It's actually pretty easy to estimate the first number - all you have to know is the apparent angular size of the sun and moon in the sky (about half a degree each) and the the time it takes the moon to orbit the earth (about one month).
Eukaryotic Organelles. 1  Nucleus-a membrane bound structure that contains the cell's hereditary (DNA) information and controls the cell's growth and reproduction. 2  It is commonly the most prominent organelle in the cell.
cell membrane. A cell membrane is like a cell's gatekeeper. It's the outer layer that surrounds a cell, letting substances in â or keeping them out. A membrane is a barrier that offers protection, like a rubber membrane that keeps rain from seeping under your roof. A cell membrane surrounds and protects the contents of a cell. It controls which substances can enter and exit the cell. The membrane also gives a cell its shape and enables the cell to attach to other cells, forming tissues.