Aim #41: How do different living organisms undergo fertilization?
What do we know about…
How do these two species of organisms reproduce? Brainstorm everything you know (or think you know) with your
group! Try to incorporate what we have been learning recently.
Aim #41: How do different living organisms undergo fertilization?
External Fertilization
Nearly all fish reproduce sexually, and most species have separate sexes. Those without separate sexes avoid selffertilization by producing sperm and eggs at different times. Each fish typically produces a large number of gametes. In
most fish species, fertilization takes place externally. These fish are oviparous. Eggs are laid and embryos develop
outside the mother’s body. In a minority of fish, including sharks, eggs develop inside the mother’s body but without
nourishment from the mother. These fish are ovoviviparous.
External fertilization is beneficial because the mother does not have to physically carry the developing offspring. She can
also lay a brood of many eggs at one time (we are talking hundreds to millions of eggs). On the other hand, it is also
more dangerous because the developing offspring are at a risk to predators gobbling them up for breakfast or second
breakfast. Humans aren’t the only ones who like caviar. Eggs are also not as protected from environmental changes
(such as pH or temperature) as they would be inside their cozy mother.
Internal Fertilization
In mammals, reptiles, birds, and some types of fish the gametes meet inside of the female's body. This is called internal
fertilization. All land dwellers need to fertilize this way because sperm still prefer swimming to walking.
The benefit is that it provides a safer environment for fertilization. In some species, the females can even safely store
the sperm until they are ready to use it. The downsides are that internal fertilization requires special body parts. It also
requires more energy than external fertilization.
Method of fertilization
External
Internal
Pros
Cons
Examples