why do humans need a complex circulatory system while an amoeba does not?

Question

keep answer simple please

Answer 1

Humans have many cells, *all* of which need to be fed and oxygenation, and need to have waste products taken away. A circulatory system is an effective way to reach every cell on a regular, cyclic basis.

An amoeba is one-celled. All of the contact with medium for nutrition and waste removal happens by diffusion and transport directly through the cell membrane.

Answer 2

amoeba is the most simple cell which contain only one cell.While human are multi cell need a complex circulatory system

Answer 3

It is simply a matter of surface to volume ratio. A very large amoeba is about 800 micrometre in size, assuming that it was to be shaped like a sphere, the maximum distance a dissolved gas would have to travel from the surface to the core would be 400 microns.
In the case of a human, you may have to go something like 10 cm to get oxygen that would be taken from the outside to diffuse to the cells deep inside your abdomen.
And oxygen is only one of the things that needs to move around; you need to get amino acids, lipids, glucids, various salts, etc.
At the size we have, a highway of sort is needed to get things around, hence the circulatory system.

Answer 4

If an amoeba was six feet tall, made up of billions of cells, could run and lift weights, had an advanced brain, and reproduced sexually, it would also need a complex circulatory system to distribute oxygen and nutrients to all those functional cells, as we do.

But it ain't.

Answer 5

simple answer would be because an amoeba is too small to require anything or the sort

Answer 6

So, you can't tell there is a difference between the 2? Why does a Nuclear Submarine has so much more complexity than a 1985 Yugo.

Answer 7

Diffusion works pretty well for cells. Humans, however, are big and multicellular...diffusion is not efficient over long distances.