The cell (from Latin cella, meaning “small room”) is the basic structural, functional, and biological unit of all known living organisms. A cell is the smallest unit of life. Cells are often called the “building blocks of life”. The study of cells is called cell biology.
Cells consist of cytoplasm enclosed within a membrane, which contains many biomolecules such as proteins and nucleic acids Organisms can be classified as unicellular (consisting of a single cell; including bacteria) or multicellular (including plants and animals).While the number of cells in plants and animals varies from species to species, humans contain more than 10 trillion (1013) cells Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometres
The cell was discovered by Robert Hooke in 1665, who named the biological units for their resemblance to cells inhabited by Christian monks in a monastery. Cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that cells are the fundamental unit of structure and function in all living organisms, that all cells come from preexisting cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells. Cells emerged on Earth at least 3.5 billion years ago
Cells are the basic building blocks of all living things. The human body is composed of trillions of cells. They provide structure for the body, take in nutrients from food, convert those nutrients into energy, and carry out specialized functions. Cells also contain the body’s hereditary material and can make copies of themselves.
Types Of Human Cells
There are over 200 different cell types in the human body, each specialised to carry out a particular function, or form a particular tissue. The main types of cells in the human body are listed below:
- Stem cells
- Red blood cells (erythrocytes)
- White blood cells (leukocytes)
- Nerve cells (neurons)
- Neuroglial cells
- Muscle cells (myocytes)
- Cartillage cells (chondrocytes)
- Bone cells
- Skin cells
- Endothelial cells
- Epithelial cells
- Fat cells (adipocytes)
- Sex cells (gametes)
Functions of the Human Cell
The functions of the human cell varies based on the type of cell and its location in the human body. All the organelles work together to keep the cell alive and allow it to carry out its specific function. Sometimes these organelles are highly specialized and can vary in size, shape and number.
The organelles are the most basic functional units but it cannot exist and operate without the cell as a whole. Its functions include intake of nutrients and other substances, processing of these compounds, production of new substances, cell replication and energy production. In specialized cells that need to be motile, like sperm cells, tail-like projections allow for cellular locomotion.
The function of each organelle has already been discussed but is worth considering in summary.
- The cell membrane allows substances to enter and leave the cell. While certain substance like oxygen can easily diffuse through the cell membrane, others have to actively transported through the process of endocytosis. Small particles are transported by the process of pinocytosis while larger particles are moved by the process of phagocytosis. These functions can become highly specialized to allow cells to perform specific activities, like the macrophages that phagocytose invading bacteria to neutralize it.
- Small and large substances that do not dissolve in the cytoplasm are contained within vesicles. Lysosomes attach to the vesicles and digest this material.
- The endoplasmic reticulum and Golgi apparatus synthesize different substances like protein and fats as required by the cell or designated according to its specific function. It utilizes basic nutrient molecules that are either dissolved in the cytoplasm or specific substances contained within vesicles.
- Some nutrients, specifically carbohydrates, are transported to the mitochondria where it is broken down further to yield energy. In the process, high-energy molecules known as ATP (adenosine triphosphate) are manufactured and provide energy for other organelles.
- The genetic material housed in the nucleus provides the blueprint necessary for the production of specific compounds by the endoplasmic reticulum and Golgi apparatus. The genes also help the cell replicate and codes for the formation of new cells.
- Secretory vesicles store some of the enzymes and other specialized substances formed by the endoplasmic reticulum and Golgi apparatus. These stored substances are released from the cell when necessary in order to complete various functions that allow the body to function as a whole.