Principle: Homology indicates common ancestry; analogy indicates convergent evolution.

Materials: Charts/specimens of forelimbs of vertebrates (homologous) and wings of insects/birds (analogous).

Homologous Organs:

Definition: Organs with similar basic structure and embryonic origin but perform different functions.
Example: Forelimbs of whale, bat, cheetah, human (all have humerus, radius, ulna, carpals, metacarpals, phalanges).
Indicates: Divergent evolution from a common ancestor.

Analogous Organs:

Definition: Organs with different basic structure and embryonic origin but perform similar functions.
Example: Wings of insect and wings of bird (insect wing is chitinous membrane, bird wing is bony skeleton covered with feathers).
Indicates: Convergent evolution due to similar environmental pressures.

Aim: To identify morphological adaptations in organisms.
Principle: Organisms develop specific features to survive in their habitats.
Materials: Specimens/charts of xerophytes (e.g., Opuntia, Acacia), hydrophytes (e.g., Hydrilla, Eichhornia), animals (e.g., fish, frog, camel, bird).
Xerophytes (Dry Habitats):
- Leaves: Reduced, spines (Opuntia), leathery, sunken stomata (Nerium), thick cuticle.
- Stem: Fleshy, flattened (phylloclade in Opuntia), green (photosynthetic).
- Roots: Extensive.
- Example: Opuntia, Acacia, Nerium.
Hydrophytes (Aquatic Habitats):
- Submerged: Finely dissected leaves, no stomata, poor vascular tissue (Hydrilla).
- Floating: Large, broad leaves (water lily), air-filled petioles (Eichhornia), stomata on upper surface.
- Roots: Poorly developed or absent.
- Example: Hydrilla, Eichhornia, Lotus.
Animal Adaptations:
- Fish (Aquatic): Streamlined body, gills for respiration, fins for movement, scales.
- Frog (Amphibian): Webbed feet, moist skin, camouflage, hibernation/aestivation.
- Camel (Desert): Hump for fat storage, thick fur, broad padded feet, ability to conserve water.
- Bird (Aerial): Streamlined body, hollow bones, wings, feathers.

Aim: To identify developmental stages from permanent slides.
Principle: Early embryonic development involves cleavage, blastulation, and gastrulation.
Materials: Permanent slides of blastula and gastrula (e.g., frog, chick).
Observation:
- Blastula:
  - Hollow, spherical structure.
  - Outer layer of cells (blastomeres) enclosing a fluid-filled cavity (blastocoel).
  - No increase in overall size from zygote.
- Gastrula:
  - Formation of primary germ layers (ectoderm, mesoderm, endoderm).
  - Blastocoel reduces or disappears.
  - Formation of archenteron (primitive gut) and blastopore.
  - Cells rearrange through morphogenetic movements.