In the first part of this video we looked at diffusion for the movement of gases and osmosis for the movement of water. They were things that could easily move from a high concentration to a low concentration. That makes sense.
So what is active transport for? Well, the clue is in the name, active. Work has to be done. Active transport moves molecules from a low concentration to a high concentration against the concentration gradient.
This is the opposite of diffusion and osmosis, and because it is not the natural direction, energy is required to make it work. Active transport is carried out by protein carriers within the cell membrane, and they have a specific binding site for the exact molecules they are transporting. The substance binds to the protein carrier on the low concentration side, and using energy from respiration, the protein carrier releases the substance on the other side of the cell membrane, where it is already at a high concentration.
See the difference between diffusion? No energy is needed because the molecules can just slide down the concentration gradient, whereas in active transport, they are joining the crowd and so more effort is needed, hence the ATP. Active transport allows cells to absorb substances from very dilute solutions, such as root hair cells taking in mineral ions from the soil and in kidneys so we can hang on to the substances our body needs such as glucose and sodium ions. Cells which carry out a lot of active transport often have lots of mitochondria to give them the energy they need. So from these two parts you should know know how cells take in substances and get rid of waste by diffusion, osmosis and active transport.
Just remember that for diffusion, the substance moves down the concentration gradient from a high concentration to a low concentration. Just think of a slide. You don't need any energy to go from high to low.
It's easy. Whereas active transport is the opposite. The substance needs to move up the concentration gradient from a low concentration to a high concentration.
Think of climbing a ladder. You need energy to go from low down to higher up.