What two objects combine to make endosperm? A. sperm cell and egg cell
B. sperm cell and polar nuclei
C. sperm cell and embryo
D. sperm cell and pollen tube

The circles, or orbits, for electrons are called energy levels. each level can hold only a certain number of electrons. add electrons to each level until you can't add any more. how many electrons can each level hold?

What causes temperature extremes in the desert

Identify the various levels of atmosphere. troposphere mesosphere exosphere stratosphere thermosphere