Revision: Class 11 >> The Living World NEET (UG) The Living World

• The diversity of life forms present on Earth, including plants, animals, and microorganisms, is called biodiversity.
• Biodiversity is the occurrence of different types of genes among the individuals of species, habitats and ecosystems, both terrestrial and aquatic within a defined area.

It is a tool used to classify organisms based on their similarities and differences.

Hotspot is a biodegradable region that is both a significant reservoir of biodiversity and is threatened with destruction.

Eutrophication: The process by which a body of water enriched in dissolved nutrients (such as phosphates) that stimulates the growth of aquatic algae usually resulting in the depletion of dissolved oxygen.

Ramsar Sites: It is a wetland site designed of international importance under the Ramsar convention. It is an inter-governmental environmental treaty established in 1971 by UNESCO and coming into force in 1975.

Biodiversity is defined as the variety of plant and animal life in the world or in a particular habitat, a high level of which is usually considered to be important and desirable

The sum total of species richness, i.e., the number of species of plants, animals and micro-organisms inhabiting in a given habitat, is known as biodiversity.

Binomial nomenclature is a system of naming species of living organisms using two Latinised names.

Systematics is the study of the relationships among organisms and their evolutionary connections.

1. The next category, family, has a group of related genera with a smaller number of similarities as compared to genus and species. Families are characterised on the basis of both vegetative and reproductive features of plant species.
2. Among plants, for example, three different genera, Solanum, Petunia, and Datura, are placed in the family Solanaceae. For example, the genus Panthera, comprising lions, tigers, and leopards, is put along with the genus  Felis (cats) in the family Felidae. Similarly, if you observe the features of a cat and a dog, you will find some similarities and some differences as well.
3. They are separated into two different families – Felidae and Canidae, respectively.

1. You have seen earlier that categories like species, genus, and families are based on a number of similar characters.
2. Generally, order and other higher taxonomic categories are identified based on the aggregates of characters. Order, being a higher category, is the assemblage of families that exhibit a few similar characters.
3. The similar characters are fewer in number as compared to the different genera included in a family. Plant families like Convolvulaceae, Solanaceae are included in the order Polymoniales, mainly based on their floral characters.
4. The animal order, Carnivora, includes families like Felidae and Canidae.

Genus comprises a group of related species that have more characters in common in comparison to species of other genera. We can say that genera are aggregates of closely related species. For example, potato and brinjal are two different species, but both belong to the genus Solanum. Lions (Panthera leo), leopards (P. pardus), and tigers (P. tigris), with several common features, are all species of the genus Panthera. This genus differs from another genus, Felis, which includes cats.

Classes comprising animals like fish, amphibians, reptiles, birds, and mammals constitute the next higher category called phylum. All these, based on common features like the presence of the notochord and dorsal hollow neural system, are included in the phylum Chordata. In the case of plants, classes with a few similar characters are assigned to a higher category called division.

A taxon is a taxonomic group at any level. It represents a group of organisms at any level.

This category includes related orders. For example, order Primata, comprising monkeys, gorillas, and gibbons, is placed in class Mammalia, along with order Carnivora, which includes animals like tigers, cats, and dogs. Class Mammalia has other orders as well.

• Living organisms are entities that show life processes and are also called living beings.
• Life involves organised chemical reactions that allow organisms to grow, develop, and function.
• Key characteristics of living things include growth, reproduction, metabolism, response to stimuli, and adaptation.
• Living organisms can interact with and respond to their environment.
• Viruses are non-living outside a host, but behave like living organisms when inside a living cell.

• Cellular organisation: All living organisms are made up of one or more cells, which are the basic units of life.
• Metabolism: Living organisms perform all chemical reactions (anabolism and catabolism) necessary for energy and growth.
• Homoeostasis: They maintain a stable internal environment despite external changes.
• Growth: Living beings grow by an increase in cell number or size, unlike non-living things.
• Reproduction: Organisms reproduce to continue their species, though it is not essential for the survival of an individual.
• Response to stimuli (Consciousness): Living organisms sense and respond to environmental changes.
• Adaptation and evolution: Organisms adapt to their environment over time, helping in survival and biodiversity.

• The world has a wide variety of living organisms, including visible and microscopic forms.
• Biodiversity increases with area; for example, dense forests have more species.
• Each type of organism is called a species, and about 1.7–1.8 million species are known.
• New species are continuously discovered, adding to Earth’s biodiversity.
• Taxonomy includes four main steps: characterisation, identification, classification, and nomenclature, to study and name organisms systematically.

• Biodiversity is the variety of life on Earth — including microorganisms, fungi, plants and animals in both terrestrial and aquatic habitats.
• Diversity exists in size, shape, colour, nutrition, habitat and reproduction. It arises due to adaptations of organisms to different environmental conditions for survival.
• Biodiversity = totality of genes, species and ecosystems in a region (as per IUCN, UNEP and WRI).
• Term coined by Walter Rosen (1982), popularised by Edward Wilson to describe diversity at all levels of biological organisation.
• Today's biodiversity is the result of 3.5 billion years of evolutionary history, influenced by natural processes and human activities.

• Taxonomy is the branch of biology that deals with the identification, classification, and naming of organisms.
• Organisms are grouped into taxa (categories) like domain, kingdom, phylum, class, order, family, genus, and species.
• Taxonomy helps in understanding biodiversity by grouping organisms based on similarities in structure and genetics.
• It provides a systematic way to study relationships and evolution among organisms.
• Modern taxonomy uses molecular and genetic techniques along with structural and ecological features for accurate classification.

• Organises living organisms into a structured hierarchy: Kingdom - Phylum - Class, and so on, making biodiversity easier to study.
• Each species gets a unique scientific name to avoid confusion caused by different local or common names.
• "Systematics" is derived from the Latin word 'systema', meaning systematic arrangement of organisms.