Why don’t scientists know the exact number of species that have lived on Earth?

Witch theory suggests all living things are made up of cell or cells

Amines amides and amino acids are categories of

Which of the following is most likely the result of an organism having lipids in its body a) water cannot be absorbed through the surface of a leaf b)human eats fruits to get a quick source of energy c) a sheep sleeps for more hours in the winter d) a warm river is filled with fish and algae