A cell is the basic unit of life. It is the smallest unit capable of performing all of life's functions, including reproduction. Robert Hooke suggested the name 'cell' in 1665 from the Latin word 'cella' meaning storeroom or chamber, after using a very early microscope to look at a piece of cork. He was the first biologist who discovered cells. The study of cells from their basic structure to the functions of every cell organelle is called 'Cell Biology'.
In this introductory lesson, we will understand what are cells.
All organisms are made up of cells. They may be made up of a single cell (unicellular organisms), or many cells (multicellular organisms).
Cells are the lowest level of organization in every life form. However, the count of the cell may vary from organism to organism. Humans have a different number of cells compared to bacteria.
Unicellular organisms are made up of only one cell that carries out all of the functions needed by the organism, while multicellular organisms use many different cells to function. Unicellular organisms include bacteria, protists, and yeast. Human beings, plants, animals, birds, and insects are all multicellular organisms.
The fact that we need a microscope to view cells shows that cells are small quite small, but do keep in mind that cells are much larger than some other substances that we have learned about. In fact, cells are made out of many atoms, so they are larger than macromolecules and viruses.
No. All cells are not the same. Although they are basic units of life, there are many different kinds of cells that make up multicellular organisms, they are of different shapes and sizes, like bricks of buildings. For example, a sperm cell is much smaller than a muscle cell. The shapes and sizes directly influence the function of the cell. Cells are complex and their components perform various functions in an organism. Some cells have specialized jobs that allow them to work with one another to perform an organism's biological functions.
The cells pictured below are just a few examples of the many different shapes that cells may have. Each type of cell in the below picture has a shape that helps it to do its job. For example, the nerve cell carries messages to other cells and it has many long extension that reaches out in all directions, allowing it to pass messages to many other cells at once. Algae cells have tail-like projections. Do you know why? Because algae live in water, these tail-like projections help them swim. Then, there are pollen grains with spikes on them to help them stick to insects such as bees, so insects can pollinate flowers.
Cells can vary greatly in size. You need a microscope to see most human cells.
Red blood cells are some of the smallest cells in the human body. These have a diameter of 0.008mm, meaning a line of 125 red blood cells is only 1mm long.
The ovum or egg cells are one of the largest cells in the human body. It has a diameter of roughly 0.1mm, so you can see them without a microscope. A line of 10 egg cells is 1mm long.
There are many different types of cells, but they all have certain parts in common. The parts include a plasma membrane, cytoplasm, ribosomes, and DNA.
1. The plasma membrane (also called the cell membrane) is a thin coat of lipids that surrounds a cell. It forms the physical boundary between the cell and its environment, so you can think of it as the "skin" of the cell.
2. Cytoplasm refers to all of the cellular material inside the plasma membrane, other than the nucleus. Cytoplasm is made up of a watery substance called 'cytosol' and contains other cell structures such as ribosomes.
3. Ribosomes are structures in the cytoplasm where proteins are made.
4. DNA is a nucleic acid found in the cell. It contains the genetic instructions that cells need to make proteins.
These parts are common to all cells, from organisms as different as bacteria and human beings. This similarity shows that all life on Earth has a common evolutionary history.
