Class 11 Biology Notes Chapter 1 (The living world) – Biology Book
Detailed Notes with MCQs of Chapter 1, 'The Living World'. This chapter forms the foundation for understanding biology and often features in various government exams. Pay close attention to the definitions and classifications.
Chapter 1: The Living World - Detailed Notes for Government Exams
1. What is 'Living'?
Biology is the science of life forms and living processes. The fundamental question is, what distinguishes living organisms from non-living matter? Living organisms exhibit certain characteristic features:
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Growth:
- Increase in mass and increase in the number of individuals are twin characteristics of growth.
- In plants, growth occurs continuously throughout their lifespan.
- In animals, growth is generally limited to a certain age.
- Non-living objects (like mountains, boulders) can also grow by accumulation of material on the surface (extrinsic growth).
- Intrinsic growth (growth from inside) is a characteristic feature of living organisms.
- Note: While growth is characteristic of living beings, it is not a defining property because non-living things can also exhibit extrinsic growth, and some living organisms might not show perceptible growth under certain conditions.
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Reproduction:
- Production of progeny possessing features more or less similar to those of parents.
- Organisms reproduce asexually (e.g., fungi - spores, yeast/Hydra - budding, Planaria - true regeneration) or sexually.
- Note: Reproduction is characteristic of living beings, but not a defining property. Many living organisms do not reproduce (e.g., mules, sterile worker bees, infertile human couples).
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Metabolism:
- The sum total of all chemical reactions occurring in our body.
- Includes Anabolism (building up reactions, e.g., photosynthesis) and Catabolism (breaking down reactions, e.g., respiration).
- All living organisms, from prokaryotes to eukaryotes, exhibit metabolism.
- Non-living objects do not exhibit metabolism.
- Metabolic reactions can be demonstrated in vitro (outside the body in a test tube), but these isolated reactions are not living things, rather living reactions.
- Note: Metabolism is considered a defining property of all living organisms without exception.
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Cellular Organization:
- All living organisms are composed of cells.
- Cells are the basic structural and functional units of life.
- Unicellular organisms perform all life functions within a single cell.
- Multicellular organisms have complex organization with tissues, organs, and organ systems.
- Note: Cellular organization of the body is the defining feature of life forms.
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Consciousness:
- Ability to sense their surroundings or environment and respond to these environmental stimuli (physical, chemical, biological).
- Plants respond to external factors like light, water, temperature, pollutants, etc.
- All organisms are 'aware' of their surroundings.
- Humans possess self-consciousness (awareness of self), which is unique.
- Note: Consciousness is considered a defining property of living organisms. (Patients in a coma are considered living as some metabolic processes and responses might still be present, supported by machines).
Defining Properties of Living Organisms: Metabolism, Cellular Organization, Consciousness.
Characteristic (but not defining) Properties: Growth, Reproduction.
2. Diversity in the Living World (Biodiversity)
- Refers to the number and types of organisms present on Earth.
- Estimated number of species known and described range between 1.7-1.8 million. This is referred to as biodiversity.
- Need for Classification: To organize this vast diversity for easier study, identification, and understanding of relationships.
3. Taxonomy and Systematics
- Taxonomy: (Greek: taxis - arrangement, nomos - law) The science of identification, nomenclature (naming), and classification of organisms. Based on characteristics.
- Systematics: (Latin: systema - systematic arrangement) A broader field that includes taxonomy but also considers the evolutionary relationships (phylogeny) between organisms. Linnaeus used Systema Naturae as the title of his publication.
- Basic Processes:
- Characterization: Understanding the characters of organisms (external and internal structure, cell structure, development process, ecological information).
- Identification: Correct description and placement of an organism in a previously established taxonomic group.
- Classification: Grouping organisms into convenient categories (taxa) based on easily observable characters.
- Nomenclature: Standardized naming of organisms such that a particular organism is known by the same name all over the world.
4. Binomial Nomenclature
- System developed by Carolus Linnaeus.
- Each scientific name has two components:
- Generic name (Genus)
- Specific epithet (Species)
- Universal Rules:
- Biological names are generally in Latin and written in italics.
- When handwritten, both words are separately underlined.
- The first word (Genus) starts with a capital letter.
- The second word (specific epithet) starts with a small letter.
- Name of the author (who first described the species) appears after the specific epithet, usually abbreviated. E.g., Mangifera indica Linn. (Linn. indicates Linnaeus).
5. Taxonomic Categories (Taxonomic Hierarchy)
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Classification involves hierarchy of steps where each step represents a rank or category.
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All categories together constitute the taxonomic hierarchy.
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Each category is referred to as a unit of classification, representing a taxon (plural: taxa).
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Obligate Categories (Ascending Order):
- Species: Group of individual organisms with fundamental morphological similarities, capable of interbreeding to produce fertile offspring. (e.g., sapiens in Homo sapiens, indica in Mangifera indica).
- Genus: Group of related species having more characters in common compared to species of other genera. (e.g., Panthera includes leo (lion), pardus (leopard), tigris (tiger); Solanum includes nigrum, melongena, tuberosum).
- Family: Group of related genera with fewer similarities compared to genus and species. Characterized based on vegetative and reproductive features (in plants). (e.g., Family Solanaceae includes genera Solanum, Petunia, Datura; Family Felidae includes genus Panthera and Felis (cat)).
- Order: Assemblage of related families exhibiting fewer similar characters. (e.g., Order Polymoniales includes families Convolvulaceae and Solanaceae based on floral characters; Order Carnivora includes families Felidae and Canidae (dogs)).
- Class: Group of related orders. (e.g., Class Mammalia includes orders Primata (monkey, gorilla, human) and Carnivora (tiger, cat, dog)).
- Phylum (for animals) / Division (for plants): Group of related classes. (e.g., Phylum Chordata includes classes like Mammalia, Aves, Reptilia, Amphibia, Pisces based on common features like notochord and dorsal hollow neural system).
- Kingdom: The highest taxonomic category. (e.g., Kingdom Animalia, Kingdom Plantae).
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As we go higher up the hierarchy (from species to kingdom), the number of common characteristics decreases.
Example Hierarchy:
- Human: Kingdom Animalia -> Phylum Chordata -> Class Mammalia -> Order Primata -> Family Hominidae -> Genus Homo -> Species sapiens
- Mango: Kingdom Plantae -> Division Angiospermae -> Class Dicotyledonae -> Order Sapindales -> Family Anacardiaceae -> Genus Mangifera -> Species indica
6. Taxonomical Aids
- Tools and procedures to store and preserve information as well as specimens for identification and classification.
- Herbarium:
- Storehouse of collected plant specimens that are dried, pressed, and preserved on sheets.
- Sheets are arranged according to a universally accepted system of classification.
- Herbarium sheets carry a label providing date and place of collection, English, local, and botanical names, family, collector's name, etc.
- Serve as quick referral systems.
- Botanical Gardens:
- Collections of living plants for reference.
- Plants are grown for identification purposes and labelled with botanical/scientific name and family.
- Famous examples: Kew (England), Indian Botanical Garden (Howrah), National Botanical Research Institute (Lucknow).
- Museum:
- Collections of preserved plant and animal specimens for study and reference.
- Specimens preserved in containers/jars in preservative solutions (like formalin).
- Plant and animal specimens may also be preserved as dry specimens.
- Insects are preserved in insect boxes after collecting, killing, and pinning.
- Larger animals like birds and mammals are usually stuffed and preserved.
- Museums often have collections of skeletons too.
- Zoological Parks (Zoos):
- Places where wild animals are kept in protected environments under human care.
- Enable us to learn about their food habits and behaviour.
- Conditions are provided as similar as possible to their natural habitats.
- Key:
- An analytical tool used for identification of plants and animals based on similarities and dissimilarities.
- Based on contrasting characters generally in a pair called a couplet.
- Each statement in the key is called a lead.
- Keys are generally analytical in nature (require choosing between two opposite options).
- Separate taxonomic keys are required for each taxonomic category (family, genus, species).
- Other Aids:
- Flora: Contains the actual account of habitat and distribution of plants of a given area. Provides an index to the plant species found in a particular area.
- Manuals: Useful in providing information for identification of names of species found in an area.
- Monographs: Contain information on any one taxon.
- Catalogues: List of species found in an area, often with brief descriptions for identification.
Multiple Choice Questions (MCQs)
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Which of the following is considered a defining property of living organisms?
(a) Growth
(b) Reproduction
(c) Metabolism
(d) Increase in mass -
The system of providing a scientific name with two components (Genus and Species) is known as:
(a) Taxonomy
(b) Binomial Nomenclature
(c) Systematics
(d) Classification -
According to the universal rules of nomenclature, the scientific name Mangifera indica Linn., 'Linn.' stands for:
(a) The Latin origin of the name
(b) The specific epithet
(c) The name of the author who first described the species
(d) The family name -
Which of the following taxonomic categories contains organisms with the maximum number of similar characters?
(a) Genus
(b) Family
(c) Order
(d) Species -
A place where dried, pressed, and preserved plant specimens are kept is called a:
(a) Museum
(b) Botanical Garden
(c) Herbarium
(d) Zoological Park -
Which taxonomic aid is based on contrasting characters generally in a pair called a couplet?
(a) Flora
(b) Key
(c) Monograph
(d) Manual -
Select the correct sequence of taxonomic categories in ascending order:
(a) Species -> Genus -> Order -> Family -> Class -> Phylum -> Kingdom
(b) Species -> Genus -> Family -> Order -> Class -> Phylum -> Kingdom
(c) Kingdom -> Phylum -> Class -> Order -> Family -> Genus -> Species
(d) Species -> Family -> Genus -> Order -> Class -> Phylum -> Kingdom -
Systematics differs from taxonomy primarily because it also considers:
(a) Identification of organisms
(b) Nomenclature of organisms
(c) Evolutionary relationships between organisms
(d) Classification based only on morphological features -
Which of the following represents a 'taxon'?
(a) Mammalia
(b) Species
(c) Classification
(d) Both (a) and (b) are ranks, representing taxa -
Which of the following organisms do not reproduce, yet are considered living?
(a) Bacteria undergoing binary fission
(b) Mules (sterile hybrid)
(c) Amoeba undergoing budding
(d) Fungi producing spores
Answer Key for MCQs:
- (c) Metabolism
- (b) Binomial Nomenclature
- (c) The name of the author who first described the species
- (d) Species
- (c) Herbarium
- (b) Key
- (b) Species -> Genus -> Family -> Order -> Class -> Phylum -> Kingdom
- (c) Evolutionary relationships between organisms
- (d) Both (a) and (b) are ranks, representing taxa (Mammalia is a Class, Species is the basic rank; both represent taxa at different levels)
- (b) Mules (sterile hybrid)
Revise these notes thoroughly. Understanding the precise definitions and the hierarchy is crucial. Good luck with your preparation!