The Living World – Class 11 Biology Free NEET Notes

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Neet Complete Note Of The Chapter Of Biology, The Living World- Taxonomy, Nomenclature, etc.

1. Understanding the Amazing Variety of Living Organisms

When you look around, you will notice many types of living beings — like small potted plants, insects flying around, birds in the sky, your pet animals, and various trees or animals. Apart from these visible ones, there are countless tiny organisms that are too small to see with our eyes but still exist around us — like bacteria and other microbes.

Now, if you observe a larger area, you will find even more variety of organisms. For example, if you visit a thick forest, you will come across many new plants, animals, and insects that you might have never seen before. This clearly shows that life exists in many forms and types.

Each distinct type of living being, whether it is a plant, an animal, or a tiny organism, is called a species. Scientists have already discovered and described around 1.7 to 1.8 million species till now.

This huge range of different living organisms on Earth is called biodiversity. As we continue to study and explore more places — whether new or old — we keep finding new species. So, the number of known organisms keeps increasing over time.

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✅ Key Terms:

Biodiversity – Variety and number of living organisms found on Earth.

Species – A particular type of living organism.

Scientific Naming of Living Organisms (Nomenclature)

2. Scientific Naming of Living Organisms (Nomenclature)

There are millions of different plants and animals found all over the world. In our local area, we often know these organisms by their local names, but these names are different in different regions — even within the same country.

Now imagine the confusion if people from different places tried to talk about the same animal or plant but used different names. It would be very hard to understand each other!

That’s why we need a standard system to name all living organisms — so that one particular organism has the same name everywhere in the world. This system of giving a fixed name is called nomenclature.

But to give a name, we first need to properly identify and describe the organism. This process is called identification — knowing exactly what the organism is.

To make this naming process easier and uniform, scientists have created rules and procedures to assign a scientific name to each known organism. These names are accepted by scientists all over the world.

For plants, naming is done using rules from the International Code for Botanical Nomenclature (ICBN).
For animals, naming follows the International Code of Zoological Nomenclature (ICZN).

The purpose of scientific names is:

• Each organism gets only one unique name.
• That name is recognized globally.
• No two organisms share the same scientific name.
• Anyone from any part of the world can identify the organism correctly using that name.

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✅ Key Concepts:

• Nomenclature – Giving a standard scientific name to an organism.
• Identification – Correctly recognizing and describing the organism.
• ICBN – Rules for naming plants.
• ICZN – Rules for naming animals.

🔹 Binomial Nomenclature – Scientific Naming System

Biologists around the world follow universal rules to name living organisms scientifically. Every scientific name has two main parts:

1. Genus name
2. Species name (also called specific epithet)

This two-part naming method is called Binomial Nomenclature. The system was developed by a scientist named Carolus Linnaeus, and it is now used worldwide.

This format is very useful and easy to use. For example, the scientific name of mango is Mangifera indica.

• Here, Mangifera is the genus.
• indica is the species (specific epithet).

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✅ Universal Rules of Scientific Naming:

1. Scientific names are always in Latin or are made to look like Latin, no matter where the organism comes from.
2. The first word is the genus, and the second word is the species.
3. When writing by hand, both words should be underlined separately.
   When typed, they should be in italics to show their Latin origin.
4. The genus name starts with a capital letter, while the species name starts with a small letter.
   Example: Mangifera indica
5. After the species name, the author’s name (who first described the species) is written in short form.
   For example: Mangifera indica Linn.
   This means Linnaeus was the first person to describe and name this species.

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✅ Key Terms:

• Binomial Nomenclature – A two-name system for scientific naming.
• Genus – The broader group of related organisms.
• Specific epithet – The unique species within the genus.
• Linnaeus – Father of modern taxonomy who created this naming system.

🔹 Classification, Taxonomy & Systematics

There are millions of living organisms on Earth, so it’s almost impossible to study each one of them individually. That’s why scientists use a method called classification.

Classification means grouping living organisms into different categories based on easily seen features — like how they look, behave, or what type they are. For example, we naturally group things as plants, animals, dogs, cats, or insects. When you hear the word “dog”, you don’t imagine a cat — because your brain connects certain features to the word “dog”.

Let’s take it further — if someone says “Alsatian”, we all know it’s a type of dog. Similarly, if we say “mammal”, we immediately think of animals that have hair on their body and external ears.
In plants, if someone says “wheat”, you’ll imagine wheat plants — not rice or sugarcane.

So, these groups like “dogs”, “mammals”, “wheat”, “plants”, and “animals” are all helpful categories that make studying life easier. In scientific terms, these groups are called taxa (singular: taxon).

But remember — taxa exist at different levels. For example:

• Dog is one taxon.
• Mammal is a bigger group that includes dogs.
• Animal is even bigger, which includes all mammals.

This method of grouping based on features is called taxonomy.

Modern taxonomy is not just based on outer appearance. It also uses:

• Internal structures (like organs),
• Cell structure,
• How the organism develops,
• Its habitat and ecological role.

That’s why taxonomy includes 4 main steps:

1. Characterisation – Studying the features of the organism
2. Identification – Figuring out what exactly the organism is
3. Classification – Grouping it into a category (taxon)
4. Nomenclature – Giving it a proper scientific name

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🧠 What is Systematics ?

Humans have always tried to understand different organisms — especially those useful for food, clothing, or shelter. In ancient times, organisms were grouped based on how useful they were to humans.

But gradually, scientists became interested not just in grouping, but also in understanding how organisms are related to each other.

This gave rise to a broader field called systematics.

The word Systematics comes from Latin “systema”, meaning a systematic arrangement. It was first used by Carolus Linnaeus, who wrote a book called Systema Naturae.

Today, systematics includes:

• Identification
• Nomenclature
• Classification
• And also studies the evolutionary relationships between organisms — that is, how closely they are related through evolution.

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✅ Key Concepts:

• Classification – Grouping organisms based on features.
• Taxa – Scientific categories like species, genus, etc.
• Taxonomy – Science of classifying and naming organisms.
• Systematics – Study of classification + evolutionary relationships.

3. Hierarchy of Taxonomic Ranks in Living Organisms

Classification of living organisms is not done in just one step — it happens through multiple levels or ranks. Each step or level is called a taxonomic category, and all such categories together make the taxonomic hierarchy.

Each category is a unit of classification, which means it holds a specific position or rank in the classification system. This unit is called a taxon (plural: taxa).

Let’s understand with an example:
Take insects – they all have some common features like having three pairs of jointed legs. Because of this similarity, they are placed in the same group or category.
So, “insects” is not just a general group — it holds a proper taxonomic rank in the classification system.

Can you think of other such groups ? Like birds, mammals, grasses, etc. — all are categories based on shared features. And each of them is a taxon, which is a part of the overall classification structure.

These categories (like species, genus, family, etc.) are not just based on appearance (morphology), but they are biological groups with real scientific meaning.

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🧬 Main Taxonomic Categories (Ranks) in Order:

1. Kingdom
2. Phylum (used for animals) / Division (used for plants)
3. Class
4. Order
5. Family
6. Genus
7. Species

Every living organism — whether it is a plant or an animal — ends up being classified down to the species level, which is the lowest and most specific rank.

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🤔 How do we decide which organism goes in which category ?

To classify an organism correctly, we need to know its features or characters. These can include:

• Its body structure (internal and external),
• How it functions,
• How it reproduces,
• And how it compares to other organisms.

This helps scientists find similarities and differences between organisms and place them in the correct taxonomic ranks.

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✅ Key Points:

• Taxonomic Category – Each level in classification (like genus or species).
• Taxon – A group at any rank (like mammals, birds, etc.).
• Taxonomic Hierarchy – The full system of arranged categories from kingdom to species.
• Species – The smallest and most specific group.
• Knowledge of characteristics is essential for correct classification.

3.1 Species

In taxonomy (the science of classification), a species is a group of organisms that are very similar to each other in their main features.

Members of a species:

• Share common characteristics (appearance, behavior, etc.)
• Can be clearly distinguished from other closely related species

For example:

• Mangifera indica is the scientific name of mango
• Solanum tuberosum is the scientific name of potato
• Panthera leo is the scientific name of lion

In these names:

• The first word (Mangifera, Solanum, Panthera) is the genus
• The second word (indica, tuberosum, leo) is the species or specific epithet

Each genus may contain one or more species that are related in appearance but different enough to be considered separate species.

For example:

• The genus Panthera includes:
  • Panthera leo (lion)
  • Panthera tigris (tiger)
• The genus Solanum includes:
  • Solanum tuberosum (potato)
  • Solanum nigrum (black nightshade)
  • Solanum melongena (brinjal/eggplant)

Similarly, humans belong to the species sapiens and the genus Homo.
So, the scientific name of humans is written as Homo sapiens.

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✅ Key Concepts:

• Species – A group of organisms with similar traits.
• Specific epithet – The second word in the scientific name; it identifies the species.
• Genus – A higher rank than species; groups similar species together.
• Scientific Name – Always written in two parts: Genus + Species (e.g., Homo sapiens)

3.2 Genus

A genus is a group that includes closely related species — species that share many common features with each other.

In simple words, we can say that:

• Species within the same genus look and behave more alike,
• And they have more similarities compared to species from different genera.

Let’s understand with examples:

• Potato (Solanum tuberosum) and brinjal (Solanum melongena) are two different species,
  but both belong to the same genus, called Solanum, because they share similar features.
• Similarly, lion (Panthera leo), leopard (Panthera pardus), and tiger (Panthera tigris) are all different species but belong to the same genus, Panthera, because they have many features in common — like strong bodies, sharp teeth, and being carnivores.

But, this genus (Panthera) is different from another genus called Felis, which includes domestic cats and other small wild cats.
Even though all these animals are cats in a general sense, Panthera and Felis are placed in different genera due to their structural and behavioral differences.

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✅ Key Concepts:

• Genus – A group of closely related species.
• Species in the same genus share more features with each other.
• Example:
  • Panthera leo (lion), Panthera tigris (tiger), and Panthera pardus (leopard) → Same genus: Panthera
  • Felis catus (domestic cat) → Different genus: Felis

3.3 Family

The family is a higher taxonomic category than genus. It includes a group of related genera (plural of genus) that share some common features, but less similarities compared to species or genus level.

In short:

• Species → Genus → Family
• Families are broader groups, made up of genera that are somewhat similar.

🪴 In Plants:

Families are classified using both vegetative features (like leaves and stems) and reproductive features (like flowers and fruits).

For example:

• The genera Solanum (includes potato, brinjal),
  Petunia (flowering plant), and
  Datura (thorn apple)
  — all belong to the family Solanaceae because they share similar floral and structural characteristics.

🐾 In Animals:

The genus Panthera (lion, tiger, leopard) and the genus Felis (domestic cats) are grouped into the same family — Felidae — because of shared features like body structure, sharp teeth, and carnivorous diet.

Now take cats and dogs — they have some similarities (like four legs, tails, sharp teeth), but they also have major differences.
So, they are placed in two different families:

• Cats → Family Felidae
• Dogs → Family Canidae

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✅ Key Points:

• Family – A group of related genera.
• Similarities in a family are less than in a genus or species.
• In plants, families are grouped based on structure of leaves, flowers, fruits, etc.
• In animals, families are based on body structure, behavior, and habits.

3.4 Order

As we move up in the taxonomic hierarchy, the category called Order comes above Family. It includes a group of related families that share a few common characteristics.

Unlike species, genus, and family — which are grouped based on many close similarities — an order is formed by grouping families that may have fewer features in common but still show some key similarities.

So, the higher we go in classification (like order, class, etc.), the fewer characteristics organisms need to share to be grouped together.

🪴 In Plants:

• Families like Solanaceae (includes potato, tomato, brinjal) and Convolvulaceae (includes sweet potato, morning glory)
  are grouped under the Order Polymoniales, mainly because they have similar floral structures (like flower arrangement and reproductive parts).

🐾 In Animals:

• The Order Carnivora includes families like:
  • Felidae (cats, lions, tigers)
  • Canidae (dogs, wolves, foxes)
    These families are grouped together in the same order because they all are meat-eating mammals and have special adaptations like sharp teeth and claws for hunting.

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✅ Key Points:

• Order – A group of related families.
• Fewer similarities than at genus or family level.
• Grouping is often based on important structural or functional traits.
• Examples:
  • Plant Order: Polymoniales (includes Solanaceae, Convolvulaceae)
  • Animal Order: Carnivora (includes Felidae, Canidae)

3.5 Class

Class is a higher taxonomic category that includes a group of related orders. It comes above Order and below Phylum/Division in the taxonomic hierarchy.

When multiple orders show some common features, they are grouped together into a class.

🐾 Example from Animals:

• The Order Primata includes animals like monkeys, gorillas, and gibbons.
• The Order Carnivora includes tigers, cats, and dogs.

Both of these orders are grouped together under the Class Mammalia because they share some key features like:

• Presence of mammary glands to feed young ones,
• Hair or fur on the body,
• External ears, and
• Giving birth to young ones (in most cases).

The Class Mammalia also includes many other orders that share these characteristics.

So, even though monkeys and tigers are very different animals, they are placed in the same class because they share some fundamental features common to all mammals.

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✅ Key Points:

• Class – A category that includes multiple related orders.
• Orders in a class share basic structural and functional traits.
• Example:
  • Class Mammalia includes:
    • Order Primata (monkeys, gorillas)
    • Order Carnivora (tigers, cats, dogs)
    • And other mammalian orders

3.6 Phylum (Animals) / Division (Plants)

When we group related classes of animals together, we place them in a higher category called a Phylum. This is one of the top levels in the classification system for animals.

🐾 In Animals:

For example, animals like:

• Fishes,
• Amphibians (like frogs),
• Reptiles (like snakes, lizards),
• Birds, and
• Mammals

— all belong to different classes, but they share some common features such as:

• Presence of a notochord (a rod-like supporting structure during development)
• A dorsal hollow nerve cord (part of the nervous system)

Because of these shared features, they are all placed in the Phylum Chordata.

So, Phylum Chordata includes all animals with a backbone or similar internal structure, even if they look very different on the outside.

🌿 In Plants:

The word Phylum is not used. Instead, the equivalent category in plants is called a Division.

For example:

• Different classes of plants (like ferns, flowering plants, etc.) are grouped into Divisions based on similarities like reproduction method, vascular tissues, etc.

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✅ Key Points:

• Phylum (in animals) = Group of related classes with some fundamental similarities.
• Division (in plants) = Similar to phylum, used for grouping plant classes.
• Example (Animals):
  • Phylum Chordata includes fishes, amphibians, reptiles, birds, mammals.
• Basis of grouping: presence of notochord, dorsal nerve cord, etc.

3.7 Kingdom – Highest Level of Biological Classification

In the biological classification system, the highest taxonomic category is called the Kingdom. It includes a large number of organisms that share only a few common features.

🐾 Kingdom Animalia:

All animals, whether they are insects, fishes, reptiles, birds, or mammals, belong to different phyla, but all of them are grouped together into a single kingdom called Animalia.
This kingdom includes all multicellular, eukaryotic, heterotrophic organisms that move and consume food.

🌿 Kingdom Plantae:

On the other hand, all plants from different divisions are grouped into Kingdom Plantae.
These are usually multicellular, photosynthetic, and non-motile organisms.

From now on, we commonly refer to these two major groups as the plant kingdom and the animal kingdom.

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🔼 Taxonomic Hierarchy – From Species to Kingdom

All the taxonomic categories — from species to kingdom — are arranged in ascending order:

👉 Species → Genus → Family → Order → Class → Phylum/Division → Kingdom

• As we move up in the hierarchy (towards Kingdom), the number of common features decreases.
• As we go lower, organisms in a category share more similar characteristics.
• That’s why species is the most specific category, and kingdom is the broadest.

At higher levels like kingdom, it becomes difficult to identify exact relationships between organisms, because they are too different from one another.

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🧠 Sub-categories in Classification:

To make classification even more accurate, scientists have created sub-categories like:

• Subspecies
• Subclass
• Suborder, etc.

These help place organisms more precisely and scientifically in the hierarchy.

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📊 Examples of Classification

Organism	Genus	Family	Order	Class	Phylum/Division	Kingdom
Human	Homo	Hominidae	Primata	Mammalia	Chordata	Animalia
Housefly	Musca	Muscidae	Diptera	Insecta	Arthropoda	Animalia
Mango	Mangifera	Anacardiaceae	Sapindales	Dicotyledonae	Angiospermae	Plantae
Wheat	Triticum	Poaceae	Poales	Monocotyledonae	Angiospermae	Plantae

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✅ Key Concepts Recap:

• Kingdom – Broadest taxonomic category.
• Animalia – All animals.
• Plantae – All plants.
• Taxonomic Hierarchy – From specific (species) to general (kingdom).
• As we move up, similarities decrease; as we go down, similarities increase.

4. Summary – The Living World

The world around us is filled with a huge variety of living organisms — from tiny microscopic forms to large animals and plants. Scientists have already discovered and named millions of species, but many are still undiscovered.

Because of the wide diversity in size, shape, color, habitat, and functions, it’s important to understand what makes something “living” and how we can group and name these organisms.

To make the study of such a large variety easier, biologists have developed a system to:

• Identify organisms,
• Name them correctly, and
• Classify them into groups based on similarities and differences.

This scientific system of naming and grouping is called taxonomy.

Taxonomy is very useful in areas like agriculture, forestry, industry, and also helps us understand our biological resources and biodiversity better.

All organisms are given a proper scientific name based on a global set of rules (like ICBN and ICZN). These names are based on the binomial nomenclature system, where each name has two parts — the genus and the species.

Every organism is placed at a specific level in a classification system. These levels are called taxonomic categories or taxa, and together they form the taxonomic hierarchy — starting from species (most specific) to kingdom (most general).

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✅ Key Concepts Recap:

• The living world is full of diverse organisms
• Taxonomy helps us identify, name, and classify organisms
• Binomial nomenclature gives every organism a two-part scientific name
• Organisms are arranged into levels: Species → Genus → Family → Order → Class → Phylum/Division → Kingdom
• This system helps in scientific study, conservation, and use of biodiversity

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