If you tried to fertilize sea urchin embryos in sodium-poor seawater, how would
ID: 213268 • Letter: I
Question
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
1). The fusion of plasma membranes of egg and sperm during the process of fertilization triggers a series of changes in the egg, which blocks polyspermy. Fusion of plasma membranes of sperm and egg cells triggers depolarization of the membrane. Now, this membrane causes “fast block to polyspermy,” which temporarily blocks the sperm penetration. This occurs prior to the cortical reaction.
Depolarization of oocyte riggers (requires the sodium ions) the exocytosis and thus releases the enzymes that cause hardening of zona pellucida. The sperm binding receptors are clipped off by the secreted materials and form the fertilization envelop, which act as a “slow block polyspermy.”
Both the fast block polyspermy and slow block polyspermy requires the sodium ions. So, in the sodium poor seawater, these processes does not occur, which results in polyspermy. So, when this is watched under microscope, the process of polyspermy (fertilization of egg by multiple number of sperms) can be observed.