Sea Urchin Fertilization

A detailed Summary of Sea Urchin Fertilization

Exploring the Fertilization of Sea Urchins

Reproduction is a major aspect in the life and the continuity of life of every organism that inhabits the world. In many cases the process of fertilization is internal, however in the case of sea urchins fertilization occurs externally. Because fertilization is external, it is easier to monitor this process. In order for fertilization to occur there are a few steps that take place: the egg's recognition of the presence of sperm, regulation of the amount of sperm allowed to penetrate the egg's membrane, and activation of metabolism prompting cell division. Fertilization of sea urchins begins with the release of the eggs and sperm cells. The egg then attracts the sperm of the same species because of the peptide attractant in the jelly coat of the egg. After the penetration of a single sperm there are two ways in which the egg prevents polyspermy. These two ways are a rapid block (influx of Na giving off an electrical charge unfavorable to sperm) and slow block (external Ca released into the space between the vitelline and plasma membranes of the egg). When fertilization in the egg occurs, the egg then has a rise in its cellular respiration and protein synthesis which

Now that the jelly coat of the egg has been removed we now see how much of an affect the jelly layer actually has on the sperm and its role in fertilization. It was already known that the egg's jelly layer contained a special chemical whose main purpose was to attract the sperm cells in the direction of the egg cell waiting to be fertilized. However, it is evident that without this jelly layer the sperm cells had no way of knowing where the unfertilized egg cells were situated. This is the reason why the fertilization percentage was so low compared to the previous experiments.

2. Clean all apparatus used. Place 1-2 mls of calcium-free sea water to the culture dish along with a drop of eggs. Activate sperm in the same way as I step one, using calcium-free sea water. Add sperm to the eggs in the culture dish, place on depression slide, view, and calculate the percentage of fertilized eggs. Compare to results of step one.

With the addition of the sperm cells to the eggs, there has not been a significant difference in the appearance of the overall solution. Under the microscope using a 20X magnification the sperm cells appear as white pin size dots floating around in the water. This is because of the fact that sperm cells are so minute that not even the microscope can give a true picture of what their actual appearance is.

is needed when the cell begins to divide. This division slowly evolves into a newly formed organism.

At the conclusion of each step the percentage of fertilized eggs was taken in order to distinguish the more reliable condition in which fertilization would occur. Each step revealed how different the response of the egg was considering the type of environment that fertilization was taking place. At the conclusion of step one there was approximately 80% of the eggs fertilized with the use of normal sea water and sperm. Step two concluded with 20% of the eggs having been fertilized in calcium-free sea water. Even with the absence of sperm, the fertilization rate at the conclusion of step three was at 60%. However, it was found that when the jelly layer of the egg was removed, fertilization only occurred at a rate of 0%. From these results it can be concluded that the more successful forms of fertilization are when there is sperm involved and when there is an influx of calcium in the eggs environment.

3. Repeat step two with the exception of adding calcium ionophore to both

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Category: Science