Class 11 Biology: The Living World (Chapter 1) - Notes

Class 11 Biology: The Living World (Chapter 1) – Notes

Life is a distinctive process formed by the aggregation of molecules. These molecules undergo a series of chemical reactions known as metabolism, which enables them to carry out specific functions. Metabolism is crucial for energy production and utilization, contributing to the growth, development, reproduction, and adaptation of living organisms through the production of various biomolecules.

Living organisms inhabit a wide variety of habitats, sharing similar genetic material whether they are found on land, in water, on mountains, in deserts, oceans, or forests.

Characteristics of Living Organisms: Living organisms exhibit several defining characteristics, including growth, development, body organization, homeostasis, reproduction, adaptation, and energy utilization.

1.1 Characteristics of Living Organisms

Growth:
Living organisms undergo growth and development, marked by an increase in cell mass and number. In multicellular organisms, this is achieved through cell division. Plants grow continuously through cell division throughout their life, while animals experience growth up to a certain age.

Examples: Non-living objects like mountains, boulders, and sand mounds can increase in size through the accumulation of material, but this cannot be equated to the growth seen in living organisms.

Metabolism:
Metabolism refers to the chemical reactions in the body that convert molecules into other biomolecules. It is present in all living organisms—plants, animals, and microbes. However, non-living things do not exhibit metabolism unless introduced artificially (in vitro).

Sensitivity:
All living organisms, whether prokaryotic or eukaryotic, respond to stimuli in their environment. These stimuli can be biological, physical, or chemical in nature, and the organisms’ responses reflect their sensitivity to their surroundings.

Reproduction:
Reproduction is the process by which living organisms produce offspring. For instance, fungi reproduce via asexual spores, while hydra reproduce through budding and planaria through regeneration. However, reproduction is absent in some living organisms like mules or infertile humans, meaning reproduction alone is not a sufficient criterion for life.

Cellular Organization:
This is a defining characteristic of life, as all living organisms are composed of cells that perform essential functions, such as metabolism and reproduction. Non-living things lack this cellular organization.

Movement:
Living organisms exhibit movement, whether it’s plants growing towards sunlight or animals actively moving. For instance, mango trees grow and reproduce, while non-living objects like candle flames and crystals remain motionless.

Consciousness:
Living organisms are aware of their surroundings, making them conscious entities.

1.2 Diversity in the Living World

Earth is home to a vast diversity of living organisms, inhabiting forests, oceans, deserts, lakes, mountains, and even extreme environments like hot springs. This variety of life is referred to as biological diversity or biodiversity.

Over 1.7-1.8 million species have been identified and studied so far. Each species plays a role in maintaining the natural balance of life on Earth.

Taxonomy:
Taxonomy is the scientific discipline of classifying and naming living organisms. Systematics is a related field that includes taxonomy and the study of evolutionary relationships. Taxonomic studies began with A.P. de Candolle, who coined the term taxonomy in 1813, while systematics traces its origins to early human civilization.

The term systematics comes from the Latin word “systema,” meaning systematic arrangement. Linnaeus published his work, Systema Naturae, which laid the foundation for modern taxonomy.

Neo-systematics focuses on species as products of evolution, a concept introduced by Julian Huxley in 1940.

Identification, Classification, Characterization, and Nomenclature:

Identification places organisms into their proper classification based on taxonomic keys.
Classification groups organisms based on shared features.
Characterization involves studying the organism’s internal and external features (e.g., morphology, anatomy, cytology, ecology).
Nomenclature refers to the naming of organisms. There are both common (vernacular) names and scientific names. Scientific names follow international codes, including:
- ICBN: International Code of Botanical Nomenclature
- ICZN: International Code of Zoological Nomenclature
- ICVN: International Code of Viral Nomenclature
- ICNB: International Code for Bacteriological Nomenclature

Binomial Nomenclature:
Introduced by Carl Linnaeus in Species Plantarum (1753), binomial nomenclature gives organisms two-part Latin names. The first part represents the genus, and the second the species. For example, Mangifera indica denotes the mango tree, where Mangifera is the genus and indica the species.

Rules of Binomial Nomenclature:

Names consist of two parts, in Latin or derived from Latin.
The first word is the genus; the second is the species.
Names are italicized or underlined when handwritten.
The genus name starts with a capital letter; the species name starts with a lowercase letter.
The author’s name may be abbreviated after the species name.

1.3 Taxonomic Categories

Taxon:
Introduced in 1956, taxon refers to a classification category based on an organism’s characteristics.

Taxonomic Hierarchy:
The hierarchy includes different categories such as species, genus, family, order, class, phylum, and kingdom. The lowest rank is species, while kingdom is the highest.

The hierarchy was proposed by Carolus Linnaeus, known as the father of systematic botany. Below is an example of the hierarchy:

Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primata
Family: Hominidae
Genus: Homo
Species: sapiens

Introduction:

Life is a complex and unique process, composed of the aggregation of molecules that undergo numerous chemical reactions. These reactions, collectively termed metabolism, facilitate the production and utilization of energy. Through metabolism, living organisms grow, develop, reproduce, adapt, and sustain themselves by synthesizing various biomolecules. Although life can be found in diverse habitats, including terrestrial, aquatic, desert, forest, and mountain environments, all living organisms share similar genetic material.

Living organisms are characterized by several essential features: growth, body organization, homeostasis, reproduction, adaptation, and energy utilization.

1.1 Characteristics of Living Organisms:

To distinguish whether an organism is living, the following characteristics are often observed:

Growth: Growth is one of the fundamental characteristics of life. Living organisms grow by increasing their mass and cell count. In multicellular organisms, this occurs through cell division. For example:
- Plants grow continuously throughout their lives via cell division in specific regions known as meristems.
- Animals, however, experience growth only up to a certain age, after which cell division is limited to tissue repair and regeneration.
Note: Non-living objects such as mountains, boulders, and sand mounds may increase in size through the accumulation of materials, but this is not considered biological growth. Thus, growth alone is not sufficient to define life.
Metabolism: Metabolism encompasses all the biochemical reactions that occur within an organism to maintain life. These reactions transform chemicals into biomolecules essential for growth, repair, and energy production. All living organisms, including plants, animals, and microorganisms, exhibit metabolism. It is absent in non-living entities but can be replicated artificially in a laboratory setting (in vitro).
Sensitivity (or Response to Stimuli): Living organisms can perceive and respond to changes in their environment, a trait absent in non-living matter. These stimuli can be physical (like light or temperature), chemical (pH, salinity), or biological (predator presence, food availability). The sensitivity of an organism to its surroundings allows it to adapt and survive.
Reproduction: Reproduction is the biological process through which organisms produce offspring. It can occur:
- Sexually, where two parent organisms contribute genetic material.
- Asexually, through processes like budding (in Hydra), spore formation (in fungi), and regeneration (in Planaria).
However, not all living organisms reproduce throughout their life span. For example, mules and infertile humans do not reproduce, yet they are still considered living organisms. Therefore, reproduction is not a defining characteristic of life, as some living organisms may not exhibit this ability.
Cellular Organization: All living organisms are composed of cells, which are the basic units of life. Cells carry out vital biological processes like metabolism, growth, and reproduction. Non-living objects, lacking cellular structure, do not exhibit these processes, making cellular organization a definitive characteristic of life.
Movement: Living organisms exhibit movement, either locomotion (as seen in animals) or more subtle movements like the bending of plants toward light. Movement indicates the presence of life, whereas inanimate objects like candles and crystals remain stationary. For instance, while a mango tree may not move visibly like an animal, it exhibits growth, movement of nutrients, and reproduction, thereby confirming it is a living organism.
Consciousness: Consciousness, or awareness of one’s surroundings, is another feature of living organisms. Being conscious of changes in the environment and responding accordingly is a crucial aspect of life.

1.2 Diversity in the Living World:

Earth is home to millions of species of living organisms, some visible to the naked eye, and others, like microorganisms, that require special tools to observe. These organisms thrive in various environments, including forests, deserts, oceans, lakes, and even extreme habitats like hot springs.

The number of species discovered so far is estimated to be around 1.7-1.8 million, but many more remain undiscovered. The diversity of life forms is essential for the stability of ecosystems, and the variety of species constitutes the Earth’s biological diversity, or biodiversity.

1.3 Taxonomy and Systematics:

Taxonomy is the science of identifying, naming, and classifying organisms. It involves four key activities:

Identification: Recognizing and placing organisms in a proper taxonomic group based on their characteristics.
Classification: Organizing living organisms into groups based on their shared traits.
Characterization: Analyzing and describing organisms in terms of their internal and external structure, cellular organization, developmental process, and ecological role.
Nomenclature: Naming organisms based on a standardized system.

Systematics extends taxonomy by also considering the evolutionary relationships among organisms. It includes not only the classification and naming of organisms but also their evolutionary history. The term “systematics” was introduced by Carolus Linnaeus, who published Systema Naturae, a work that classified organisms based on their morphological traits.

Neo-systematics, introduced in 1940 by Julian Huxley, is the modern approach to systematics, incorporating evidence from various biological fields to classify organisms based on evolutionary relationships.

Nomenclature:

Living organisms have two types of names:

Vernacular (Common) Names: Local names used in everyday language. However, they are often imprecise, leading to confusion.
Scientific Names: Names given according to internationally recognized rules to ensure that organisms are uniformly named worldwide.

Binomial Nomenclature:

Introduced by Carl Linnaeus in his 1753 work Species Plantarum, the binomial nomenclature system gives each organism a two-part Latin name:

The first part is the genus.
The second part is the species.

Example: Mangifera indica (Mango tree), where Mangifera is the genus, and indica is the species.

1.4 Taxonomic Hierarchy:

The taxonomic hierarchy is a system of classifying organisms in a structured manner, from the most specific (species) to the most general (kingdom). The main ranks are:

Kingdom (e.g., Animalia)
Phylum (or Division in plants)
Class
Order
Family
Genus
Species

Each level, or taxon, groups organisms that share similar characteristics, with species being the most specific category.

Key Taxonomic Categories:

Species: The most specific rank, referring to organisms that are similar in structure and can interbreed.
- Example: Homo sapiens (Humans)
Genus: A group of closely related species.
- Example: Panthera (which includes lions and tigers)
Family: A higher taxonomic category that includes related genera.
- Example: The family Felidae includes lions, tigers, and domestic cats.
Order: A group of related families.
- Example: The order Primates includes monkeys, apes, and humans.
Class: A group of related orders.
- Example: Mammalia (mammals)
Phylum: A broader category that includes related classes.
- Example: Chordata (animals with a notochord, like vertebrates)
Kingdom: The highest taxonomic rank, which includes all forms of life. The five kingdoms are Monera, Protista, Fungi, Plantae, and Animalia.

This hierarchy reflects the evolutionary relationships among organisms and provides a standardized framework for their classification.

1.4 Taxonomical Aids

Taxonomical aids are tools and techniques that help in the identification, nomenclature, and classification of organisms. These aids are essential for the study of bioresources, and they are widely used in agriculture, forestry, and industry. These aids can be used both in the field and the laboratory. Taxonomists rely on these aids to properly classify and identify species. Some of the most significant taxonomical aids include herbaria, botanical gardens, museums, zoological parks, and keys. Each of these aids plays a unique role in taxonomy and the biological sciences.

1.4.1 Herbarium

A herbarium is a collection of preserved plant specimens that are carefully dried, pressed, and mounted on sheets of paper. Each specimen is labeled with important information such as its scientific name, date of collection, and location. Herbaria serve as important reference systems for taxonomists and researchers.

Steps in Herbarium Preparation:

Collection of Specimens: Plant specimens are collected from different regions or habitats.
Drying: The specimens are dried by placing them between layers of newspaper or other absorbent materials. In some cases, plants may be dried using heat from an iron.
Poisoning: To prevent decay or insect infestation, the dried specimens are dipped in a mercuric chloride solution or treated with other chemicals.
Mounting: The dried specimens are carefully mounted on herbarium sheets using glue, tape, or in some cases, the thicker parts like stems may be stitched to the sheets.
Preservation: A preservative spray is applied to the herbarium sheets to ensure long-term preservation.
Labeling: Each specimen is labeled with important details, including its scientific name, the name of the collector, the location, the date of collection, and other relevant information. This label is typically placed on the lower left-hand corner of the herbarium sheet.
Storage: Herbarium sheets are stored in specially designed cupboards or storage units. They are often arranged according to plant families or genera for easy reference.

The data from herbarium collections is often published in the form of a flora, which provides detailed information about the plant species found in a specific region. Some well-known Indian floras include the Flora of British India, Flora of Delhi, Flora of Madras, and Flora of Travancore.

World’s Largest Herbarium: The Royal Botanical Garden at Kew in England is the largest herbarium in the world.
India’s Largest Herbarium: The Central National Herbarium located at the Indian Botanical Garden in Kolkata is the largest herbarium in India.

1.4.2 Botanical Gardens

A botanical garden is a dedicated space where a variety of plant species are cultivated and preserved. These gardens are organized in such a way that visitors can observe, study, and learn about different plants. Botanical gardens also play a critical role in scientific research, education, and conservation.

Features of Botanical Gardens:

Plant Collections: Botanical gardens house a diverse range of plants, including exotic, rare, and indigenous species. These plants are grown in different sections, often arranged based on their ecological or botanical characteristics.
Educational Displays: Many botanical gardens also have educational tours, art exhibitions, and public lectures that help educate visitors about plant science and conservation.
Scientific Research: These gardens are usually linked to universities or research institutions, where scientists conduct research on plant species and their uses.
Examples:
- World’s Largest Botanical Garden: The Royal Botanical Garden at Kew in England is the largest botanical garden in the world.
- India’s Largest Botanical Garden: The Indian Botanical Garden in Kolkata is the largest botanical garden in India.
- Largest Tropical Botanical Garden: The Tropical Botanical Garden in Thiruvananthapuram, Kerala, is the largest tropical botanical garden in Asia.

1.4.3 Museum

A museum is an institution where various specimens, including plants, animals, minerals, fossils, and cultural artifacts, are preserved, stored, and exhibited for public viewing and education. Museums are important taxonomical aids because they preserve biological specimens for future reference and research.

Types of Museums:

Natural Science Museums: These museums focus on biological and geological specimens, including preserved animals, plants, fossils, and minerals.
Zoological Museums: Zoological museums preserve animal specimens, often stored in jars containing chemical preservatives. Some animals are preserved through taxidermy.
Botanical Museums: Botanical museums preserve plant specimens, which are usually pressed and dried, similar to herbarium collections.

Insect specimens are often pinned and placed in display boxes, while larger animals such as birds and mammals are stuffed and preserved. Museums also store skeletons and other biological structures for study.

1.4.4 Zoological Parks

Zoological parks, or zoos, are specially designed spaces where animals are housed in enclosures that simulate their natural habitats. These parks serve as centers for education, conservation, and research on animal behavior and biology.

Features of Zoological Parks:

Animal Enclosures: Animals are kept in enclosures that mimic their natural environments to allow for natural behavior.
Walkthrough Exhibits: Visitors can observe non-aggressive animals in their enclosures, often through special walkways or viewing areas.
Conservation: Many zoological parks focus on the conservation of endangered species and may participate in breeding programs.
Examples:
- World’s Largest Zoological Park: The Kruger Zoological Park in South Africa is the largest zoo in the world.
- India’s Largest Zoo: The Zoological Park in Kolkata is the largest zoo in India.

1.4.5 Keys

A key is a taxonomic tool used to identify organisms based on their characteristics. Keys consist of a series of statements, or couplets, that describe contrasting characteristics of different organisms. Taxonomists use keys to narrow down the identification of a species by selecting between two contrasting options at each step.

Types of Keys:

Dichotomous Keys: These keys consist of a series of choices that lead the user to the correct identification of a specimen. The choices are presented in pairs, or couplets, where each pair presents two contrasting statements.
Indented Keys: In an indented key, the couplets are arranged with the choices equidistant from the left margin. The selected lead directs the user to the next couplet.
Bracketed Keys: Bracketed keys present the choices side by side, and they are numbered or lettered. This format makes it easy to follow the choices back and forth.

Other Taxonomic Aids

Flora: A flora is a comprehensive list of plant species in a particular region, along with descriptions and other relevant data. Floras are important for cataloging plant diversity in a specific area. The first complete flora of India was compiled by Hooker.
Monographs: Monographs are detailed handbooks or treatises that provide comprehensive information about a single taxon, such as a family or genus.
Manuals: Manuals provide information on the species found in a specific region, often aiding in their identification and classification.
Catalogues: Catalogues are lists of books, periodicals, and dictionaries that serve as references for taxonomic studies. They help scientists stay updated on the latest taxonomic research and information.