Question

In Earthworm, gizzard is present in segments
A. 8-9 Segment
B. 10-12 Segment
C. 4-5 Segment
D. 15-16 Segment

Answer 1

Hint: Earthworm comes under phylum Annelida. There are several genera of earthworms. These are very common in gardens, green pastures, lawns, fields. They are rare in acidic, alkaline or sandy soils and heavy days. It mostly prefers to stay in the burrow during the day and comes out at night and in damp cloudy weather. They have metameric segmentation.

Complete answer:
1.Alimentary canal of earthworm is a complete and straight tube running throughout the length of the body.
2.Whole of the alimentary canal is not uniform in diameter. The alimentary canal is distinguished into various parts or regions-mouth, buccal cavity, pharynx, oesophagus, gizzard, stomach, intestine and anus.
3.Mouth- It is a crescentic aperture ventral to the prostomium and situated at the anterior end of the first segment or peristomium.
4.Buccal cavity- The buccal cavity or buccal chamber is a short thin wall tube, extending behind up to the middle of 3rd segment.
5.Pharynx- The buccal cavity leads into a small, but thick, pear-shaped pharynx extending up to the end of the 4th segment. The wall of pharynx is thick and muscular.
6.Oesophagus- Pharynx is followed by a straight, narrow thin walled long tube called oesophagus or gullet. The thin oesophageal wall has no glands. It is internally folded. It extends from the fifth segment to the end of the seventh segment.
7.Gizzard- The oesophagus leads behind into a small, bulb-like, oval, hard and thick-walled muscular organ, the gizzard, lying in the 8th or 9th segment. The wall of the gizzard is very thick due to a massive circular muscle layer.
8.Stomach- The gizzard is followed by a narrow, thin-walled, tube the stomach, which extends from 9th or 10th to the end of the segment 14th, with a sphincter at each end.
9.Intestine- It is the largest and widest part of the alimentary canal, extending behind from the segment 15th to the end of the body.
10.Anus- The anus is a small, slit-like aperture at the end of the last segment called the anal segment.

Hence, the correct answer is option (A)

Note: The wall of the alimentary canal is made up of four layers: Peritoneum, Musculature, Enteric epithelium, Cuticle.
1. Peritoneum- It is the visceral layer of coelomic epithelium, covering the gut wall and formed of squamous mesodermal cells.
2. Musculature- These lying below the peritoneum include the outer layer of longitudinal muscle fibres and inner layer of circular muscle fibres.
3. Enteric epithelium- It consists of a single row of columnar cells which become ciliated on the roof of pharynx.
4. Cuticle- It covers the enteric epithelium in the buccal cavity and gizzard.