Video Transcript
Consider the dichotomous key
provided below. Which of the following statements
is true about primates? (A) They have pouches and they live
in colonies. (B) They have no pouch and no
wings. (C) They lay eggs and have no
pouch. (D) They give birth and have
wings.
This question asks us about a
dichotomous key, which is a tool that uses a series of statements to help identify
organisms from a defined group. Here, the overarching group is
mammals, since this is written along the top of our dichotomous key. As you can see, all the organisms
branch from this main group.
We are asked specifically about
primates, which you can see written along the bottom. In order to determine the kinds of
characteristics that primates have, we are able to move backwards along the
dichotomous key to see what questions were asked and answered to get there.
The closest branch, or juncture,
involves the question if organisms have wings or not. And you can see here that primates
follow along the branch of no wings. This is in comparison to
Chiroptera, which do have wings.
Both of these groups belong to
Eutheria since this is written directly above this juncture and both organisms
result from these branches. The juncture leading to Eutheria
involves the question of whether or not the organism has a pouch. Members of Eutheria, which includes
primates, do no have pouches.
Finally, we get to our final
juncture that separates organisms based on whether they lay eggs or give birth to
live young. Since we follow the line that says
“give birth to live young” on the way to this juncture, we know that primates have
this characteristic.
So primates give birth to live
young, have no pouch, and have no wings. Therefore, the option that is true
regarding primates, based on this dichotomous key, is given by answer choice
(B). They have no pouch and no
wings.
