6)From the menu on the left on Virtual Urchin, click on "embryogenesis to hatching". This will display a video of sea urchin development. Photos of key stages taken with a scanning electron microscope (SEM) are shown next to the video. In addition to watching the video by clicking the play button, you can use the slider at the bottom to move through the stages step by step. Doing this will allow you watch how cell division increases the number of cells from the initial zygote. You'll notice that these divisions start off dividing cells evenly, but at a certain point, there are some smaller cells created. These smaller cells will play very important roles in the later development stages of the urchin, so their creation is a key milestone.
Which round of cell division is uneven? (hint: the SEM images will be helpful)
a)First
b)Second
c)Third
d)Fourth
e)Fifth
During early development, sea urchins exhibit radial holoblastic cleavage.
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