The illustration above shows a cell and a large particle. Many substances, such as proteins and polysaccharides, are too large to be transported into a cell by carrier proteins. In a process called endocytosis, the large particle is brought into the cell. Which of the following statements correctly summarizes this process?
A cell membrane is composed of a double layer of lipids in which many kinds of proteins are embedded. Many of these proteins act like gates, allowing only certain particles to enter or leave the cell.
When a particle has to go against its concentration gradient through one of these gates, energy is supplied by the cell to the correct protein to move the particle through the membrane. A sodium‐potassium ion pump is an example of a type of carrier protein that uses a large portion of the cell’s energy to move sodium ions through the cell membrane.
Why does the study of cell membranes lead to a better understanding of cell function?
The arrows in the diagrams represent the direction of movement of a certain type of molecule through the cell membrane of two different cells. The dots represent the relative concentrations of this molecule. Which processes are illustrated in the diagrams?