Cacti in the deserts of southwestern North America and some euphorbs of the deserts of Africa, have barrel-shaped stems, short-lived leaves, and spines, yet these two types of plants are from different evolutionary lineages. This is an example of A. selective breeding. B. transitional forms. C. homologous traits. D. convergent evolution. E. concave evolution.

       The right answer to this question is option D. Convergent evolution.

Explanation:

       Convergent evolution is a process defined by when an organism develops the same, or at least near that, characteristics, for a specific reason, but they don't have the same origin. In this case, the cacti in both deserts have pretty much the same characteristics, and this happens because both these plants need water to survive, and in order to save it, they have barrel-shaped stems, short-lived leaves, and spines. All of these things help them in saving the water and capturing it when it's possible.

        The convergent evolution is when both these organisms develop equally, but are not originally from the same place, the environment being the one to shape this.

the nitrogen cycle provides nitrogen to the ecosystem from the atmosphere, ground and oceans. nitrogen is an important component of complex molecules such as amino acids and nucleotides, which lead to the creation of proteins and dna, the building blocks of all life. plants absorb nitrogen in the form of ammonium, nitrate ion and, on rare occasions, as amino acids. animals receive nitrogen necessary for biological processes from feeding on living or dead organic matter.