PLEASE ANSWER AND EXPLAIN 1)If you tried to fertilize sea urchin embryos in sodi

Question

PLEASE ANSWER AND EXPLAIN

1)If you tried to fertilize sea urchin embryos in sodium-poor seawater, how would this affect the fast block to polyspermy? How would it affect the slow block to polyspermy? What might you observe if you watched this under the microscope?

2)You are a TA preparing for a sea urchin fertilization experiment. Two species are being used in the lab. You collect sperm and eggs from each species but forgot to label which species each of your samples came from. What experiment would you do to determine which sperm and egg samples came from the same species? What observations would you make in your experiment?

Explanation / Answer

Answer:

1)

Fast block to polyspermy in sodium-poor sea water-

First, Na+ channels in the egg open, allowing Na+ to flood into the egg. This causes a depolarization of the egg from it’s normal resting potential.

While depolarization is occurring, the remainder of the jelly layer is dissolving. With the dissolution of the jelly layer and the depolarization of the plasma membrane, the first block to preventing fertilization by multiple sperm is put into place.

These two simple changes are part of the first block to polyspermy, known as the fast block. Within 1/10th of a second of contact, the fast block to polyspermy is initiated.

Slow block to polyspermy in sodium-poor sea water-

Fusion of the two membranes causes a release of inosital triphosphate. The release of inosital triphosphate, or IP3, causes Ca2+ to be released into the egg’s cytoplasm.

Waiting in the cytoplasm are cortical vescicles, which are allowed to fuse with the egg’s plasma membrane and release their contents when the appropriate signal is sent. Ca2+ released is that necessary signal, and the vesicles fuse with the membrane. The cortical vescicles contain enzymes which cause a number of changes to occur in the egg.

1. The egg’s sperm receptors are removed

2. H2O is absorbed, causing the membrane to swell and push the vitelline membrane away from the plasma membrane.

3. The vitelline membrane hardens.

These changes ensure that fertilization of the egg by additional sperm is prevented. They are part of the slow block to polyspermy.

Under the microscope-

You can identify the first sperm to penetrate because it becomes immobile and begins to enter the egg. The remaining sperm continue to move until they are detached. You will also sea the one sperm that is beginning to penetrate an egg. When you have found it, you will soon see a fertilization membrane form at that point and spread outward over the entire egg.

2)

The fertilization of gametes in sea urchins is species specific meaning the sperm and the egg of the same species will only be attracted towards each other.This species - specific adhesion of the sperm to the egg is because of a specific protein called bindin and a complementary adhesion site in the egg;

This can be easily observed under the microscope.The sperm and the egg samples can be easily identified by their colour. The sperm sample will be whitish and the egg sample will be reddish.

Taking all precautions of handling the samples take a drop of the egg sample on a depressed glass slide and without dropping the coverslip observe under the microscope. You can see the eggs. Now carefully take a diluted drop of the sperm sample with a pippette and add it to the slide. If the sperm is from the same species there will be quick movement and adhesion of the sperm head to the receptor site of the egg.

If the sperm is from a different species there will be no attraction. Though the sperms move fast they will not get attached to the egg. This can be easily observed under the microscope.

as per chegg rules one question has to answer but i answer two questions next time post one question only

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