Question

Two-part question about animals:

1a. Why do smaller animals typically have a simple respiratory system, while larger animals require more complex respiratory structures like gills or lungs?

1b. Many immune system functions in animals are completed by individual cells that can travel throughout the body, instead of remaining stationary within specialized organs. Why is this important for the immune system to function well?

Answer 1

Ans .1(a) The complexity of respiratory system is correlated with size of organism. As animal size increase, diffusion distances increase and ratio of surface area to volume drops. In unicellular organisms, diffusion across cell membrane is sufficient for supplying oxygen to the cell. Diffusion is slow, passive transport. If the cells are very large or thick, diffusion would not be able to provide oxygen quickly enough to inside of cell.Therefore, dependence on diffusion as means of respiration remains feasible only for small organisms.

To get enough energy to survive, the larger animals require efficient respiratory system.

Larger organisms had to evolve specialized respiratory tissues, such as gills, lungs, and respiratory passages accompanied by a complex circulatory systems, to transport oxygen throughout their entire body.

Fish and many other aquatic organisms have evolved gills to take up the dissolved oxygen from water. The folded surfaces of gills provide a large surface area to ensure that the fish gets sufficient oxygen.

The lungs are very efficient : they take in much more oxygen per breath than other animals do.

Ans .1(b) It is a fundamental property of immunity that no part of our body is cut off from its surveillance.

When there is injury or inflammation in the body, immune cells (also called lymphocytes) leave the blood stream and travel to the damaged site to get the problem under control.

Neutrophils are considered the first responders of the innate immune system.Neutrophils and macrophages circulate through the blood and reside in tissues watching for potential problems.

The antibodies travel through the blood stream looking for specific pathogens. The body can create new antibodies in response to new pathogens or vaccines.