 What is the first thing you want when you wake up hungry and sluggish in the morning? What do you need for that boost of energy? Maybe a cup of coffee or a yummy breakfast. Maybe your mom's yummy aloo parathas. But how does our body extract energy from them? Well, before you tell me that your mom's food has magic in it, let me tell you that we have a digestive system. We all know that and the digestive system breaks down all the food we eat into simpler forms like fats, proteins, carbohydrates, which can be easily utilized by our cells to produce energy. But how? What exactly is there inside the cell that does this magic? Well, we have a very special organelle called the mitochondria, which is also called the powerhouse of the cell. This very tiny organelle is the one that fuels your body and leads up each and every living cell. Now, we will talk in detail about this bundle organelle. But before that, I have a question for you. Well, we understood that we get our dose of energy from food, but where does the energy come from into our food in the first place? Hmm. How about you close your eyes and think of what you had for breakfast? If it was coffee or tea, then it's a plant product, right? And if you had bread or chapatis or parathas with it, then it is made of wheat mostly, which is again a plant product. Or let's say you have consumed meat early in the morning, then you must have had meat of an animal that feeds on plant or grass, right? And plants, rather I should say the green plants and the green algae, has the power to utilize the energy from the ultimate source, which is the sun. They are blessed with the power to convert solar energy into food through a process called photosynthesis. And all other life forms on this planet, including you and me, we all consume plants or plant products and derive energy from it. But tell me something, what is so special about these green plants? Why can't we utilize the solar energy? It is so much in abundance everywhere. How wonderful it would be if we could use the sun's power to produce energy for ourselves, right, without being dependent on green plants? Well, the answer is pretty simple. It's all because of a very tiny organelle that plant cells have, but we don't. These are these small, small green organelles that you see in the plant cell, which we call the chloroplast. Chloroplast have green pigments in it, which gives the leaves the bright green colour it has. Now, how about we cut open a chloroplast? Let's cut it longitudinally. Let's do a cross-section and see how it looks from the inside. And this is how it looks. It has two membranes, one on the outside called the outer membrane and one on the inner side called the inner membrane. And inside of the chloroplast, inside the inner membrane is a fluid which fills up the whole chloroplast, which we call the stroma. Now, in the stroma, you can see there are stack of coin-like structures, which are suspended in the stroma. And this is where resides the most important pigment, the pigment which makes photosynthesis possible, the chlorophyll. And this is the pigment that can convert solar energy in the presence of water and carbon dioxide into carbohydrates and oxygen. And there you go. This is what our mitochondrias were waiting for. This is all they require to produce energy, both in plant cell and animal cell. So now that the ingredients are ready, it's time we look into the mitochondria and see what it does to produce power. So just like we did with the chloroplast, let's do a longitudinal section of mitochondria. And this is what it looks like from inside. Just like chloroplast, it has two membranes, the outer membrane and the inner membrane. But the difference here is that the inner membrane is extremely folded. And the part inside the inner membrane, let me do the inner membrane with a different color. The yellow one is the inner membrane and the part inside which I have made in pink is called the matrix. All right, now that we know the different parts of mitochondria, let me tell you where the magic happens. Where exactly our food, our digested food is converted into energy. It is this inner membrane. The inner membrane has enzymes that can convert the food we eat into usable form of energy into molecules which are called the energy currency of the cell and they are the ATP's or adenosine triphosphate. And since such an important event takes place in this inner membrane, there was the need to increase the surface area of this membrane and that's the reason it is extremely folded. Folding increases the surface area and more the surface area means a more is the number of ATP formation, right? And the entire process of formation of ATP from food is called cellular respiration. And in cellular respiration along with ATP, certain by-products are also released by the cell. So the by-products are carbon dioxide and water. Now I want you to pause the video and look carefully at the products of photosynthesis and cellular respiration. Okay, so what did you observe? The products of photosynthesis is utilized by mitochondria to produce energy and it also produces certain by-products and these by-products are utilized by the chloroplast in plant cell in the presence of sunlight to produce carbs and oxygen which is again utilized by mitochondria and the cycle continues and this is how life continues on this planet. And because of this superpower of these two organelles, the chloroplast and mitochondria were able to attract the attention of a lot of researchers. Many came up with their own hypothesis explaining how these two organelles came into existence in living cells. And before we end this video, I would like to share with you a very interesting theory about the existence of these two super organelles inside living cells. So it speaks of the time when life began on this planet almost 3.5 billion years ago in some strange puddle on a hostile and vastly empty planet. We don't know what these first living beings did or what their deal was but what we can guess is that they somehow figured out how to transform the chemistry around them into stuff they could use while also acquiring the energy to keep things going. They must have been simple prokaryotic organisms and some of them over time became very efficient in utilizing the sun's energy. They could photosynthesize, let's say the green ones could photosynthesize really well. While others like these ones here, they specialized and became very efficient in say aerobic respiration. Now gradually as the Earth's collision became more favorable, eukaryotic cells evolved and it is believed that they were amoeba like that got nutrient cells. Once it so happened that an eukaryotic cell ingested a bacteria which is capable of aerobic respiration and instead of digesting it, they developed a symbiotic relationship. Maybe the prokaryote said that hey look, don't eat me up, I can help you in energy production, I am very efficient at it and in return you just provide me shelter and protection. So they must have agreed on that and allowed this prokaryote not just to stay but also divide and grow inside this eukaryotic cell. And this prokaryote is what we call the mitochondria today. So when the eukaryotic cell divides, the daughter cells also had this prokaryote inside it and it acted just like a cell organelle. Now back then such an eukaryote must have ingested another prokaryote which is capable of photosynthesis and that prokaryote was also successful in maintaining a symbiotic relationship and it became the chloroplast of the present times. And the entire story I just narrated is called the endosymbiotic theory. Alright so this was all about chloroplast and mitochondria and the endosymbiotic theory that tells us about their existence inside the present day eukaryotic cells. Now before we conclude this video I want to draw your attention towards this pigment, the chlorophyll, the green pigment that gives the leaves the green color. Now not just leaves, if you talk about raw fruit or raw vegetables that are green in color, it is all because of this pigment which is present in the chloroplast. Now tell me one thing, when a fruit or a vegetable ripens, how does it change color? Does the chlorophyll inside them vanishes? Well not exactly but the amount of chlorophyll pigment reduces and instead some other pigment that gives the plant cells some other color increases and then we no longer call it a chloroplast, we call it the chromoplast. And chromoplast consists of pigments that gives rise to all other colors, so all other fallowages except green is due to the chromoplast. Now again there are certain parts of the plants that are used to store nutrients in them, for example a potato tuber which is filled with carbs. So any part of the plant where carbs, proteins or fats are just stored, we call them the leucoplast and we can call them the storage unit of the cell. And if we look at every individual cell, leucoplast appears colorless. So if it's a green colored plant part, it will have a lot of chlorophyll in them. If it is of some other color other than green, then it has chromoplast that has all other colored pigments in them. And if it is a storage part of a plant, it will have a lot of leucoplast in itself. So a single organelle is interchangeable based on where they are, what role they play. They can be called a chromoplast, leucoplast or chloroplast and they are collectively called the plastids.