Video Transcript
The diagram shows a detailed drawing of an animal cell. Using the labels on the diagram, in which structure of this cell are the majority of phospholipids found? Option (A) Golgi apparatus, option (B) nucleus, option (C) ribosome, option (D) mitochondrion, or option (E) plasma membrane.
The question asks us to review various components of the cell and recall where the majority of phospholipids are found. So what are phospholipids? Phospholipids are lipids that are composed of two fatty acid tails, a phosphate head, and a glycerol backbone. They are a key component of the bilayer membranes. Let’s have a closer look at their organization.
The hydrophilic phosphate heads lie on the interior and the exterior surfaces of the membrane, as shown in the diagram. They interact with water molecules via polar interactions. The hydrophobic lipid tails are sandwiched inside the phosphate heads, forming two layers that are not permeable to water. This way, the phospholipids bilayer is able to form a protective continuous barrier surrounding all cells, the plasma membrane. The same kind of bilayer membrane surrounds other structures within the cell, called membrane-bound organelles, for example, the mitochondria, nucleus, and Golgi apparatus.
As you can see on the diagram provided in the question, one example of an organelle where the continuous membranes are clearly visible is the endoplasmic reticulum, which is an organelle that lies immediately adjacent to the cell nucleus and its membrane is continuous with the outer membrane of the nuclear envelope that surrounds the nucleus.
So now let’s take a look back at our choices to see if we can identify the answer. Ribosomes do not contain phospholipids or membranes, so we can eliminate this choice. If we compare the individual membrane-bound organelles to the overall size of the cell, we can presume that the majority of the cell’s phospholipids must be found in the plasma membrane. Therefore, the correct answer is (E). The majority of phospholipids are found in the plasma membrane.
