Mechanism of respiration in lower animals - SS2 Biology Lesson Note

Lower animals, such as insects, rely on different mechanisms for respiration compared to higher animals. Here are some mechanisms of respiration in lower animals:

1.       Tracheal System:

·         Many insects, including beetles, butterflies, and flies, possess a specialized respiratory system called the tracheal system.

·         The tracheal system consists of a network of tiny tubes called tracheae that extend throughout the insect's body, delivering oxygen directly to the cells.

·         Openings called spiracles are present on the surface of the insect's body, allowing air to enter and exit the tracheal system.

·         Oxygen from the surrounding environment diffuses through the spiracles and enters the tracheae, reaching the cells by diffusion.

2.       Book Lungs:

·         Some arachnids, such as spiders and scorpions, possess a respiratory structure called book lungs.

·         Book lungs are specialized respiratory organs located within the abdomen of these animals.

·         The book lungs consist of layers of thin, leaf-like structures (lamellae) that are highly vascularized.

·         Oxygen diffuses into the book lungs through small openings on the abdomen's underside and passes through the lamellae, where gas exchange occurs, supplying oxygen to the animal's tissues.

3.       Gills:

·         Aquatic organisms, including certain invertebrates and fish, use gills for respiration.

·         Gills are specialized respiratory organs that extract oxygen from water.

·         They consist of thin, filament-like structures with a large surface area.

·         As water passes over the gills, oxygen dissolves into the thin membranes and diffuses into the bloodstream, while carbon dioxide diffuses out of the bloodstream and into the water to be expelled.

·         Gills are highly efficient in extracting oxygen from water due to the large surface area and a counter-current exchange system that maximizes oxygen uptake.

4.       Diffusion:

·         Some simple aquatic organisms, such as sponges and flatworms, rely on diffusion for respiration.

·         These organisms have a relatively small size and a high surface area-to-volume ratio, allowing gases to diffuse directly through their body surfaces.

·         Oxygen from the surrounding water diffuses into the cells, while carbon dioxide produced by cellular respiration diffuses outwards.