Video Transcript
What is the difference between the
structure of monocotyledonous and dicotyledonous seeds? (A) In dicots, the endosperm food
store is moved into the cotyledons. (B) In dicots, two embryos develop
within the endosperm. (C) In dicots, there is twice as
much endosperm as monocots. (D) In dicots, the starch of the
endosperm is broken down into sugars. Or (E) in dicots, the endosperm
contains less water than monocots.
Angiosperms are flowering
plants. There are two main types of
angiosperms: monocotyledons, also known as monocots, and dicotyledons, also known as
dicots. A cotyledon is a structure within
the angiosperm’s seed that eventually becomes the plant’s first leaf. The prefix mono- means one and di-
means two. So, while monocotyledonous seeds
have one cotyledon, dicotyledonous seeds have two cotyledons. Let’s remove the answer choices for
now so that we have some more space to take a look at seed’s anatomy.
A seed has a seed coat, which
protects the plant embryo within the seed. A plant embryo contains the
earliest forms of a plant’s root, stem, and the cotyledon or cotyledons. Monocot plant seeds also contain a
food store called an endosperm, which provides the seedling with food after it
breaks out of the seed coat. So the seedling does not have to
start to photosynthesize immediately. In dicotyledons, the two cotyledons
have often absorbed the endosperm before the embryo breaks out of the seed coat. This means that the plant will rely
on photosynthesis in these first leaves to provide the seedling with nutrients.
Now, let’s take a look back at our
answers. First, we can eliminate answer
(B). In dicots, there are two cotyledons
within the embryo, not two embryos. We can eliminate answer (C) as
well, as we know that there is more endosperm in monocots, as in dicots the two
leaves absorb most of the food store. Dicots would therefore have less,
not two times more, endosperm than monocots.
We can also eliminate answer choice
(D). In dicots, the endosperm is used
for the development of the two embryonic leaves, not to produce sugars. Finally, we can eliminate answer
(E). It is not necessarily true that the
endosperm contains less water in dicots compared to monocots. In fact, in many dicots, there is
no endosperm left toward the end of embryo development. We can’t compare the water content
of an endosperm in monocots to a nonexisting endosperm in dicots.
As we have learned that in dicots
the two embryonic leaves, or cotyledons, absorb the endosperm, we know that the
correct answer must be (A). In dicots, the food store is moved
into the cotyledons.
