help you to easily recall important information from the chapter and will provide you with an insight into the exam pattern.

These notes will help the students to recall all the answers to the important questions and concepts related to the chapter such as how organisms adapted to the environment, what are major biomes in India, what are major abiotic factors, what are the responses to abiotic factors, Organisms adaptation, what are populations and populations attributes, what is population growth, what is life history variations, what is population interactions like predation, competition, Parasitism, Commensalism, Mutualism. 

Important Topics of Organisms and Populations

• Organism and Its Environment

• Major Abiotic Factors

• Response to Abiotic Factors

• Adaptations

• Populations

• Populations Growth

• Life History Variation

• Population Interactions

Important Concepts

Organisms 

A contagious living system living in an environment is called an organism. The organisms have the ability to adapt and retain various behaviours and structures to collectively form populations. 

Organisms and Their Environment

Each organism plays a role in its ecosystem. The term niche is used to describe the role an organism or population plays within its community or ecosystem. It encompasses all relationships that the organism (or population) has with its environment and with other organisms and populations in its environment.

• Habitat is the type of natural environment in which an organism lives.

• Herbivory is a practice of organisms wherein they only consume plants and do not meet.

• Niche is the role of a species in a community, including the type of food it eats, where it lives and how it reproduces, etc.

• Interaction is communication or direct involvement with something. An organism does not have a role in it.

Major Abiotic Factors

Abiotic components or abiotic factors are nonliving factors that impact an ecosystem. These factors are part of the ecosystem and influence the associated living things but they are not living.

• Temperature

• Water 

• Light

• Soil

Responses to Abiotic Factors

They maintain homeostasis by ensuring constant body temperature, that is, thermoregulation, and constant osmotic concentration, that is, osmoregulation.

• Regulate 

• Conform

• Migrate 

• Suspend

Adaptations

The feature that helps the organism to survive or to reproduce in their habitats is

called adaptation. It is observed that the organisms usually adapt themselves

according to the environment they live in. 

For example, in the case of the desert plants like Opuntia, they have thick cuticles, leaves modified into spines, and sunken stomata so as to reduce the rate of transpiration and undergo photosynthesis with the help of the CAM pathway while in the case of the higher altitudes like mountains and hills, humans have shown altitude sickness resulting in nausea, short breaths, fatigue, heart palpitations, etc. 

But after some time they acclimatize themselves according to the environment and resulting in the higher production of red blood cells so that more oxygen can bind to them and increase the rate of respiration. There are certain behavioural responses that can be observed in various animals based on environmental conditions.

Populations

Population is defined as the total number of individuals of a species living in a specific geographical area. The individuals can interbreed under natural conditions to produce fertile offspring and they function as a unit of a biotic community.

• Population attributes

• Population growth

1. Natality

2. Mortality

3. Immigration

4. Emigration

Growth Models

• Exponential Growth: Something which always grows in relation to the current value is known as exponential growth. Exponential growth is also known as doubling the existing number. Let us take an example:  If the population of rabbits grows every month, then we would have 2, then 4, 8, 16, 32, 64, 128, 256, and further carried on. The formula used in solving exponential growth equations is y = abx.

• Logistic Growth: The number of individuals in the population changes with time which is also referred to as its growth. Thus the population is said to be changing now and then. This type of population growth is represented by a logistic growth curve.

Life History Variations

Variation in terms of biology is any difference between cells or organisms of any species caused either by genetic differences or environmental factors.

Population Interactions

Table Showing Population Interactions

Solved examples from Chapter

1. Define phenotypic adaptation with an example.

Ans: Phenotypic adaptations refer to changes in the appearance of an organism as a result of genetic mutation and environmental conditions. These adjustments to which the organism responds positively, occur in them to cope with environmental conditions present in their natural habitats.

Example: 

• The evolution of light-coloured moths in dark-coloured populations is a phenotypic adaptation that imparts a survival advantage in polluted areas.

• Presence of thick cuticle and sunken stomata on the leaf surface of desert plants to prevent loss of water during transpiration.

• Elephants have long ears that work similarly to that of a hand fan we use during summer when the temperature is high. Thus we can say that it acts as a thermoregulator.

2. If a population grows double exponentially in size in 3 years, what is the intrinsic rate of increase (r) of the population?

Ans: The intrinsic rate of increase of this population will be towards maximum as the population grows double exponentially in size in 3 years 

Solved Problems of Previous Year Question from Chapter

1. Asymptote in a logistic growth curve is obtained when 

a) The value of 'r' approaches zero 

b) K = N 

c) K > N 

d) K < N 

Ans: K = N

Asymptote in the logistic growth curve is obtained when carrying capacity is equal to the number of people during a population.

2. Mycorrhizae are the example of 

a) Fungistasis 

b) Amensalism

c) Antibiosis 

d) Mutualism  

Ans: Mutualism

A mycorrhiza is a relationship between fungi and the roots of higher plants. Mycorrhiza is also known as root fungi. Both the plant and fungal components benefit from this kind of relationship. Mycorrhiza helps plants to draw more nutrients and water from the soil. It also increases plant tolerance to environmental stresses.

3. Which of the following is correct for r-selected species? 

a) Large number of progeny with small size 

b) Large number of progeny with large size 

c) Small number of progeny with small size 

d) Small number of progeny with large size 

Ans:  Large number of progeny with small size 

r-selected species show semelparity (single reproduction), early reproduction, and rapid development.

Practice Questions

1. When certain exotic species are introduced into a geographical area they become invasive mainly because: 

a) The invaded land has unlimited resources for the introduced species 

b) The invaded land does not have its natural predator 

c) The population of the introduced species in the invaded land is very low 

d) Introduced species do not face any competition in the introduced land 

Ans: The invaded land does not have its natural predator

When certain exotic species are introduced into a geographical area, they become invasive and start spreading fast because the invaded land does not have its natural predators.

2. Which of the following is not an ectoparasite? 

a) Lice on humans 

b) Copepods on marine fishes 

c) Mistletoe on other plants 

d) Female Anopheles on humans 

Ans: Lice on humans

Ectoparasites live on the outside of the host. Example- human body lice

Conclusion

This article on Organisms and Populations contains all the important information as per the NEET 2022 aspirants’ point of view and this can be very helpful for quick and effective revision at the same time. It covers all the important concepts and topics of the chapter. This article also has some questions from previous year's NEET question papers which you can try to solve on your own. You can also refer to the Organisms and Population NCERT PDF notes and can try to solve Organisms and Populations NEET questions.