Detailed Concepts of Discovery of Cells, Cell Theory and Characteristics of Cell
|
Topic Under |
|
|
Concepts covered |
|
Introduction to Cell
Cell is the basic structural and functional unit of life. Cells are considered as basic unit of life because all organisms including plants, animals are made up of cell. They are known as functional unit of life because cells are capable of independent existence and performing essential functions of life.
Discovery of Cells
The discovery of cell is one of the remarkable advancements in the field of science. It helped us know that all the organisms are made up of cells, and these cells help in carrying out various life processes. The structure and functions of cells helped us to understand life in a better way.
Robert Hooke discovered the cells. He was the first to discover cell in 1665 in a thin cork slice with the help of primitive microscope. He was one of the earliest scientists to study living things under a microscope.
While examining a thin slice of cork, Robert Hook saw the internal structure of cork that looks same as the structure of a honeycomb which consists of many little compartments. In 1665, he made a self-designed primitive microscope, and observed the same slice through it. Ultimately, he called these boxes cells. So, earlier these cells were named as compartments but later on it was replaced by term cell.
Cork: It is a dead part of tree, which comes from bark of tree.
Contribution of other scientist in discovery of the cells:
- Anton Van Leeuwenhoek observed cells under improved microscope with higher magnification. This time, he had noted that the cells exhibited some form of movement. As a result, A. V. Leeuwenhoek in 1674 was the first to discover free living cells in pond water with the improved microscope.
- Robert Brown, a Scottish botanist, provided the very first insights into the cell structure. He discovered the nucleus in the cell in 1831.
- Purkinje coined the term ‘protoplasm for the fluid substance of the cell in 1839.
- The discovery of electron microscope in 1940 made it possible to study the complex structures of the cell and its various organelles.
Cell Theory
By the early 1800s, scientists had observed the cells of many different organisms. These observations led two German scientists, named Theodor Schwann and Matthias Jakob Schleiden, to propose that cells are the basic building blocks of all living things.
Around 1850, a German doctor named Rudolf Virchow was studying cells under a microscope when he happened to see them dividing and forming new cells. He realized that living cells produce new cells through division. Based on this realization, Virchow proposed that living cells arise only from other living cells.
The ideas of all three scientists (Schwann, Schleiden, and Virchow) led to cell theory, which is one of the fundamental theories unifying all of biology.
Cell theory states that:
- All organisms are made of one or more cells: all living organisms’ weather they are plants or animals, unicellular or multicellular, all are composed of cells.
- All the life functions of organisms occur within cells: a cell can independently perform all necessary activities to sustain life like nutrition, excretion, respiration, etc.
- All cells come from already existing cells: spontaneous generation of living things comes from inanimate matter that does not occur over periods as short as our lifetimes. Every multi-cellular organism has come from a single cell. Because cells divide to produce cells of their own kind. All cells thus come from pre-existing cells.
Characteristics of Cell
Cells are the basic units of structure and function of living things. They are the smallest units that can carry out the processes of life. All cells have certain parts in common. These parts include a plasma membrane, cytoplasm, ribosomes, and DNA.
Some important characteristics of cells are following:
- Cells provide structure and support to the body of an organism.
- Every cell has one nucleus and membrane-bound organelles in the cytoplasm. Nucleus holds genetic information necessary for reproduction and cell growth. A cytoplasm (jelly like structure), Cell membrane and Ribosomes (production of proteins).
There are certain characteristics of both plant and animal cells which signify it and help us to identify which one is plant cell or which one is animal cell.
- Shape: Animal cell is look like round or irregular shape while plant cells are in rectangular shape.
- Cell wall: The cell wall is absent in animal cell while it is present in the plant cell in the form of cellulose.
- Plasma membrane: In animal cell, only cell membrane is present but in plant cell, cell membrane is present but with cell wall.
- Centrioles: In animal cells, centrioles present while in plant cell centrioles are present only in lower plants. While it is absent in higher plants.
- Chloroplast: Animal cell does not have chloroplast. But, Plant cells have chloroplast because they made their own food by the process of photosynthesis.
- Plastid: In animal cell, there is absence of plastid. But in plant cells plastids are present. Plastid is a major double membranous organelle found in the cell of the plant and algae that contain chlorophyll that can carry out photosynthesis.
- Vacuole: Small vacuoles are present in animal cell, mostly vacuole are absent in it. While, in plant cell one large central vacuole is present, it makes plant cell rigid and takes up 90% of cell volume.
The different cell organelles like cytoplasm, ribosomes, mitochondria, endoplasmic reticulum, Golgi complex, microtubules all are present in animal as well as plant cell too.