* Pregygotic barriers prevent mating or ovum from being fertilized if different species attempt to mate. There are four barriers in this category.
* Postzygotic barriers occur after fertilization between different species. The hybrid zygote formed may be abnormal or infertile. There are three barriers in this category.
Carbon is stored on our planet in the following major sinks (1) as organic molecules in living and dead organisms found in the biosphere; (2) as the gas carbon dioxide in the atmosphere; (3) as organic matter in soils;
la ósmosis, la difusión simple, la difusión facilitada y el transporte activo son mecanismos que permiten la entrada y salida de sustancias a través de la membrana celular
