Digestive System of Earthworm (Pheritima posthuma) | Biology Class 11

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Digestive System of EarthwormZoology | Notes
Digestive System of Earthworm (Pheritima posthuma)
For: Science Class 11

The process of ingestion, digestion, absorption, and excretion is called digestion. The digestive system is divided into following heads.

Alimentary Canal: The alimentary canal is long tube, which starts from mouth and ends to anus.
Mouth: Mouth is small cresentric aperture. It is situated below prostomium at first segment.
Buccal Cavity: It is thin walled, short tube behind mouth, which extends upto 3rd segment. It helps to ingest food.
Pharynx: It is pear shaped muscular chamber, which extends up to 4th segment. On inner dorsal side of the pharynx, there is salivary gland. Two lateral enfolding are also present called shelves. Pharynx helps to pump the food inside the mouth.
Oesophagus: It is narrow, elongated; thin walled tube extends up to 7th segment. It acts as food pipe.
Gizzard: It is oval, hard, thick walled, highly muscular organ, which extends up to 9th segment. It helps to grind the food particles.
Stomach: It is a narrow tube, which extends from 9th to 14th segment. It is longitudinally internal folded.
Intestine: It is very long, wide tube, which extends from 15th segment to anus. In 26th segment two lateral finger like projections move forward up to 22nd segment, which is called intestinal Intestinal caeca. Internally intestine is highly folded. The foldings are called villi. On mid dorsal side there is a large vilus called typhlosole. Based on presence of typhlosole intestine is divided into 3 parts.

  • Pretyphlosolar region : It is the region between 14th segments to 26th segment where typhlosole is absent.
  • Typhlosolar region : It is the region from 26th segment to 23-25th segment in front of anus where typhlosole is present.
  • Post tyhlosolar region : It is the region form last 23rd segment to 26th segment where typhlosole is absent. This region is also called rectum.

Anus: It is circular aperture situated at last segment through which undigested food materials is thrown out.

Feeding mechanism/physiology of digestion
The earthworm feeds upon dead organic matter in the soil. Sometimes it feeds up on grasses, microorganisms etc. the food is ingested by pumping and sucking activities of pharynx.

In the pharynx
In pharynx, food is mixed with saliva. The saliva is secreted by salivary gland. The saliva is composed of mucin and proteolytic enzymes. The mucin present here lubricates food and proteolytic enzymes digest proteins.

In gizzards
In gizzard, food is grinded up in fine state. Physical digestion or mastication takes place in gizzard due to the contraction of circular muscles of gizzard.

In stomach
The stomach secretes proteolytic enzymes from glandular cells present on stomach wall, which digest proteins present in the food, and calcium, which is also present, neutralizes acidic food.

In Intestine
The intestine secretes juice called intestinal juice where following enzymes are present
Amylase: Digests carbohydrate into glucose
Lipase: Digests fat into fatty acid and glycerols.
Pepsin: Digests protein into peptones
Trypsin: Digests peptones into amino acids.
Cellulase: Digests cellulose.
Chitinase: Digests chitin present in food.

The digested food is absorbed through villi of intestine and undigested food is thrown out through anus.

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