Suppose a molecule in present in unequal concentrations on either side of a cell membrane if the substance is small enough to cross the cell membrane in which direction do you think the molecules will move?

Well, think about the types of movements (transportation) that happens between what surrounds the cells and inside the cell. When talking about active transport, materials will move from low to high concentration. There are sodium potassium pump that allows certain things to move sodium inside the cell and potassium outside the cell. The other two types of active transport are endocytosis and exocytosis which uses the cell membrane to move large amount of materials in and out of the cell. In the other hand, passive transport move things from high to low concentration that requires no energy at all. First of all, there are three types of passive transport. One of them (which will definitely will answer your question) is osmosis. Although osmosis moves water in and out of the cell, there are pretty special. One type of Osmosis is hypertonic, in which causes the cell to release its materials, if the concentration inside the cell is greater than outside the cell. The other type is hypotonic, in which materials move inside the cell causing the cell to get bigger if only if the concentration outside the cell is greater than inside the cell. Finally, the isotonic is when they're an equal distribution between inside and outside the cell (no movement of materials). That's all, and I hope I gave you enough information so you can master this topic! If you have any questions like this, please respond and I am happy to answer your questions!

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.