Answer : The correct answer for the blank is -
Lipids.
Lipids can be described as one of the four major macromolecules that are essential for the survival of life forms. They are water soluble organic compound and are major constituent of cell membrane in biological systems.
There are three major categories of lipids, which include steroids, phospholipids, and triglycerides (obtained from food sources such as fats and oil).
Thus, Lipids is the right answer.
