 Now, we know that algae are usually broadly classified based upon their pigments because this is visible to us, but we also classify algae based upon their cellular organization. That is how their cells are organized, we classify them based upon the cellular organization into three types, the unicellular algae, the filamentous algae and the colonial algae. The unicellular algae are those algal species, which lives as single organisms. For example, euglena, euglena lives as in pond water or in a lakes water, all of the euglena, the euglena organisms we can say lives as single organisms and these are microscopic. Clemedomonas is another example. Then comes the filamentous algae, filamentous algae are the multicellular algae, which lives or which makes long filaments, which are mostly septated, which have septa here in the diagram. You can see a filamentous algae called spirogyra. This is a very common algae of the ponds near Lahore and in mostly Pakistan and many areas of the world. So the filamentous algae, they appear under microscope just like long thin filaments. Then comes the colonial algae. Look at a picture, it shows you wall walks, very another very common algae which is present in most of the ponds water, in water of the lakes. Wall walks makes rounded circular colonies and the daughter colonies, the newer cells grows inside the parent colony that is the larger colony. And when they grow to a specific size, then they are released from the colony and they make their own mature large colony. So based upon the cellular organization, we divide algae into three groups. Unicellular algae, the multicellular and filamentous algae and the colonial algae. Now about the distribution and significance of algae, though we already talked about different kinds of algae but we summarize it. Algae are widely distributed all over the world, green algae being the most abundant form of algae on earth, present in almost all types of water bodies, red algae are mostly distributed in the marine waters. The brown algae are also mainly distributed in marine waters, golden algae are almost exclusively marine, they are present in the waters of ocean. They are very important for us because they reduces the greenhouse effect. They utilize this carbon, whenever they are present, in no matter which type of environment they are present, they utilize the carbon dioxide gas and convert this carbon dioxide gas into carbohydrates as their own food. In this way they reduces carbon dioxide from the environment. And secondly, when they carry out photosynthesis, just like plants, they release oxygen in the environment. So and we know that oxygen is a necessary gas which is required by the animals and other organisms for their respiration, for their life processes. Red algae, these are used to produce different types of products, includes cosmetics and certain types of foods. The brown algae, they are specifically used for making agar, that is from weeds and they are also used for some salad dressings, some types of these brown algae, they are also used as salad dressings, the small parts are used in foods. In the golden brown algae, they are very important, they are used in making some petroleum products. Euglenoids, they are important at their place because they are the main producers of the freshwater ecosystems. So in the freshwater ecosystems, euglenoids have to carry out photosynthesis and without them other organisms, animal like, protists or fish and other organisms cannot survive. The blooms, this is a common term that we hear in the seasons, whenever when the organic matter, when the inorganic say carbon dioxide and sunlight is available to a good extent, then algae in specific season grow very well and they appear as very beautiful scum or surfaces upon the waters, we call them algal blooms. So it means that algae are very important producers in many of the food chains and the food webs in ecosystem, they convert sunlight into energy and to carbohydrates and they help in reducing the greenhouse effect by absorbing the carbon dioxide from environment, they are as used as human diet alternative, that is in place of gelatin, they are gelatin like materials and agar are used, weeds are past parts of many salads, some algae are used to make certain specific tastes in the ice creams, other materials from algae are also used in making some desserts, that is the sweets, sweets of specific kinds and agar as we previously talked about is the most important material for different types of microbiological preparations. Whenever we have to grow a microorganism on a solid surface, we have to convert our medium into a gel with the help of agar, you can see in the picture an agar plate on which microorganisms bacteria are growing and we know that growing bacteria is extremely important because some bacteria, there are lot many bacteria which produces different types of diseases in human beings and animals and plants and there are different types of bacteria which are beneficial for us. For example, the bacteria which produces yogurt for us, the bacteria which produces different types of antibiotics and some other important products like some hormones in saline, so agar is a very useful material. Which is extracted from the brown algae, the seaweeds, algal biofuels, this is one of the very important alternatives of the fossil fuels which are thought to be, we think that they are going to be finished in coming years and in the world, this is one of the most important type or kind of researchers that we need some fuels from biological materials. We know that algae, they are widely distributed, they grow very fast and they grow very well and from algal biomass, we can extract biodiesel and we can extract ethanol and we know that ethanol is an inflammable material and we can use it into petrol engines for running our vehicles. Even in United States from ethanol, some aeroplanes could also be fly. So, algae are the potential source of biofuels in near future. So, this was about the algae, one of the most important producers on the planet earth and they make various products for us.