Cell Theory Definition
Cell theory is a fundamental scientific theory in biology that states that all living organisms are made up of cells, which are the basic units of structure and function. It was first formulated in the mid-nineteenth century by Matthias Schleiden and Theodor Schwann.
Cell Theory Overview
Cell theory is a fundamental scientific theory of biology that states that all living organisms are composed of individual cells, which are the basic units of life, and that new cells arise from preexisting cells.
The cell theory was developed in the mid-19th century by Matthias Schleiden and Theodor Schwann, who proposed spontaneous generation as the method for cell origination. However, it is now known that life comes from preexisting life and that cells come from preexisting cells.
The history of cell theory is a history of the actual observation of cells. Early prediction and speculation about the nature of the cell were generally unsuccessful. The decisive event that allowed the observation of cells was the invention of the microscope in the 16th century.
Antony van Leeuwenhoek observed Protista using his lenses in the 1600s, but it wasn’t until staining techniques were developed in the late 1830s that botanist Matthias Schleiden and zoologist Theodor Schwann were able to propose the unified cell theory. Rudolf Virchow later made important contributions to this theory.
Cell theory is a conceptual advance in biology and resulted in renewed attention to living processes that go on in cells. It explains how energy flows within cells and how they divide and pass on hereditary information.
3 Parts of Cell Theory
Cell theory is a fundamental concept in biology that describes the basic unit of life. The three parts of cell theory are:
- all living organisms are made up of cells,
- cells are the most fundamental unit of life, and
- cells come from other cells.
The first part of cell theory states that all living things, including bacteria, viruses, plants, animals, and humans, are composed of cells. Cells consist of a group of specialized structures that work together to perform specific functions. For example, skin tissue is composed of cells that protect the body from external damage.
The second part of cell theory states that cells are the most fundamental unit of life. This means that all living organisms are made up of one or more cells and that a cell is the basic structural and functional unit of living organisms.
Cells have different structures and functions depending on their type. For example, nerve cells transmit signals throughout the body while muscle cells contract to produce movement.
The third part of cell theory states that cells come from other cells. This means that no cell on Earth has arisen spontaneously and all cells are the result of cell division. When a cell is large enough, it replicates its DNA and important components. These components can then be divided into two daughter cells which are copies of each other.
Cell Theory Examples
Single-Celled Organisms
A unicellular organism is an organism that consists of a single cell, unlike a multicellular organism that consists of multiple cells. Unicellular organisms perform all vital functions including metabolism, excretion, and reproduction within one cell.
Unicellularity is not exclusive to prokaryotes. Some eukaryotes live singly as well. Examples of single-celled eukaryotes are the unicellular algae.
Prokaryotes lack membrane-bound organelles such as mitochondria or a nucleus. They have a nucleoid chromosome, which is in contrast to eukaryotes that typically have linear chromosomes.
Bacteria are one of the world’s oldest forms of life and are found virtually everywhere in nature. They reproduce through binary fission and can also undergo a sexual process in about 80 different species.
Unicellular organisms can be multinucleate like Caulerpa, Plasmodium, and Myxogastria. Some unicellular organisms are partially unicellular like Dictyostelium discoideum.
Many algae are unicellular and are usually found on rocks, soil or in coastal waters. The largest single-celled organism is one of the aquatic algae.
Unicellular organisms include bacteria, protists, and yeast. For example, paramecium is a slipper-shaped unicellular organism found in ponds.
In Plants
The cell theory is a fundamental concept in biology that states that all living things, whether plants or animals, consist of one or more cells. The theory further states that new cells can only be made from existing ones, and organisms can grow and reproduce because their cells are able to divide.
German botanist Matthias Jakob Schleiden and German physiologist Theodor Schwann are credited with establishing the cell theory as a basic, unifying theme of all biology.
Plant cells vary in size from about 7 µm to fiber cells a few micrometers wide but a meter or more in length. Most plant (and animal) cells are between 10–100 µm and thus too small to be seen without magnification since human eyes have a limited resolution.
Plant cells contain many organelles such as mitochondria and chloroplasts which differ from other organelles in their semi-independence. In many ways, they resemble bacteria: both bacteria and the organelles can divide, their DNA is organized similarly, and both have double membranes.
The modern cell theory holds that all organisms are composed of one or more cells. New cells come from pre-existing cells; lifeforms today have descended in unbroken continuity from the first primitive cells that arose on earth more than 3.5 billion years ago.
In Animals
Animal cells are eukaryotic cells that do not have a cell wall, unlike plant and fungal cells. They have a plasma membrane, a membrane-bound nucleus, and organelles. The nucleus is where the cell’s DNA is located. Animal cells also have lysosomes and centrosomes. The centrosome has two bodies, the centrioles.
Animal cells are capable of cell division because they lack centrioles. Flagella and cilia are long, hair-like structures that extend from the plasma membrane and are used to move an entire cell.
When present, the cell has just one flagellum or a few flagella. When cilia are present, however, they are many in number and extend along the entire surface of the plasma membrane.
Animals are a diverse group of organisms that make up about three-quarters of the species on Earth. They range from corals and jellyfish to ants, whales, elephants, and more.
Other Organisms
Cell theory is a fundamental scientific theory of biology that states that cells are the basic units of all living tissues.
The theory was first formulated in the mid-nineteenth century by Theodor Schwann and Matthias Jakob Schleiden, who proposed that living organisms are made up of cells and that they are the basic unit of life. Rudolf Virchow later added to this theory, stating that all cells arise from preexisting cells.
Cell theory applies to all living organisms, including single-celled and multicellular organisms. Although cell theory was first developed based on observations of plant cells, it applies to all types of cells found in animals, plants, fungi, and bacteria.
The history of cell theory is a history of actual observation of cells. Early prediction and speculation about the nature of the cell were generally unsuccessful until the invention of the microscope in the 16th century allowed for their observation.
Contributions to Cell Theory
Matthias Jakob Schleiden was a German botanist who, along with Theodor Schwann, founded the cell theory. In 1838, Schleiden defined the cell as the basic unit of plant structure.
He observed that different parts of the plant organism are composed of cells or derivatives of cells and became the first to formulate what was then an informal belief as a principle of biology equal in importance to the atomic theory of chemistry. A year later, Schwann extended Schleiden’s cell theory to animals.
Schleiden’s “watch-glass” theory of cell formation was wrong – he believed that cells crystallized in a formative liquid containing sugar, gum, and mucous – but it focused attention on the problem of cell reproduction and provided a testable hypothesis. More significant was Schleiden’s insistence that plants consisted entirely of cells and cell products.
