KH

From Invertebrates to Vertebrates & Biological Classification

Amphibians

  • Cold-blooded vertebrates that must stay near water because reproduction and egg-laying occur in aquatic environments.

  • Life cycle of a frog illustrates amphibian metamorphosis:

    • Egg → hatchling (tadpole) lives like a fish, swims with fins and breathes through gills.

    • Gradual transformation:

    • Gills and fins are replaced by lungs and legs.

    • Enables juveniles/young frogs to crawl onto dry land.

  • Skin is moist (lacks scales); loses water easily, so adults generally remain in damp habitats.

  • Examples referenced: frogs, toads, salamanders (implicit from “amphibians”).

Reptiles

  • Evolved ≈50 million years after amphibians; ushered in the “Age of Reptiles.”

  • Cold-blooded vertebrates adapted to much drier environments than amphibians.

  • Key adaptations:

    • Shelled, hardened eggs laid on land; eggshell prevents embryo and nutrients from desiccating.

    • Dry, scaly, waterproof skin (scales retain body moisture and give some protection).

  • Dominated Mesozoic Era; included dinosaurs and many giant species.

  • Modern reptile descendants: snakes, turtles, tortoises, lizards, iguanas, geckos, skinks, crocodiles, alligators, gavials, mambas, taipans, anacondas, cobras, vipers, basilisk, anapsids, Doswellia, Hylonomus, etc.

Reptiles vs. Amphibians (Summary)

  • Habitat of eggs:

    • Amphibians: always water.

    • Reptiles: always land.

  • Skin type:

    • Amphibians: moist, smooth, permeable.

    • Reptiles: dry, scaly, waterproof.

  • Development:

    • Amphibians: larvae with gills → metamorphosis.

    • Reptiles: miniature adults hatch directly from egg.

Frog Life-Cycle Detail (Pages 7–8)

  • Stages (aquatic ➜ terrestrial):

    1. Egg cell / embryo surrounded by jelly.

    2. Newly hatched tadpole with external gills and tail; lives on stored yolk/tail nutrients.

    3. External gills disappear; hind legs appear; tail continues growing.

    4. Front legs form; tail starts shrinking.

    5. Young frog with lungs; tail nearly gone; leaves water.

    6. Adult frog capable of reproduction on land yet returns to water to lay eggs.

Transition to Warm-Blooded Vertebrates

  • End of Age of Reptiles (~65 million y ago) marked by a mass extinction (one of six in Earth history); dinosaurs vanished.

    • Hypothesized cause: comet/asteroid impact → rapid climate change + food-web collapse.

  • Two new warm-blooded groups evolved before/during the transition:

    • Mammals

    • Birds

Mammals

  • Endothermic (produce internal heat), maintain steady body temperature.

  • Body covering: hair/fur (insulation).

  • Reproduction:

    • Internal fertilisation.

    • Embryos develop internally (placental nourishment).

    • Young nourished after birth by milk from mammary glands.

    • Do not lay eggs (exceptions monotremes not discussed in transcript).

  • Survived extinction and flourished → “Age of Mammals.”

  • Familiar examples: cats, dogs, cattle, bats, humans, rabbits, horses.

Birds

  • Warm-blooded, feather-covered for insulation and flight efficiency.

  • Close reptile relatives; still lay hard-shelled eggs on land.

Cold-Blooded vs Warm-Blooded Summary

  • Cold-blooded (ectothermic): body temperature varies with environment (fish, amphibians, reptiles).

  • Warm-blooded (endothermic): regulate internal temperature via metabolism (birds, mammals).

  • Advantage for warm-blooded animals: tolerate seasonal/rapid temperature changes.

Mass Extinctions (Page 14)

  • “Extinction” defined: every individual of a species dies out.

  • Six major extinction events recorded; Age of Reptiles ended ≈65 Ma.

Classification of Animals (Linnaean System)

  • “Classification” = science of grouping organisms by similarity.

  • Carolus Linnaeus introduced binomial nomenclature (genus + species) and hierarchical ranks.

    • Example: human = Homo sapiens.

  • Modern taxonomy incorporates evolutionary relationships (phylogeny).

Major Animal Divisions (Pages 11–12)

  • Invertebrates: no backbone (e.g., porifera, cnidaria, annelida, mollusca, arthropoda, echinodermata, etc.)

  • Vertebrates (phylum Chordata): fish, amphibians, reptiles, birds, mammals.

  • Temperature relation breakdown:

    • Cold-blooded: fish, amphibians, reptiles.

    • Warm-blooded: birds, mammals.

Taxonomic Ranks (general ➜ specific)

  • Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species.

  • As you move downward:

    • Characteristics become \text{more specific}.

    • Number of organisms per level \text{decreases}.

Human Example (multiple pages 20–23)

  • Domain: Eukaryota

  • Kingdom: Animalia

  • Phylum: Chordata

  • Class: Mammalia

  • Order: Primates

  • Family: Hominidae

  • Genus: Homo

  • Species: sapiens

Bear Example (Page 24–25)

  • Kingdom: Animalia

  • Phylum: Chordata

  • Class: Mammalia

  • Order: Carnivora

  • Family: Ursidae

  • Genus: Ursus

    • Species examples: Ursus arctos (brown/Kodiak bear), Ursus maritimus (polar bear), Ursus americanus (black bear).

Evolutionary Overview (Pages 26–28)

  • Evolution = change in genetic composition of a population over successive generations.

  • Hominin lineage progression (diagram):

    • Australopithecus afarensis → Homo habilis → Homo erectus → Homo neanderthalensis → Homo sapiens.

Producers vs Consumers & Energy Flow

  • All life requires energy + organic matter.

  • Producers (autotrophs):

    • Convert inorganic materials + external energy (sunlight) into organic matter (food).

    • Examples: green plants, algae, some bacteria.

  • Consumers (heterotrophs):

    • Obtain energy/matter by eating other organisms.

    • Include all animals, fungi, many protists, some bacteria.

Photosynthesis (Pages 37–40)

  • Occurs only in cells with chlorophyll (green pigment in chloroplasts).

  • Equation:
    6CO2 + 6H2O \xrightarrow{\text{light}} C6H{12}O6 + 6O2

  • Steps:

    • Chlorophyll captures solar energy.

    • Energy drives conversion of atmospheric CO2 and soil H2O into glucose.

    • O_2 released to atmosphere.

  • Partnership cycle: autotrophs release O2; heterotrophs inhale O2 & exhale CO_2 which plants reuse.

Organic vs Inorganic Matter (Pages 41–44)

  • Organic matter: carbon-based molecules with C–H bonds (carbohydrates, proteins, lipids, nucleic acids). Originates from living organisms; vital for nutrient cycling & soil fertility.

  • Inorganic matter: lacks C–H bonds; includes minerals, metals, salts, gases, water, rocks. Often resultant of non-biological processes.

  • Illustrative examples (Page 43):

    • Organic compounds: fats, proteins, carbohydrates.

    • Inorganic compounds: water, salt, elemental carbon, oxygen.

Sample Exercise Highlights (Pages 29–33)

  • Reptile scales advantage: prevent water loss from skin (answer B).

  • Rabbits & horses share same kingdom, phylum, class (answer A).

  • Scientific name Icterus galbula (Baltimore oriole) contains genus + species (answer a).

  • Fill-in-the-blank key terms (Page 32) correspond to: (a) mammals, (b) order, (c) reptiles, (d) vertebrates, (e) amphibians, (f) Age of Mammals, (g) fossil record.

Ethical / Practical Implications Mentioned

  • Warm-blooded adaptations (hair, feathers) enable survival amid climate fluctuation, illustrating evolutionary solutions to environmental stress.

  • Mass extinction events demonstrate fragility of ecosystems and inform modern conservation efforts.