Description
The “Earthworm: Digestion, Skin & Excretion” (55×90 cm) educational chart provides labeled diagrams and concise notes covering the structure and functions of the earthworm’s digestive system, skin adaptations, and excretory organs, supporting in-depth zoology and physiology lessons.
Digestive System
Alimentary Canal: A straight tube running through the body, differentiated into mouth, buccal cavity, pharynx, esophagus, crop (storage), gizzard (grinding), stomach, and intestine. Food is ingested, lubricated with mucus, ground in the gizzard, and chemically digested in the intestine by enzymes like protease, amylase, lipase, cellulase, and chitinase.
Absorption: The typhlosole (internal fold of the intestine) increases surface area for absorption. Digested nutrients are absorbed in the intestine, and undigested matter is expelled as worm castings through the anus.
Digestive Glands: Includes pharyngeal, gastric, and intestinal glands that release essential enzymes for food breakdown.
Skin Structure
Body Wall: Covered by a thin cuticle, underlain by a one-cell-thick epidermis and layers of muscle.
Respiration: The moist, vascularized skin serves as the main respiratory organ—O₂ diffuses in, CO₂ out—so a wet habitat is essential for survival.
Cutaneous Adaptation: Mucus maintains surface moisture and aids gas exchange.
Excretory (Nephridial) System
Nephridia Types: Segmentally arranged in most body segments, including septal, pharyngeal, and integumentary nephridia.
Septal nephridia excrete waste into the coelom, pharyngeal nephridia open into the alimentary canal, and integumentary nephridia release waste directly to the outside through nephridiopores.
Function: Nephridia collect wastes from coelomic fluid and blood, filter it, and expel nitrogenous waste (mainly ammonia and urea) either into the gut or directly out. This is functionally parallel to vertebrate kidneys.
This chart is an essential resource for understanding the functional biology of earthworms and reinforces practical knowledge of invertebrate organ systems.