0:00 Hello Curious Explorers and welcome to Magnet Brains where knowledge flows and idea grows. I am your Science Educator and in today's lecture we will revise the chapter 2 of class 8 science "The Invisible Living World Beyond Our Naked Eye". In this lecture we will study the entire concepts of this chapter. So first of all let's see what we have to study in this lecture, what is there to study in this chapter. First of all, introduction. In introduction, we will ask some questions as usual. After that we will see how lenses are made, how microscopes are made, who did the search of the cell, who brought the living cell, we will see all these things. Then we will see what is a cell and we will study its different shapes and structures. Then we will see that after all Some organisms are at the simple level,
0:50 of one cell or some are made of some cells, some are very complex. Like we have different systems in the body to do everything, digestive system, respiratory, excretory. So what is our body type? It is a complex body type. So we will study about the level of organization. Then we will see what are the microorganisms? And if we know about the microorganisms, then we will also know how we are connected to them. How they are helping to keep the environment clean. How microorganisms are found in our food and they are benefiting us. Along with that, we will see what are the microalgae? and we will study about the many benefits of microalgae. Then we will see why we consider cells to be the most
1:40 basic unit of life, the most fundamental unit of life. Okay? So let's start our chapter with questions. Have you ever wondered what you might see if the invisible world around you became visible? Have you ever wondered what you might see if the invisible world around you became visible? How do you think your observation of this hidden world might change your way of thinking, way you think about size, complexity or even what counts as living? So what do you think if you start seeing these things, then how will your perspective of seeing things change? Like what is the smallest
2:27 and biggest thing about the size of something? How complex is something's structure? Have you thought Have you thought how these tiny living beings interact with each other? Have you ever thought how these tiny living beings interact with each other? Do you have such questions in your mind? And if you have more questions in your mind, then what do you have to do? You have to share them with us. Okay? The human eye can only see objects that are above a certain size. Human eye has the
3:13 capability to see only a certain size of object. Like if you see a very small dust, dust, dust, dust, dust, dust, dust, dust, dust, dust, dust, dust, dust, dust, dust dust dust dust dust dust dust dust dust dust dust dust dust dust dust dust, dust, dust, dust, dust, dust, dust, dust, dust, dust, dust time many tiny things around us remained unknown or is he was Jose que que ha maria I Joe hey whoa a fixed amount Joe hey size Joe hey Oscar de Sakti hey what's a chote cheese naive a party is silly a boat sorry Joe tiny organisms say whoa I'm say Joe hey bahut Salo take care hey unknown Rahe long ago people
4:00 discovered that curved piece of glass could make small things look bigger though People observed and discovered that if you use curved objects piece of glass say kissy cheese could a her hair to do chotee cheese have okay say the key here we'll buddy the canela T the pieces of glass were shaped like a lentil seed to Joe glass copy stock just say look they can make a cautious character joke of piece of glasses in K barren my bath or a hair okay up curve piece of glass say they can get the app go to her How will the things you see look like? Will they look big in size? What was their shape? Their shape was like lentil seeds. Let me tell you an example of lentil seeds. You must have seen
4:49 lentils or you must have seen Masoor Dal. It comes in pink color. How does it come out of the middle? How does it come out on the side? It is thin on the side. It is thick in the middle and thin on the side. It looked the same. What? The curved shaped glass thick in the middle and thin at the edge. That is why it was called lens. So taking reference from lentil seed, what did people call the curved piece of glass? They called it lens. Over time, the lenses got more improved and more powerful. Every new tool was Chahe wo simple magnifying glass ho, chahe wo microscope ho, usne help kiya humans ko wo cheeze dekhne me jo
5:38 humans normal eyes se nahin dekh paate the. The invention of the microscope opened a fascinating fascinating hidden world filled with tiny living creatures. So the invention of Microscope opened the door for a whole new world of tiny living world which we were not able to see with naked eye. We will explore some of these life forms in this chapter. So, what will we do? We will explore some of these life forms in this chapter. You have already learnt about the amazing variety of living beings. Just look around, there are so many
6:25 beautiful plants and animals. We have already read about them. Different varieties of living beings like plants, animals, fishes etc. We have mostly studied about their varieties. Their shapes, sizes and colours are different. Some living organisms are tiny. There are some big ones. You can take from whales to small hummingbirds, small fish or even a small frog. We get to see all living beings. They differ not only in their structure but also in many other features. You are not only seeing the difference in the
7:10 external structure, their features are also different. Someone is breathing in water, someone is breathing in air, someone eats something, someone eats vegetarian food, someone eats non-veg. By doing this, what is there? food What is common in all things? All people are living organisms. So these living organisms, these living beings, what do we call them? We call them organisms. So these living beings, whether they are plants or animals, we call them
7:58 organisms. So now in this chapter, if the word organism comes anywhere, then what do we have to understand? We are denoting a living creature. Next, let's move on. Have you ever noticed that smallest organism around you that is visible to the naked eye? Have you ever noticed that the smallest organism around you that you can see with the naked eye? Some people will say that we have seen an ant, a mosquito or any very small one. It is possible that people mostly tell about some insect. Okay? think about it how small a thing can you actually see? How small a
8:44 thing can you actually see? You might have seen that some people use reading glasses. Like I have put on my glasses. Why? Because my normal vision is It is not like a normal person who does not wear glasses or reading glasses To correct my vision, it should be normal. As much as we can see with a naked eye, with a healthy eye, my eyes should be like that. That's why I have put on glasses. Just help them to see better. I told you how it is helping to see. Because what is the defect in my eye? So, like a normal person's healthy eye should be, my eye should be like that only. That's why I have attached it with a
9:34 separate power. What happens when we use a magnifying glass to observe something or What happens when you try to observe something with a magnifying glass? So what happens? That magnifying glass shows big, what does the small thing do? Magnify means that it is making it bigger, it is making its size many times bigger. Let's see by doing an activity related to this, so what do we have to do in this? that we have to take a round bottom flask, fill it with water and cover its mouth. So we took a round bottom flask, which was made of glass, gave it water, put water in it and covered its mouth. Now you keep it on
10:21 an open book and try to see its letters through it. When you try to see its letters through it, you will see that the letters written in the book How is their size? Their size is bigger. The letters are appearing larger when we see through the flask. Why? Because the flask is acting like a magnifying glass. So when we put water in a curved bottom flask, we tried to see if the letters looked big. Because now that flask was working like a magnifying glass. Now use
11:06 a real magnifying glass to look at small organisms like an ant. Now what you have to do is, take a real magnifying glass and experiment with it and try to see an ant from it. Were you able to see the details of its body more clearly? When you saw an ant with a magnifying glass, were you able to see the details of its body clearly? Were you able to see its size clearly? Absolutely. If you see letters or magnifying glass, how do both things act? For a
11:53 long time People were curious to explore tiny organisms around them but they could not see them with their naked eye. People were curious to see the small things around them but they could not see with their naked eye. So finally, which discovery opened the door of this invisible world for us? Do you know which scientific discovery helped us see tiny world for the first time? Do you know which discovery opened the door
12:39 of this tiny world for us? So what was the discovery of this thing? Microscope. When the microscope came, then what did it do? It magnified the size of the smallest thing by many times and started showing us. And then we came to know that there are many such tiny living organisms which we cannot see with naked eye. So today let's see what is in ever heard of. In 1665, a scientist named Robert Hooke published a book called Micrographia. So in 1665, a scientist named Robert Hooke published a book called Micrographia. He was a
13:26 very careful observer and a very keen observer. He was a very good artist. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawing of very small things, tiny things. He had made a very detailed drawings of very small things, tiny things. He had microscope ki help se. Thik hai? Inho ne kis ki help se cheeze dekhi thi? Microscope ki help se dekha aur uska bohot hi detailed aur bohot hi clear picture apni is book mein, Micrographia mein inho ne dikhaayi. His microscope made things look 200 to 300 times bigger. In their microscope, if you are
14:14 looking at something from their microscope, then it used to look 200 to 300 times bigger. That what one could see with the unaided eye. One day he looked at a thin slice of cork and saw it was made of many small empty spaces. One day what did they do? They took the dead part of the tree which we call cork and kept a thin slice of it under their microscope and saw. So they saw how the cork was made. They looked like different compartments of different shells. So what did they say? They said that what is
15:00 that thing? That is a shell. Okay? These different compartments, which were made of different compartments and made of cork, What did they call it? That one compartment is a cell and what is that cell made of? It is a whole cork. This was the first time the word cell was used in the science to discover anything. The basic unit of life, this was the first time that in our world of science, which word came? In that word came the word cell and what did they call the cell? That cell is the basic unit of life. Means this cell is the smallest unit from which
15:46 a small body or a big body, from any shark to whale to human to that ant, whose body is made of? So, all the vegetables are made of these small cells. So, where did they see for the first time? They saw for the first time that a tree was kept in a cork under their microscope. So, they saw different compartments and gave its name to the cell. Now around the 1660s, there was a scientist named Anthony Von Leeuwenhoek. What did he do? He made better lenses. He was a very good scientist and
16:33 he also made very good lenses. What did he do? He made his good lenses and made powerful better microscopes. He was the first person to see clearly and describe tiny living things like bacteria and blood cells. Inho ne jo hai pehli baar kya kara? Yeh pehle person the jinho ne live living cells ki khoj ki thi. Kehne ka kya matlab hai? Iske pehle jab humne Robert Hooke ko padha to unho ne dead cells khoje the. Matlab ki unho ne kaha par dekha tha? Unho ne dekha tha cork mein ek jo humare bar The bark of the tree, the cork, what did they see? They saw
17:18 the cells but they are dead. They first, Antony von Leeuwenhoek, they first discovered living cells. And the living cells, along with that they described a lot of bacteria, our blood cells, about all this too. That's why they are called They are called father of microbiology. What do they call them? They are called father of microbiology. And when did they find the living cell? They found it in 1674. Okay? So who is the father of microbiology? Father of microbiology is Anthony Van Leeuwenhoek. Now let's see what is a cell? When we are talking about finding a cell, what
18:04 is a cell? Let's see this. All living beings are made up of cells. So let's perform an activity first and see that finally a plant made of a cell and an animal made of a cell are they really made of a cell? Because we have a microscope. So what we have to do is take an onion bulb, cut it into pieces and Then you have to remove the thin transparent layer from the inside of the layer using the help of a
18:50 forceps. We will call it onion peel. So what we did is we removed the onion peel from there. Now what we will do with this onion peel is we will keep it in a Petri dish in which we will add a little bit of saffron. Why are we adding saffron? Because I told you that when you see, the inner layer of the onion is transparent. When you see it in the microscope, how it is visible. It will look white and transparent so you will not be able to visualize it properly. So what we will do for that is, if we add color to it, it will become colorful. That is why saffronine is of red color. So how long did we keep it in saffronine? We kept
19:36 it for 30 seconds. Because of that, it will get pinkish color. And what will we do? We will be able to see it clearly. After that, with the help of a thin brush, you have to put this onion peel in another Petri dish which has a little water in it so that the extra saffron is removed and it gets removed from there. Now carefully transfer the peel under the microscope and make sure that the peel does not break or
20:21 crack. add glycerin to the peel. Glycerin will prevent the peel from drying out. Now carefully apply a cover slip to the peel. Apply a cover slip in such a way that So that there is no bubble left. So what we did is we applied the cover slip. Now there is no bubble left in it. Now take a blotting paper and gently wipe the extra glycerin with it. Now we have the slide ready. We have to see this slide in the microscope. So when you will see this slide under
21:08 the microscope, you will see something like this. So what are you doing? You will see it in the microscope. So what are the similarities you are seeing from Figure 2.3? What you are seeing is a brick wall. Are you seeing any similarity? So what are the arrangements you are seeing here? It is similar to the way you see the cells of onion peels when you put bricks on a wall. So you will see that the onion peels are made of this. See this brick is one cell
21:53 and the whole onion is made of this. So we have seen this. You will observe nearly rectangular structures under the microscope. So you saw those rectangular structures under the microscope like the brick. What are these? These are cells. onion peel. Okay? This is completely compactly attached together. You will see. So in between them you will not find space anywhere. Okay? How is this? Completely compactly attached to each other. There is no space anywhere. Without any space which is arranged. Regular brick like cells arranged tightly visible visible cell wall
22:40 in plant cell and in plant cell cell wall is also present. What is cell wall? I will tell you now when I will tell you the parts of a cell. So, these rectangular cells which are completely compactly arranged, these one by one cells are coming in compact arrangement and making our whole onion peel. We have seen this. Now what you have to do is, by removing the peel of different plant leaves etc., you have to observe and see the structure of their cells, how they are looking. that all the plants are made up of cells. Now if we talk about plants, then we can talk about
23:26 animals also. So, what is animal made of? Let's find out that too. Let's see what animal is made of and how animal cells are made. So, what we have to do for this activity? We have to take a toothpick on the inner lining of the cheek from the inside. Toothpick has one side pointed and the other side is blunt. We have to scrape the blunt side a little bit. So we have to remove the material from there. What will we do with that? We will observe it by keeping it on the slide. So first of all, we cleaned the mouth very well. Then we scraped the material from the inner teeth with the help of toothpick. Now put a drop of water
24:17 on the clean glass side of the scraped material. So what we did is we put water on the glass side and put the material on it and spread it well. spread it properly so that there should be no fold or cracks. Spread it properly. Put Methylene blue on it. Just like we put Saffron in there, we are putting Methylene blue here so that stain comes on it and it is easily visible. After that, after applying stain, the visibility will increase. After one minute, we will apply glycerin on it. Okay? We will apply glycerin, then we will
25:03 do the same thing, cover with a cover slip and remove the extra glycerin from the blotting paper. And while applying the cover slip, we will take care that no bubble comes under the cover slip on the slide. Okay? So we have done this now what we have to do is observe it under the microscope. So when you see, you will see such cells. Why do you see blue in it? Because we put blue color Methylene blue stain. So you are seeing polygonal shapes. Some are square, some are five sides, some are six sides. By doing this, you are getting to see different polygonal shaped
25:49 cells. So how do our cheek cells look? They are of a polygon shape. And what do these cheek cells make? They make the inner lining of our mouth. What similarities and differences did you observe between the cell of onion peel and human cheek cell? So did you see any similarity? And did you see any difference when you saw onion peel and human cheek cell? So you will see this is animal cell and this is our plant cell. We saw the example of plant cell from onion peel and And the example of the human cell, the example of the animal cell,
26:34 who did we see? We saw it from the human cheek cell. So you will see in both cases, whether it is a plant cell or an animal cell, different cells were visible to us that one cell, two cells, three cells are connected to each other. So we noticed one thing in both. You have observed that cells have three main parts. You must have seen that cells have three main parts. As you can see, one has outer lining and the other one is inside which we will call nucleus. and a fluid is filled in between these three things when you saw them like a brick our onion peel was also visible
27:23 in that that how was our cell made? see this how is our cell made? that cell is also a cell whose outer surface is visible as a proper lining and then we see a nucleus inside it and here fluid matrix is filled like jelly we call it as cytoplasm we got to see all these things but along with this I told you that a cell wall term came. In whose case did the cell wall term come? The cell wall term came in the case of our plants. What was the difference in the plant cell? It was
28:09 that in our plant cells, a cell wall is also present outside. So our cells are made up of three main parts. First of all, A thin outer lining. This outer lining you are seeing, this is talking about this. This outer lining is also in this. This. Okay? Now you will say that the dark green you are seeing, what is that? That is a cell wall but this lining is what we are talking about here. What is this? This is called a cell membrane. I will tell you in more detail. Then a central region. Then you will see a central region here and
28:54 here too. After that you will see a nucleus. and here also you will see a nucleus. These two structures are very detailed. If you see the basic structure then you will see this. This is an outer lining, one is a nucleus in the middle and what is made in the middle? our jelly-like fluid, jelly-like matrix is filled. These three parts you will get to see in plant cell and in animal cell also. What are they? A thin outer lining, a central region and small round structure which we will call nucleus. So this outer lining,
29:41 what is this? This outer lining is a cell membrane. The lining A cell is separating from another cell. What is that? That is the cell membrane. The round structure in the middle is the nucleus. Now the round structure in the middle, what is that? This is the nucleus. What do we call this? It is called nucleus. which is also covered by a thin membrane. There is a membrane outside the nucleus also. Like, there is a membrane outside the cell, we call it cell membrane. Similarly, there is a covering on the round structure, what are we calling it? If it is a nucleus, we will call
30:27 it nuclear membrane. The space between the cell membrane and the nucleus is filled with cytoplasm. And the space between the nucleus and the cell membrane is filled with cytoplasm. How to understand this? Just understand that there is a balloon in which you have put a small ball and filled it with water. So how is our balloon working? It is working like a cell membrane. How is the ball inside it? The ball is working like a nucleus and the water we have filled is our cytoplasm. We have to understand that it is present in plant cells as well as in animal cells. cell membrane, cytoplasm
31:14 and nucleus. What are these? These are the basic parts of the cell. But, along with these three things, in the plant cell, you will get to see another layer outside. Okay? When it comes to the plant cell, then you will get to see this cell membrane, Alright? What did we get to see in the plant cell? We got to see the cell wall. So in the onion peel cell, we will get to see the cell
32:03 wall because onion comes from the plant. What is the importance of these structures in a cell? What functions do they perform? Are these functions important for maintenance of life? After all, what is the importance of these parts? What is the function? Is it helpful in maintaining our life? Let's see. So students, what is the cell membrane doing? What is the thin covering inside? It is keeping cytoplasm and nucleus inside. Along with that, what does the cell membrane do to one cell from another cell? separate the cell membrane from the cell cell membrane. Cell membrane keeps cytoplasm and nucleus inside and
32:49 one cell membrane will protect its own cell and the other cell membrane will protect the other cell membrane. By doing this, the cells of the cell membrane are separated. How does this happen? Porous is done. What is the work of the cell? I told you that the cell What is the need of all cells for growth? For growth, energy is needed. Now for energy, food is needed. And this energy production, if glucose is producing energy by breaking in the presence of oxygen, this is called respiration. So what will happen in the process of respiration? we have to bring food from outside and the
33:35 waste material inside, what is cell? It is a unit of life. So this cell is the smallest thing which performs all the life processes living condition. So if this life process is performing then some things will have to be used, some waste material will have to be taken out. So how will that happen? It will happen in such a way that if there are some pores in the outer wall, so that the waste comes out and the necessary things come in. But now we cannot bring everything inside. So, how does it happen? It is selectively permeable. It gives permission to the selective things to go inside and out. If it is porous and anything can go inside and out, then the cytoplasm inside will not come out.
34:24 Similarly, what do we have to do? What do we have to remember? the cell membrane is porous but it is porous for selective things. It is the entry of the essential things of life processes. and the waste material is removed. So this is about the cell membrane. Now, the cytoplasm contains the other components of the cell. Like carbohydrates, protein, fat, minerals, all these things are found here. How does it happen? It is like jelly. It is like a jelly matrix. It is like
35:10 a liquid substance. Most of the life processes take place within the cytoplasm. The cell which is performing different activities, where do most of the activities take place? They take place in the cytoplasm which is the nucleus. What is the use of nuclear? Nuclear is the head. Like India, the capital of India, all the head offices are there. Similarly, Delhi is the capital of India. Similarly, who is the head of our cell? It is a nucleus. So what is the nucleus doing? It is regulating everything. How a process is to be done, its regulation, who
35:57 is doing that? It is doing the nucleus. It is the control center of all activities. It also regulates growth. The genetic information that we have, when it comes to DNA etc., we will talk about the nucleus only. Okay? Now let's talk about cell wall. Cell wall is present in plant cells only. It provides rigidity and strength to plants. It makes plants rigid and gives strength. That is why it is present in them. Cell wall present. Ok. That's why all the cells are arranged compactly in plant cell. How are all the cells arranged in plant cell? They are arranged without
36:42 space so that they remain rigid and their strength remains good. Ok. So, let's see what else is present in plants. So, students, cells in all parts of plants have tiny rod-shaped structures called plasters. You will see that our cell is an animal cell. But here, you will see that you will see structures like rods and we will call those rod structures as Plastids and one of these Plastids is called Chloroplast Plastids can be of different varieties like Chloroplast, Chromoplast, Leucoplast but what will we study about? We will
37:28 study about chloroplasts. What do chloroplasts contain? They contain chlorophyll. We know about chlorophyll. Chlorophyll traps sunlight and makes photosynthesis. Chlorophyll is a green pigment due to which the plant's parts look green. So what is this plastid? It is a chloroplast. The plastic present in one form is a chloroplast. The green things that you see here are chloroplasts. Because of this, plants look green and there is photosynthesis as well. And the non-green parts, I have taught you in the previous
38:14 class that that plants will lose their leaves in the autumn season. So will it not make food then? It does not have the green part. So where does it store the food? In the non-green part. So the non-green part stores the substances. There is a large empty space in the plant cell which we call vacuole. So this large vacuole in the middle is found in plant cells. It is either very small or absent in the animal cell. This is also found in our plant cell. What is
39:00 its function? It stores some important substances in our plant cell and helps to remove the waste material. Along with this, it also helps to remove the shape It maintains the shape of the cell and stores the good things and takes out the bad things. This is done by the vacuole. The size of the vacuole is big so the cell does not shrink. Because of this, we get support and strength in our plant. So, we have
39:45 got the idea. So, where are the plasters? They are present in the plant cell. We have seen three things till now. First cell wall, plastids, what is in that? Chloroplasts and third vacuole. What are these three things? Only in plant cell. Okay? So in animal cells, Animal cell vacuoles are either not present or very small. These small vacuoles store certain substances dissolved in water. These vacuoles store some things that are already dissolved in water. Now what is mitochondria? We have read so many things, so now let's read mitochondria.
40:31 So we were talking about energy. Where does energy come from? Energy is given by mitochondria. Mitochondria is called the powerhouse of the cell. This powerhouse is called mitochondria and it is the source of energy in our cells. It is mitochondria. Cells have many structures like Golgi body, lysosomes etc. You will learn all these in higher classes. We have already studied all the parts that you need. then a cell is not just a bag of liquid, it has many structures present
41:16 which make different parts of it and all have their own special function and all these things, the different parts of the cell, they function. That is why an organism is living. Okay? Did you understand? So we have now understood the basic structure of cell and we now also understand that plant and animal cells differ in shape and structure. So we have understood that everything is made up of cells whether it is plant or animal body and their shape and structure is also different. So different animal cells are different in their structure and shape. If the animal cells are of different types,
42:05 then are their shape and structure different? So let's see about this variation. Variation in shape and structure of cell. We will see about animal and plants. So our muscle cell and nerve cell are shown in figure. This is muscle cell and what is this? This is nerve cell. There are multiple in this muscle cell. One muscle cell is of this shape. How is it shaped? This is the shape of the nucleus. This is called the spindle shape. So what is the muscle cell? It is the spindle shape. And you will see that the nerve cell
42:52 is long. and it is branched. You will see many branches. So, are you getting to see similarities and differences? Absolutely. One is that these are muscle cells and nerve cells. Both are different types of cells. Second, their shape is completely different. So, how is muscle cell? It is of spindle shape and nerve cell is long and branched. Similarly, some cells are round in shape while others are long and thin. Some cells are round shaped like our white blood cells are round. Some are long and thin. All those cells are of different shapes and structures. So the number
43:38 of cells also vary in different organisms. How many number of cells does an organism have? What does this do to the organism? differ karta hai? Why do cells look so different from each other? Does the shape and structure of a cell relate to its function? Jo hamara cell hai aakhir wo ek dusre se itna alag kyun dikhta hai? Aur jo hamara structure hai aur function hai, kya wo kisi tarah se related hain cells ke? Aaye hum jaante hain. Toh unique shape size or structure is because it is totally dependent on its function. So shape, size, structure of the cell is made according to
44:24 the function of that cell. According to that function its shape and structure is made. But how do the do these cells help in performing various functions of the body let us find out so after all how these cells perform different body functions let's see you saw in activity 2.3 that how were the inner cheek cells thin and flat you saw that when we were looking at human cells how were the inner cheek cells they were thin and flat So I told you that the inner lining of our mouth was being made. So how should it be? If they are thin, if they are flat and thin, then only it
45:11 will be a product. protective layer. That's why our cells are thin and flat because they make protective lining on our inner surface of the cheek. What do we call nerve cell? We call it neurons. What is the function of the nerve cell? It is to bring messages to our body. For example, if there is an emergency and you have put your hand on the hot pan, how can you remove your hand immediately? Even if you have put it by mistake, you are not seeing it. But how does it remove the hand immediately? That happens because the
45:58 nerve cell present there shows immediately that it is a dangerous thing. It immediately sends a message to the brain that this signal is coming. What did the brain do? It immediately read it and said that it is dangerous and it again told the organ to remove the hand from there. So why is this message transferred in milliseconds? This is happening because nerve cells are present and their job is to bring messages. Now they are elongated and branched. Why? If they are elongated, then the message will pass quickly. If they are branched, then how will their connection with the nearby cells be? It will be good. If they are branched, then what will be the connection? It will be spread. That's why it will be easy for
46:46 them to work. So it is easy for them to reach different parts and pass messages because of their structure. Similarly, you will see variations in the plant cells. you will see that rectangular elongated oval or tube like all types of plant cells will also be seen. Some plants form long tubes which take water. We had read in 7th standard that who takes water in plants? Xylem takes it and who takes food? It takes phloem. So what are these? These are thin tubes from which water
47:32 and food are transported. So how are their cells made? Their cells are elongated. If they are long, then it is the work of transport. So making a tube will be easily done. Different parts of the digestive system are made up of different types of cells. Our digestive system also has different types of cells. A group of muscle cells are present in food pipe. In our food pipe, our esophagus, you will see that muscle cells are present. How do muscle cells exist? I have shown you. They are of spindle shape. is of spindle shape. Now what is the work of food pipe? The work of food pipe is to take
48:18 the food in the mouth to the stomach. And how? With the help of contraction relaxation peristaltic motion. So if the contraction relaxation of our cell is like this So, it will contract and then relax. Contract and then relax. That is why there are muscle cells present there because their structure is such that they can easily contract and relax and they can move the food forward. Pushing the food down the stomach. Did you understand the next part? This movement is possible because how are the muscle cells? thin flexible or spindle shape and now let's talk about the food pipe, let's talk about the stomach There are different types of cells present in the stomach
49:05 which perform different functions. For example, the muscle cell will contract the stomach and due to contraction relaxation of the muscle cells, the mixing of food with the digestive juices and acid will be done properly and digestion will be done properly. There are more cells present in the inner lining of the stomach that produce digestive juice and acid. Which help in the digestion of food in a simple form. All these cells together make digestion possible and easy.
49:52 So how is the shape and structure of a cell? Why is it like that? Because their function is specialized and their organ is able to perform its task due to that shape. Alright? So let's see how the level of different organisms is. It means that it is of a simple body formation or complex body formation. And we are saying that this fundamental unit of life, the cell, how are we able to make such a big human being from this cell? Let's know that. So how are all
50:38 living organisms? complex way. Like we have digestive system to digest food, respiratory system to breathe, excretory system to remove waste. So we have different systems. So this whole system is working together properly. Only then we have made the human body. So how is this complex? How did this complexity come to this point? Let's see. So what is a cell? It is a basic unit of life. Just like a brick becomes a house, similarly a cell becomes a human. What is in this? A group of
51:24 similar cells are making tissues. tissue. What does this mean? Let's say we have a cell. What did we do with it? We saw similar cells and called them tissue. There is a group of people who can perform one task and another group of people who can perform another task. So, we have assigned one task to one group of people and they can perform all the tasks in the same way. So they became one group of tissue. Other cells and people like them, what did we call them? They became another group of tissue because they were the same and were
52:11 able to work in the same way. So the similar cells together, what did we call them? We called them tissues. Now what did different tissues make? They made organs. Many tissues came together and made the same tissue. organs. Now when organs started working, an organ worked with its associated things. It worked with the nearby organs and it made a whole system. Like digestive system, first the stomach was made, then the organ was made. Then when the whole So when the digestive system is formed, it becomes the organ system. What was it doing? It was performing a major function of the body.
52:58 And all the organ systems, like we had different organs for different purposes, then they formed their own organ systems. And all the organ systems came together and made what? organism bana lia. Thik hai? Chahe wo plant ho, chahe wo animal ho. Toh alag alag level of organization kya hai? Cell hai, tissue hai, phir organ aaya, organ system aaya aur organism aa gaya. Jaise ki muscle cell ho gaya maan lije, usne kya bana ya? Ek jaise muscle cells aake, unhone muscle tissue bana liya. Uske baad, in muscle tissues ne maan lije wo stomach me present hai, toh un So they did the same thing, they did contraction relaxation and churning of food, mixing of food. So what happened? Our stomach became an organ. After that, what system
53:48 was formed? System was formed, digestive system. And the organism which was formed, whose digestive system was, what was that? It was human. Okay? So this is how different levels of organization are. This level of organization helps us understand that from a simple cell, the basic building block, we slowly came to a complex thing that we made a living being. complex living organism begin with simple cell called egg so now if you see how complex body structure is that starts with
54:38 one egg when female egg and male sperm meet then what happens a single cell is formed which we will call as a new life will be formed from here and that cell will divide in 2, 4 and then more and then slowly if we are talking about human then human will make a baby then that baby will come out after delivery and then slowly it will change into an adult human So, where did his life start? It started from a single cell. If we talk about here, then take an example, then what is ostrich egg yolk? It is the simplest
55:25 single cell, the largest. We are talking about the large yolk of the ostrich egg, not the long one. The largest single cell is the yolk of the ostrich egg. Now if we talk about the largest cell, then let me tell you that the longest single cell is our neuron, which we also call the nerve cell. So the longest cell is the neuron and the largest cell is the yolk of the ostrich egg. The egg of many organisms has an amazing ability to divide repeatedly to form a complete living being made up of many cells. What is the ability of many organisms to divide? And when
56:12 they divide, they become multiple cells. And what do they become from multiple cells? Tissues, organs and organ systems. Pura ka pura organism ban jata hai. The living organisms are called multicellular because they are not made up of one cell. They have multiple cells. So they are called multicellular organisms. Alright? Animals including humans and plants, all of these animals, humans, plants, all of them are multicellular organisms. So if we talk about the largest cell, then the cell of the ostrich egg, if we talk about the smallest cell, then it is the mycoplasma
56:59 and if we talk about the longest cell, then the nerve cell which we call the neuron. Alright, let's move on. So, in ever heard of, let's talk about the cell of ostrich egg. The yellow part of the ostrich egg is a single cell. It is made up of only one cell. And it is considered to be the largest cell in the living world. It is the only cell and it is the largest. Its size is 130 to 170 mm in diameter. The white part of the egg is extra non-cellular material and
57:44 that white liquid is used for nourishment. and the shell of the egg comes for protection and the yolk inside is the actual living so we are saying that the yolk of the egg is the largest cell in the living world. Alright, this is written here. Now let's see what are micro organisms? Let's know about micro organisms. Some living cells are made up of one cell or multiple
58:34 cells. Multicellular organisms are made up of many cells. If an organism is made up of one cell, then what will we call it? Unicellular organisms are so small that they cannot be seen with naked eye. Now, if this unicellular is made up of one cell or some cells, then it is very small. Like it is written here that very few cells. One cell is made up of few cells, how small will they be? It is not possible to see them with our naked eye. We call them micro organisms. Micro means very small. What kind of organisms are micro organisms? Living
59:19 organisms that we cannot see with our naked eye. Okay, so what are micro organisms? living beings which are very small to see from naked eye micro means very small now which are the bacteria in them? how are they all made up of one single cell? how is bacteria made up of single cell? how is amoeba made up of one single cell? these are all micro organisms examples ok these are made up of one cell that is why we call them unicellular now see So fungi, algae are made up of few cells. Not that they are very complex structure. They are made up of few cells. That is why
1:00:06 they are small. We cannot see them with naked eye. That is why they are also an example of microorganisms. But they have more than one cell. So we call them multi cellular microorganisms. Now these microorganisms can be found everywhere, in water, soil, air, our body, even inside our gut. And how do these cells look? The plant cells, the animal cells look like these. or look different from them? Let's find out that too. So to observe these cells of microorganism again we need to use a microscope which will increase their size
1:00:56 and make them visible to us. So what will we need to observe? Microscope. And what will the microscope do? It will increase its size. When the size increases, we will see the magnified thing. Scientists have also created a low cost and foldable paper microscope which we call a foldoscope. Scientists have made a low cost foldable microscope which we call a paper microscope.
