In biological systems, there are several membrane transport systems responsible for the passage of ions like Na+ and K+. a. True
b. False

The correct answer is: a. True.

Explanation:

There are several membrane transport systems responsible for the passage of ions like Na+ and K+.

Cell membranes are semipermeable, which means they can regulate which molecules may and cannot flow through them. Some molecules may simply drift in and out of a cell (this is called simple diffusion), while others require specific structures to enter and exit (this type of diffusion is called facilitated diffusion), and still, others require an energy boost to pass the cell membrane (this is known as active transport).

Both simple diffusion and facilitated diffusion are types of passive transport: they happen without the energy boost that ATP gives, unlike active transport.

In passive transport, molecules follow their chemical gradients and travel through the most concentrated compartment to the less concentrated one to equal the concentrations. In active transport, on the other hand, the cell makes an effort to enter or exit ions against their chemical gradients and this is done particularly to maintain said gradients (they are required for the correct functioning of the cell).

Sodium and Potassium are two of the most important ions when it comes to maintaining these gradients: sodium is very concentrated in the outside of the cells (the extracellular compartment), while potassium is highly concentrated in the intracellular compartment. These differences in concentrations are maintained thanks to the Na+/K+ pump, a form of active transport. Apart from the Na+/K+ pump, these ions go through the membrane through passive transport as well, without requiring energy.

d. the weight of the book