The law of thermodynamics of conservation of energy
Chromosomes is the answer
The main food sources of the birds( the plentiful recourses within the environment occupied by the species)
The cell membrane functions as a selective barrier. We call these kind of membranes as differentially permeable or semi permeable membrane. It can decide what substances can pass in and out. Therefore it can surround the cytoplasm (which is the inside of a cell) to separate the cell's content from the surroundings.
