Neurons are the central building blocks of the nervous system. a neuron’s outer surface is made up of which allows smaller molecules and molecules without an electrical charge to pass through it, while stopping larger or highly charged molecules.

semipermeable membrane

Explanation:

Neurons are the cells of the nervous system and have the plasma membrane as their outer covering. Their plasma membrane is also made up of two layers of phospholipids and the proteins are embedded in it. Therefore, the plasma membrane of neurons is a semipermeable membrane as charged and polar substances can not cross its nonpolar core made up of the hydrophobic tails of the phospholipids.

Similarly, the substances with a larger size can also not move freely across it. A semipermeable membrane allows only certain substances to move through it.

this would be a math

it has to be understood that the sea water contains a huge amount of sodium and chlorine ions and if they enter the cell of the atlantic cod fish, the cell will shrivel and the fish will die. to avoid such a condition, the fish uses active transport for the purpose of removing the ions against the gradient.

explanation:

the atlantic cod is not a maritime osmoconformer. its native application of salts is less than that of the seawater it lives in. it is continually falling water from the gills to the ocean via osmosis.

countering that, the fish is going to be swallowing seawater. but since its internal collection of salts is lower than seawater, the fish will want to go free of excess salt, and since that's going upon a gradient, then active transport, requiring energy, must be used to pump out the salt. much marine fish use the organs to filter out the salt and these fish discharge very straight urine.