Most important and abundant one are the phospholipids - amphiphatic molecules with an hydrophilic head and a hydrophobic hydrocarbon tails. They compose the membrane bilayer. Also important are the membrane proteins, which can be periheric and internal and can serve as channels, receptors, pumps etc.
Depending on the cell type the membrane can also contain cholesterol (in animal cells, enhances the membrane stability) or hopanes(in prokaryotes, same function as cholesterol) or ether-phospholipids with branched hydroharbon tails(in archaea, make the membranes more stable and resistant to severe conditions, as archaeas are extremophiles)
Crude density and ecological density are both related but different. Ecological density is the portion of land that a certain species can colonize, where as crude density is the land within the organism's range.
A cave because it’s hollow
The answer is another allele masks the recessive allele.
Recessive alleles are only expressed when they are paired with another recessive allele. If there is a dominant copy of the allele present, that is the one that will be expressed instead. Recessive alleles are common in the population, probably one of the most well known recessive traits is blue eyes.
