All About the Earthworm

Earthworm Dissection Pre-AP Biology Period 2 - Bowen Song

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Lumbricus terrestris

The earthworm is a unit well-adapted to a life of burrowing through the soil. It's streamlined shape allows it to move quickly and easily through the soil. Earthworms are invertebrates, meaning they lack a backbone. Instead of a backbone, it retains its structure through a hydrostatic skeleton (fluid filled coelom).

Earthworms are also hermaphrodites. They contain both the male and the female sex organs. They are present in most places where the soil is moist and undisturbed.

Objectives

Students will learn about the internal and external anatomy of the earthworm. They will focus on the organs, structures, and functions of the digestive system. Students will also focus on the ecological presence of the earthworm as well as the human influence to the earthworm. Finally, students will learn the evolutionary characteristics of the earthworm.

Earthworm Digestive System

Getting More in Depth

Parts of the earthworm digestive system: mouth, pharynx, esophagus, crop, gizzard, intestine

Functions: The gut of the earthworm is a straight tube which extends from the worm's mouth to its anus. It is differentiated into a buccal cavity (generally running through the first one or two segments of the earthworm), pharynx (running generally about four segments in length), esophagus, crop, gizzard (usually) and intestine.

Food enters through the mouth then moves into the esophagus, where calcium (from the blood and ingested from previous meals) is pumped in to maintain proper blood calcium levels in the blood and food pH. From there the food passes into the crop and gizzard. In the gizzard, strong muscular contractions grind the food with the help of mineral particles ingested along with the food. Once through the gizzard, food continues through the intestine for digestion. The intestine secretes pepsin to digest proteins. Instead of being coiled like a mammalian intestine, an earthworm's intestine increases surface area to increase nutrient absorption by having many folds running along its length.

Ecological Presence

The earthworm has a very big ecological presence in everyday life because of the way that it eats the soil. It plays an important role in decomposition and replenishing nutrients in soil.

Evolutionary Characteristics

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Earthworm Dissection Lab

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