Allotropy is a property of some chemical elements to exist in two or more different forms in the same phase. For example, due too structural modifications, the element carbon can exist as diamond (with a different structure due to the arrangement of the carbon atoms), as graphite and so on.
Other chemicals can form allotropes in different states, e.g. oxygen can exist in solid form as dioxide O2) and in gaseous state as ozone (O3). Can you think of other chemical elements that have allotropes?
In order to identify organisms, scientists/biologists designed a way of classifying them into different clusters based on certain physical characteristics. Organisms that share these physical characteristics are thus said to be in the same species. With evolving technology, it is now possible to differentiate further these characteristics by using DNA, which is a special code that makes each organism unique.