Comprehensive Study Notes for Class XI Biology

TEXTBOOK INFORMATION AND ADMINISTRATIVE DETAILS

• Title: Biology: Textbook for Class XI.
• Publication Details: Published by the National Council of Educational Research and Training (NCERT), Sri Aurobindo Marg, New Delhi.
• Edition and Reprints: First Edition in February $2006$. Revised Edition in November $2022$. Reprint $2025-26$.
• Price: $\text{Rs. } 185.00$.
• ISBN: $81-7450-496-6$.
• Publication Team: Head of Publication Division M.V. Srinivasan, Chief Editor Bijnan Sutar, Chief Production Officer Jahan Lal, Chief Business Manager Amitabh Kumar.
• Offices: NCERT Campus (New Delhi), Hosdakere Halli Extension (Bengaluru), Navjivan Trust Building (Ahmedabad), CWC Campus (Kolkata), CWC Complex (Guwahati).
• Foreword: Based on the National Curriculum Framework (NCF) $2005$, which aims to link school life to life outside the school, discouraging rote learning and encouraging creativity and initiative in children.
• Advisory Group Members: Chairperson J.V. Narlikar, Chief Advisor K. Muralidhar.
• Rationalisation of Content: Updated in view of the COVID-19 pandemic to reduce content load, focusing on overlapping content, difficulty level, and self-learning accessibility according to the National Education Policy $2020$.

THE CONSTITUTION OF INDIA: PREAMBLE

• Resolution: We, the people of India, resolve to constitute India into a Sovereign Socialist Secular Democratic Republic.
• Objectives for Citizens:
  • Justice: Social, economic, and political.
  • Liberty: Of thought, expression, belief, faith, and worship.
  • Equality: Of status and opportunity.
  • Fraternity: Assuring the dignity of the individual and the unity and integrity of the Nation.
• Adoption Date: $26^{th}$ day of November, $1949$.

BIOLOGY: AN INTEGRATED SCIENCE

• Definition: Biology is the science of life forms and living processes. It is the story of life on Earth.
• Historical Development: Initially ancillary to human medicine, it moved to fundamental questions of biodiversity and evolution. Physical sciences led to the creation of biochemistry and biophysics.
• Molecular Biology: Facilitated by the discovery of the double-helical structure of DNA and macromolecular structures.
• Current Perspective: Modern biology is a synthesis of classical and molecular disciplines, with ecology and systems biology serving as unifying fields. It is taught as an interdisciplinary science.
• Structural Units: There are $22$ chapters grouped into $5$ thematic units.

UNIT I: DIVERSITY IN THE LIVING WORLD

• Living Species Range: Identified species range from $1.7-1.8$ million, constituting global biodiversity.
• Taxonomy Foundations: Characterisation, identification, nomenclature, and classification.
• Binomial Nomenclature: Proposed by Carolus Linnaeus. Each name has a Generic name and a Specific epithet.
  • Rules: Names are in Latin/italics. Genus starts with a capital letter, specific epithet with small. Both are underlined separately when handwritten.
  • Example: Mangifera indica Linn.
• Taxonomic Hierarchy: Species $\rightarrow$ Genus $\rightarrow$ Family $\rightarrow$ Order $\rightarrow$ Class $\rightarrow$ Phylum/Division $\rightarrow$ Kingdom.
  • Species: Fundamental similarities (e.g., Panthera leo).
  • Genus: Aggregates of related species (e.g., Solanum includes potato and brinjal).
  • Family: Related genera with fewer similarities (e.g., Solanaceae includes Solanum, Petunia, Datura).
  • Order: Assemblage of families (e.g., Carnivora includes Felidae and Canidae).
  • Class: Related orders (e.g., Mammalia includes Primata and Carnivora).

ERNST MAYR ($1904-2004$)

• Profile: Known as the 'Darwin of the $20^{th}$ century'. One of the $100$ greatest scientists.
• Contributions: Pioneered the biological species definition. Almost single-handedly made species diversity a central evolutionary question.
• Awards: The 'triple crown of biology' (Balzan Prize $1983$, International Prize for Biology $1994$, Crafoord Prize $1999$).

BIOLOGICAL CLASSIFICATION

• Aristotle: Earliest classification. Plants into trees, shrubs, herbs; animals into those with red blood and those without.
• Two Kingdom System: Linnaeus (Plantae and Animalia). Inadequate for prokaryotes/eukaryotes and unicellular/multicellular.
• Five Kingdom System: R.H. Whittaker ($1969$). Criteria: Cell structure, body organisation, mode of nutrition, reproduction, and phylogenetic relationships.
  • Kingdom Monera: Bacteria are sole members. Shapes: Coccus (spherical), Bacillus (rod), Vibrio (comma), Spirillum (spiral). Includes Archaebacteria (extremophiles) and Eubacteria (cyanobacteria like Nostoc).
  • Kingdom Protista: Single-celled eukaryotes. Includes Chrysophytes (diatoms), Dinoflagellates (Gonyaulax), Euglenoids (Euglena), Slime moulds, and Protozoans.
  • Kingdom Fungi: Heterotrophic organisms. Cell walls of chitin and polysaccharides. Classes: Phycomycetes (Mucor), Ascomycetes (Penicillium), Basidiomycetes (mushrooms), Deuteromycetes (imperfect fungi).
  • Viruses: Non-cellular, inert crystalline structure outside living cells. Obligate parasites containing either RNA or DNA. Viroids (free RNA, discovered by T.O. Diener) and Prions (abnormally folded proteins) cause diseases like BSE and CJD.
  • Lichens: Symbiotic association between algae (phycobiont) and fungi (mycobiont).

PLANT KINGDOM

• Classification Evolutions: Earlier systems were artificial (superficial characters). Natural systems (Bentham and Hooker) and Phylogenetic systems are now used.
• Algae: Simple, thalloid, autotrophic. Classes: Chlorophyceae (green), Phaeophyceae (brown - contain fucoxanthin), Rhodophyceae (red - contain r-phycoerythrin).
• Bryophytes: 'Amphibians of the plant kingdom'. Includes Liverworts (Marchantia) and Mosses (Funaria, Sphagnum). Dominant stage is gametophyte.
• Pteridophytes: First terrestrial plants with vascular tissues (xylem and phloem). Includes horsetails and ferns. Heterospory is seen in Selaginella and Salvinia.
• Gymnosperms: Naked seeds. Includes Sequoia (giant redwood). Genera: Cycas, Pinus, Ginkgo.
• Angiosperms: Flowering plants with seeds in fruits. Divided into Dicotyledons and Monocotyledons.

ANIMAL KINGDOM

• Levels of Organisation: Cellular (Sponges), Tissue (Coelenterates), Organ (Platyhelminthes), Organ System (Annelids to Chordates).
• Symmetry: Asymmetry (Sponges), Radial (Coelenterates), Bilateral (Arthropods, Chordates).
• Germ Layers: Diploblastic (Ectoderm/Endoderm) and Triploblastic (Mesoderm present).
• Coelom: Coelomates (lined by mesoderm), Pseudocoelomates (pouches, e.g., Aschelminthes), Acoelomates (absent, e.g., Platyhelminthes).
• Phyla:
  • Porifera: Canal system, choanocytes.
  • Coelenterata: Cnidoblasts, polyp/medusa forms.
  • Arthropoda: Largest phylum. Jointed appendages, chitinous exoskeleton.
  • Chordata: Notochord, dorsal hollow nerve cord, pharyngeal gill slits.
• Vertebrata Classes: Cyclostomata, Chondrichthyes (cartilaginous fish), Osteichthyes (bony fish), Amphibia, Reptilia, Aves, Mammalia.

MORPHOLOGY AND ANATOMY OF FLOWERING PLANTS

• Root Systems: Tap root (dicots), Fibrous root (monocots), Adventitious roots (from parts other than radicle). Regions: Root cap, meristematic, elongation, maturation (with root hairs).
• The Stem: Ascending axis with nodes and internodes. Develops from plumule.
• The Leaf: Parts: Leaf base (pulvinus in legumes), petiole, lamina. Venation: Reticulate (dicots), Parallel (monocots).
• Aestivation: Mode of arrangement of sepals/petals: Valvate, Twisted, Imbricate, Vexillary.
• The Flower: Reproductive unit. Parts: Calyx, Corolla, Androecium (male), Gynoecium (female).
• Anatomy:
  • Epidermal Tissue System: Stomata with guard cells (dumb-bell shaped in grasses).
  • Vascular System: Open bundles (cambium present in dicots), Closed (no cambium in monocots). Radial (roots), Conjoint (stems).
• Katherine Esau ($1898-1997$): Author of 'Plant Anatomy' ($1954$) and 'The Anatomy of Seed Plants' ($1960$). Awarded National Medal of Science in $1989$.

CELL: STRUCTURE AND FUNCTION

• Cell Theory: Schleiden and Schwann. Virchow added 'Omnis cellula-e cellula' (all cells from pre-existing cells).
• Prokaryotic Cell: No membrane-bound nucleus. Includes bacteria, PPLO ($0.1 \, \mu m$). DNA is circular (genomic) plus plasmids.
• Eukaryotic Organelles:
  • Mitochondria: Double membrane, site of ATP production through aerobic respiration.
  • Chloroplast: Site of photosynthesis. Contains thylakoids/grana.
  • Nucleus: Described by Robert Brown ($1831$). Contains chromatin (DNA/Proteins).
• Biomolecules:
  • Proteins: Polymers of $20$ amino acids. Collagen is the most abundant animal protein; RuBisCO is most abundant in the biosphere.
  • Polysaccharides: Cellulose (structural), Starch (storage), Glycogen (animal storage), Chitin (exoskeleton).
  • Enzymes: Protein catalysts. Lower activation energy. Affected by pH, temperature, and substrate concentration.
• Cell Cycle: Phases include Interphase ($G_1$, $S$, $G_2$) and M Phase (Mitosis or Meiosis).

PLANT PHYSIOLOGY

• Photosynthesis: $6CO_2 + 12H_2O \xrightarrow{\text{Light/Chlorophyll}} C_6H_{12}O_6 + 6H_2O + 6O_2$. Light Reaction (Z-scheme) and Dark Reaction (Calvin Cycle). $C_4$ pathway avoids photorespiration (Kranz anatomy in maize).
• Respiration: Breakdown of glucose. Glycolysis (cytoplasm) $\rightarrow$ TCA Cycle (matrix) $\rightarrow$ ETS (inner membrane). Net gain: $38 \, \text{ATP}$.
• Plant Growth Regulators (PGRs):
  • Auxins: Apical dominance.
  • Gibberellins: Increase stem length, bolting.
  • Cytokinins: Cell division.
  • Ethylene: Fruit ripening.
  • Abscisic Acid (ABA): Stress hormone, closure of stomata.

HUMAN PHYSIOLOGY

• Breathing: Inspiration (diaphragm contraction) and Expiration. Tidal Volume ($500 \, \text{mL}$). Oxygen transported as oxyhaemoglobin; $CO_2$ mainly as bicarbonate.
• Circulation: Human heart is $4$-chambered with SAN (pacemaker, $70-75 \, \text{beats/min}$). Double circulation: Pulmonary and Systemic. Blood groups: ABO and Rh.
• Excretion: Human system: Kidneys, ureters, bladder, urethra. Nephron is functional unit. Counter current mechanism concentrates urine ($1200 \, \text{mOsmolL}^{-1}$).
• Locomotion: Sliding filament theory (Actin/Myosin). Skeleton has $206$ bones. Joints: Fibrous, Cartilaginous, Synovial (Ball and socket, etc.).
• Neural Control: Brain parts: Forebrain ($Cerebrum, Thalamus, Hypothalamus$), Midbrain ($Corpora quadrigemina$), Hindbrain ($Pons, Cerebellum, Medulla$).
• Chemical Coordination: Endocrine glands: Pituitary (master gland), Thyroid ($T_3/T_4$), Pancreas (Insulin/Glucagon), Adrenal (Emergency hormones).