Art in Motion: Passive and Active Transport Text Version
In order to live and function, cells must let certain materials enter and leave. The cell membrane controls how materials move into or out of a cell.
An illustration displays a cross-section of a cell membrane. Within the body of the cell membrane are two structures: a protein channel, which is a narrow opening in the membrane, and a transport protein, which is open on one side of the membrane and closed on the other side. Groups of different types of molecules float on both sides of the cell membrane.
The cell membrane is selectively permeable, which means that some substances can pass through the membrane, while others cannot.
A large, irregular shape floats toward the cell membrane, bounces off, and floats away.
Substances move into or out of a cell by one of two processes: passive transport or active transport.
The movement of dissolved materials through a cell membrane without using cellular energy is called passive transport. In passive transport, molecules are able to pass through the cell membrane in both directions.
Molecules labeled “sugar,” “water,” and “oxygen” pass back and forth across the cell membrane, moving into and out of the cell.
When there are more molecules in one area, materials will gradually move from an area of higher concentration to an area of lower concentration.
The groups of molecules labeled “sugar,” “water,” and “oxygen” are highlighted. An arrow points from the oxygen group inside the cell, which is larger, to the oxygen group outside the cell, which is smaller. Another arrow points from the large group of water molecules outside the cell to the smaller group inside the cell. Water and oxygen molecules drift from their smaller to their larger groups, passing through the cell membrane.
Diffusion is one type of passive transport.
Small molecules, like oxygen, move into or out of the cell by passing through the cell membrane.
The path of the drifting oxygen molecules, which are the smallest molecules present, is highlighted. These molecules pass directly through the cell membrane.
Osmosis is another type of passive transport.
Water molecules diffuse into or out of the cell by traveling directly through the cell membrane.
The path of the drifting water molecules, which passes directly through the cell membrane, is highlighted.
Facilitated diffusion is a third type of passive transport.
Molecules that cannot pass directly through the cell membrane, like sugar, move through protein channels in the cell membrane.
The path of the sugar molecules, which are larger than the oxygen or water molecules, is highlighted. These molecules pass into and out of the cell through the opening labeled as the protein channel.
Passive transport maintains balance inside the cell.
The movement of materials through the cell membrane using cellular energy is called active transport.
The illustration focuses on the structure labeled as the transport protein. Inside the cell are molecules labeled “calcium.” Outside the cell are more calcium molecules. There is an opening on the end of the transport protein that is outside the cell.
Energy is needed to move molecules from a place of lower concentration to a place of higher concentration.
The calcium molecules on both side of the cell membrane are highlighted. There are eight molecules inside the cell and three molecules outside the cell. An arrow points through the transport protein from the outside to the inside of the cell.
Proteins in the cell membrane “pick up” specific molecules, like calcium. Using energy from the cell, the transport protein carries the molecule across the membrane and releases the molecule on the other side.
One of the calcium molecules outside the cell enters the open end of the transport protein and is pulled to its center. A burst labeled “Energy” appears briefly inside the cell, and the inside end of the transport protein opens while the outside closes. The calcium molecule moves from the center of the transport protein toward its opened end and is released inside the cell. This process repeats with another of the calcium molecules outside the cell.
The illustration returns to an overview of the cell membrane with both the protein channel and the transport protein visible. Sugar, water, oxygen, and calcium molecules float around the cell membrane. The transport protein opens and closes with bursts of energy as calcium molecules pass through.
Materials are constantly entering and leaving the cell through passive and active transport.