Anything less than a complete cell cans neither lead an independent existence nor perform all the functions of life. A multicellular organism is made of many cells. A higher animal or plant contains billions of cells. For example, a newly born human infant has 2 x cells. The number increases to trillion x or cells in the body of 60 kg human being. A drop of blood contains several million cells. The large sized organisms do not have large sized cells. Instead they possess higher number of cells.
In multicellular organisms, cells are building blocks of the body or basic units of body structure. Human body has some types of cells, e. Cells are grouped into tissues, tissues into organs and organs into organ systems. Occurrence of different types of tissues, organs and organ system results in division of labour or performance of different functions of the body by specialised structures.
Cells are not only the building blocks of the organisms, they are also the functional units of life. Life passes from one generation to the next in the form of cells. The activities of an organism are actually the sum total of activities of its cells. A new cell always develops by division of a pre-existing cell. Cells are totipotent, i. Internally each cell is build up of several organelles. The organelles perform different functions just like the ones carried on by different organ systems of the body.
All life activities of the organism are present in miniature form in each and every cell of its body. Thus, cell is a basic unit of life and structural and functional unit of an organism. It is the smallest unit capable of independent existence and performing the essential functions of life. Work on the study of cell has continued for more than the last three and a half centuries.
It required microscopes or instruments with good resolving power and magnification. Improvement in tools and techniques has continued all this period to enhance our knowledge about the cell. The first microscope was built by Zacharias Janssen in It was first modified by Galileo and then by Robert Hooke Fig. Robert Hooke was a mathematician and physicist. He developed a new microscope with which he studied the internal structure of a number of plants.
His work is famous for the study of cork cells. He took a piece of cork of spanish oak and prepared thin slice by means of sharp pen knife. A deep planoconcave lens was used for throwing light on cork piece. The latter was observed under the microscope.
He did not know the significance of these structures and regarded them as passages for conducting fluids. Robert Hooke found that the cells or boxes were not very deep. A cubic inch contained ,, cells, a square inch 1, 66, and one inch strip cells. Cells were also observed prior to Hooke, by Malpighi , who called them saccules and utricles. Leeuwenhoek was first to observe, describe and sketch a free living cell.
He observed bacteria, protozoa, spermatozoa, red blood cells, etc. In the beginning of nineteenth century it became clear that the bodies of organisms are made of one or more cells. Robert Brown discovered the presence of nucleus in the cells of orchid root. Living semifluid substance of cells was discovered by Dujardin and named sarcode. Schleiden found all plant cells to have similar structure— cell wall, a clear jelly-like substance and a nucleus.
Schwann discovered that animal cells lacked cell wall. Purkinje and von Mohl , renamed sarcode or the jelly like substance of the cells as protoplasm Gk. Cell membrane was discovered by Schwann but was provided with a name by Nageli and Cramer Soon various organelles were discovered inside the cells. Electron microscope has elaborated our knowledge about cells. Development of cell theory illustrates how scientific methodology operates. It involves observation, hypothesis, formulation of theory and its modification.
Observations were started by Malthias Schleiden , a German botanist who examined a large number of plant tissues. He found that all plant tissues were made of one or the other kind of cells. Therefore, he concluded that cells constitute the ultimate units of all plant tissues. Theodore Schwann , a German Zoologist, studied different types of animal tissues including development of embryos.
Other cells divide when they reach maturity through the Mitosis or Meiosis types of cell division. The cells that do divide do so in what is called the cell cycle, the cycle of a cell life from one division to the next. A cell cycle from one division to the next is also called a generation as it is with human beings from one set of parents to the children.
Most cells both eukaryotic and prokaryotic divide through the Mitosis processes which is asexual. An example of this might be eukaryotic human skin cells and or prokaryotic bacteria; they replicate themselves exactly but not sexually.
Eukaryotic cells are different that the prokaryotic cells however because they contain much more DNA and their reproduction process is more complicated.
Eukaryotic cells also reproduce sexually through Meiosis in more developed higher on the evolutionary scale plants and animals. During, the sexual type of cell division called Meiosis special cells called gametes eggs and sperm come together to create a finished product called a zygote fetus. The main differences between Meiosis and Mitosis is that one is a form of replication without sexual contact and the other is a blending of chromosomes through the sexual process.
When a cell divides by Mitosis, it makes an exact copy of its DNA and transfers this to a daughter cell, sort of like cloning. There are individual steps during the process of Mitosis called interphase, prophase, metaphase, anaphase and telophase. It is asexual reproduction where the parent cell clones itself or makes a copy of itself in the daughter cell. Meiosis, however is a different process of replication where two sex cells that are called gametes come together to form a zygote.
During the first cell division, the same stages occur that occur in Mitosis, but the new cells have half of the amount of DNA needed by a cell. The cell does a second division soon after the first, which divides the number of chromosomes in the cell in half.
When a cell has half the number of chromosomes it is called a haploid cell. Haploid means half the regular number and diploid is the opposite meaning two halves.
Normal cells are considered to be diploid cells and the merging of the haploid cells, thus sexual reproduction, creates them. The individual steps in the process of Mitosis are called interphase, prophase, metaphase, anaphase and telophase.
Interphase is the normal condition of a cell where it grows and collects materials and sort of hangs out waiting to change. After interphase, when the cell reaches a certain point, it readies itself for prophase. Then comes metaphase, where all the pieces called centinoles arrange in a line.
DNA is lined up along a central axis and the centinoles send out tubules that connect to the DNA that is condensed into chromosomes, then strands of a chromosome are connected at the center with something called a centromere.
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Studer English 3 Embryonic Stem Cells Many people don't agree with the research of stem cells, but what the people don't know is how useful stem cells are, and how the could change medicine as we know it as well as saving lives too Stem Cells Stem cells can be described as "? Stem Cells A stem cell is a certain type of cell that has the capability to develop into different types of cells. There are two types of stem cells: One population, called hematopoietic stem cells, forms all the types of blood cells in the body The early stage of development is about 5 days Scientists are working to learn about how stem cells function.
ADVERTISEMENTS: Read this Essay on Cells in Human Body! The body of any living organism is made up of cells. Cells are very minute in size and extremely complicated in structure. Human is no exception. Each cell is basically a unit of protoplasm, which is said to .
Cells, the building blocks of the human body, contain genetic information (DNA) that is passed on from parent cell to daughter cell through the cell reproduction process called cell division. When a cell divides the genetic information contained in DNA copies itself and transmits to /5(7).
Essay on the Types of Cells Essay on Compartmentalization for Cellular Life Essay on Cell— An Open System Essay on the Shapes of Cells Essay on the Functions of Cell Parts ; Essay . Cells Essays: Over , Cells Essays, Cells Term Papers, Cells Research Paper, Book Reports. ESSAYS, term and research papers available for UNLIMITED access.
Types Of Cells Essay Examples. 9 total results. An Analysis of the Cell Theory in Cell Biology. words. 1 page. An Introduction to Different Types of Tissues in a Human Body. 1, words. 4 pages. An Overview of the Cellular Structure and Function. words. 1 page. Free Coursework. Home. Coursework. Coursework c. Cell Essay. Cell essay. Cell Essay. Cells, the building blocks of the human body, contain genetic information (DNA) that is passed on from parent cell to daughter cell through the cell reproduction process called cell division. When a cell divides the genetic information contained in DNA.