of millions of small balloons. These are the hydrophilic heads of the (1) molecules that make up most of the membrane surface. Through the transparent surface, you can see their flexible, (2)_ interior of the cell membrane, and beyond them an inner layer of (3)_ molecules with their tails pointing toward you. Here, there are (4)_ embedded on the cell membrane; some rest lightly on the surface, but most project all the way into the interior of the cell. The cell membrane is indeed a (5)_ mosaic, the proteins are embedded like the pieces of a picture, but you can see that they are free to move around. You push on one of the proteins, and it bobs like an iceberg. Some of the phospholipids and proteins have (6)_ which serve as an effective interaction with the aqueous environment that surrounds the cell. You notice that one of the proteins has a dimple in its surface. Just then a minute, plump molecule floating in the blood plasma installs in a depression of a protein. The molecule is a hormone, a chemical signal, and the dimpled protein is the (7) tails projecting inward toward the proteins attached to them that enables the cell to respond to it. In your light beam, you can see the sparkle and shimmer of many molecules, large and small, in the blood and pass through the cell membrane. You see that the transparent gas of oxygen is moving from the plasma and enters the cell interior. This movement is (8). called (9) down its (10)_ concentrated, to the blood, where it is (12)_ ; which it occurs through biological membrane, it is transport. Similarly, carbon dioxide is flowing out of the cell, gradient, from the cell interior, where it is (11)_ concentrated. You note that water molecules are passing through the cell membrane equally a both directions. The total concentration of solutes in the cell and in the blood must ali the solution must be (13)_ You signal the control team to inject a