The answer is; a) they are naturally occurring.
I don't know the answer sorry
The type of blood vessel which has the function of having to
allow passage easily of other substances such as nutrients, carbon dioxide,
oxygen and even waste in the cell wall is known to be the capillary. It is known to be a branching blood vessel in
which it has a role of being a network with both the venules and arterioles.
They need to cope with changing seasons and be able to withstand cold winters and hot summers
when excess fertilizers wash off of the nearby farms and into the lake, they become food for the algal blooms that can plague the lake in the summer. So, reducing fertilizer use and preventing runoff directly into the lake would be one way of reducing eutrophication.
