* Mitosis: Used for growth, repair, and asexual reproduction. It produces two identical daughter cells with the same number of chromosomes as the parent cell.

* Meiosis: Used for sexual reproduction. It produces four genetically unique daughter cells with half the number of chromosomes as the parent cell.

Here's why some species use both:

* Sexual Reproduction: Organisms that reproduce sexually require meiosis to create gametes (sperm and egg cells) with half the number of chromosomes. This ensures that when the gametes fuse during fertilization, the offspring receives the correct number of chromosomes.

* Genetic Diversity: Meiosis also shuffles genetic material through processes like crossing over and independent assortment, creating genetic variation within a species. This diversity is crucial for adaptation to changing environments and for resisting diseases.

Here's why some species only use mitosis:

* Asexual Reproduction: Many single-celled organisms and some multicellular organisms reproduce asexually. In these cases, mitosis is sufficient to create genetically identical offspring. This can be advantageous in stable environments where there's no need for rapid evolution or adaptation.

* Simpler Process: Mitosis is a simpler process than meiosis, requiring less energy and resources. This is beneficial for organisms with limited resources or that prioritize rapid reproduction.

In summary:

* Organisms that reproduce sexually need both mitosis and meiosis to create genetically diverse offspring.

* Organisms that only reproduce asexually can rely solely on mitosis for growth, repair, and creating offspring.

The choice of which process or processes to use depends on the organism's specific needs and evolutionary strategies.