Based on this video, the definition for an Invasive Species is a ... species that is not native to an area and was brought by people.

or
species that is not native to an area, has no limiting factors to control its population which then causes harm.

Option 2

Explanation:

I did not see the video referenced, but an invasive species is not always brought by people. Furthermore generally there are no limiting factors because it has no natural predators in the environment and often uses up all the resources in that particular environment. Hope this helps!

sex cells are usually half's then they find another half and make a fertilize egg