Test: Ascaris - 3 (Old NCERT) - NEET MCQ

Humans, along with a wide variety of other animals, are known as intermediate hosts; smaller animals which raccoons prey on and are intermediate hosts are known as paratenic hosts. Unlike an Ascaris lumbricoides infection, intermediate hosts cannot spread the roundworm through defecation of the eggs.

Ascaris lumbricoides is a nematode worm which leads a parasitic life in the intestine of man. Hence it is an endoparasite. Body is long and round so that it can easily fit in the lumen of the intestine. Cuticle covering the body protect the worm from digestive juices secreted in the host's intestine.

Pseudocoelom is characteristic body cavity of round worms (Ascaris/Nemathelminthes). It is filled with protein rich pseudocoelomic fluid and carries five giant mesenchyme cells, known as pseudocoelomocytes that occupy fixed positions in the anterior third of the body. Pseudocoelomic fluid is composed of about 93% water and substances such as protein, glucose, non-protein nitrogenous substances, sodium chloride and phosphate.
So, the correct answer is 'Psedocoelom'.

Excretory Organs: In marine nematodes, the excretory system consists of one or two large renette gland cells lying ventrally in the pseudocoel near the junction of the pharynx and intestine, a duct arises from each renette cell, these ducts join and open by an excretory pore mid-ventrally.

Ascariasis is a disease caused by the parasitic roundworm Ascaris lumbricoides. Infections have no symptoms in more than 85% of cases, especially if the number of worms is small.Infection occurs by eating food or drink contaminated with Ascaris eggs from feces.

Male Ascaris are 2- 4 mm in diameter and 15- 31 cm long. The male's posterior end is curved ventrally and has a bluntly pointed tail. Females are 3- 6 mm wide and 20- 49 cm long. The vulva is located in the anterior end and accounts for about one- third of its body length. 

Ascaris is an animal genus comprised of intestinal roundworms. Ascaris lumbricoides lives in humans, and ascaris suum in pigs. Although the male and female worms look similar, there are several characteristics that distinguish the two sexes, both externally and internally. Externally, the sexes can be identified by size and the presence or absence of bodily structures. Internally, they can be distinguished by their reproductive organs.

Ascaris is a cylindrical worm, white to light pinkish in colour, tapering at both ends. Female measures 30-40 cm and male 15-30 cm. Posterior end of male is curved. Four longitudinal streaks run through the body.
So, the correct answer is 'Four'.

Roundworms belong to the phylum Nematoda, while flatworms belong to the phylum Platyhelminthes.
Roundworms have bilateral symmetry and three-tissue layer construction. In contrast with flatworms, roundworms have a fluid-filled cavity, called as the pseudocoelom and a digestive tract with two openings. Pseudocoelom is called so as it is not completely lined with mesoderm and flatworms are acoelomate.

Ascaris is an intestinal parasite of humans. It is the most common human worm infection. The larvae and adult worms live in the small intestine and can cause intestinal disease.

The male roundworm also displays typical duties of males species that produce sexually. When mating, the male erects one or more spicules out of the cloaca and uses them to penetrate the female's genital pores. The sperm then travels down the spicules and into the uterus.

The fine structure of the body wall in Ascaris was investigated by electron- microscopic techniques. The body wall is composed of a cuticle, epidermis and a single layer of muscle cells.

Ascaris is a human parasite. It usually needs oxygen for its survival but in absence of oxygen, it can survive in the intestine. It can switch to aerobic mode to anaerobic mode. Hence, ascaris is facultative anaerobe.

In Ascaris, the excretory system is simple and H-shaped. There is a longitudinal excretory canal in each lateral side.The excretory system has no internal opening, nephridia or flame cells and cilia. The nitrogenous waste comprises of urea which diffuses into pseudocoelomic fluid.

Ascaris have a terminal mouth, triradiate which surrounds three denticulate lips. One median dorsal and two ventrolateral (ventral and lateral sides). Dorsal lip bears two sensory double papillae. Both sensory papillae and amphids are present on ventrolateral lips.

Phylum Nematoda consists of the nematodes or roundworms. They are characterized by their long, thin, tube-like appearance that lacks a visually distinct head or tail. Nematodes are mostly microscopic and are found in nearly every environment (excluding the dry ones) and as parasites of a variety of plants and animals.
Another characteristics :
Primitive Body Cavity. Roundworms are classified as pseudocoeloms, because they do not have a full-fledged body cavity.
Shape and Body Structure. Nematodes are often confused with flatworms because of similarities in physical appearance
Simple Digestive System
Protective Cuticle
Parasitism & Crytobiosis.

Undulatory locomotion is the type of motion characterized by wave-like movement patterns that act to propel an animal forward.

The fine structure of the body- wall in Ascaris, the body wall is composed of a cuticle, epidermis and a single layer of muscle cells. The cuticle contains several layers, a superficial membrane, a cortex, the fibrillar layer. Beneath the cuticle in Ascaris lies a thin epidermis having scattered nuclei and no separate syncytial.

Nematodes, or roundworms are considered to be part of the phylum Nematoda, also known as Nemathelminthes. Around one third of a nematode's cells are nerve cells called ganglia. The equivalent of a brain; a dense, circular nerve ring surrounding the pharynx located in the anterior part of the organism.

Ascaris lumbricoides is a nematode worm which leads a parasitic life in the intestine of man. Hence it is an endoparasite.
Body is long and round so that it can easily fit in the lumen of the intestine.
Cuticle covering the body protects the worm from digestive juices secreted in the host's intestine.
Ascaris also secretes some antienzymes against digestive enzymes of the host.

An excretory pore lies mid-ventrally just back of the mouth. Rossett cells (one per each canal) are associated with each tube in other species of nematodes. There is no sign of flame cells.

Nematology

The study of roundworms, also known as nematodes, is called nematology. Nematodes are a diverse group of worms that are found in almost every type of habitat on Earth, including soil, water, and inside the bodies of plants and animals. They are important in many ecological and agricultural systems, and are also a significant cause of diseases in humans and other animals.

Ascaris worms are a genus of helminths (parasitic worms), meaning that they live off of a host organism, to the detriment of that host. The two most common species are Ascaris suum and Ascaris lumbricoides. While A. suum generally infects pigs, they can infect humans as well.

Ascaris is belongs to Aschelminlthes also known as Roundworms.
And it is known that Aschelminltes are bilaterally symmetrical
triploblastic and Psevdocoelomate.
Hence Ascaris is also Triploblastic.

The excretory canals are said to secrete this urea which is eliminated through the excretory pore; some ammonia and urea are also passed out along with the faecal matters. Observations are also there to suggest that Ascaris Lumbricoides excretes more urea when water is scarce.

Male are female sexes are separate in Ascaris and these roundworms also show sexual dimorphism. Males are smaller than the females and they also have a curved tail with pre and post anal papillae, cloaca and a pair of spicules. Gonads are attached at the genital pore in females and at the cloaca in the male worms.

The round worm (Ascaris) may be regarded as specialized animal and not a degenerated one because of the fact that, it has cuticle over the body wall which is resistant to host's digestive juices which is a parasitic adaptation.

Urea and Ammonia

Ascaris is a genus of parasitic roundworms that can infect humans and other animals. The excretory system of Ascaris worms consists of a pair of tubular structures called nephridia, which are responsible for removing waste products from the body. The excretory product of Ascaris worms is a mixture of urea and ammonia. Urea is a nitrogenous compound produced as a byproduct of protein metabolism, while ammonia is a highly reactive compound that is produced when amino acids are broken down.