Zoology — Last-Minute Revision
30 must-know Zoology points covering all 8 units. Read this the night before or morning of your TGBIE exam.
Biodiversity: genetic (allelic variation within species), species (different species in an area), ecosystem (variety of habitats).
IUCN Red List categories: Extinct → Extinct in Wild → Critically Endangered → Endangered → Vulnerable → Near Threatened → Least Concern.
Levels of organisation in animals: cellular → tissue → organ → organ system → organism.
Coelom: true coelom lined by mesoderm (annelids, chordates); pseudocoelom not lined (nematodes); acoelomate = no coelom (flatworms).
Porifera: no true tissues, spongocoel (central cavity), choanocytes (collar cells), canal system — ascon, sycon, leucon.
Cnidaria: cnidocytes (stinging cells), radially symmetrical, diploblastic, polymorphic (polyp + medusa).
Platyhelminthes (flatworms): acoelomate, bilaterally symmetrical, triploblastic. Include tapeworms and liver flukes (parasites).
Annelida: segmented worms, setae for locomotion, closed circulatory system. Earthworm = Pheretima posthuma.
Arthropoda: largest phylum, jointed appendages, chitinous exoskeleton, open circulatory system, compound eyes.
Chordates have: notochord, pharyngeal gill slits, dorsal hollow nerve cord, post-anal tail — at SOME stage of their life.
Cyclostomata: jawless vertebrates (lamprey, hagfish), lack scales, ecto-parasites. Only living agnathans.
Chondrichthyes (sharks): cartilaginous endoskeleton, placoid scales, spiracle. Osteichthyes (bony fish): bony endoskeleton, cycloid/ctenoid scales, operculum.
Amphibia: dual life (water + land), moist skin for cutaneous respiration, gills in tadpole → lungs in adult, ectothermic.
Reptilia: dry scaly skin, amniotic egg (no need for water), ectothermic. Extinct (dinosaurs) and living (lizards, snakes, crocodiles).
Aves (birds): feathers (modified scales), hollow bones for flight, 4-chambered heart, warm-blooded (endothermic).
Mammalia: hair/fur, mammary glands, 3 middle ear ossicles, warm-blooded, live young (except monotremes).
Paramecium locomotion: cilia beat in coordinated waves (metachronal rhythm). Euglena locomotion: flagellum rotates.
Binary fission: transverse in Paramecium (two daughter cells side by side); longitudinal in Euglena (flagella split).
Plasmodium: sporozoite infects liver first (exo-erythrocytic cycle), then RBCs (erythrocytic cycle = fever). Female Anopheles is vector.
Ascaris: white roundworm. Eggs in soil → human ingests → larvae migrate via blood to lungs → coughed up → swallowed → adult in intestine.
Periplaneta — digestive: crop = storage, gizzard = grinding, gastric caeca = enzyme secretion, Malpighian tubules = excretion.
Periplaneta — nervous: supra-oesophageal ganglion = brain. Connected to sub-oesophageal ganglion by circumoesophageal connectives.
Ommatidium: structural unit of compound eye. Corneal lens + crystalline cone + rhabdom + 8 retinal cells + pigment cells.
Ecosystem: abiotic (light, temperature, water, soil) + biotic (producers, consumers, decomposers).
Food chain: Producer → Primary Consumer → Secondary Consumer → Tertiary Consumer → Decomposer. Energy lost at each level (~90%).
Pyramid of energy: always upright (energy always decreases from lower to higher trophic levels).
Carbon cycle: photosynthesis removes CO₂; respiration, combustion, decomposition release CO₂.
Nitrogen fixation: Rhizobium (symbiotic in legumes), Azotobacter (free-living). Denitrification: Pseudomonas returns N₂ to atmosphere.
Population growth: biotic potential (rmax) in unlimited resources → J-curve; with limiting factors → S-curve (logistic growth).
Ozone depletion: CFCs release Cl• radicals that catalytically destroy O₃. Each Cl• can destroy thousands of O₃ molecules.