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The Cell in Its Environment
Transcript of The Cell in Its Environment
A Cell Is Like A Building:
In a way, a cell is like a building. Or, more specifically, a fortress. Both have a protective wall that can allow things through, and both have a way to keep things out. After all, there has to be some way to get food and water into a fortress without letting enemies in, right? Cells are the same way.
Osmosis is the diffusion of water molecules through a selectively permeable membrane. This means that if there are a lot of water molecules outside of the cell, they will eventually be distributed equally inside and outside of the cell through the process of diffusion. Cells cannot live without water, and many cellular processes depend on osmosis.
Active and Passive Transport
There are two kinds of transport: active and passive. Active transport requires energy, while passive transport does not. Let's take our fortress, for example. If someone wants to send a message to someone outside of the fortress walls, it takes energy for them to walk out of the fortress to where their friend lives. This would be active transport. But if the same person instead sends a pigeon with the same message, he would not use any of his energy. This would be passive transport.
Why Are Cells So Small?
Most cells are so small that you cannot see them without a microscope. This is because of the way materials move into and out of cells. When cells get larger, the cytoplasm moves farther from the cell membrane. After a molecule goes into a cell, it is carried by moving cytoplasm to its destination. If a cell was much larger than it is, it would take longer for the molecule to reach the center of the cell than it would if the cell was small. If a cell was too large, it could not work well enough to live.
Most molecules move across the cell membrane (the walls of our fortress) using diffusion. Diffusion is the process by which molecules move from an area of higher concentration to an area of lower concentration. This means that if there are a lot of a certain type of molecules in one area, the molecules will gradually move from this area (the area of higher concentration) to the area were there aren't any molecules (the area of lower concentration).
Why does diffusion occur?
Diffusion happens because molecules are always moving, and because the more there are in one area, the more the molecules bump into each other. Eventually, this means that the molecules will drift away from each other, spreading away from where most of the molecules are located.
Active Transport Methods: Transport Proteins
There are several different methods of active transport. One method requires transport proteins, which is were the transport proteins in the cell membrane collect molecules outside of the cell and carry them inside, using energy.
There is only one method for passive transport. This method is where dissolved materials are taken into the cell.
Active Transport: Transport by Engulfing
Another method of active transport is transport by engulfing. To do this, the cell membrane surrounds and closes around a particle. Once the particle has been engulfed, it is turned into a vacuole inside the cell.
Effects of Osmosis
Osmosis can have many important effects for a cell. To keep a cell in its normal shape, the concentration of water should be the same as it is inside the cell. If there is less water outside the cell, water will leave the cell, causing it to shrink. If there is a lot of water outside the cell, the cell will take in water, causing it to enlarge.
How Does Oxygen Diffuse?
One-celled organisms that live in pond water require oxygen to survive. Since there is a higher concentration of oxygen molecules outside the cell, these organisms obtain the oxygen they need through diffusion, so that eventually there is an equal concentration outside and inside the cell.
Selectively Permeable: A property of cell membranes that allows some substances to pass through, while others cannot.
Diffusion: The process by which molecules move from an area of higher concentration to an area of lower concentration.
Osmosis: The diffusion of water molecules through a selectively permeable membrane.
Passive Transport: The movement of materials through a cell membrane without using the cell's energy.
Active Transport: The movement of materials through a cell membrane using energy.