In general, the surface of a tree has a harder “feel” than does the surface of a dog. what cell characteristic or cell structure of each organism can be used to explain the difference?

The presence of cell wall in plants.

Explanation:

A plant cell possesses a cell wall, the presence of a cell wall provides rigidity to it. On the other hand, the cell in animals exhibits no cell wall. The animal cells possess a cell membrane that is, also known as the plasma membrane.  

The surface of a tree feels harder in comparison to the surface of a dog is because of the presence of cell wall in plant cells, which is lacking in the cells of a dog. A cell wall refers to a structural layer enveloping certain kinds of cells and is present external to the membrane of the cell. It can be flexible, tough, and rigid as well. It offers the cell with both structural protection and support, and also functions as a filtering mechanism.  

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

the answer is a) cell division.

hope this !