[Music] hi I'm welcome after three science lessons co uk by the end of this video you should be able to describe how substances are absorbed by active transport you should then be able to describe examples of active transport in animals and plants we've already seen how substances move by diffusion remember that diffusion is the net movement of particles from an area of higher concentration to an area of lower concentration and the word net just means overall I'm showing you here a cell membrane with a high concentration of particles on one side and a low concentration on the other side as we saw scientists call this a concentration gradient because we have a region with a high concentration and a region with a low concentration there'll be a net movement of particles by diffusion down the concentration gradient and I'm showing you that here now there's a problem here what if a cell needs to bring in a molecule which is already at a high concentration inside the cell I'm showing you that in this example here there's a higher concentration of the molecule inside the cell than outside this means that these molecules cannot diffuse into the cell in fact they could diffuse out so how can a cell bring these molecules in to do this the cell uses a process called active transport active transport moves substances from a more dilute solution to a more concentrated solution in other words against the concentration gradient this requires energy from respiration now you'll notice that active transports different from diffusion in two key ways firstly in diffusion particles move down the concentration gradient whereas an active transport particles are moved against the concentration gradient secondly diffusion does not require energy from respiration whereas active transport does we often see active transport in biology and you need to know two examples this shows the cells lining the human small intestine we're going to see these cells again in a later video the cavity of the small intestine where foods digested is called the lumen and we can see that here in the lumen we find the molecules produced when foods digested and a good example of this are sugars such as glucose you can see that the concentration of sugars in the lumen is lower than the concentration of sugars inside the cell so these sugars cannot diffuse into the cell instead the sugars are carried in by active transport like this once inside this cell the sugars can then be transported into the blood and carried around the body now you'll notice that these cells have got lots of mitochondria these carry out respiration providing the energy needed for active transport let's take a look at an example of active transport in plants this shows a root hair cells found in the roots of plants we saw these cells in an earlier video lute hair cells transport ions such as magnesium into the plant from the soil plants need magnesium to make colorful in the leaves the concentration of ions in the soil is lower than the concentration inside the root hair cell so active transports used to move the ions into the cell like this these ions are then transported to the xylem vessels are moved to the leaf again we can see that root hair cells have got lots of mitochondria to provide the energy for active transport we will find plenty of questions on active transport in my vision workbook and you can get that by clicking on the link above ok so hopefully now you should be able to describe how substances are absorbed by active transport you should then be able to describe examples of active transport in animals and plants [Music]