Answer:
Sperm-egg interaction
Explanation:
The formation of fertilization envelope is well-studied on the model system- sea urchin. It has been shown that, the fertilization envelope is formed after the initial sperm-egg interaction from the egg surface vitelline envelope and the paracrystalline protein fraction which is derived from cortical granules. Secretion from cortical granules, prevents polyspermy.
If the earth wasn't spinning , we wouldn't have summer, winter, fall, spring etc, it is important because we need the sun for certain seasons and no sun for others.
Coal seams are far deep underground to be considered for opencast minings. These coal seams require underground mining. Since it is too deep underground, it can be used for mapping and correlation of sedimentary rocks or as a key bed.
