Cell
The cell is the smallest unit of a living thing that can display structural and functional features. The presence of the cell began to be recognized by the discovery of the microscope. Robert Hooke identified the cell in 1665 in the section he received from the cork.
With the development of the microscope, information about the cell has developed and Cell Theory has emerged. According to cell theory:
- The basic structure and task unit of living things are cells.
- All living things are made up of one or more cells.
- Cells are independent, but can also join the division of labor.
- New cells are formed by dividing existing cells. With cell division, hereditary substances in the parent cells are transferred to the offspring.
- All metabolic events take place in the cell.
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| Animal Cell |
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| Plant Cell |
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Types of Cells
Cells are divided into two as prokaryotes and eukaryotes according to their structure.
1. Prokaryotic Cell: Bacteria, cyanobacteria and arcs have a prokaryotic cell structure. All prokaryotic organisms are one-celled. Bacteria and arches can only be made from prokaryotic living things. In prokaryotic cells;
- They have no nucleus.
- Organelles surrounded by membrane are not found, only the membrane-free ribosome is found.
- It has cell wall, cell membrane, cytoplasm, ribosome and nucleic acids (DNA, RNA).
- Its genetic material is distributed throughout the cytoplasm.
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| Prokaryotic Cell |
2. Eukaryotic Cell: Cells with nuclear membranes and membrane organelles. Plants, animals, fungi and animals in the protozoans have a eukaryotic cell structure.
- They have nucleus.
- It has organelle with and without membranes.
- It can be found in single-celled and multi-celled organisms.
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| Eukaryotic Cell |
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Shape of Cells
The shape of the cells varies according to the work it does and where it is located. Because there is a close relationship between its structure and function. For example, the immobile egg cell is generally spherical, while the mobile sperm cell is long and flagellated. The white blood cells change their shape as they make the amoeba move. Tissue cells can be cubic, cylindrical, prismatic or flat under pressure.
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Size of cells
The size of the cell varies. The egg cell, which is the largest cell of human, is 200 microns in diameter. In addition, some of the nerve cells can be 1 to 1.5 meters tall with their axons. Red blood cells are 7.5 microns in diameter. Cell size is not related to body size. For example, the kidney and liver cells of elephant and mouse are the same size. The size of the organism is related to the excess number of cells.
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Number and Color of Cells
The number of cells in an adult varies with body size. A person has an average of 1013-1014 cells, excluding blood cells. In all vertebrate animals and humans, the number of cells of some organs (such as the central nervous system, retina, corti organ) is fixed. It does not reproduce later, only its volumes increase.
The cells are mostly colorless. However, some cells may appear in yellow, brown, black and other colors, depending on the pigment type in their cytoplasm.
The consistency of the cell also varies according to the cell type. This consistency is determined by the water and colloid substances it carries. For example, although the brain cells are very soft, some cells of the skin that are exposed to external effects are hard.
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Chemical Structure of the Cell
Inorganic and organic substances are found in the structure of a living cell.
Inorganic Substances:
Water: It plays an important role in the cell's vital activities. There are different amounts of water in the cells depending on the type of living being, the task of the cell, whether it is old or young.
Elements and Inorganic Compounds:
C, H, O, N, K, Ca, Mg, Fe, S and P are the basic elements of the cytoplasm. In the absence of these elements, the cell cannot fully function. For example, hemoglobin in Fe deficiency and chlorophyll cannot occur in Mg deficiency. Inorganic substances in living cells are acids, bases and salts. they are ionized in cell water. Inorganic substances adjust the cell's pH balance and osmotic pressure.
Organic Matters:
Organic substances that make up the cell; carbohydrates, lipids, proteins, nucleic acids and enzymes.
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Cell Structure
Cells are basically examined in three parts.
- Cell membrane
- Cytoplasm and cell organelles
- Nucleus
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| Cell Structure |
The Original Author: Mrs. Şerife (Erden) SARICA
