Welcome to MooMooMath and Science. The cell theory states that cells are alive. If you watch these single cell organisms you can see that they are alive.
In order to stay alive and maintain homeostasis, cells must move objects in and out of the cell. A very simple method of moving objects in and out like oxygen and carbon dioxide is diffusion. A simplistic way to understand diffusion is High to low is the only way to go.
Particles will move from an area of high concentration to an area of low concentration. Some objects can easily pass through the cell membrane, which is a phospholipid bilayer. It is composed of two layers and the phospholipids have a polar head and a non-polar tail. Particles moving with diffusion move with the concentration gradient. or in other words from high to low.
This type of movement does not require energy from the cell. However, there are other methods of passive transport called facilitated diffusion. With facilitated diffusion, a channel or protein is used to help move the particles in and out of the cell.
For example, glucose will move from an area of high concentration to low concentration but will need a protein, a carrier protein, to move into and out of the cell. These karyoproteins do not require ATP and move objects into and out of the cell using diffusion. However, sometimes these objects are either too large or need to go against the concentration gradient.
Active transport comes to the rescue. However, active transport requires energy in the form of ATP to move these objects in and out. Let's take a look at three types of active transport.
Membrane pumps. Endocytosis and Exocytosis A membrane pump moves substances against the concentration gradient or from a low concentration to a high concentration. A good example is the sodium potassium pump.
Three sodium ions attach to the carrier protein. ATP attaches a phosphate to the carrier protein and it changes its shape. This allows three sodium ions to leave the cell and then two potassium ions now attached to the carrier protein. The phosphate detaches from the protein and it changes shape once again and the potassium now travels into the cell.
This allows sodium and potassium to go against the concentration gradient. The cell also uses two types of vesicle movement endocytosis and exocytosis. Endocytosis allows the cell to move larger objects into the cell by engulfing the object and then moving this object into the cell. There are three types of endocytosis. Phagocytosis, which is when a cell moves in solids.
Phenocytosis, which is when a cell moves in liquids. And receptor-mediated endocytosis, which is a form of endocytosis in which receptor proteins on the cell surface Capture a specific target molecule. When the receptors bind to their molecule, endocytosis is triggered and the receptors and their attached molecules are taken into the cell in a vesicle. Exocytosis occurs when the cell expels an object out of the cell. Objects inside the cell are encased in a vesicle which is expelled.
If you'd like to know more about active transport, this playlist will help. And as always, thanks for watching and Moving Math uploads a new math and science video.