Red blood cells transport oxygen in the blood.
The answer to the question above is letter A. competition. The animals compete for their territories that is why they feel the need to mark the land by urine in order to discourage other animals claiming the same territory. Some of the animals doing this are cats and dogs.
Amino group, carboxyl group, hydrogen atom, and variable group (represented with R). The r-group is a side chain and amino acids are grouped together by their side chains. The product of these groupings may be hydrophobic or hydrophilic.
