Video Transcript
Which of the following correctly
labels an egg cell? (A), which shows the corona radiata
as the outermost structure, followed by the jelly coat, then cytoplasm, and nucleus
as the innermost structure. (B), which shows the jelly coat as
the outermost structure, followed by the corona radiata, then cytoplasm, and nucleus
as the innermost structure. (C), which shows the corona radiata
as the outermost structure, followed by the nucleus, then jelly coat, and cytoplasm
as the innermost structure. (D), which shows the corona radiata
as the outermost structure, followed by the jelly coat, then midpiece, and head as
the innermost structure.
To answer this question, let’s
review what we know about the structure of an egg cell. The mature egg cell is a large,
spherical cell measuring about 0.1 to 0.2 millimeters in diameter, which is roughly
the same size as a single grain of table salt. The outermost structure of an egg
cell is called the corona radiata. The word “corona” means crown in
Latin, which describes how the cells that compose the corona radiata surround the
egg cell like a crown. The corona radiata provides
physical protection to the egg cell while it develops.
Under the corona radiata is the
jelly coat. The jelly coat releases chemical
signals that attract and guide sperm toward the egg cell. It also limits access to the
nucleus of the egg cell to ensure that only one sperm can fuse with the nucleus of
the egg cell. The jelly coat surrounds the
cytoplasm of the egg cell. The cytoplasm contains the
nutrients that nourish the egg cell as it develops. The nucleus of an egg cell is found
within the cytoplasm. It contains the genetic material
that will be inherited by the offspring from the parent that produced the egg
cell.
From this review, we now recall
that the outermost structure of the egg cell is the corona radiata. Underneath the corona radiata is
the jelly coat, which surrounds the cytoplasm. Within the cytoplasm is the
nucleus. With this information, we are ready
to answer the question. So the image that correctly labels
an egg cell is (A), which shows the corona radiata as the outermost structure,
followed by the jelly coat, then the cytoplasm, and the nucleus as the innermost
structure.
