1. The Living World – Class 11 Biology Notes

Here are the complete notes on “The Living World – Class 11 Biology Notes”:

Science: 

• The word ‘science’ is derived from the Latin word ‘Scientia’ which means ‘to know. 
• Science is a process that is used to answer questions about nature.  
• Science is a body of knowledge derived from observations and experiments, which are directed to determine the principles underlying what is being studied. 

Biology:

• Biology (Bios- life, logos- to discover) is the science that deals with studying living organisms.  
• The term ‘Biology’ was proposed by Lamarck & Traveranus in 1802. 

Life:

• Biology is the science that deals with the study of life.
• Life is a unique, complex organisation of molecules, expressed through chemical reactions which lead to growth, development, responsiveness, adaptation & reproduction.
• Some essential characteristic features of living beings, which separate living organisms from non-living organisms, are Growth, reproduction, response to stimuli, metabolism, and the ability to self-replicate.
• Living Organisms are those which have characteristics of Life which separate them from those Non-living Organisms. 

Characteristics features of Living things: 

Non-defining Properties:

1. Growth
2. Reproduction

Defining Properties:

3. Metabolism
4. Cellular organisation
5. Consciousness

1. Growth: 

• All living organisms Grow.
• Growth is the increase in mass & number of cells by cell division.
• In plants, growth occurs through cell division and continues throughout their lifespan. Hence it is indefinite.
• In animals, growth is seen only up to a certain age, hence it is definite. But cell division occurs to replace dead/ lost cells. 
• The non-living objects also grow. The mountains, boulders and sand mounds increase the mass of the body from the outside (extrinsic growth). 
• In living organisms, growth is from the inside (Intrinsic growth).
• Hence, Growth cannot be a defining property of living organisms.

2. Reproduction: 

• Reproduction is a characteristic of living organisms.
• It is defined as the production of progeny(offspring) having features more or less similar to those of the parents. 
• Living organisms can reproduce asexually as well as sexually.
• In unicellular organisms like the amoeba, growth & reproduction are the same because they reproduce by cell division.
• Asexual reproduction is seen mainly in lower organisms by different methods like spores, budding, fragmentation, regeneration etc.
• Sexual reproduction involves the fusion of gametes.
• Many organisms do not reproduce (mules, sterile worker bees, infertile human couples, etc).
• Hence, reproduction is also not a defining property of living organisms.
• Reproduction and growth are NOT defining properties.

Mode of Reproduction

• Multicellular Organisms – sexual
• Fungi – asexual spores
• Yeast & Hydra – budding
• Planaria, Flatworms – true regeneration
• Fragmentation – fungi,filamentous alga,protonema of mosses
• Unicellular (amoeba) – growth and reproduction are synonymous
• Binary fission – bacteria

3. Metabolism

• Metabolism is also a characteristic of life. 
• All living organisms are made of chemicals.
• The sum total of all the chemical reactions occurring in our body is metabolism.
  • Catabolism:  It is defined as the molecules being broken down and energy being released.  E.g. – the breakdown of food during digestion.
  • Anabolism-  It is defined as the energy utilised to combine smaller molecules to yield complex molecules.  E.g. – photosynthesis.
• Metabolic reactions can also be demonstrated outside the body in cell-free systems (Isolated metabolic reaction).
• Isolated metabolic reactions, and invitro are not living things but are living reactions.
• Metabolism is the defining feature of living organisms.

4. Cellular organisation

• Living Organisms are made up of one or more cells.
• Hence, it is the defining feature of living organisms.

5. Consciousness

• All living organisms have the ability to sense and respond to external environmental stimuli.
• All living organisms, from the prokaryotes to the most complex eukaryotes can sense and respond to environmental factors like light, water, temperature, other organisms, pollutants etc.
• Humans are the only organism having self-consciousness. 
• Whereas the Coma patients are brain dead but the body is responding (as the heart and lungs get replaced by machines)
• The best example is the Folding of leaves in Mimosa pudica which occurs due to the external stimulus of touch. 
• Hence, Consciousness is a defining property of living organisms.

Important

• Living organisms are self-replicating, evolving and self-regulating interactive systems capable of responding to external stimuli. 
• Biology is the study of life and the evolution of living organisms on earth.
• All living organisms are linked to one another by the sharing of common genetic material but to varying degrees.
• Growth and Reproduction are NOT defining properties of living organisms.
• Metabolism, Cellular Organisation and Consciousness are defining properties of living organisms.

Diversity In The Living World

• The number and types of organisms present on earth refer to biodiversity
• 1.7-1.8 million species have been known and described which refers to biodiversity.

• The process of understanding the characteristics of organisms such as external and internal structure, cell structure, development process etc. is known as Characterisation. 
• The process of naming living organisms with a particular name all over the world is called Nomenclature.
• Classification is the process by which anything is grouped into convenient categories based on some easily observable characteristics.
• The process by which the characteristics of an organism are known for naming and identifying is known as Identification.

Nomenclature:

• Nomenclature is the process of naming living organisms with a particular name all over the world.
• Nomenclature provides a standard, distinct and proper name for an organism. 
• Thus, it becomes easy to recognise and differentiate a particular organism from others.
• The system of naming with two components is called Binomial Nomenclature. It was proposed by Carolus Linnaeus. 
• Linnaeus is Known for his two works, namely Species Plantarum (1753) for plants and Systema Naturae (1758).
• In Systema Naturae, Linnaeus named 4,400 animal species and 7,700 plant species using the binomial nomenclature system.
• Binomial Nomenclature has two components – the Generic name and the specific epithet. Example: Mangifera indica (Mango) 
  • Generic name – E.g. – Mangifera
  • Specific epithet – E.g. – indica
• Examples: Homo sapiens ( Human), Panthera pardus (Leopard), Felis domestica (Cat)
• Various Codes for Nomenclature:
  • ICBN – International Code of Botanical Nomenclature
  • ICZN – International Code of Zoological Nomenclature
  • ICNB – International Code for Nomenclature of Bacteria
  • ICNCP – International Code of Nomenclature for Cultivated Plants
  • ICTV – International Committee for the Taxonomy of Viruses

Rules Of Binomial Nomenclature

• Biological names are generally in Latin. They are Latinised or derived from Latin irrespective of their origin. 
• The first word in a biological name represents the genus while the second component denotes the specific epithet.
• Both the words in a biological name, when handwritten, are separately underlined, or printed in italics to indicate their Latin origin.
• The first word denoting the genus starts with a capital letter while the specific epithet starts with a small letter. It can be illustrated with the example of Mangifera indica.
• The name of the author appears after the specific epithet, i.e., at the end of the biological name and is written in an abbreviated form, for example, Mangifera indica Linn. It indicates that this species was first described by Linnaeus.

TAUTONYMS

                Animal species having the same name for both genus and species are known as tautonyms. Examples: Eurasian eagle owl (Bubo bubo), European grass snake (Natrix natrix).

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Taxonomy vs Systematics:

Taxonomy: All living organisms are classified into different groups based on their characteristics according to principles of identification, classification and nomenclature. This branch is known as Taxonomy.

• Based on characteristics, all living organisms can be classified into different taxa (categories or taxa or ranks). 
• The basis of modern taxonomic studies is External and internal structure, along with the structure of cells, development process and ecological information of organisms.
• The processes that are basic to taxonomy:
  • a. Characterization – includes morphological and all other characters
  • b. Identification – finding similarities with already known organisms
  • c. Classification – grouping organisms under a particular taxon or category
  • d. Nomenclature – giving a proper scientific name

Systematics: It is the branch of biology that deals with different kinds of organisms, their comparative and evolutionary relationships and the grouping of organisms at every level of classification right from species to the kingdom.

• It deals with the classification of organisms based on their diversity and relationships among them. 
• The word Systematics is derived from the Latin word ‘systema’ which means the systematic arrangement of organisms.

Taxonomic Categories: 

• Classification involves a hierarchy of steps in which each step represents a taxonomic category (rank) 
• A group of organisms occupying a particular category is termed a taxon(pl. taxa).
• All categories together constitute a taxonomic hierarchy.
• Taxonomic hierarchy is also called the Linnaean hierarchy as it was first proposed by Linnaeus.
• Seven Taxonomic categories are 
  • Species → Genus → Family → Order → Class → Phylum (for animals) / Division (for plants) → Kingdom

Species: 

• Groups of individuals with fundamental similarities and can interbreed among themselves are called Species.
• The term is given by John Ray. And the biological concept of species proposed by Ernst Mayr.
• Members of a species have a large number of similar characters.
• Each genus may have one or more than one specific epithets representing different organisms, having morphological similarities.
• Examples: 
  • Homo sapiens (Man), Solanum tuberosum(potato), Panthera leo(lion), Mangifera indica(Mango).  
  • Sapiens, tuberosum, leo, indica  represent species names.

Genus: 

• A group of closely related species is called Genus.
• The genus comprises a group of related species which has more characteristics in common in comparison to species of other genera.
• Examples- 
  • Potato, tomato and brinjal are three different species but all belong to the genus Solanum. 
  • Lion (Panthera leo), leopard (Panthera pardus) and tiger (Panthera tigris) are members of the genus Panthera.

Family: 

• A group of closely related genera is called a Family.
• The family has still less number of similarities as compared to genus and species.
• Examples: 
  • Family Solanaceae includes Genus Solanum, Genus Petunia and Genus Datura.
  • Family Felidae includes Genus Panthera and Genus Felis.

Order: 

• A group of closely related families is called Order.
• The similar characters are fewer in number as compared to different genera included in a family.
• Example- 
  • The plant families  Convolvulaceae and Solanaceae belong to the order- Polymoniales. 
  • Felidae and Concidae belong to the order- Carnivora.

Class: 

• The group of closely related orders is called Class. 
• Example- 
  • Order Primata and Carnivora belong to the class Mammalia.
  • Order Sapindales (Mango) and Polymoniales belong to class Dicotyledonae. 

Phylum: 

• A group of closely related classes is called Phylum. 
• The term Phylum used for animals whereas Division for plants. 
• Example- 
  • Classes Pisces, Amphibia, Reptilia, Aves and Mammalia belong to the Phylum- Chordata.
  • Classes Dicotyledon and Monocotyledon belong to Division- Angiospermae.

Kingdom: 

• The group of all the related phyla is called the Kingdom. 
• It is the highest category.
• Example- 
  • All autotrophic organisms which are eukaryotic and contain chloroplast are kept under the Plant Kingdom. 
  • All heterotrophic organisms which are eukaryotic and lack a cell wall are kept under Animal Kingdom.

NOTE

• As we go higher from species to kingdom, the number of common characteristics goes on decreasing. 
• Lower the taxa, the members within the taxon share more similar characteristics.
• The higher the category, the greater the difficulty of determining the relationship to other taxa at the same level. 
• Taxonomists have also developed sub-categories in this hierarchy to facilitate more sound and scientific placement of various taxa.

Organisms with their Taxonomic Categories

Taxonomical aids-

• The collection of actual specimens of plant and animal species is essential and is the prime source of taxonomic studies.
• Biologists have established certain procedures and techniques to store and preserve the information as well as the specimens using Taxonomical aids.
• Taxonomic Aids are- Herbarium, Botanical garden, Museum, Zoological parks, Key, Monographs, Manuals, Flora.

Herbarium: 

• Store house of collected plant specimens that are dried, pressed and preserved on sheets.
• The plant specimens are collected then dried, pressed, and preserved on sheets and arranged systematically according to the universally accepted system of classification. 
• The herbarium sheet contains labels regarding the date, place of the collection, scientific name, family, collector’s name, etc. of the specimen.
• The largest Herbarium in the world is located at Royal Botanical Garden, Kew, England (more than 6 million)
• The largest Herbarium in India is located at Central National Herbarium, Kolkata, West Bengal (more than 2 million).

Herbarium Technique/ Preparation of Herbarium Sheets: 

• Plants should be collected in the flowering stage having all floral organs.
• The details about the plant such as locality, ecological conditions, vegetative and floral characters, etc. should be noted.
• Plants are evenly pressed by unfolding all the plant parts between blotting papers (or newspapers) with the help of plant pressers. 
• Blotting papers are required to be changed regularly until the plant gets dried. The main objective of pressing is to flatten and dry the specimens.
• The pressed, then dried specimen is affixed on the herbarium sheets of 28 x 42 cm (± 1 cm) size.
• The herbarium sheet is labelled in the lower right-hand corner representing the name of the plant specimen, date of collection, collector name, location etc.
• After mounting herbarium arranged based on the standard system of classification. It is used for future reference.

Botanical Garden: 

• Specialised gardens that have collections of living plants for reference.
• The plant species are grown for identification and reference. 
• Each plant contains labels indicating its botanical/ scientific name and family.
• The famous botanical gardens are at Kew (England), the Indian Botanical Garden, Howrah (India) and at National Botanical Research Institute, Lucknow (India).
• Famous botanical gardens are 
  • Indian Botanical Garden, Howrah (in India)
  • Royal Botanical Garden, Kew, England (largest in world till date)
  • National Botanical Research Institute, Lucknow (India)

Museum: 

• Biological museums are mostly set up in educational institutes such as schools and colleges.
• Museums have collections of preserved plant and animal specimens for study and reference.
• The organisms are preserved either in containers or preservative solution or in the form of dry specimens. 
• Insects preserved in insect boxes after collecting, killing and pinning.
• It often has a collection of skeletons of animals also.
•  Larger animals like birds and mammals are usually stuffed and preserved.

Zoological Park: 

• Places where wild animals are kept in a protected environment under human care and enable us to learn about their food habits and behaviour.
• Useful for Ex-situ conservation and breeding of endangered animals.
• All animals in zoos are provided with conditions similar to their natural habitats.

Keys: 

• Keys are used for the identification of plants and animals on the basis of similarities and dissimilarities.
• Keys are based on the contrasting characters generally in a pair called couplets.
• Each couplet has two opposite options in which only the relevant option is accepted and the other is rejected. 
• Each statement in the key is called a lead.
• Separate taxonomic keys are required for each taxonomic category for identification purposes.
• Keys are generally analytical in nature.

Flora- 

• It contains the actual account of the habitat and distribution of plants of a given area.
• It indexes plant species found in a particular area.

Manuals- 

• Manuals Provide information for the identification of name of species in an area.

Monograph- 

• Monographs contain the records that contain information on any one taxon.

Catalogue:

• A list which methodically enumerates all species found in a particular place is called a catalogue.