 Today, we are going to talk about the organization of life. First of all, we will have a brief look on what is life? Anything is considered living if it has few properties. One, it acquires energy from the environment and utilizes that energy for performing its various functions. Second property is that it reproduces itself for continuation of its race. For example, lions eat other animals to acquire energy and deers eat the leaves of the other plants or the grasses and convert them into the chemical energy for their performing their functions. There is a third property of life which is almost equally important. That is, anything is living if it mutates a change itself in response to the change in environment. Sometimes these changes are mutations as they are spontaneous. If they are useful for the organism, they continue in the race. If they are sometimes lethal or they are not useful, they are discarded or sometimes they may become very lethal for the organism and the organism dies. Now we look at the next thing. What is biology? Biology is the study of life, bios, life, logos, study or reasoning. So biology means the study of life or the reasoning about life, about the living part of the world. Why this is important and why this is useful? Because the living part of the world is related to the human beings and the science is basically for the benefit of human being and for the sustainability of the systems upon the environment, particularly for the whole of the biosphere. Now we look at how life is organized. What are various levels of organization in life? We look at a flow chart. As you can see in this flow chart, there are different levels of organization in life. We just have a brief look on these levels and then we will go in the detail one by one. Anything or any matter or mass mainly consists of atoms. Atom is atom not to cut. It is assumed that atom is the smallest particle of the elements which are not divided further. They have all the properties of that particular element. Atoms makes molecules. Atoms join together. They rarely live in the environment in isolation but they live in combinations. They join together by a particular type of bonding to make molecules. Molecules makes large molecules or the macromolecules. Then these molecules make cells. Cells makes tissues that is groups of cells which work together to make larger forms called organs. Organs makes the organ systems. Organ systems makes organisms and organisms makes populations. Populations makes communities. Communities makes the ecosystems and all of the ecosystems of the world makes biosphere. We look at all these levels now one by one. Atoms. And comes from Greeks. Atom not to cut. This is the smallest part of an element that is not dividable further. Atoms are but they retain the properties of that particular element. In nature there are about 92 elements. Among these 92 elements there are only 16 that makes the living things. Among these 16 there are about few elements which makes about 99% of the living beings. These are oxygen, carbon, hydrogen, nitrogen, calcium and phosphorus. There are many others including calcium, potassium, iron, zinc which makes another 1%. We call all of these elements the bio elements. What is atom itself? As you can see in the diagram an atom consists of an orbital or maybe more than one orbital and a nucleus, a central part. In the nucleus or in the central part there are two types of subatomic particles called protons which are positively charged. The other called neutrons which don't have a charge. And there is a third type of subatomic particles called electrons which keep moving around in orbitals surrounding that nucleus all the time. So it means that an atom have three types of subatomic particles electrons negatively charged and always moving protons positively charged stay inside the nucleus and the neutrons which also stay inside the nucleus. Atoms do not live in isolation. Atoms join together to make molecules. Now there are two types of bondings by which atoms join together. One is called ionic bonding and other is called covalent bonding. In ionic bonding one atom gives away its electrons to the second atom and they stay together. The other type is called covalent bonding in which both atoms share their electrons and they stay together. Covalent bonding is more strong type of bonding in comparison to the ionic bonds. Molecules are of two types. One are called micromolecules and others are called macromolecules. Micromolecules are those molecules which have a low molecular weight. And the macromolecules as the name says macrobig they are the molecules which are large which have a higher molecular weight. For example, micromolecules include the glucose molecule, the water molecule and the macromolecules they include the proteins, carbohydrates and the lipids. There are different types of macromolecules which are present inside an organism. Carbohydrates, lipids, proteins may make different types of structures. They may perform different types of functions. For example, if we take proteins we can call proteins structural proteins or we can call them functional proteins. Structural proteins if they are making a structure for example, they are making cell, a part of cell. They are called functional if they are an enzyme and they have to help a reaction inside the cell. Now we look at the structures of various micromolecules and macromolecules. Here you can see in the diagram there are two micromolecules. One is called the water molecule and the other is the glucose molecule. Both are models which are showing you that how these molecules look like and how they bond together. In the next diagram you can see various macromolecules. Here you can see a hemoglobin molecule. Hemoglobin is a very important protein that is present inside the blood cells and it carries oxygen and it transports oxygen in all of the organism, organism's body through blood. Blood is a liquid tissue. As you can see there is a red blood cell and we are showing hemoglobin molecule outside the blood cells which have different protein chains and have you iron molecules as here is the next DNA. DNA is the genetic material of the organisms. Here you can see a molecule of DNA which have a double helix. Both helixes there are two chains which are running in a helix form parallel to each other and this is the genetic material. This is we can say the blueprint of life which makes all the living organisms. Here is the third important form, the lipids or the fats. Lipids or fats these are present in the form of long carbon chains which have hydrogen molecules attached on the various sides. Lipids may be of two types called saturated lipids present in animal cells and unsaturated lipids present in the blood cells. Saturated lipids as you can see in their structure they are straight and they are solid at room temperature but the unsaturated lipids which are present in plants have double bonds in their structure and with the result they have mix or bendings in their structure. Due to these bendings they remain liquid at the room temperature. Now we go to the next part that is the organelles. Molecules, micromolecules and macromolecules join together to make larger structures. These structures are called organelles. Organelles are subcellular structures that is these are the structures which makes cells. Organelles are of different kinds according to the type of cell there are different types of organelles there are few organelles which all cells to have like mitochondria which is called powerhouse of the cell and it produces energy like nucleus which have the genetic material of the cell and it is responsible for the heredity and genetic information transfer like ribosomes which makes proteins which are the sites where protein synthesis takes place. So there are different kinds of organelles and these organelles combine to make a cell. Cell the basic unit of life. Here you can see in the diagram on the right side there is a diagram of the powerhouse of the cell mitochondria in the left you can see an electron microscope a transmission electron microscope image of the same mitochondrion which is drawn on the right side that is the real life image of mitochondria taken through a transmission electron microscope as you can see it have many membranes this organelle actually produces all the energy required by the cell in the form of ATP adenosine tri phosphate cells organelles join together to make cells. Cells are the basic units of life. Cells are the smallest living thing if we can say all the living organisms they consist of cells. Cells are of various kinds there are different types and they consist of different types of organelles. There are certain organisms which consist of only one cell we call them unicellular organisms for example various protozoans like a paramecium like an amoeba there are other organisms which consist of many cells there are more organisms which consist of billions and trillions of cells. So cell is the basic unit of life here you can see in the diagram a unicellular organism a bacteria this diagram shows you the inner part of bacteria and the outer part of bacteria in the inner part you can observe the nucleoid region actually the prokaryotes say prokaryotes pro means old karyo means nucleus they have a old type of nucleus which is actually not technically called a nucleus because this is not enclosed by the membrane it have its genetic material in the form of a chromosome. You can see the cytoplasm of that cell and you can see the membranes and walls which are covering the bacterial cell. Now in the next diagram you can see the plant cell the plant cell is covered by thick wall then cell membrane then comes if it's different organelles as you can observe in the diagram you can see a vacuole a large vacuole plant cells have a very large vacuole when they are mature you can see a nucleus which is slightly on a side due to presence of a large vacuole you can see different mitochondria you can see the Golgi apparatus and lot many other organelles inside the cell. In this diagram you can see an animal cell animal cell is different from plant cell in the sense it don't have a wall it don't have a cell wall it is covered by only a cell membrane in its inside you can observe almost the same organelles like the nucleus mitochondria the endoplasmic reticulum Golgi bodies ribosomes and lot many other organelles. There is still another type of cells called stem cells you have seen the plant cells animal cells bacterial cells all of these cells are differentiated differentiated means that they are they are developed they are adopted to perform a specific function in the adult human being in the adult animals and more precisely in their embryos there are few types of cells which are almost undifferentiated we call these cells stem cells these cells are important for us because they are undifferentiated why they are undifferentiated because almost all of their genes are switched off these genes are not doing anything it means that we can convert these cells into any type of cells now this is very important for us because if a person for example these days there are lot many diseases due to which people become become disabled like if there is a spinal injury if there is a person of patient of hepatitis their liver is damaged and the result is this that their organ is not functioning now we can develop these stem cells into different types of tissues and organs and we can replace the damaged tissue of tissue or organ of the patient and the patient can run the healthy life so these cells are very important for us these are present in various adult organisms and mostly these are present in embryos but using the embryonic stem cells is considered by most of the religions unethical and there is a debate on the stem cell use but still there are various sources of stem cells which are which are not debatable and which are still in use in the medical sciences so there are different types of cells present inside organisms cells may be epithelial cells which makes the skin of the organisms cell may be the nervous cells which make different types of nerve cells the neurons which transmit the messages between all of the organisms cells may be of stomach which which contract and relax for the movements of stomach cells may be of muscles which are long long fibers and which makes which makes our body move and change its directions so on the cells makes tissues tissues what are tissues now tissues are the groups of similar cells which perform a similar function there are different types of tissues present inside the organisms bodies there are few organisms which consist of only two layers of tissues called ectoderm and endoderm there are few organisms which have more layers and there are few organisms as complex as the human beings which have lot many types of tissues which perform their different functions now we look at these diagrams which show you different types of tissues and their functions let's have a look on the diagrams here in the first diagram you can observe the epithelial cells simple columnar epithelium these cells are elongated quite long and these are present in the intestine these cells can absorb different types of nutrients these cells are specialized in their functions and their function is to absorb nutrients they are designed in a way in a fashion that they can absorb nutrients from its environment as you know that when food is digested it is passing through the intestine and within the intestine there are these cells which have property of absorbing these different types of foods when the digested food pass through these cells pass from near of these cells then these cells absorb the digested part in the second diagram you can see a slightly different types of cells these cells are present in our trachea below our throat in our respiratory tract as you can see in their structure these cells have cilia on their surface cilia cilia are basically small hair light projections of the cell membrane these cells produce mucus as well and as you know that when we take in the air this air passes through the trachea passes through the airways and there are a lot many dirt particles and molecules present in that air these particles are trapped by the movement of the cilia and they are trapped inside these the mucus present on the surface of these cells and hence the air which goes inside our lungs is clean clear here you can see in the next diagram another type of cells which are called stratified cells which are present in our mouth in our esophagus in our digestive tracts and these cells perform different types of functions these have to allow the food pass through and below these cells we have muscle cells which contract and relax on intervals to move our food down our esophagus down our food canal in a regular fashion if this movement is changed if this movement is in the other direction we experience vomiting vomiting is the anti-normal direction of the movement of the food so there are different types of tissues still we can say talk about for example the nervous tissue the nervous tissue or the nerve or the tissue in the spinal cord and the brain they have various different properties they have nerve cells in them and they are supported by different other cells these cells collectively perform the transmission of information from the brain to the body and from the body back to the brain so cells are specialized and they when they make tissues that is groups of similar cells which perform a specific function then they makes the tissue specific as well that is one tissue will perform one function it will consist of similar type of cells