 Movements across cell membranes, the active transport. First the contents. Definition of active transport. Energy requirements for inactive transport. Role of membrane proteins in active transport. And some examples of active transport. That the movement of sodium potassium and calcium mines. So first the definition. Active transport is the movement of molecules from low concentration to high concentration. With the help of energy through semi permeable membrane. So students when in active transport, there are three or three things that you have to remember. First one, that active transport is the movement of molecules from low concentration to high concentration. So the movement of molecules from low to high concentration is against concentration gradient. So active transport basically is the movement of molecules against concentration gradient. If it is against concentration gradient, then it will not be without energy. So it means it will utilize ATP molecules. So in active transport, against concentration gradient movement, energy is utilized. And this movement is through semi permeable membrane. That means it will cross the membrane. The one that the molecules cross was the membrane. Energy requirements. Active transport. You always remember that when word active comes, it means simply that there is utilization of energy. There are energy requirements. If someone says passive transport, it means energy requirement is not there. So in active transport, there is always energy requirement. So usually the molecules that are there use ATP as energy. Role of membrane proteins in active transport. In active transport, what is present in cell membrane? There are lipids and proteins. Lipids and molecules never take part in active transport. Whereas the actual active transport when molecules play a role, they are actually the protein molecules. And these protein molecules are basically the carriers proteins. They are carriers. Now in facilitated diffusion, carrier proteins are used. And in active transport, there are carrier proteins as well. The difference is that in facilitated diffusion, carrier proteins do not utilize energy. It is simply that it takes molecules from high to low. In active transport, carrier proteins take molecules from low to high. And it will utilize ATP. The protein that ATP uses, we use a word for pump. So that means in active transport, the proteins involved, they are the pumps. They give the name of the protein pumps. Now for example, the protein that the hydrogen ion moves through active transport, we will say that it is a hydrogen pump. What will we use to transport the sodium? We will use sodium pumps. There are some proteins that transport both sodium and potassium. What will we use for that? We will use sodium potassium pumps. Here in this diagram, we have a general diagram that tells us how in active transport, transportation is material. The movement from here the concentration is low of molecules, while here the concentration is high. Now, the movement is low to high concentration. When the movement is higher than low, we say it is against concentration gradient. Now, for against concentration gradient, molecules will never move from low to high. Rather, they will take specific proteins from low to high concentration. They are actually carrier proteins. And these carrier proteins will utilize this energy for this movement. For the transport of molecules, they will use energy. If they use energy, then after that, the energy in this transport will be utilized. Different types of proteins which are used by the cells for active transport. Now, if we look here, for example, we have mentioned sodium potassium pump or calcium pump. Basically, sodium potassium pump is now sodium ion concentration. In this, it will be simple that for sodium ion concentration the molecules outside the cell have more sodium ion concentration. Whereas inside the cell, sodium ion concentration is less. So, from low to high concentration, the proteins will be transported. That will be called the sodium pump. Now, this same protein is moving potassium molecules. This is called the sodium potassium pump. We will name it. For the transport of calcium, we name it calcium pump. These two pumps, sodium potassium pump have a very important role in our body. If calcium ions are not pumped or transported, then there is no movement in our body. Because all the muscle contractions have a role in calcium ions. When calcium ions come, then there is muscle contraction. This means that calcium ions if calcium pump doesn't work, if calcium ions don't move, then there will be no muscle contraction. The important role of sodium potassium pump is in the nervous system. Our nerve impulse moves from the brain and controls all the body parts through it. If sodium potassium pump doesn't work, sodium and potassium ions won't be transported, then in this situation, the nerve impulse can't be generated. Here, if we look at the diagram, which is very clear to us, sodium ions outside the cell have a lot of sodium ions. How much is this? 150 millimolar. How much is the sodium ion inside the cell? 15 millimolar. That is, sodium ions are more than 10 times outside the cell. But despite this, sodium ions have to be taken out of the cell. Because to generate nerve impulse, it is necessary to have maximum of sodium ions outside the cell. For this, to take out the sodium ions, the sodium potassium pump that we are talking about is present here. It will take out 3 sodium ions from here, from low concentrations and from high concentrations. Similarly, this will be the active transport of the sodium ions. The reverse of the sodium ions is that the sodium ions work outside the cell because they have more concentration inside the cell. Potassium ions are 5 millimolar outside the cell. Whereas, the concentration inside the cell is 150 millimolar. Potassium ions will also go from low concentrations to high concentrations. The same protein that will take out the sodium ions will come inside the potassium ions. That is, the sodium potassium pump is basically a sodium potassium pump. It will take out 3 sodium ions at a time whereas, it will take out 2 potassium ions inside the cell. Now, when these ions go out of the potassium ion and the sodium ions go out, there is a charge on the overall cell. There will be a positive charge because there are more positive ions outside the cell. Whereas, there is a negative charge on the inside of the cell. That is why the action potential of the nerve impulse will travel on our neurons.