Why are penicilins often more effective against gram-positive bacteria than gram-negative bacteria?

Because Gram negative bacteria have an extra protective layer of lipopolysaccharide surrounding their cell wall!

Explanation:

Mechanism of action of penicillin is:

Effect on gram negative :

As you can see in the image, the gram negative bacteria has an extra layer of protection on its cell wall by lipopolysaccharide. Penicillin can't reach the cell wall to bind to the D-D Transpeptidase, so it is more effective on gram positive bacteria than gram negative bacteria.

to take away from

explanation:

answer: no, they are not.*

although rubber bands that contain excessive amounts of dye, toxins, or additives are sometimes toxic, most rubber bands do not cause any health issues. since they are typically made of latex, (a natural substance that is extracted from trees) they are not dangerous in any way if you chew them or accidentally ingest a piece of rubber band. however, chewing rubber bands does pose a choking hazard and is not a good habit to have.

*depending on the type of rubber band. the typical rubber bands that you see at stores are not toxic, but other types of rubber or latex that contains certain chemicals may be unhealthy and hazardous.