NEET Microbes in Human Welfare and Organisms and Populations Notes by PW

Chapters such as Microbes in Human Welfare and Organisms and Populations include several biological processes, terms and concepts that can be difficult to recall during NEET revision. Revising these chapters from scattered sources can also make it harder to identify important points and revise them quickly.

To make chapter-wise revision easier, Physics Wallah provides NEET notes for Microbes in Human Welfare and Organisms and Populations, covering important concepts and key points from both chapters. These notes help you quickly revise the topics, strengthen concept recall and prepare for related NEET questions.

Microbes in Human Welfare

Microbes are microscopic organisms that can be observed using a microscope. They occur in different groups of organisms and are present in diverse environments such as soil, water, air and the human body. While some microorganisms cause diseases, many are useful in food production, medicine, agriculture, environmental treatment and industrial processes.

Microbes as Components of Biological Systems

Microorganisms occur in several biological groups.

Microorganisms occur in almost every environment. Some organisms, such as archaebacteria, can survive extreme environmental conditions.

Bacteria have different shapes:

Viruses are also microscopic infectious agents. Adenovirus can cause respiratory infections. Tobacco Mosaic Virus (TMV) is rod-shaped and contains single-stranded RNA.

Microbes in Household Products

Microorganisms are widely used to prepare fermented food products and beverages. Curd, idli, dosa, bread, cheese and several traditional fermented products involve microbial activity.

Curd Formation by Lactic Acid Bacteria

Lactic Acid Bacteria (LAB), particularly Lactobacillus, help convert milk into curd.

A small amount of previously prepared curd is added to warm milk. The bacteria present in the curd multiply and produce lactic acid. The acid causes the coagulation and partial digestion of milk proteins, resulting in curd formation.

Curd is easier to digest than milk because some of its proteins are partially digested by the bacteria. It also contains beneficial microorganisms that support the microbial balance of the intestine.

Idli, Dosa, Bread and Alcoholic Beverages

Idli and dosa batter undergo fermentation through microbial activity. Bacteria such as Leuconostoc and Lactobacillus are involved in the fermentation process.

Saccharomyces cerevisiae, commonly called yeast, is used in baking and alcoholic fermentation.

During alcoholic fermentation, yeast converts sugars into alcohol and carbon dioxide. Carbon dioxide trapped in bread dough causes the dough to rise.

Toddy is a traditional fermented beverage prepared from palm sap.

Cheese and Fermented Products

Different microorganisms are used in the production of different varieties of cheese.

In Swiss cheese, carbon dioxide produced during fermentation forms the characteristic holes.

Microbial fermentation is also used in preparing products such as soy sauce and other traditional fermented foods.

Microbes in Industrial Products

Microorganisms are used on a large scale to produce alcoholic beverages, organic acids, enzymes, antibiotics and pharmaceutical products.

Alcoholic Beverages

Saccharomyces cerevisiae is used to produce alcoholic beverages by fermenting sugars.

• Beer is produced through fermentation of cereals.

• Wine is produced by fermenting grape juice.

• Whisky, brandy and rum are distilled alcoholic beverages.

• Distillation increases the alcohol concentration by separating alcohol from the fermented mixture.

Antibiotics and Penicillin

Antibiotics are chemical substances produced by some microorganisms that can inhibit or kill disease-causing microorganisms.

Penicillin was discovered by Alexander Fleming when he observed that a mould growing on a bacterial culture prevented bacterial growth around it. The mould was identified as Penicillium notatum.

Ernst Chain and Howard Florey contributed to the development of penicillin for therapeutic use. Fleming, Chain and Florey received the Nobel Prize in Physiology or Medicine in 1945 for their work related to the discovery and therapeutic application of penicillin.

Microbial Chemicals, Enzymes and Medicines

Microorganisms are used to produce several commercially important chemicals, enzymes and pharmaceutical substances.

Lipases are used in detergents to remove oily stains. Proteases and pectinases are used in the processing and clarification of fruit juices.

Streptokinase, produced by Streptococcus, is used as a clot-dissolving agent in certain medical conditions.

Cyclosporin A, produced by Trichoderma polysporum, acts as an immunosuppressive agent and is useful in organ transplantation.

Statins, produced by Monascus purpureus, help reduce blood cholesterol by inhibiting cholesterol synthesis.

Sewage Treatment and Biogas

Sewage treatment involves the removal and decomposition of organic matter and other contaminants from wastewater.

Primary Treatment

Primary treatment is mainly a physical process.

Large particles are removed by filtration, while heavier particles settle through sedimentation. The settled material forms sludge, and the remaining liquid is called the primary effluent.

Secondary Treatment

The primary effluent is transferred to an aeration tank, where air is pumped into the wastewater. Aerobic microorganisms grow into masses called flocs.

These microorganisms consume organic matter and reduce the biochemical oxygen demand (BOD) of the wastewater.

The flocs settle down as activated sludge. A part of this sludge is returned to the aeration tank, while the remaining sludge is transferred to an anaerobic digester.

Biogas Production

Anaerobic microorganisms called methanogens break down organic matter in the absence of oxygen and produce biogas.

Biogas mainly contains methane, along with carbon dioxide and other gases.

Biogas plants commonly use cattle dung and other organic waste. The digested slurry remaining after biogas production can be used as manure.

Biocontrol and Biofertilizers

Biocontrol

Biocontrol involves using living organisms or their products to control pests instead of relying only on chemical pesticides.

Ladybird beetles help control aphids, while dragonflies feed on mosquitoes.

Bacillus thuringiensis (Bt) produces insecticidal proteins that are effective against specific insect pests. Bt genes have been introduced into crops such as cotton to provide protection against certain insect pests.

Baculoviruses, particularly nucleopolyhedroviruses, are highly specific biological control agents and can target particular insect pests.

Biofertilizers

Biofertilizers contain microorganisms that improve nutrient availability to plants.

Ecology and Ecological Organisation

Ecology is the study of interactions between organisms and their environment.

The environment contains:

• Biotic components: Living organisms such as plants, animals and microorganisms.

• Abiotic components: Non-living factors such as light, temperature, water and soil.

The major levels of ecological organisation are:

Organism → Population → Community → Ecosystem → Biome → Biosphere

Organism

An organism is an individual living entity.

Population

A population consists of individuals of the same species living in a particular geographical area and capable of interbreeding.

Community

A community consists of populations of different species living and interacting in an area.

Ecosystem

An ecosystem includes both biotic and abiotic components and their interactions.

Biome

A biome is a large geographical region characterised by a particular climate and associated vegetation and animal life.

Biosphere

The biosphere represents the global zone where life exists.

Population Attributes and Growth

Population characteristics include population density, natality, mortality, sex ratio and age structure.

The size of a population changes because of four major processes:

• Natality: Addition of individuals through birth.

• Mortality: Removal of individuals through death.

• Immigration: Movement of individuals into a population.

• Emigration: Movement of individuals out of a population.

The change in population size can be represented as:

Final Population = Initial Population + Natality + Immigration − Mortality − Emigration

Exponential Growth

When resources are unlimited and environmental resistance is absent or minimal, populations can show exponential growth.

The growth produces a J-shaped curve.

The exponential growth equation is:

dN/dt = rN

where:

• N = population size

• r = intrinsic rate of natural increase

• t = time

Logistic Growth

Natural resources are generally limited. Under such conditions, population growth slows as the population approaches the environmental carrying capacity.

Logistic growth produces an S-shaped curve.

The carrying capacity is represented by K.

The logistic growth equation is:

dN/dt = rN(K − N)/K

where K represents the maximum population size that the environment can sustain under given conditions.

Population Interactions

Organisms living together interact with one another in different ways. These interactions may benefit, harm or have no significant effect on the interacting organisms.

Mutualism

In mutualism, both interacting species benefit.

Examples include lichens, which involve an association between an alga and a fungus, and mycorrhizal associations between fungi and plant roots.

Commensalism

In commensalism, one organism benefits while the other is neither significantly benefited nor harmed.

Amensalism

In amensalism, one organism is negatively affected while the other remains unaffected.

Parasitism

In parasitism, the parasite obtains nourishment from the host and harms the host.

Parasites may live on the external surface of the host or inside the host.

• Ectoparasites: Live on the external surface of the host.

• Endoparasites: Live inside the host.

Plasmodium is the causative organism of malaria, while the female Anopheles mosquito acts as its vector.

Competition

Competition occurs when organisms require the same limited resources. Both competitors may experience reduced access to the required resource.

Predation

In predation, one organism captures and consumes another organism. Predators can influence prey populations and contribute to the regulation of ecological communities.

Predation can also be used in biological control. For example, ladybird beetles feed on aphids and help control their population.

Resource Partitioning

Closely related species may coexist by using different resources or using the same resource in different ways.

This division may involve:

• Different food resources

• Different feeding locations

• Different feeding times

This is known as resource partitioning and can reduce direct competition between species.

Somatic Hybridization

Somatic hybridization involves the fusion of two plant protoplasts.

A protoplast is a plant cell from which the cell wall has been removed.

The major steps include removal of cell walls, fusion of protoplasts and development of the hybrid cell through tissue culture.

When protoplasts fuse, the resulting cell may contain two separate nuclei and is called a heterokaryon. Fusion of the nuclei produces a syncaryon.

The hybrid cell can subsequently undergo cell division and tissue culture to develop into a complete plant.

Key Takeaways for NEET 2026

• Lactobacillus helps convert milk into curd through lactic acid production.

• Saccharomyces cerevisiae is used in baking and alcoholic fermentation.

• Propionibacterium shermanii is associated with Swiss cheese.

• Penicillin was discovered by Alexander Fleming.

• Streptokinase is used as a clot-dissolving agent.

• Cyclosporin A acts as an immunosuppressive agent.

• Methanogens produce methane during anaerobic digestion.

• Rhizobium fixes atmospheric nitrogen in the root nodules of leguminous plants.

• The ecological hierarchy progresses from organism to population, community, ecosystem, biome and biosphere.

• Population size changes through natality, mortality, immigration and emigration.

• Exponential growth produces a J-shaped curve, while logistic growth produces an S-shaped curve.

• Carrying capacity represents the maximum population size that an environment can sustain under given conditions.

• In mutualism, both species benefit, while in parasitism, the parasite benefits and the host is harmed.

• Resource partitioning can reduce competition and allow species to coexist.

• In malaria, Plasmodium is the causative organism and the female Anopheles mosquito is the vector.

Microbes in human welfare and organisms and populations cover important concepts from biotechnology, microbiology and ecology. Revise microbial products, antibiotics, sewage treatment, biogas, biocontrol, biofertilizers, population growth and ecological interactions along with the associated microorganisms and examples. For NEET 2026 preparation, PW resources such as PYQs, mind maps, sample papers, formula sheets, MCQs and video lectures can support concept revision and regular practice.

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