Larger animals tend to reproduce sexually
and smaller organisms reproduce asexually. Larger animals have developed more
complex organ systems and with these organ systems they can adapt to their
environment more easily than smaller organisms. The complex brain and sense
organs of larger organisms allows them to adapt to their environment.
Organisms that reproduce asexually cannot
develop much variety, because they are "copying" the original
organism almost exactly. Sexual reproduction allows for great diversity,
because the zygote is different from the mother's egg and father's sperm; it
is a combination of both. Sexual reproduction produces a greater chance of
variation within a species than asexual reproduction would. This variation
improves the chances that a species will adapt to his environment and survive.
Heliozoa, Amoeba, and Euglena all reproduce
by binary fission, which is the mother cell dividing into two daughter cells.
The Heliozoa and Amoeba belong to the Protista Kingdom. The Euglena is an odd
one celled plant that sometimes have characteristics of a protist. Heliozoa
live in fresh water and have pencil like axopods that aid in eating. Amoebas
live in fresh water, and move in a unique manner. An amoeba will move its
entire body in a "blobby" motion. Euglenas live in fresh water and
have a long tail that helps move the organisms through the water.
Planaria, round worms, and leeches are
mostly hermaphroditic. The male and female reproductive systems are distinct,
but may join terminally in a common chamber on the same organism. Self
fertilization is rare. Some of the representatives of these groups are
parthenogenetic: females asexually produce females. Planaria also are capable
of extensive regeneration.
Gorillas, elephants, rats, zebras, and
dolphins are all mammals that reproduce sexually. There is a male and female
in each of these species. Kangaroos are mammals but they are marsupials. There
are female and male kangaroos, but after sexual reproduction the fetus leaves
the mother and goes into her pouch until it is large enough to leave.
Fish and frogs have sexual reproduction,
but it is externally. The female lays eggs and the male externally fertilizes
the eggs but squirting sperm in the water. Frogs develop differently, in that
they have a tadpole stage and them metamorphose into a frog.
A turtle lays eggs, but like a bird and
probably a dinosaur, fertilization occurs internally. Dinosaurs are extinct,
but because we have found dinosaur eggs, we believe that they reproduced much
like chickens. The male internally fertilized the female, and then the female
laid her eggs.
- In this lab activity, have students cut
out the pictures on the asexual and sexual reproductive chart.
- They are to divide the pictures into two
groups, those that they predict would reproduce sexually and those that the
believe reproduce asexually.
The discussion after the grouping should
be centered on how the organisms reproduce, and what characteristics seem to
be more common in the sexual versus asexual modes of reproduction.