Asmall polar molecule enters a cell with from a membrane protein.

This is called facilitated diffusion(facilitated by membrane proteins) examples would be diffusion of ions such as sodium, potassium etc.

Hope this helps;)

The small polar molecule enters a cell with help from a membrane protein by    a process known facilitated diffusion.

Explanation:

The facilitated diffusion also known as passive diffusion. It allows movement of molecules along the concentration gradient whereas the process of active diffusion involves energy as it is against the concentration gradient.

The facilitated diffusion involves carrier protein and channel protein. Thus small molecules can easily pass through channel proteins.  

answer: zinc is the substance which has a volume of 1.38 .

density is defined as the mass of an object per unit volume.

it can be calculated by dividing mass of a substance by its volume i.e.

si unit of density is kg per cubic meter and cgs unit of the same is gram per cubic centimeter.

now from the given data volume can be calculated by the formula .

hence, the volume of aluminium will be = which comes out to be 1.703 .

similarly, volume of zinc, chromium, and nickel will be 1.378 , 0.869 , and 0.356 respectively.