1. Water currents in the ocean are much stronger than any sperm. How do sperm and egg find each other?
  2. In humans there are no water currents and the volume of the female reproductive tract is relatively limited. Then, why does the male have so many sperm?
  3. Why do sea urchins have external fertilization?
  4. Then why don't the parents take care of the young?
  5. Because the urchin life involves two or more ecological niches, they are more susceptible to predation and exposure to environmental toxins. What environmental conditions, predators and toxins might they be exposed to at each stage?