The Living World: Complete Chapter Revision Notes For Class 11 NEET by PW

The Living World includes several terms, taxonomic categories, naming rules, and characteristics of life that can be easy to confuse during NEET preparation. A quick revision can help you bring these concepts together and understand how organisms are identified, named, classified, and distinguished as living forms.

The The Living World Class 11 NEET revision by PW covers topics including biodiversity, classical and modern taxonomy, systematics, phylogeny, taxonomic steps, scientific names, binomial nomenclature, taxonomic hierarchy, species concepts, and the characteristics of living organisms. It also covers growth, reproduction, metabolism, cellular organisation, and consciousness, making it useful for revising the chapter in one sitting.

The Living World Introduction

The living world includes immense biological diversity, from bacteria and insects to plants and animals. Scientific classification makes this diversity easier to study. This chapter explains biodiversity, taxonomy, nomenclature, taxonomic hierarchy, species concepts, and the defining properties of living organisms important for Class 11 Biology and NEET preparation.

Biodiversity And Classification

Biodiversity refers to the number and types of organisms present on Earth. It includes elephants, horses, ants, bacteria, insects, plants, and all other living forms.

The International Union for Conservation of Nature and Natural Resources (IUCN) maintains records of taxonomically known species. Approximately 1.7–1.8 million species are currently taxonomically known on Earth.

Studying every organism separately is difficult. Therefore, organisms are arranged into groups based on similarities.

Classification = Dividing organisms into groups based on similarities

Taxonomy is the branch of science concerned with the process of classification.

Classical And Modern Taxonomy

Classical Taxonomy

Classical taxonomy was based only on morphology, or the external features of organisms.

Modern Taxonomy

Modern taxonomy considers morphology along with:

• Anatomy: Internal structure

• Cytology: Cell structure

• Embryology: Embryo development

• Ecological Information: Habitat and occurrence

• Developmental Processes: Pattern of development

A key examination point is that phylogeny is not included in the stated definition of modern taxonomy. Phylogeny becomes part of systematics.

Systematics And Phylogeny

Systematics is derived from a Latin word and means the systematic arrangement of organisms. The term was first used in Systema Naturae, written by Carolus Linnaeus.

Initially, systematics studied organismal diversity. Its scope later expanded to include taxonomy, classification, and evolutionary relationships.

Systematics = Taxonomy + Phylogeny

Phylogeny is the study of ancestral history, evolutionary history, species evolution, and organismal ancestors.

Steps Of Taxonomy

Taxonomy follows four steps in a definite sequence:

Characterisation → Identification → Classification → Nomenclature

1. Characterisation: Recording all the features of an organism.

2. Identification: Comparing these features with known groups.

3. Classification: Placing the organism in the appropriate group.

4. Nomenclature: Assigning a universal scientific name.

Scientific Names And Nomenclature Codes

Vernacular names are local or regional names. They vary with language and location, so they are not universal. For example, the same plant may be called “mango” in English and “aam” in Hindi.

Scientific names remain consistent worldwide. Carolus Linnaeus, known as the Father of Taxonomy, introduced binomial nomenclature.

Memory Tip: In ICBN, “I” means International, not Indian, and “C” means Code, not Council.

Binomial Nomenclature

Under binomial nomenclature, a scientific name has two parts:

1. Genus Name or Generic Name

2. Species Name or Specific Epithet

Rules include:

• The genus name is written first and begins with a capital letter.

• The specific epithet is written second and begins with a small letter.

• Names are written in Latin or are Latinised.

• Typed or printed names are written in italics.

• Handwritten genus and specific epithet names are underlined separately.

Latin is used because it is a dead language and is less likely to change.

An author’s name may follow the scientific name. It is not part of the scientific name, is not italicised or underlined, and is usually abbreviated.

Taxonomic Hierarchy

The seven major taxonomic categories are:

Kingdom → Phylum → Class → Order → Family → Genus → Species

Species is the smallest major category, and kingdom is the largest.

Memory Tip: Remember the sequence as Keep Pots Clean Or Family Gets Sick.

A rank, category, or taxon refers to an individual step in classification. Taxon is singular, while taxa is plural.

Taxon = Unit of Classification

There are seven major or obligatory categories. Intermediate categories include subspecies, variety, subfamily, and domain. The lecture states that there are 21 intermediate categories.

Moving from species towards kingdom:

• Group size increases.

• Specificity decreases.

• Similar characters decrease.

• General characters increase.

• Classification becomes more complex.

• Difficulty in establishing relationships increases.

Species And Biological Species Concept

Species is the smallest taxonomic category and the real basic unit of classification.

Ernst Mayr, called the Darwin of the twentieth century, gave the Biological Species Concept. Members of the same species generally:

• Are morphologically similar.

• Can interbreed.

• Produce offspring.

• Share a gene pool.

• Exchange genes.

Members of different species are generally reproductively isolated.

This concept has exceptions. Male and female members of the same species may look different due to sexual dimorphism, as in lions and lionesses. Also, different species may sometimes produce hybrids, such as a horse and donkey or a lion and tiger.

Genus, Family, Order, Class, Division, And Kingdom

A genus is a group of related species. Its plural is genera.

• Panthera includes Panthera tigris, P. leo, and P. pardus.

• Solanum includes potato, brinjal, and black nightshade.

• Homo currently contains Homo sapiens and is a monotypic genus.

• A genus with more than one species is a polytypic genus.

A family is a group of related genera.

• Animal families commonly end in -idae, such as Felidae, Canidae, and Hominidae.

• Plant families commonly end in -aceae, such as Solanaceae, Poaceae, and Malvaceae.

Memory Tip: -idae → Animal Family and -aceae → Plant Family.

An order is a group of related families. Examples include Carnivora, Primata, Rodentia, Sapindales, and Poales. Plant orders are commonly identified by the suffix -ales, and floral characters receive major importance.

A class is a group of related orders. Mammalia includes Primata, Carnivora, and Rodentia. In plants, Dicotyledoni and Monocotyledoni are major classes.

A phylum is a group of related animal classes. Phylum Chordata includes organisms with a notochord and dorsal, hollow neural system. In plants, the term division is used instead of phylum. Examples include Angiospermae, Gymnospermae, Bryophyta, and Pteridophyta.

The five-kingdom system includes:

1. Monera

2. Protista

3. Fungi

4. Animalia

5. Plantae

What Is Living?

Living organisms are commonly described through:

1. Growth

2. Reproduction

3. Metabolism

4. Cellular organisation

5. Consciousness

Growth and reproduction are not defining properties because exceptions occur. Growth can occur in non-living objects, and mules, hinnies, worker bees, and some sterile human couples cannot reproduce.

Metabolism, cellular organisation, and consciousness are defining properties because they occur in living organisms and are absent from non-living objects.

Growth And Reproduction

In living organisms, growth means an increase in cell number and mass. It is usually irreversible and occurs internally. This is called intrinsic growth.

Non-living objects may show extrinsic growth, caused by external material accumulation. For example, a soil mound may grow as more soil gathers on its surface.

In unicellular organisms, growth and reproduction may occur together. During binary fission, one cell becomes two cells, increasing cell number and producing new organisms.

In multicellular organisms, growth and reproduction are separate processes.

Reproduction may be:

• Asexual: Usually uniparental and without gamete fusion.

• Sexual: Usually biparental and involving gamete fusion.

Asexual methods include binary fission, budding, fragmentation, sporulation, and regeneration. Examples include binary fission in Amoeba, budding in yeast and Hydra, fragmentation in Spirogyra, and true regeneration in Planaria.

Metabolism

Metabolism refers to all the chemical reactions occurring in an organism.

• Anabolism: Constructive reactions in which small molecules form larger molecules. Photosynthesis is an example.

• Catabolism: Breakdown reactions in which large molecules form smaller molecules. Respiration is an example.

Enzymes catalyse metabolic reactions inside cells. Metabolic reactions can also occur outside cells under in vitro or cell-free conditions. Such reactions are not living organisms, but they are considered living reactions.

Cellular Organisation

Cellular organisation is a defining feature of life. Every living organism is made of one or more cells.

Atoms → Molecules → Subcellular Entities → Cells → Tissues → Tissue Systems → Organs → Organ Systems → Organisms

The cell is the fundamental unit of life. Viruses lack cellular organisation and are not considered living in this framework.

Unicellular organisms have only one cell. Plants show organisation up to organs, while animals show the complete sequence up to organ systems.

Higher levels may show emergent properties. These properties arise from interactions among constituent units and are not present in each unit separately.

Memory Tip: The overall property of a company arises through the interaction of its employees, not from one employee alone.

Consciousness

Consciousness is the ability to perceive a stimulus and produce an appropriate response.

Stimulus Perception + Appropriate Response = Consciousness

Stimuli may be physical, biological, or chemical. Light, temperature, photoperiod, viruses, antibodies, pollutants, and gases can act as stimuli.

Self-consciousness means awareness of personal identity, appearance, family, goals, and career. It is described as the highest degree of consciousness and is found only in humans.

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