Cell, tissues, organs and systems

Our planet is inhabited by different kinds of living organisms. Some are big, some are small, some are even invisible to our naked eyes. These living organisms range from smaller – archaebacteria, bacteria, protists, increasing in size, to larger ones – fungi, plants and animals. The body of these living organisms is made up of microscopic units and we call these units as cells, similar to what we say atoms in physics as units of matter.

The cell is the basic structural and functional unit of living organisms.

Study of form, structure and composition of cells is called cytology. And remember that the branch of biology that deals with various aspects of structure, chemistry, development, genetics and functioning of cells is called cell biology.

So, what we have understood that all living organisms are made up of cells. Although, these cells may differ in shape, size and number of different organisms but they all share a common basic structure. (We will study the basic structure of the cell in next lessons.)

Some organisms are made up of only one cell and some organisms including us are made up of more than one cell.

Unicellular Organisms: Organisms made up of a single cell are called unicellular organisms. These are Bacteria, Amoeba, Paramoecium. Hence, they are not visible by our naked eyes.

Multicellular Organisms: The organisms made up of two or more cells are called multicellular organisms. These are fungi, plants and animals. That’s why they are large and easily visible by our naked eyes.

But in multicellular organisms, all cells are not similar in shape, size and functions. There is a division of labour (work distribution) in a multicellular organism, where a group of cells perform a specific function. So, based on specific function, these cells are differentiated into shapes and sizes appropriate to the functions they are assigned.  Like group of cells having contractile property are differentiated to muscle. These differentiated cells aggregate to form different tissues. Tissues form organs and organs give to organ systems that perform specialized functions.

Now-a-days, you are well aware of virus, especially coronavirus. Let’s have an idea about it also. Virus lie on the borderline between the living organism and non-living things. They are considered neither living nor non-living and thus are acellular, because they lack cytoplasm and membrane bound cell organelles. They do not have their own metabolic machinery. Therefore, they do not show characteristics of life until they enter any living cell as a host. Virus uses cellular machinery of the host for their multiplication.

let’s delve into the fascinating world of human anatomy and physiology using analogies to make it easier to understand.

1. Tissues: Tissues in the body are like building blocks in a construction project. Just as various types of bricks, concrete, and steel come together to form different parts of a building, different types of cells and substances come together to form tissues. These tissues have specific functions and structures that help the body function effectively.
2. Organs: Organs are akin to specialized departments in a company. Each department has a specific role and expertise. For instance, the heart acts like the central management department, overseeing and regulating the flow of resources (blood) to all parts of the company (body). The lungs can be compared to the ventilation and air conditioning system, ensuring a steady supply of fresh air (oxygen) for optimal performance.
3. Systems: Systems in the body can be likened to interconnected networks within a city. Just as the transportation system (circulatory system) moves people and goods efficiently throughout the city (body), the nervous system can be compared to the communication network, transmitting messages and coordinating activities. Similarly, the digestive system acts like waste management, processing and removing unwanted materials.

Understanding human anatomy and physiology in these terms helps to visualize the intricate and coordinated workings of our body, enabling a clearer comprehension of how everything fits together to maintain health and well-being.