How can a membrane be permeable to one substance while being impermeable to another substance?

It varies due to their polarities.

Explanation:

Remember, a membrane is a semi-permeable membrane. There are some substances that can cross the membrane and others have to take different route. It all comes down to their polarity. If we were to examine a membrane made of phospholipid bilayers, one side of it has hydrophilic heads and the inside has hydrophobic tails. The membrane is therefore polar, allowing polar substances to enter in and out of the cell. Non polar substances, such as water have to take a different route, through special proteins called aquaporins.

dna is made up of six smaller molecules -- a five carbon sugar called deoxyribose, a phosphate molecule and four different nitrogenous bases (adenine, thymine, cytosine and guanine).

the rocks are classified by the geological process they are formed by. the three main groups of rocks are igneous, metamorphic, and sedimentary. minerals are not they are classified under the chemical classes they are in. these groups include silicates, sulfates and carbonates.