Biology जीवशास्त्र

Quick summary

There is huge diversity of living organisms on earth. This chapter explains what makes something "living" and introduces taxonomical aids — herbarium, botanical gardens, museums, zoological parks, biodiversity parks and keys — that help us study, identify and conserve this diversity.

Key points

• Basic properties of life: metabolism (catabolism + anabolism) for energy, growth and development from within, ageing, reproduction (asexual or sexual) for continuity of race, death, and responsiveness (irritability).
• Non-living things like sand mounds may "grow", but only by addition from outside, not from within.
• Reproduction is not an all-inclusive property: mules and worker bees are sterile but living. Metabolism and responsiveness are more inclusive characters.
• Herbarium: dried, pressed and treated plant specimens mounted on standard-size sheets with a label at the lower right corner (name, family, date, place, collector, local name). The word was coined by Tournefort; the art was started by Luca Ghini.
• Luca Ghini set up the world's first botanical garden at Pisa, Italy (1543). Kew (England) has a very large collection of specimens and herbaria.
• Botanical gardens grow living plants from many regions scientifically, with labels showing scientific and common names. Greenhouses in them grow plants needing special conditions.
• Museums keep preserved specimens — in formalin (10–40 % formaldehyde) jars, stuffed animals (taxidermy), dried specimens, shells, skeletons and insect boxes.
• Zoological parks keep wild animals in captivity in conditions like their natural habitat (ex-situ). Animals are acclimatised, e.g. Humboldt penguins at Jijamata Udyan, Mumbai.
• Biodiversity parks are self-sustaining communities created on degraded land, e.g. Late Uttamrao Patil Biodiversity Park, Gureghar, Mahabaleshwar.
• Key: a taxonomic aid for identification; dichotomous keys use pairs of contrasting characters, each statement called a lead.
• Flora, manuals, monographs and catalogues are other records of biodiversity.
• Dr S. P. Agharkar explored the Western Ghats and found a freshwater jellyfish; ARI, Pune is named after him. Sacred groves (devrai) protect forests in the name of a deity.

Important terms

• Metabolism – sum of all chemical reactions in the body (breaking and making of molecules).
• Biodiversity – the degree of variation of life forms in an ecosystem.
• In-situ conservation – protecting organisms in their natural habitat (sacred groves, national parks).
• Ex-situ conservation – protecting organisms outside their natural habitat (zoo, botanical garden).
• Taxidermy – stuffing and preserving large animals like birds and mammals.
• Flora – plant life of a particular area at a particular time.
• Monograph – detailed account of any one selected group of organisms.

Key facts

5 important questions

Q1. Which property of life is all-inclusive? Why is reproduction not one?

Metabolism (and responsiveness) are shown by all living beings and never by non-living things. Reproduction is not all-inclusive because sterile organisms like mules and worker bees cannot reproduce but are still living.

Q2. What is a herbarium? What are the essentials of a good herbarium?

A collection of dried, pressed and preserved plant specimens mounted on standard sheets. A good herbarium sheet is properly dried and poisoned against insects, neatly mounted, and has a complete label: scientific name, family, local name, date and place of collection, and collector's name.

Q3. Distinguish between in-situ and ex-situ conservation.

In-situ: conservation in the natural habitat, e.g. sacred groves, national parks, sanctuaries. Ex-situ: conservation outside the natural habitat, e.g. zoos, botanical gardens, seed banks.

Q4. Why should penguins be acclimatised when kept away from their natural habitat?

Penguins live in cold regions. In a warm place like Mumbai they need gradual adjustment and conditions (temperature, water, food) similar to their natural habitat, otherwise they cannot survive.

Q5. A seasonal plant has to be studied in the laboratory throughout the year. Which aid is best?

A herbarium, because the dried specimen is available any time of the year, even when the living plant is not.

Exam tip

Learn the difference between botanical garden, zoo and biodiversity park in table form — it is a common "distinguish" question.

Quick summary

Systematics is the study of the kinds and diversity of organisms and their evolutionary relationships. This chapter covers types of classification, three domains of life, modern approaches (chemotaxonomy, numerical taxonomy, cladograms, DNA barcoding), taxonomic hierarchy, binomial nomenclature, Whittaker's five kingdoms and acellular forms such as viruses, viroids and prions.

Key points

• Systematics was defined by G. Simpson (1961). The term taxonomy (taxis = arrangement, nomos = law) was introduced by A. P. de Candolle.
• Types of classification: artificial (few visible characters, e.g. Linnaeus), natural (many significant characters, e.g. Bentham and Hooker) and phylogenetic (evolutionary descent, e.g. Engler and Prantl).
• Carl Woese (1990) proposed three domains: Archaea, Bacteria (both prokaryotic) and Eukarya. Domain is larger than kingdom.
• Modern approaches: chemotaxonomy (chemical constituents, e.g. cell wall of chitin in fungi vs cellulose in plants), numerical taxonomy (Sokal and Sneath, 1963), cladogram (branching diagram of common ancestry) and DNA barcoding (identifying species from a short DNA sequence).
• Taxonomic hierarchy: Kingdom → Division/Phylum → Class → Order → Family → Genus → Species. Going upward, common characters decrease.
• Example: China rose — Plantae, Angiospermae, Dicotyledonae, Malvales, Malvaceae, Hibiscus rosa-sinensis. Cobra — Animalia, Chordata, Reptilia, Squamata, Elapidae, Naja naja.
• Binomial nomenclature by Carl Linnaeus in Species Plantarum (1753): genus name (capital first letter) + species name (small letter), italic when printed, underlined separately when handwritten, e.g. Mangifera indica L.
• Plant names were governed by ICBN; after the International Botanical Congress at Shenzhen, China (2017) the code is ICNAFP — International Code of Nomenclature for Algae, Fungi and Plants (the "Shenzhen code").
• Whittaker (1969) five kingdoms: Monera, Protista, Fungi, Plantae, Animalia.
• Monera: unicellular prokaryotes; DNA as nucleoid, plasmids, 70S ribosomes, peptidoglycan cell wall. Shapes: coccus, bacillus, vibrio, spirillum. Archaebacteria (extremophiles: halophiles, thermophiles, methanogens) and Eubacteria (true bacteria, cyanobacteria with heterocysts). Mycoplasma are the smallest living forms, without a cell wall.
• Protista: unicellular eukaryotes — chrysophytes (diatoms), dinoflagellates (Gonyaulax, red tide), euglenoids (pellicle), slime moulds and protozoans (Amoeba, Entamoeba, Trypanosoma, Paramoecium, Plasmodium).
• Fungi: eukaryotic heterotrophs with chitin cell wall and hyphae/mycelium. Phycomycetes (Mucor, Rhizopus, Albugo), Ascomycetes (yeast, Penicillium, Neurospora), Basidiomycetes (Agaricus, Puccinia, Ustilago), Deuteromycetes (Alternaria). Lichens = alga + fungus; pollution indicators.
• Viruses: acellular nucleoprotein particles (capsid + DNA or RNA, never both); inactive outside a host. Viroids (Diener, 1971) are free RNA without protein coat. Prions are infectious abnormally folded proteins (mad cow disease).

Important terms

• Taxon – a taxonomic group of any rank (e.g. Malvaceae).
• Species – the basic unit; a group of organisms that interbreed naturally to produce fertile offspring.
• Genus – a group of closely related species (lion, tiger, leopard in Panthera).
• Coenocytic hyphae – non-septate hyphae with many nuclei.
• Bacteriophage – virus that infects bacteria (usually double-stranded DNA).
• Plasmid – small extra-chromosomal circular DNA in bacteria.

Key facts

5 important questions

Q1. Why is binomial nomenclature important?

Common names differ from place to place and language to language. A scientific name is unique, universal and understood by scientists everywhere, so it avoids confusion.

Q2. Write the salient features of Monera.

Unicellular prokaryotes found everywhere; no nuclear membrane (nucleoid); plasmids often present; no membrane-bound organelles; 70S ribosomes; cell wall of peptidoglycan; reproduction by binary fission (rarely conjugation); autotrophic or heterotrophic.

Q3. Differentiate between viruses and viroids.

Viruses have a protein coat (capsid) around DNA or RNA and are larger. Viroids (discovered by Diener, 1971) are small single-stranded RNA without any protein coat, e.g. potato spindle tuber disease.

Q4. Write short notes on useful and harmful bacteria.

Useful: Lactobacilli (curd), Azotobacter (nitrogen fixation), Streptomyces (antibiotics), methanogens (biogas), decomposers. Harmful: cause typhoid, cholera, tuberculosis, tetanus.

Q5. Identify the correctly written name: Helianthus annuus L. or Helianthus Annuus l.

Helianthus annuus L. is correct — genus starts with a capital, species with a small letter, and the author's abbreviation (L. for Linnaeus) has a capital.

Exam tip

Practise diagrams of Paramoecium, Euglena, TMV and bacteriophage, and remember one example for each fungal class.

Quick summary

Kingdom Plantae is divided on the basis of seeds, vascular tissue and body differentiation. Cryptogamae (spore-producing: Thallophyta/algae, Bryophyta, Pteridophyta) do not form seeds; Phanerogamae (seed-producing: Gymnosperms and Angiosperms) do. The chapter also explains alternation of generations and haplontic, diplontic and haplo-diplontic life cycles.

Key points

• Cryptogamae (kryptos = hidden): sex organs concealed, no seeds or flowers. Phanerogamae (phaneros = visible): seed-producing plants.
• Algae (Thallophyta): mostly aquatic, thalloid body (no root, stem, leaf), pyrenoids on chloroplasts, alternation of generation with dominant haploid phase. Size from microscopic Chlorella, Chlamydomonas to Sargassum over 60 m long.
• Chlorophyceae (green): chlorophyll a and b, cellulose wall, true starch (Spirogyra, Chara, Volvox, Ulothrix).
• Phaeophyceae (brown, mostly marine): chlorophyll a, c and fucoxanthin; wall with cellulose, fucans and algin; food stored as mannitol and laminarin; body of holdfast, stipe and frond (Laminaria, Sargassum, Fucus).
• Rhodophyceae (red): chlorophyll a, d and phycoerythrin; Floridean starch; source of agar-agar (Gelidium, Gracilaria, Porphyra, Polysiphonia).
• Bryophyta ("amphibians of the plant kingdom"): live on land in moist shady places but need water for fertilization. The dominant plant is the haploid gametophyte with rhizoids; the sporophyte (capsule) depends on it. Liverworts (Riccia, Marchantia), hornworts (Anthoceros), mosses (Funaria, Polytrichum, Sphagnum). Mosses have a protonema stage and leafy stage; Sphagnum gives peat.
• Pteridophyta: first true land vascular plants with root, stem, leaves; called vascular cryptogams. Sporophyte is dominant and independent. Xylem has only tracheids, phloem only sieve cells; no cambium, so no secondary growth. Examples: Nephrolepis (fern), Selaginella, Lycopodium, Equisetum (xerophytic), Azolla and Marsilea (aquatic).
• Gymnosperms: naked seeds; mostly evergreen woody plants; tracheids and sieve cells; cambium present so secondary growth occurs. Coralloid roots of Cycas hold blue-green algae; Pinus roots have mycorrhiza. Ginkgo biloba is a living fossil; Sequoia sempervirens is the tallest living plant; Zamia pygmaea the smallest gymnosperm.
• Angiosperms: seeds enclosed in fruit (ovary); flowers; heterosporous; gametophytes reduced and inside the sporophyte; double fertilization.
• Monocots: one cotyledon, adventitious roots, parallel venation, trimerous flowers, closed vascular bundles, no secondary growth (Zea mays, Sorghum).
• Dicots: two cotyledons, tap root, reticulate venation, tetra- or pentamerous flowers, open vascular bundles with cambium, secondary growth (sunflower, China rose).
• Alternation of generations: diploid sporophyte (2n) → meiosis → spores (n) → gametophyte (n) → gametes → fertilization → zygote (2n) → sporophyte.

Important terms

• Thallus – plant body not differentiated into root, stem and leaves.
• Rhizoids – root-like structures (unicellular in liverworts, multicellular in mosses).
• Protonema – green, branched, filamentous juvenile gametophyte of mosses.
• Heterosporous – producing two kinds of spores (microspores and megaspores).
• Haplontic – only the zygote is diploid; e.g. some algae and fungi.
• Diplontic – only gametes are haploid; e.g. animals.
• Haplo-diplontic – both haploid and diploid multicellular phases; e.g. land plants, many algae.

Key facts

5 important questions

Q1. Why are bryophytes called amphibians of the plant kingdom?

They live on land (in moist, shady places) but cannot complete their life cycle without water, because the sperms need water to swim to the egg for fertilization.

Q2. Fern is a vascular plant, yet it is not a phanerogam. Why?

Phanerogams are seed-producing plants. Ferns have vascular tissue but reproduce by spores and never form seeds or flowers, so they belong to Cryptogamae (vascular cryptogams).

Q3. The girth of a maize plant does not increase over time. Justify.

Maize is a monocot. Its vascular bundles are closed (no cambium between xylem and phloem), so secondary growth does not take place and the stem does not thicken.

Q4. Distinguish between Bryophyta and Pteridophyta.

Bryophyta: no vascular tissue; gametophyte dominant and independent; sporophyte dependent; rhizoids instead of roots. Pteridophyta: vascular tissue present; sporophyte dominant and independent with true roots, stem and leaves; gametophyte small and short-lived.

Q5. Radha saw a plant on the school wall in the rainy season with root-like structures but no true roots. Which group is it?

Bryophyta (a moss such as Funaria): it grows in moist places in the rainy season and has rhizoids instead of true roots.

Exam tip

Draw Spirogyra, Chlamydomonas, Funaria, Nephrolepis and the life-cycle diagrams neatly — diagram questions are common in this chapter.

Quick summary

Kingdom Animalia includes multicellular, eukaryotic, heterotrophic organisms without cell walls. Animals are classified using grade of organization, body plan, symmetry, germ layers, body cavity (coelom), segmentation and notochord. This chapter describes the non-chordate phyla from Porifera to Hemichordata and Phylum Chordata with its subphyla and vertebrate classes.

Key points

• Criteria: grade of organization (cellular, tissue, organ, organ-system); body plan (cell aggregate in sponges, blind-sac in cnidarians and flatworms, tube-within-tube from Aschelminthes/Annelida onwards); symmetry (asymmetrical, radial, bilateral); germ layers (diploblastic, triploblastic); body cavity (acoelomate, pseudocoelomate, coelomate); segmentation.
• Porifera (sponges): pores called ostia, water exits by osculum, canal system, choanocytes (collar cells), spicules or spongin fibres; e.g. Sycon, Euspongia, Euplectella.
• Cnidaria: radial, diploblastic, blind-sac; cnidoblasts (stinging cells); polyp and medusa forms; metagenesis in Obelia; e.g. Hydra, Aurelia, Physalia, Adamsia.
• Ctenophora (comb jellies, minor phylum): marine; 8 rows of ciliated comb plates; bioluminescence; colloblasts instead of cnidoblasts; e.g. Pleurobrachia.
• Platyhelminthes (flatworms): dorso-ventrally flat, acoelomate, triploblastic; flame cells; hermaphrodite; hooks and suckers in parasites; e.g. Planaria, Taenia, Fasciola.
• Aschelminthes (roundworms): pseudocoelomate, cylindrical, tough cuticle, complete gut, sexes separate with sexual dimorphism; e.g. Ascaris, Wuchereria, Ancylostoma.
• Annelida: metameric segmentation, true coelom, closed circulation, nephridia, setae/parapodia/suckers, clitellum; e.g. Pheretima, Nereis, Hirudinaria.
• Arthropoda (largest phylum): jointed appendages, chitinous exoskeleton (moulting), open circulation (haemocoel); gills, trachea, book lungs; Malpighian tubules; e.g. cockroach, prawn, scorpion; Limulus is a living fossil.
• Mollusca (second largest): soft body with head, foot and visceral mass, mantle secreting shell, radula, ctenidia, haemocyanin; e.g. Pila, Sepia, Octopus, Pinctada.
• Echinodermata: marine, spiny skin, pentamerous radial symmetry in adults, calcareous ossicles, water vascular system with tube feet; no excretory system; e.g. Asterias, Echinus, Antedon.
• Hemichordata: worm-like marine animals with proboscis, collar and trunk; e.g. Balanoglossus.
• Chordata: notochord, dorsal hollow nerve cord and pharyngeal gill slits at some stage. Subphyla: Urochordata (Herdmania), Cephalochordata (Amphioxus) — together protochordates — and Vertebrata.
• Vertebrate classes: Cyclostomata (jawless, Petromyzon), Chondrichthyes (cartilaginous fish, Scoliodon), Osteichthyes (bony fish, Labeo rohita, Catla), Amphibia (Rana), Reptilia (Crocodylus has a nearly four-chambered heart), Aves (feathers, hollow pneumatic bones, beak without teeth), Mammalia (hair, mammary glands, pinna, diaphragm).

Important terms

• Coelom – body cavity lined by mesoderm.
• Metameric segmentation – body divided into similar repeated segments internally and externally.
• Metagenesis – alternation of polyp (asexual) and medusa (sexual) generations.
• Ecdysis – moulting of the exoskeleton for growth.
• Parthenogenesis – development of an egg without fertilization (honey bee drones).
• Venous heart – a heart that pumps only deoxygenated blood (fish, e.g. Rohu).

Key facts

5 important questions

Q1. Which phylum first shows closed circulation?

Annelida (e.g. earthworm) — blood flows in closed vessels.

Q2. Crab and snail both have a protective covering. Is it of the same material?

No. A crab (arthropod) has a chitinous exoskeleton. A snail (mollusc) has a calcareous shell (calcium carbonate) secreted by the mantle.

Q3. Sponge and sea star both have calcareous material. Do they belong to the same phylum?

No. Sponges (Porifera) have calcareous spicules and a canal system; sea stars (Echinodermata) have calcareous ossicles as endoskeleton and a water vascular system.

Q4. How does the skeleton of birds help reduce weight?

Bird bones are hollow and pneumatic (filled with air spaces), teeth are absent and some bones are fused, making the body light for flight.

Q5. Write three basic features of Phylum Chordata.

(1) A notochord along the dorsal side at some stage of life. (2) A dorsal, hollow, tubular nerve cord. (3) Paired pharyngeal gill slits at some stage. Heart is ventral.

Exam tip

Learn one example of every phylum and class with its scientific name, and draw Sycon, Aurelia, Amphioxus and Scoliodon labelled.

Quick summary

The cell is the structural and functional unit of life. This chapter covers cell theory, cell size, prokaryotic and eukaryotic cells, plant and animal cells, and the structure and function of each component — cell wall, plasma membrane (fluid mosaic model), ER, Golgi complex, lysosomes, vacuoles, microbodies, mitochondria, plastids, ribosomes, cytoskeleton, cilia, flagella, centrioles and the nucleus.

Key points

• The term cell was first used by Robert Hooke (1665). Cell theory was proposed by Schleiden and Schwann. Rudolf Virchow (1855) added that new cells form only from pre-existing cells (Omnis cellula e cellula).
• Smallest cell: Mycoplasma (0.3 µm); bacteria 3–5 µm; largest: ostrich egg (about 15 cm); longest: nerve cells.
• Prokaryotic cell: no nuclear membrane (nucleoid), no membrane-bound organelles, 70S ribosomes, often plasmids (bacteria, cyanobacteria). Eukaryotic cell: true nucleus, membrane-bound organelles, 80S ribosomes in cytoplasm.
• Plant cells have a cell wall, plastids and a large central vacuole; animal cells have centrioles and small vacuoles, no cell wall.
• Cell wall: middle lamella (calcium pectate) → primary wall → secondary wall; plasmodesmata connect neighbouring cells. The wall grows in surface by intussusception and in thickness by apposition.
• Plasma membrane: lipids, proteins and some carbohydrates. Fluid mosaic model (Singer and Nicolson, 1972): a fluid phospholipid bilayer with proteins floating in it (peripheral and integral). It replaced the Danielli–Davson sandwich model. It is selectively permeable.
• Endoplasmic reticulum: rough ER (with ribosomes, protein synthesis) and smooth ER (lipid and steroid synthesis, detoxification).
• Golgi complex (Camillo Golgi): cisternae that modify, package and secrete proteins; forms lysosomes and the cell plate.
• Lysosomes ("suicide bags"): hydrolytic enzymes for intracellular digestion and autophagy.
• Microbodies: sphaerosomes (lipid storage, half-unit membrane), peroxisomes (make and break H₂O₂, detoxify alcohol in liver), glyoxysomes (convert fats to sugar in germinating seeds).
• Mitochondria: double membrane, inner one folded into cristae; site of aerobic respiration and ATP production — "power house of the cell"; have their own circular DNA and 70S ribosomes (semi-autonomous).
• Plastids: chloroplasts (green, photosynthesis; grana of thylakoids in stroma), chromoplasts (coloured pigments), leucoplasts (storage: amyloplasts – starch, elaioplasts – oil, aleuroplasts – protein).
• Nucleus: double nuclear envelope with pores, nucleoplasm, chromatin and nucleolus (not membrane-bound; makes ribosomal RNA).
• Cilia and flagella have a 9 + 2 arrangement of microtubules; centrioles and basal bodies have a 9 + 0 (9 triplets) arrangement.

Important terms

• Protoplasm – living matter of the cell (cytoplasm + nucleus).
• Plasmodesmata – cytoplasmic channels through cell walls that join adjacent plant cells.
• Cristae – folds of the inner mitochondrial membrane.
• Thylakoids / grana – flat sacs in chloroplasts / stacks of thylakoids.
• Cytoskeleton – network of microtubules (tubulin), microfilaments (actin) and intermediate filaments that gives shape and helps movement.
• Tonoplast – membrane around the vacuole.

Key facts

5 important questions

Q1. Why did the fluid mosaic model replace the sandwich model?

The sandwich model showed a fixed protein–lipid–protein layer. Later studies showed that the lipid bilayer is fluid and proteins are scattered, some embedded across it and able to move sideways. The fluid mosaic model of Singer and Nicolson explains this fluidity and the role of membrane proteins.

Q2. Distinguish between smooth and rough ER.

Rough ER has ribosomes on its surface, is made of cisternae and helps in protein synthesis. Smooth ER has no ribosomes, is mostly tubular and helps in lipid, steroid synthesis and detoxification.

Q3. Mitochondria are called the power house of the cell. Give reason.

Aerobic respiration (Krebs cycle and electron transport) takes place in mitochondria, releasing energy stored as ATP, which the cell uses for all its activities.

Q4. Which organelles contain DNA? Why are they called semi-autonomous?

Mitochondria and chloroplasts. They have their own circular DNA and 70S ribosomes, so they can make some of their own proteins and divide on their own, but still depend on the nucleus for most proteins.

Q5. Onion cells have no chloroplasts. How can we tell they are plant cells?

They have a cellulose cell wall and a large central vacuole, and no centrioles — features of plant cells.

Exam tip

Draw and label plant cell, animal cell, mitochondrion, chloroplast and fluid mosaic model — at least one such diagram comes every year.

Quick summary

Living things are built from a few elements (mainly C, H, O, N, P, S) that form biomolecules. This chapter covers carbohydrates, lipids, proteins and nucleic acids (DNA and RNA) — their building blocks, bonds, types and roles — then enzymes (properties, mechanism, factors, classification), the metabolic pool and secondary metabolites.

Key points

• Micromolecules (sugars, amino acids, fatty acids, nucleotides) join to form macromolecules (polysaccharides, proteins, nucleic acids), which are polymers.
• Carbohydrates (Cₓ(H₂O)ᵧ): monosaccharides (glucose, fructose, ribose), disaccharides (sucrose, maltose, lactose) and polysaccharides (starch, glycogen, cellulose, chitin). Monosaccharides join by glycosidic bonds.
• Polysaccharides: homopolysaccharides (one type of monomer: starch, glycogen, cellulose) and heteropolysaccharides (more than one: chitin derivatives, hyaluronic acid). Starch has amylose (unbranched) and amylopectin (branched).
• Reducing sugars have a free aldehyde or ketone group and reduce Benedict's/Fehling's solution (glucose, maltose); sucrose is non-reducing.
• Lipids: simple lipids (fats and oils = triglycerides of glycerol + 3 fatty acids, waxes), compound lipids (phospholipids in cell membranes, glycolipids), derived lipids (steroids like cholesterol). Saturated fatty acids have no double bonds (palmitic, stearic); unsaturated have C=C (oleic, linoleic). Linoleic, linolenic and arachidonic acids are essential fatty acids.
• Proteins: polymers of about 20 amino acids joined by peptide bonds (–CO–NH–). Structure levels: primary (sequence), secondary (α-helix, β-pleated sheet by hydrogen bonds), tertiary (3D folding) and quaternary (more than one polypeptide, e.g. haemoglobin).
• Protein types: simple (albumin, globulin), conjugated (haemoglobin, glycoproteins) and derived. Roles: collagen (connective tissue), actin and myosin (muscle contraction), immunoglobulins (antibodies), haemoglobin (O₂ transport), fibrinogen (clotting), enzymes and hormones (insulin).
• Nucleic acids: polymers of nucleotides (sugar + phosphate + nitrogen base). Purines: adenine, guanine; pyrimidines: cytosine, thymine (DNA), uracil (RNA).
• DNA (Watson and Crick, 1953): double helix, antiparallel strands, A=T (2 hydrogen bonds), G≡C (3), deoxyribose sugar. RNA: single strand, ribose, uracil; types mRNA, tRNA (clover-leaf, carries amino acids) and rRNA (part of ribosomes, the most abundant).
• Enzymes are biocatalysts, mostly proteins; specific, work at optimum temperature and pH, required in small amounts. Holoenzyme = apoenzyme (protein) + cofactor (metal ion, coenzyme or prosthetic group).
• Mechanism: lock and key model (Emil Fischer) and induced fit model (Koshland) — the active site changes shape to fit the substrate.
• Factors: enzyme concentration, substrate concentration, temperature and pH.
• Enzyme classes: oxidoreductases, transferases, hydrolases, lyases, isomerases and ligases.
• Metabolic pool: the common pool of intermediates from catabolism and anabolism; lets one type of molecule be converted to another (carbohydrates ⇌ fats).
• Secondary metabolites (alkaloids, pigments, rubber, essential oils, antibiotics) are not needed for basic life but are very useful to humans.

Important terms

• Glycosidic bond – bond between two monosaccharides (also sugar–base bond in nucleosides).
• Peptide bond – amide bond formed between –COOH of one amino acid and –NH₂ of the next, releasing water.
• Nucleoside – sugar + nitrogen base; nucleotide = nucleoside + phosphate.
• Active site – region of the enzyme where the substrate binds.
• Km (Michaelis constant) – substrate concentration at which the reaction rate is half of maximum velocity.
• Denaturation – loss of the 3D shape (and activity) of a protein by heat or pH.

Formulas

• Glucose: C₆H₁₂O₆ ; sucrose = glucose + fructose ; maltose = glucose + glucose ; lactose = glucose + galactose
• Chargaff's rule (DNA): A = T, G = C, so (A + G) = (T + C)
• Km = [S] at which v = Vmax/2. Low Km → high affinity of enzyme for substrate.

5 important questions

Q1. Explain the peptide bond.

It is an amide (–CO–NH–) bond formed when the carboxyl group of one amino acid reacts with the amino group of another, removing one water molecule (condensation). Many peptide bonds form a polypeptide chain.

Q2. What is a reducing sugar?

A sugar with a free aldehyde (–CHO) or ketone (C=O) group that can reduce Cu²⁺ in Benedict's or Fehling's solution to red Cu₂O. Examples: glucose, fructose, maltose. Sucrose is non-reducing.

Q3. Distinguish between saturated and unsaturated fatty acids.

Saturated: only single C–C bonds, solid at room temperature (palmitic, stearic acid; animal fats). Unsaturated: one or more C=C double bonds, liquid at room temperature (oleic, linoleic acid; vegetable oils).

Q4. Explain the induced fit model of enzyme action.

Proposed by Koshland. The active site is flexible, not rigid. When the substrate binds, the active site changes shape to fit it closely, forming an enzyme–substrate complex. After products form and are released, the enzyme returns to its original shape.

Q5. What is RNA? List its types.

RNA is a single-stranded nucleic acid with ribose sugar and bases A, G, C and U. Types: mRNA (carries genetic message to ribosomes), tRNA (brings amino acids; clover-leaf shape) and rRNA (structural part of ribosomes, 50–60 % of ribosome).

Exam tip

Learn the protein-function chart (collagen, actin/myosin, IgG, haemoglobin, fibrinogen) and the graphs of enzyme activity against temperature, pH and substrate.

Quick summary

All multicellular organisms grow from a single cell, the zygote, by cell division. This chapter explains the cell cycle (interphase and M-phase), the three types of cell division — amitosis, mitosis and meiosis — their stages and significance, and how cell division is controlled.

Key points

• Cell cycle = interphase + M-phase. Interphase is the longest phase: G1 (8 hours or more; RNA, protein and membrane synthesis), S (6–8 hours; DNA replication and histone synthesis, so DNA per cell doubles) and G2 (2–5 hours; proteins for division made; in animal cells a new pair of centrioles appears). Mitosis takes 1–3 hours.
• Cells that stop dividing enter the G0 (quiescent) phase, e.g. nerve cells.
• M-phase has karyokinesis (division of nucleus) and cytokinesis (division of cytoplasm).
• Amitosis: simplest division; the nucleus elongates, constricts and divides without spindle or disappearance of the nuclear membrane, e.g. Paramoecium, bacteria-like simple cells.
• Prophase – chromatin condenses into chromosomes with two chromatids; nucleolus and nuclear membrane disappear; spindle starts forming.
• Metaphase – chromosomes line up at the equator (metaphase plate); spindle fibres attach to centromeres (kinetochores). Chromosomes are clearest now.
• Anaphase – centromeres split; sister chromatids move to opposite poles.
• Telophase – two groups of chromosomes at the poles; nuclear membrane and nucleolus reappear.
• Mitosis (equational division) has four stages:
• Cytokinesis: by furrowing (constriction) in animal cells; by cell plate formation in plant cells.
• Mitosis keeps the chromosome number constant; it helps growth, repair of wounds, replacement of cells and asexual reproduction.
• Meiosis (term by J. B. Farmer, 1905; reductional division) occurs in meiocytes and gives four haploid cells. Meiosis I is reductional; Meiosis II is like mitosis. The gap between them is interkinesis.
• Prophase I has five sub-stages: leptotene (chromosomes condense), zygotene (synapsis – pairing of homologous chromosomes into bivalents), pachytene (crossing over between non-sister chromatids), diplotene (homologues separate except at chiasmata) and diakinesis (terminalisation of chiasmata, nuclear membrane disappears).
• In anaphase I, homologous chromosomes separate (centromeres do not split); in anaphase II, sister chromatids separate.
• Meiosis keeps the chromosome number constant from generation to generation (n + n = 2n) and creates variation by crossing over and independent assortment.
• Cell cycle is controlled by proteins like cyclins and cyclin-dependent kinases (CDKs). Loss of this control leads to uncontrolled division — cancer.

Important terms

• Chromatid – one of the two identical halves of a replicated chromosome joined at the centromere.
• Bivalent (tetrad) – a pair of synapsed homologous chromosomes (four chromatids).
• Chiasma – X-shaped point where crossing over has taken place.
• Crossing over – exchange of segments between non-sister chromatids of homologous chromosomes.
• Synaptonemal complex – protein structure that holds homologues together during synapsis.
• Interkinesis – short gap between meiosis I and meiosis II (no DNA replication).

Key facts

5 important questions

Q1. How many meiotic divisions are needed to form 80 sperms?

One meiosis forms 4 sperms. So 80 ÷ 4 = 20 meiotic divisions.

Q2. In an onion root tip slide, a cell shows two groups of chromosomes at opposite ends. Which phase is it?

Late anaphase / telophase of mitosis — the chromatids have moved to opposite poles (telophase if they have reached the poles and are uncoiling).

Q3. Paramoecium divided without disappearance of nuclear membrane and without spindle. Is it cell division?

Yes. It is amitosis (direct division): the nucleus elongates, constricts and splits into two, followed by division of cytoplasm. No spindle forms and the nuclear membrane stays intact.

Q4. Give the significance of meiosis.

(1) It forms haploid gametes or spores. (2) It keeps the chromosome number constant across generations; without it the number would double every generation. (3) Crossing over and random assortment create genetic variation, which helps evolution.

Q5. What happens during the S-phase?

DNA is replicated, so the amount of DNA per cell doubles (each chromosome now has two chromatids). Histone proteins are also made in this phase.

Exam tip

Practise labelled diagrams of all four stages of mitosis and the five stages of prophase I with one key event for each.

Quick summary

A tissue is a group of cells with common origin, structure and function. This chapter covers meristematic and permanent plant tissues (simple and complex), the three tissue systems, types of vascular bundles, the internal structure (anatomy) of dicot and monocot root, stem and leaf, and secondary growth with wood formation.

Key points

• Meristematic tissue: small, living, thin-walled, actively dividing cells with dense cytoplasm and large nucleus, no intercellular spaces.
• By position, meristems are of three types: apical (tips of root and shoot; growth in length), intercalary (at bases of internodes/leaves, e.g. grasses) and lateral (vascular cambium and cork cambium; growth in thickness).
• Simple permanent tissues: parenchyma (living, thin-walled, storage; chlorenchyma when it has chloroplasts, aerenchyma with air spaces), collenchyma (living, cellulose and pectin thickening at corners; mechanical support to young stems and petioles) and sclerenchyma (dead, lignified thick walls; fibres and sclereids/stone cells; main mechanical tissue).
• Complex permanent tissues: xylem (tracheids, vessels, xylem fibres, xylem parenchyma; conducts water and minerals; only xylem parenchyma is living) and phloem (sieve tubes, companion cells, phloem parenchyma, phloem fibres; conducts food). Sieve tubes have sieve plates; companion cell nucleus controls the sieve tube.
• Three tissue systems: epidermal (epidermis, cuticle, stomata with guard cells and subsidiary cells, trichomes, root hairs), ground (cortex, endodermis, pericycle, pith, mesophyll) and vascular (vascular bundles).
• Vascular bundles: radial (xylem and phloem on different radii – roots), conjoint collateral (open with cambium in dicot stems; closed in monocot stems), bicollateral (phloem on both sides of xylem – Cucurbitaceae) and concentric (hadrocentric – xylem surrounded by phloem, as in ferns; leptocentric – phloem surrounded by xylem).
• Dicot root: epiblema with root hairs, cortex, endodermis with casparian strips, pericycle, radial bundles with exarch xylem, 2–6 xylem bundles (usually 4), small or no pith.
• Monocot root: similar but many (more than 6) xylem bundles and a large pith; no secondary growth.
• Dicot stem (sunflower): epidermis with multicellular trichomes and cuticle; cortex (hypodermis of collenchyma, parenchyma, endodermis/starch sheath); vascular bundles in a ring, conjoint collateral open, endarch; pith present.
• Monocot stem (maize): sclerenchymatous hypodermis; many scattered closed vascular bundles with bundle sheath in ground tissue; no pith or cambium. Some monocots (Dracaena, Agave, palms) show anomalous secondary growth.
• Dorsiventral leaf (dicots): mesophyll differentiated into palisade (upper) and spongy (lower) parenchyma; more stomata on the lower surface. Isobilateral leaf (monocots): both surfaces alike, stomata on both sides, mesophyll not differentiated.
• Secondary growth in dicot stems: vascular cambium (intrafascicular + interfascicular) forms secondary xylem inside and secondary phloem outside; cork cambium (phellogen) forms cork (phellem) outside and secondary cortex (phelloderm) inside — together the periderm.
• Spring (early) wood is light, wide, low density; autumn (late) wood is dark, narrow, dense. One spring + one autumn band = one annual ring, which helps to find the age of a tree. Heartwood (duramen) is inner, dark, non-functional and durable (tyloses, resins, gums); sapwood (alburnum) is outer and conducts water.

Important terms

• Tissue – group of cells with common origin, structure and function.
• Casparian strip – band of suberin on radial walls of endodermis cells.
• Exarch / endarch – protoxylem towards the periphery (roots) / towards the centre (stems).
• Periderm – cork + cork cambium + secondary cortex.
• Tyloses – ingrowths of parenchyma that plug vessels of heartwood.

Key facts

5 important questions

Q1. Why do trees in Kashmir show distinct annual rings, but not in Maharashtra?

Kashmir has clear seasons — a favourable spring and a harsh winter — so cambium forms light spring wood and dark autumn wood alternately, giving distinct rings. In Maharashtra the climate is fairly uniform, so the two kinds of wood are not clearly different.

Q2. Distinguish between collenchyma and sclerenchyma.

Collenchyma: living cells, thickened at corners with cellulose and pectin, gives flexible support to young organs. Sclerenchyma: dead cells, uniformly thick walls with lignin, gives rigid mechanical strength (fibres, sclereids).

Q3. A section shows scattered vascular bundles. The teacher says it is a fern rachis, not a monocot stem. Why?

In a monocot stem, bundles are conjoint collateral and closed (xylem and phloem side by side). In a fern rachis the bundles are concentric (hadrocentric) — xylem in the centre surrounded by phloem.

Q4. Why does a wooden stopper not rot for many years?

It is made of heartwood. Its vessels are plugged by tyloses and filled with resins, gums, oils and tannins, which make it durable and resistant to microbes.

Q5. Many stomata were seen on the upper surface of a leaf section. The teacher said the slide was placed correctly. Explain.

The leaf was an isobilateral (monocot) leaf, such as maize or grass, which has stomata on both surfaces.

Exam tip

Draw T.S. of dicot root, dicot stem and monocot stem side by side and learn the differences in a table.

Quick summary

Morphology is the study of the external form and structure of plants. This chapter describes the root, stem and leaf of angiosperms and their modifications, phyllotaxy and venation, inflorescence, the parts of a flower, fruits and seeds, and two important families — Fabaceae (pea) and Solanaceae (Datura).

Key points

• A flowering plant has a root system (below ground, positively geotropic) and a shoot system (stem, leaves, flowers, fruits).
• Regions of root: root cap, region of cell division (meristematic), region of elongation and region of maturation (bears root hairs).
• Tap root develops from the radicle (dicots); adventitious roots arise from any part other than the radicle (monocots).
• Modified tap roots for storage: fusiform (radish), conical (carrot), napiform (beet, turnip). Respiratory roots (pneumatophores) grow upward in mangroves like Rhizophora and are seen at low tide.
• Modified adventitious roots: fasciculated tuberous (Dahlia, Asparagus), prop roots (banyan), stilt roots (maize, sugarcane — from lower nodes for extra support), climbing roots (betel), epiphytic roots with velamen (orchids — not parasites), sucking roots/haustoria (Cuscuta), nodulose, moniliform.
• Underground stem modifications: rhizome (ginger), tuber (potato, with eyes), bulb (onion, garlic — we eat the fleshy scale leaves), corm (Colocasia, Amorphophallus).
• Sub-aerial stems: runner (grass), stolon (strawberry), sucker (Chrysanthemum, banana), offset (Pistia, Eichhornia).
• Aerial stem modifications: thorn (Bougainvillea, Carissa), stem tendril (grapes), phylloclade (Opuntia — flat green stem; leaves reduced to spines), cladode (Asparagus), bulbils.
• Leaf = leaf base, petiole and lamina. Venation is reticulate (dicots) or parallel (monocots). Leaves are simple or compound (pinnate, palmate).
• Leaf modifications: spines (Opuntia), tendrils (pea), hooks (Bignonia), phyllode (Australian Acacia — flattened petiole).
• Phyllotaxy: alternate, opposite (decussate or superposed) and whorled.
• Inflorescence: racemose (main axis grows indefinitely, flowers acropetal — raceme, spike, catkin, umbel, head) and cymose (main axis ends in a flower, basipetal — solitary cyme as in Hibiscus).
• Flower parts: calyx (sepals), corolla (petals), androecium (stamens) and gynoecium (carpels). Sepals and petals not distinguishable = perianth (tepals).
• Position of ovary: hypogynous (superior ovary — mustard, China rose), perigynous (half-inferior — rose, plum), epigynous (inferior ovary — sunflower, guava).
• Aestivation: valvate, twisted (contorted), imbricate, vexillary (pea). Placentation: marginal (pea), axile (tomato), parietal, free central, basal.
• Fruit develops from the ovary after fertilization; pericarp = epicarp, mesocarp, endocarp (mango is a drupe). Apple is a false fruit (thalamus becomes fleshy).
• Fabaceae (pea): root nodules, pinnately compound leaves with tendrils, racemose raceme, zygomorphic flowers, vexillary aestivation (vexillum, 2 wings, keel), diadelphous stamens (9) + 1, monocarpellary superior ovary, marginal placentation, legume fruit. Floral formula: % K(5) C1+2+(2) A(9)+1 G1.
• Solanaceae (Datura): simple leaves, solitary cymose flowers, actinomorphic, persistent gamosepalous calyx, gamopetalous contorted corolla, 5 epipetalous stamens, bicarpellary syncarpous superior ovary with axile placentation on swollen placenta, berry or capsule. Floral formula: ⊕ K(5) C(5) A5 G(2).

Important terms

• Phyllotaxy – arrangement of leaves on the stem.
• Inflorescence – arrangement of flowers on the floral axis.
• Aestivation – arrangement of sepals or petals in a flower bud.
• Placentation – arrangement of ovules on the placenta inside the ovary.
• Perennation – survival through unfavourable seasons using stored food (underground stems, roots).
• Thorn vs spine – a thorn is a modified stem/branch (Carissa); a spine is a modified leaf (Opuntia).

Key facts

5 important questions

Q1. Opuntia has spines but Carissa has thorns. What is the difference?

Spines of Opuntia are modified leaves (reduce water loss). Thorns of Carissa are modified axillary branches (stems), hard and pointed, arising from the axil of leaves.

Q2. Beet and Arum both store food. Are they the same type?

No. Beet is a modified (napiform) tap root, while Arum (Colocasia) is an underground stem — a corm.

Q3. Hibiscus is described as a solitary cyme. What does this mean?

A single flower terminates the main axis (cymose growth), and only one flower is produced in the axil or at the tip — so it is a solitary cymose inflorescence.

Q4. Many plants in marshy regions had upward-growing roots seen at low tide. What are they?

Respiratory roots (pneumatophores) of mangroves such as Rhizophora. They have small pores (lenticels) that help in gaseous exchange because the marshy soil lacks oxygen.

Q5. Write the floral characters of Fabaceae.

Zygomorphic, bisexual flowers; calyx of 5 fused sepals; corolla papilionaceous with vexillary aestivation; 10 stamens, diadelphous (9) + 1; monocarpellary, unilocular superior ovary with marginal placentation; fruit legume. Floral formula: % K(5) C1+2+(2) A(9)+1 G1.

Exam tip

Make a chart of root, stem and leaf modifications with one example each — "identify and explain" questions use these examples.

Quick summary

Histology is the study of tissues. Animal tissues are of four basic types — epithelial, connective, muscular and nervous. This chapter explains the structure, location and functions of each, including types of epithelia, cell junctions, glands, connective tissues (areolar, adipose, dense, cartilage, bone, blood), three kinds of muscle and the structure of a neuron.

Key points

• Marie François Xavier Bichat is called the "Father of Histology".
• Epithelial tissue covers body surfaces and lines cavities; cells are closely packed on a basement membrane with little matrix and no blood vessels.
• Simple epithelia: squamous (flat cells; walls of blood vessels, alveoli), cuboidal (kidney tubules, glands), columnar (inner lining of stomach and intestine; may have microvilli), ciliated (trachea, fallopian tube), glandular and sensory (retina, taste buds).
• Compound (stratified) epithelium has many layers and protects against wear and tear — skin (keratinised), buccal cavity, oesophagus, vagina.
• Glands: exocrine (with ducts — salivary, sweat, sebaceous), endocrine (ductless, secrete hormones into blood — thyroid, pituitary, adrenal). Pancreas is both.
• Cell junctions: tight junctions (prevent leakage, keep polarity), adherens junctions, desmosomes (mechanical strength), hemidesmosomes (anchor cells to basement membrane via integrins) and gap junctions (exchange of ions and small molecules).
• Connective tissue is the most widely spread; it has cells and fibres in abundant matrix. Loose: areolar (fibroblasts, macrophages, mast cells; white collagen and yellow elastic fibres — under skin) and adipose (fat cells; insulation, shock absorption, energy store — white and brown adipose).
• Dense connective tissue: tendons (muscle to bone, white fibres) and ligaments (bone to bone, elastic).
• Cartilage: matrix chondrin, cells chondrocytes in lacunae, covered by perichondrium. Types: hyaline (ends of long bones, trachea), elastic (ear pinna, epiglottis — flexible), white fibrous (between vertebrae), calcified.
• Bone: hard matrix of ossein with calcium salts; compact bone has Haversian systems (canal with artery, vein, nerve; lamellae; osteocytes in lacunae; canaliculi); spongy bone has trabeculae and no Haversian system.
• Blood is a fluid connective tissue: plasma + RBCs, WBCs and platelets.
• Muscle tissue: skeletal (striated, voluntary, multinucleate unbranched fibres – syncytium), smooth (non-striated, involuntary, spindle-shaped, one central nucleus — walls of gut, blood vessels, iris), cardiac (striated, involuntary, branched, with intercalated discs).
• Nervous tissue: neurons (structural and functional unit) and neuroglia (supporting cells that can divide). Neurons cannot regenerate as they lack centrioles.
• A multipolar neuron has a cyton (cell body with Nissl's granules), many dendrites and one long axon covered by myelin sheath with nodes of Ranvier, ending in synaptic knobs.

Important terms

• Tissue – group of similar cells with the same origin and function.
• Basement membrane – thin non-cellular layer below epithelium.
• Matrix – intercellular substance of connective tissue.
• Syncytium – a multinucleate cell formed by fusion of cells (skeletal muscle fibre).
• Intercalated disc – thickened junctions between cardiac muscle cells for quick impulse spread.
• Myelin sheath – fatty insulating covering of axons.

Key facts

5 important questions

Q1. What enables the ear pinna to be folded and twisted while the nose tip cannot?

The pinna is supported by elastic cartilage, which has many yellow elastic fibres in its matrix, making it flexible. The nose tip has hyaline cartilage, which is less flexible.

Q2. Why do animals of cold regions have a fat layer below the skin?

Adipose tissue is a poor conductor of heat. It insulates the body and reduces heat loss, and stored fat is a reserve source of energy.

Q3. Supriya's pupils shrank when she stepped into bright light. Which muscle is responsible?

Smooth (involuntary, non-striated) muscles of the iris — the circular muscles contract and make the pupil smaller.

Q4. Distinguish between smooth and skeletal muscles.

Smooth: spindle-shaped, unbranched, uninucleate, no striations, involuntary, in walls of internal organs. Skeletal: long cylindrical, multinucleate, striated, voluntary, attached to bones, tire quickly.

Q5. Identify the tissue: inner lining of intestine, heart wall, skin, inner lining of buccal cavity.

Inner lining of intestine – simple columnar epithelium; heart wall – cardiac muscle; skin – stratified (keratinised) squamous epithelium; buccal cavity – stratified (non-keratinised) squamous epithelium.

Exam tip

Draw the multipolar neuron, areolar tissue and Haversian system with labels — these diagrams are asked often.

Quick summary

The cockroach (Periplaneta americana) is a common insect studied as a model of Phylum Arthropoda. This chapter covers its habitat, systematic position, external features, body cavity, and the digestive, respiratory, circulatory, excretory, nervous and reproductive systems, along with its sense organs and life history.

Key points

• Cockroaches live in warm, dark, moist places; they are omnivorous, nocturnal and cursorial (fast runners). Common Indian species: Periplaneta americana, Blatta orientalis, Blatta germanica.
• Systematic position: Kingdom Animalia → Phylum Arthropoda → Class Insecta → Genus Periplaneta → Species americana.
• Exoskeleton of chitin (a nitrogenous polysaccharide); each segment has a dorsal tergum, ventral sternum and two lateral pleura (sclerites).
• Body = head, thorax (prothorax, mesothorax, metathorax) and abdomen (10 segments). Three pairs of jointed legs and two pairs of wings (forewings = tegmina, leathery; hindwings membranous, used for flight).
• Head has a pair of filiform antennae, a pair of compound eyes made of many ommatidia (giving mosaic vision) and chewing and biting mouthparts (labrum, mandibles, maxillae, labium, hypopharynx).
• Abdomen bears a pair of anal cerci (sensory) in both sexes; males also have a pair of anal styles on the 9th sternum — used to tell male from female.
• Digestive system: foregut (pharynx, oesophagus, crop for storage, gizzard with six chitinous teeth for grinding), midgut (stomach/mesenteron with 6–8 hepatic caecae for digestion and absorption), hindgut (ileum, colon, rectum). Salivary glands open at the base of the hypopharynx.
• Respiratory system: 10 pairs of spiracles (2 thoracic, 8 abdominal) lead into a network of tracheae and tracheoles, which carry air directly to tissues. Blood does not carry gases.
• Circulatory system: open type. Colourless haemolymph (no respiratory pigment) fills the haemocoel. The tubular heart has 13 chambers (3 thoracic, 10 abdominal) with ostia.
• Excretory system: about 150 yellow Malpighian tubules at the junction of midgut and hindgut remove nitrogenous wastes as uric acid (uricotelic). Fat bodies, nephrocytes, urecose glands and cuticle also help.
• Nervous system: ventral, solid and ganglionated. Supra-oesophageal (cerebral) ganglia act as the brain; nerve ring and ventral nerve cord with ganglia.
• Sexes are separate. Male: testes in 4th–6th segments, mushroom-shaped (utricular) gland, phallomeres. Female: ovaries, spermatheca, collaterial glands.
• Fertilization is internal. Collaterial gland secretion forms the ootheca (egg case, about 8 mm, 14–16 eggs). A female produces 9–10 oothecae.
• Development is paurometabolous — through nymph stages that look like small adults and moult several times.

Important terms

• Haemocoel – body cavity filled with blood (haemolymph) due to open circulation.
• Ommatidium – structural and functional unit of the compound eye.
• Mosaic vision – image made of many small parts, one from each ommatidium; sensitive to movement but less clear.
• Ootheca – dark reddish-brown egg case of the cockroach.
• Nymph – young stage that resembles the adult but is smaller, wingless and sexually immature.
• Tegmina – thick, leathery forewings that protect the hindwings.

Key facts

5 important questions

Q1. How will you identify a male and a female cockroach?

Male: abdomen long and narrow, 9 visible terga, has anal styles on the 9th sternum; wings extend beyond abdomen. Female: abdomen broad, 7 visible terga, no anal styles; brood pouch formed by 7th sternum.

Q2. Write a note on the gizzard of cockroach.

The gizzard (proventriculus) is a small, rounded, thick-walled muscular organ at the end of the foregut. It has six chitinous teeth that crush food and backward bristles that filter it, so only fine particles pass into the midgut.

Q3. What would happen if a cockroach had no gizzard?

Food would not be ground into fine particles. Large food pieces would enter the midgut, digestion and absorption would be slow and poor, and the gut could be damaged.

Q4. Give the functional difference between the respiratory systems of cockroach and human.

In cockroach, air enters spiracles and tracheae carry oxygen directly to tissues; blood does not carry gases. In humans, lungs exchange gases and blood (haemoglobin) carries oxygen to tissues.

Q5. What is ootheca?

A dark reddish to blackish brown capsule about 8 mm long formed by secretion of collaterial glands in the female. It holds 14–16 fertilized eggs in two rows and is glued to a humid, safe surface near food.

Exam tip

Learn the diagrams of digestive system, mouthparts and the life history — and the numbers: 13 heart chambers, 10 pairs of spiracles, about 150 Malpighian tubules.

Quick summary

Photosynthesis is the process by which green plants use light energy, CO₂ and water to make carbohydrates and release oxygen. This chapter covers chloroplast structure, pigments and light, absorption and action spectra, the light reaction (photophosphorylation), the dark reaction (Calvin cycle, C₃ pathway), photorespiration, C₄ pathway and Kranz anatomy, CAM plants, and factors affecting photosynthesis.

Key points

• Overall equation: 6CO₂ + 12H₂O → (light, chlorophyll) → C₆H₁₂O₆ + 6H₂O + 6O₂.
• Van Niel proposed (from sulphur bacteria) that O₂ comes from water; Ruben (1941) proved it in Chlorella using H₂¹⁸O.
• Chloroplast: double membrane; stroma (site of dark reaction) and thylakoids stacked as grana (site of light reaction).
• Pigments: chlorophyll a (main pigment), chlorophyll b, carotenes and xanthophylls (accessory pigments). Chlorophyll has a porphyrin head (with Mg) and a phytol tail.
• Absorption spectrum: chlorophyll absorbs mostly blue and red light. Action spectrum: rate of photosynthesis is highest in blue and red regions.
• Photosystems: PS I (reaction centre P700) and PS II (P680) with light-harvesting complexes.
• Light reaction (in thylakoids): photo-excitation of chlorophyll, photolysis of water (2H₂O → 4H⁺ + 4e⁻ + O₂, at PS II), electron transport and formation of ATP and NADPH₂ (assimilatory power).
• Cyclic photophosphorylation: only PS I; electrons return to P700; makes only ATP; no O₂ or NADPH₂.
• Non-cyclic photophosphorylation (Z-scheme): PS II and PS I; water is split, O₂ released, ATP and NADPH₂ formed.
• ATP is made by chemiosmosis: H⁺ gradient across the thylakoid membrane drives ATP synthase.
• Dark reaction / Calvin cycle (C₃ pathway) in stroma: carboxylation (RuBP + CO₂ → 2 molecules of 3-PGA, by RuBisCO), reduction (to glyceraldehyde-3-phosphate using ATP and NADPH₂) and regeneration of RuBP. First stable product: 3-PGA (3C).
• To fix one CO₂: 3 ATP + 2 NADPH₂. For one glucose (6 CO₂): 18 ATP + 12 NADPH₂.
• Photorespiration (C₃ plants, in light, high O₂): RuBisCO acts as oxygenase forming phosphoglycolate; involves chloroplast, peroxisome and mitochondrion; wastes fixed carbon and energy.
• C₄ (Hatch–Slack) pathway (sugarcane, maize, sorghum): CO₂ first fixed by PEP carboxylase in mesophyll cells into OAA (4C); then released in bundle sheath cells for the Calvin cycle. Kranz anatomy: bundle sheath cells with large chloroplasts around vascular bundles. No photorespiration; more efficient in hot, dry conditions.
• CAM (Crassulacean Acid Metabolism; Bryophyllum, pineapple, Opuntia): stomata open at night; CO₂ stored as malic acid; used in the day — saves water.
• Factors: light intensity, CO₂ concentration, temperature, water. Blackman's law of limiting factors: rate is controlled by the factor in shortest supply.

Important terms

• Photophosphorylation – formation of ATP from ADP and Pi using light energy.
• Assimilatory power – ATP and NADPH₂ produced in the light reaction.
• Reaction centre – special chlorophyll a (P680 or P700) that passes electrons to acceptors.
• RuBisCO – ribulose-1,5-bisphosphate carboxylase-oxygenase, the most abundant enzyme on earth.
• Kranz anatomy – wreath-like arrangement of bundle sheath cells in C₄ leaves.

Formulas

• 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂
• Photolysis: 2H₂O → 4H⁺ + 4e⁻ + O₂
• Calvin cycle per CO₂: 3 ATP + 2 NADPH₂ ; per glucose: 18 ATP + 12 NADPH₂

Key facts

5 important questions

Q1. Distinguish between cyclic and non-cyclic photophosphorylation.

Cyclic: only PS I, electrons return to P700, only ATP formed, no photolysis, no O₂, no NADPH₂. Non-cyclic: PS II and PS I, electrons from water reach NADP, photolysis of water, O₂ evolved, both ATP and NADPH₂ formed.

Q2. Distinguish between absorption spectrum and action spectrum.

Absorption spectrum shows how much light of each wavelength a pigment absorbs. Action spectrum shows the rate of photosynthesis at each wavelength. Both peak in blue and red, showing chlorophyll absorbs the light used for photosynthesis.

Q3. Explain photorespiration. Why is it wasteful?

In C₃ plants at high O₂ and temperature, RuBisCO adds O₂ to RuBP instead of CO₂, forming phosphoglycolate (2C) and PGA. Glycolate is processed in peroxisomes and mitochondria, releasing CO₂. No ATP or sugar is formed, so fixed carbon and energy are lost.

Q4. How many ATP and NADPH₂ are needed to make one glucose in the Calvin cycle?

Six turns of the cycle fix 6 CO₂: 6 × 3 = 18 ATP and 6 × 2 = 12 NADPH₂.

Q5. Why are C₄ plants more efficient than C₃ plants?

PEP carboxylase has high affinity for CO₂ and does not react with O₂. CO₂ is concentrated in bundle sheath cells, so RuBisCO works as carboxylase and photorespiration is almost absent. They photosynthesise well even at high temperature, strong light and low CO₂.

Exam tip

Practise the Z-scheme, Calvin cycle flow chart and C₄ pathway diagram — they carry 3–4 marks each.

Quick summary

Respiration is the stepwise oxidation of food (mainly glucose) inside cells to release energy, stored as ATP. This chapter explains ATP as the energy currency, anaerobic respiration (glycolysis and fermentation), aerobic respiration (glycolysis, link reaction, Krebs cycle, electron transport system), the ATP balance sheet, respiratory quotient and significance of respiration.

Key points

• Respiration is a catabolic process; energy is released in small steps and trapped in ATP (adenosine triphosphate), the "energy currency" of the cell.
• The most common respiratory substrate is glucose; fats and proteins can also be used.
• Glycolysis (EMP pathway): glucose (6C) → 2 pyruvic acid (3C) in the cytoplasm, in 10 steps (preparatory and pay-off phases). Net gain: 2 ATP + 2 NADH+H⁺. It is common to aerobic and anaerobic respiration.
• Anaerobic respiration / fermentation (no O₂): in yeast, pyruvate → ethyl alcohol + CO₂ (alcoholic fermentation); in muscles during heavy exercise, pyruvate → lactic acid (causes fatigue). Only 2 ATP per glucose.
• Link reaction (oxidative decarboxylation) in the mitochondrial matrix: pyruvate + coenzyme A → acetyl CoA (2C) + CO₂ + NADH+H⁺.
• Krebs cycle (TCA / citric acid cycle, Hans Krebs) in the mitochondrial matrix: acetyl CoA + oxaloacetic acid (4C) → citric acid (6C) → … → oxaloacetic acid. Per acetyl CoA: 2 CO₂, 3 NADH+H⁺, 1 FADH₂ and 1 GTP/ATP (substrate-level phosphorylation at succinyl CoA → succinate).
• Electron transport system (ETS) on the inner mitochondrial membrane (cristae): electrons from NADH and FADH₂ pass through carriers (cytochromes) to oxygen, the terminal electron acceptor, forming water. Energy released makes ATP by oxidative phosphorylation through F₀–F₁ particles (ATP synthase).
• Each NADH+H⁺ gives 3 ATP and each FADH₂ gives 2 ATP (as counted in the textbook).
• Total ATP per glucose in aerobic respiration = 38 (34 from ETS). In eukaryotes the net is often given as 36, as 2 ATP are used to move glycolytic NADH into mitochondria.
• Glycolysis, Krebs cycle and ETS are linked: pyruvate from glycolysis becomes acetyl CoA for the Krebs cycle, and NADH/FADH₂ from both feed the ETS.
• Red muscle fibres (many mitochondria, myoglobin) do sustained aerobic work; white fibres depend on glycolysis and tire quickly.
• Respiratory quotient (RQ) = volume of CO₂ released ÷ volume of O₂ consumed. Carbohydrates 1; fats about 0.7; proteins about 0.9; anaerobic respiration — infinity.
• Krebs cycle intermediates are used to make amino acids, fatty acids and other molecules, so it is an amphibolic pathway.

Important terms

• Respiratory substrate – organic compound oxidised in respiration (glucose, fats, proteins).
• Substrate-level phosphorylation – ATP made directly from a high-energy substrate, not through ETS.
• Oxidative phosphorylation – ATP made using energy of electron transport, with O₂ as final acceptor.
• Fermentation – incomplete breakdown of glucose without oxygen into alcohol or lactic acid.
• Chemiosmosis – ATP synthesis driven by a proton gradient across a membrane.

Formulas

• Aerobic: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (38 ATP)
• Alcoholic fermentation: C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + 2 ATP
• Lactic acid fermentation: C₆H₁₂O₆ → 2CH₃CHOHCOOH + 2 ATP
• RQ = volume of CO₂ evolved ÷ volume of O₂ consumed

5 important questions

Q1. What is RQ? What is its value for fats?

RQ is the ratio of the volume of CO₂ given out to the volume of O₂ taken in during respiration. For fats it is about 0.7, because fats need more oxygen for oxidation than the CO₂ they release.

Q2. Which is the terminal electron acceptor in aerobic respiration? What happens if it is absent?

Molecular oxygen. It accepts electrons and H⁺ to form water. Without O₂, ETS stops, NADH cannot be reoxidised, the Krebs cycle stops and the cell switches to fermentation, giving only 2 ATP per glucose.

Q3. Write a note on glycolysis.

Glycolysis is the breakdown of one glucose into two pyruvic acid molecules in the cytoplasm through 10 enzyme steps. In the preparatory phase 2 ATP are used; in the pay-off phase 4 ATP and 2 NADH+H⁺ are formed. Net gain: 2 ATP and 2 NADH+H⁺. It needs no oxygen.

Q4. What is the advantage of stepwise energy release in respiration?

If all energy were released at once it would be lost as heat and could damage the cell. Releasing it in small steps allows it to be trapped efficiently as ATP and lets intermediates be used for other syntheses.

Q5. How would you show that yeast respires both aerobically and anaerobically?

Keep yeast in sugar solution in two flasks — one aerated, one sealed with an oil layer. Both give out CO₂ (turns lime water milky). Only the sealed flask smells of alcohol, showing anaerobic respiration; the aerated flask grows faster due to aerobic respiration.

Exam tip

Learn the ATP balance sheet table and the Krebs cycle flow chart with the number of carbons at each step.

Quick summary

Nutrition is the process of taking in food and using it for energy, growth and repair. This chapter describes the human digestive system — alimentary canal, teeth, histology of the gut wall and digestive glands (salivary glands, liver, pancreas) — the process of digestion and absorption, hormonal regulation of digestive juices, and common nutritional and digestive disorders.

Key points

• Alimentary canal: mouth → buccal cavity → pharynx → oesophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine (caecum, colon, rectum) → anus.
• Teeth: human dentition is thecodont (each tooth in a separate socket of the jaw bone), diphyodont (two sets — milk and permanent teeth) and heterodont (four types: incisors, canines, premolars, molars). Adult dental formula = I 2/2, C 1/1, PM 2/2, M 3/3 = 32 teeth. Molars are the most numerous.
• A tooth has a crown, neck and root; enamel (hardest substance in the body), dentine, pulp cavity with nerves and blood vessels; fixed by gomphosis joint.
• Tongue helps in taste, mixing saliva, swallowing (and speech). Three pairs of salivary glands: parotid, submandibular, sublingual.
• Stomach regions: cardiac, fundic, body and pyloric. Gastric glands have chief cells (pepsinogen), oxyntic/parietal cells (HCl, intrinsic factor) and mucous cells.
• Gut wall layers (outer to inner): serosa, muscularis (longitudinal + circular), submucosa, mucosa.
• Small intestine mucosa forms villi with microvilli (brush border) to increase absorption area; villi contain capillaries and lacteals (lymph vessels). Brunner's glands in submucosa of duodenum.
• Liver: largest gland; two lobes covered by Glisson's capsule; hepatic lobules; Kupffer cells destroy toxins and worn-out cells; secretes bile (no enzyme; emulsifies fats), stored in the gall bladder. Alcohol damages liver cells (fatty liver, cirrhosis).
• Pancreas is heterocrine: acinar cells secrete pancreatic juice (exocrine); islets of Langerhans secrete insulin and glucagon (endocrine).
• Digestion: salivary amylase (ptyalin) — starch → maltose (pH about 6.8); pepsin — proteins → peptones (acidic, pH about 2); trypsin (activated by enterokinase) and chymotrypsin — proteins → peptides; pancreatic amylase and lipase; intestinal enzymes (maltase, sucrase, lactase, dipeptidases, nucleotidases, lipase) complete digestion. Pepsin stops working in the alkaline small intestine.
• Absorption: glucose and amino acids into blood capillaries; fatty acids and glycerol into lacteals; water mostly in the large intestine.
• Regulation by nerves and hormones: gastrin stimulates gastric juice; secretin and cholecystokinin (CCK) stimulate pancreatic juice and bile (CCK also gives a feeling of fullness); GIP inhibits gastric secretion.
• Disorders: Protein Energy Malnutrition (PEM) — kwashiorkor (protein deficiency, children 1–3 years) and marasmus (protein and calorie deficiency, infants); jaundice (bile pigments in blood, yellow skin and eyes), vomiting, diarrhoea, constipation, indigestion.

Important terms

• Peristalsis – wave-like muscular contractions that push food along the gut.
• Chyme – semi-liquid acidic food leaving the stomach.
• Emulsification – breaking fat into tiny droplets by bile salts.
• Lacteal – lymph vessel in a villus that absorbs fats.
• Heterocrine gland – a gland that is both exocrine and endocrine (pancreas).

Key facts

5 important questions

Q1. Why is human dentition called thecodont, diphyodont and heterodont?

Thecodont: each tooth sits in a separate socket in the jaw. Diphyodont: we get two sets of teeth in life — milk teeth and permanent teeth. Heterodont: teeth are of four different kinds — incisors, canines, premolars and molars — for different jobs.

Q2. For an athletic meet, Shriya was advised Glucon-D or fruit juice but not sugarcane juice. Why?

Glucose (Glucon-D) and fruit juice (glucose, fructose) are monosaccharides absorbed directly into blood, giving quick energy. Sugarcane juice has sucrose, which must first be digested by sucrase, so energy comes more slowly.

Q3. Digestive action of pepsin stops when food reaches the small intestine. Justify.

Pepsin works only in the acidic medium of the stomach (about pH 2). In the duodenum, bile and pancreatic juice make the medium alkaline, so pepsin becomes inactive.

Q4. Explain the heterocrine nature of the pancreas.

Exocrine part: acinar cells secrete pancreatic juice with trypsinogen, amylase and lipase into the duodenum through the pancreatic duct. Endocrine part: islets of Langerhans secrete hormones insulin (β cells) and glucagon (α cells) directly into blood.

Q5. Alcoholic people may suffer from liver disorders. Do you agree?

Yes. The liver detoxifies alcohol. Regular heavy drinking damages liver cells, causing fat deposits (fatty liver), inflammation and scarring (cirrhosis), which reduce bile production and other liver functions.

Exam tip

Learn the enzyme table and the diagrams of tooth (L.S.), T.S. of gut wall and digestive system.

Quick summary

Excretion is the removal of nitrogenous and other metabolic wastes from the body; osmoregulation is the control of water and salt balance. This chapter covers types of nitrogenous waste, excretory organs in different animals, the human excretory system and nephron, urine formation and concentration, hormonal regulation (ADH, RAAS), the role of other organs, and kidney disorders with dialysis and transplant.

Key points

• Ammonotelic animals excrete ammonia — highly toxic, very soluble, needs a lot of water but little energy (bony fishes, tadpoles, aquatic invertebrates, protozoa).
• Ureotelic animals excrete urea — less toxic, made in the liver by the ornithine (urea) cycle (Krebs and Henseleit, 1932) using 3 ATP per urea (mammals, adult frogs, marine fishes). Sharks keep urea in blood to stay isotonic with sea water.
• Uricotelic animals excrete uric acid — least toxic, almost insoluble, saves water but costs the most energy (birds, many reptiles, insects, land snails). In humans, uric acid comes from nucleic acid (purine) metabolism.
• Excretory organs in invertebrates: flame cells (Platyhelminthes), nephridia (earthworm), Malpighian tubules (insects), green glands (prawn).
• Human excretory system: two kidneys, two ureters, urinary bladder and urethra. Kidneys also secrete renin, erythropoietin (for RBC production) and calcitriol.
• Kidney: outer cortex, inner medulla with renal pyramids; columns of Bertini; minor and major calyces collect urine into the renal pelvis.
• Nephron (about one million per kidney) = Malpighian body (Bowman's capsule + glomerulus) + renal tubule (PCT, Henle's loop, DCT) opening into a collecting duct. The inner (visceral) layer of Bowman's capsule has podocytes; PCT is lined by cuboidal cells with a brush border.
• Ultrafiltration in the glomerulus — blood pressure forces water and small solutes into Bowman's capsule, giving deproteinised plasma (glomerular filtrate).
• Selective reabsorption — mainly in PCT: all glucose and amino acids, most Na⁺ and water are taken back into peritubular capillaries.
• Tubular secretion — H⁺, K⁺, creatinine and drugs are added to the filtrate (in PCT and DCT).
• Urine formation in three steps:
• Concentration of urine: Henle's loop works as a counter-current mechanism with the vasa recta, creating a high salt concentration in the medulla. The descending limb is permeable to water; the ascending limb to salts, not water — so filtrate becomes hypotonic in the ascending limb.
• ADH (from posterior pituitary, triggered by osmoreceptors in the hypothalamus) increases water reabsorption in DCT and collecting duct, making urine concentrated (higher specific gravity). Lack of ADH causes diabetes insipidus.
• RAAS: when blood pressure/volume falls, JGA releases renin → angiotensin → aldosterone, which increases Na⁺ and water reabsorption.
• Urine is pale yellow due to urochrome. Micturition is the act of passing urine.
• Other excretory organs: lungs (CO₂), skin (sweat, sebum), liver (bile pigments, urea formation).
• Disorders: kidney stones (urolithiasis; calcium oxalate — avoid tomatoes, spinach), uremia (blood urea above 0.05 %), nephritis, renal failure. Treatment: haemodialysis, peritoneal dialysis, kidney transplant.

Important terms

• Osmoregulation – maintaining balance of water and salts in body fluids.
• Glomerular filtrate – deproteinised plasma collected in Bowman's capsule.
• Counter-current mechanism – opposite flow in the two limbs of Henle's loop and vasa recta that builds medullary concentration.
• Juxtaglomerular apparatus (JGA) – cells near the glomerulus that release renin.
• Dialysis – artificial removal of wastes from blood when kidneys fail.

Key facts

5 important questions

Q1. Which organism spends maximum energy in producing nitrogenous waste — polar bear, flamingo, frog or shark?

Flamingo. Birds are uricotelic, and making uric acid needs the most energy (though it saves the most water).

Q2. Describe the three steps of urine formation.

Ultrafiltration: blood pressure in the glomerulus filters water and small solutes into Bowman's capsule. Selective reabsorption: useful substances (glucose, amino acids, Na⁺, water) are taken back, mostly in PCT. Tubular secretion: wastes like H⁺, K⁺ and creatinine are actively added to the tubule. The remaining fluid is urine.

Q3. How does ADH regulate urine concentration?

When blood becomes concentrated (sweating, salty food), osmoreceptors in the hypothalamus cause the posterior pituitary to release ADH. ADH makes DCT and collecting duct walls permeable to water, so more water is reabsorbed and a small volume of concentrated urine forms.

Q4. A person with kidney stones is advised not to eat tomatoes. Why?

Tomatoes contain oxalic acid. Oxalate combines with calcium to form calcium oxalate crystals, the most common type of kidney stone.

Q5. What is haemodialysis?

When kidneys fail, the patient's blood is passed through a dialyser (artificial kidney) with a semi-permeable membrane bathed in dialysate. Urea and other wastes diffuse out into the dialysate, and the cleaned blood is returned to the body.

Exam tip

Draw a labelled nephron with blood supply and the L.S. of kidney — almost every paper has one of them.

Quick summary

Movement is a basic feature of living beings, and locomotion is movement from one place to another. This chapter covers types of movement, structure of skeletal muscle and the sliding filament theory of contraction, properties of muscles, the human skeleton (axial and appendicular, 206 bones), types of joints, and common disorders of muscles and bones.

Key points

• Types of movement: amoeboid (pseudopodia — leucocytes), ciliary (cilia — ciliated epithelium, Paramecium), flagellar/whiplash (sperms) and muscular (limbs, jaws, tongue).
• Skeletal muscle is attached to bones by tendons; it is made of bundles (fascicles) of muscle fibres. Each fibre has many myofibrils with alternating dark (A) and light (I) bands.
• The sarcomere (between two Z-lines) is the functional unit of contraction. Thick filaments = myosin; thin filaments = actin with tropomyosin and troponin.
• Sliding filament theory (H. E. Huxley and A. F. Huxley): a nerve impulse at the neuromuscular junction releases acetylcholine → action potential → Ca²⁺ released from the sarcoplasmic reticulum → Ca²⁺ binds troponin, exposing active sites on actin → myosin heads (using ATP) form cross bridges and pull actin towards the centre → sarcomere shortens. I-band and H-zone shorten; A-band stays the same.
• Relaxation: Ca²⁺ is pumped back, active sites are covered again, filaments slide back.
• Muscle properties: single twitch (latent, contraction, relaxation periods), summation, tetanus (sustained contraction from rapid stimuli), refractory period (about 0.02 s), threshold stimulus and all-or-none principle.
• Oxygen debt / fatigue: in heavy exercise muscles work anaerobically and accumulate lactic acid, causing tiredness and cramps; extra oxygen is used during recovery.
• Antagonistic muscle pairs: flexor–extensor, abductor–adductor, levator–depressor, sphincter–dilator (e.g. biceps and triceps).
• Adult human skeleton: 206 bones — axial (80: skull 29 including ear ossicles and hyoid, vertebral column 26, sternum 1, ribs 24) and appendicular (126: girdles and limbs).
• Vertebral column: 7 cervical (1st atlas, 2nd axis), 12 thoracic, 5 lumbar, sacrum (5 fused) and coccyx (4 fused) = 26 bones in adults. Ribs: 7 pairs true, 3 pairs false, 2 pairs floating.
• Newborns have six soft spots (fontanelles) between cranial bones, which later close.
• Joints: fibrous (immovable — sutures of skull, gomphosis of teeth, syndesmosis), cartilaginous (slightly movable — between vertebrae, pubic symphysis) and synovial (freely movable, with synovial fluid): ball and socket (shoulder, hip), hinge (elbow, knee), pivot (atlas–axis), gliding (carpals), saddle (thumb carpometacarpal), condyloid (wrist).
• Disorders: muscular dystrophy, myasthenia gravis (autoimmune, neuromuscular junction), arthritis (osteoarthritis, gout — uric acid crystals in joints, rheumatoid arthritis), osteoporosis (porous, brittle bones; common in older women; linked to low calcium and hormones; also caused by excess parathormone).

Important terms

• Sarcomere – part of myofibril between two Z-lines; unit of contraction.
• Sarcolemma / sarcoplasm – membrane / cytoplasm of a muscle fibre.
• Cross bridge – link formed when a myosin head attaches to actin.
• Tetanus – continuous contraction due to rapid repeated stimuli.
• Ligament / tendon – joins bone to bone / muscle to bone.
• Synovial fluid – lubricating fluid in the cavity of a freely movable joint.

Key facts

5 important questions

Q1. What is the role of calcium in muscle contraction?

Ca²⁺ released from the sarcoplasmic reticulum binds to troponin. This changes its shape and moves tropomyosin, exposing the active sites on actin, so myosin heads can form cross bridges and contraction begins.

Q2. A person breaks his ankle bone. Which bones are involved?

Tarsals (the ankle bones), possibly along with the lower ends of tibia and fibula.

Q3. Why does muscle fatigue occur?

During strenuous exercise, oxygen supply is not enough, so muscles respire anaerobically and lactic acid accumulates. Lactic acid gives less ATP and is toxic, causing tiredness, pain and cramps.

Q4. Raju trains his biceps with dumbbells. Which joints move and which stay still?

The elbow (hinge) joint should move as the biceps bends the forearm. The shoulder and wrist joints should remain stationary so that only the biceps does the work.

Q5. A passer-by tied a wooden plank to Moses' fractured leg. Why?

The plank acts as a splint. It keeps the broken bone ends still, prevents further damage to muscles, nerves and blood vessels, reduces pain and helps correct healing.

Exam tip

Draw and label a sarcomere and explain sliding filament theory step by step; learn one example of each type of synovial joint.