Question

In most of the Aschelminthes, the respiratory and circulation systems are absent. Where do they get oxygen needed for their metabolism?
(a) They can absorb oxygen directly from air.
(b) They have a special oxygen cylinder attached to them.
(c) They have an air bubble that feeds them.
(d) They obtain oxygen from their host through their body wall.

Answer 1

Hint: Aschelminthes do not have a respiratory system that can allow the intake of oxygen and a circulatory system which can help in the distribution of oxygen in the whole body. The body walls of aschelminthes are very thin and thus it acts as their respiratory system.

Complete answer:
The aschelminthes are also known as Nemathelminthes. Roundworms are bilaterally symmetrical. They have an organ-system level of organization. The organ associates to form a distinct system concerned with a specific physiological function such as digestion, excretion, and reproduction. These roundworms lack the respiratory and circulatory systems. Aschelminthes utilizes diffusion for the circulation of oxygen. Their body walls are thin so that they can obtain oxygen from their host through their body walls in which they live as a parasite.
Instead of using blood vessels for the transport of oxygen to the cells, nematodes exchange material through their skin using diffusion. Nematodes respire by exchanging gases i.e. they use oxygen for metabolism and produce carbon dioxide gas as the waste products. Since they are using oxygen for metabolism, there is a concentration gradient created inside and outside of their bodies which drives the diffusion process.
So, the answer is, ‘They obtain oxygen from their host through their body wall.’

Note: - These are commonly known as roundworms because the body appears circular in transverse cross- section. - The complete digestive tract starts from the Phylum Aschelminthes. The phyla lower than the Aschelminthes lacks a complete digestive tract in them. - Since the circulatory system is absent, the metabolic waste is excreted by two ducts i.e. an excretory pore and the anus that their body has. - The Aschelminthes are pseudocoelomate as the body cavity is present but is not lined by mesoderm.