Final answer:
It's false that lecithin must be supplied by the diet, as the body can synthesize it. Phospholipids and cholesterol are two types of lipids in cell membranes, with roles including structure and signaling.
Step-by-step explanation:
The statement 'Because lecithin is found in all cell membranes, it must be supplied by the diet' is False. Lecithin, a type of phospholipid called phosphatidylcholine, is indeed found in all cell membranes and is important for their structure and function. However, the human body can synthesize lecithin itself; it is not considered an essential nutrient that must be provided by the diet like essential fatty acids such as omega-3 and omega-6.
Two types of lipids that are part of the cell membrane are phospholipids and cholesterol. The phospholipids create a fluid bilayer, which provides the basic structure of the membrane, while cholesterol impacts membrane rigidity. Fatty acids, another type of lipid, are made up of long hydrocarbon chains and are not composed of triglycerides, though triglycerides are formed from fatty acids and glycerol.
Another important function of certain lipids in the cell membrane is that they can act as chemical messenger molecules. These include various types of lipids like steroid hormones derived from cholesterol.