Single & Multicellular Organisms 5.L.1.1 SWL why some organisms are capable of surviving as a single cell while others require many cells that are specialized to survive.

Essential Question How do single and multi cell compare and contrast?

Introduction to Cells BrainPop: Cells

Cells Every living thing has cells within their body, and these are the building blocks of all life forms. The composition, distribution and the number of cells that are present in an organism determine where it is multicellular or unicellular. Cells in the human body play a vital role in the sustenance of life.

Cells In simple terms the difference between unicellular and multicellular organisms arises from the number of cells that are present in them. As the name suggests, unicellular organisms contain one single cell, while multicellular organisms contain more than one cell within them. All their physical characteristics and traits can be traced to this difference in the number of cells they contain.

Unicellular Organisms Due to the presence of only one cell in them, these organisms are much smaller in size and are very simple in structure. Most of these organisms fall under the category of 'prokaryotes', or 'prokaryotic entities‘, because their composition and structure is not complex. The structure known as the cell nucleus is completely absent in these prokaryotes, and this leads to their inability to handle their surface area to volume ratios. Owing to this reason, their sizes are very small.

Unicellular Organisms Most unicellular organisms are so small and microscopic in nature, that they are almost invisible to the naked human eyes. They do not have internal organs as well, and this means that the membranes which are organic coats around the organs are also absent. Due to their highly simplistic life form, these can exist in areas that are perceived to be hazardous for human life and are highly acidic or radioactive in nature.

Unicellular Organisms It is believed by many scientists that the human race is the result of long term evolution of many unicellular organisms that existed millions of years ago. The two sets of organisms exist in harmony with each other on our planet, and all these organisms have their own specific roles to play in nature's ecosystem.

Unicellular Organisms Examples: All forms of bacteria, amoeba, yeast and paramecium. Watch an Amoeba!

Unicellular Organisms

Multicellular Organisms On the other hand, these organisms are those forms of life that have more than one cell present in them. In fact they have millions of cells present in them.

Multicellular Organisms The larger number of cells means that these organisms are much bigger in size and are very complex and intricate in their composition and structure. Human beings are the best example of multicellular organisms, and the large number of cells leads to the birth of many different organs for carrying out different functions. Most 'eukaryotes' or 'eukaryotic entities are multicellular.

Multicellular Organisms The cell nuclei are present in eukaryotes and the DNA of the organisms are separately placed, unlike the case of unicellular organisms. All these cells work in tandem with each other to keep the life form alive, and this leads to a variety of complex functions working simultaneously.

Multicellular Organisms The organisms in both the categories differ greatly in their appearance, and even though multicellular organisms grow to large sizes some of them are still microscopic in nature. These are also known as 'myxozoa'.

Multicellular Organisms Examples: Human beings, animals, plants, myxozoa and all kinds of fungi. https://www.youtube.com/watch?v=MfopLilIOeA

Cells Scientists discovered all the differences between multicellular organisms and unicellular organisms and this laid the foundation for the rest of biology to develop. The advanced study of the structure of all animals and plants would not be impossible without proper knowledge about the cell structure of these organisms, since the cells are the primary life force and no organism can be alive without the presence of cells in them.

Cells The desire to know the differences between organisms is an important event in human history, and medical science would not be where it is today without this discovery.

Let’s Review! Single-celled organisms are made of only one cell. Example: algae, amoeba, paramecium Multi-cellular organisms, such as plants and animals, have a higher degree of specialization where the cells work together and function to create a living organism.  Example: a human – starts as a single cell. Then organize themselves into three groups called germ layers. One layer will form the skin and nerves, Another layer becomes the lining of the digestive tract. The third layer produces all other body parts.

Cells Introduction to Cells

Activity Now, your job is to create a Double Bubble Map to compare and contrast single and multicelluar organisms using the notes you have taken on your tree map.