Cell- Cell is the tinest particle of the organism,s body by which an organism is composed of. It performs various activites which is essential for the gowth and survival of living organism. Cell also gives a structure to the organism,s body.
Cells share many common features, yet they can look wildly different. In fact, cells have adapted over billions of years to a wide array of environments and functional roles in its evolution peroid. For example:
1. Nerve Cells have long, thin extensions that can reach for meters and serve to transmit signals rapidly from brain to body and body to brain.
2.bPlant cell have closely fitting and have a rigid outer layer that helps to provide the structural support that trees and other plants require to stand.
3. Muscle cell are Long, tapered and have an intrinsic stretchiness that allows them to change length within contracting and relaxing biceps.
Still, as different as these cells are but, they all rely on the same basic strategies to keep the outside out, allow necessary substances in and permit others to leave, maintain their health, and replicate themselves. In fact, these traits are precisely what make them a cell.
Types of cell:
i) Eukaryotic cell ii) Prokaryotic cells
Eukaryotic cell- This type of cells consist nucleus, so many chrmosomes, membrane bound cell organalle. Its size is generally big in size about 5 to 100 m.
Prokaryotic cell- This type of cells does not consist nuclus, membrane bound cell organelle and only one chromosome. Its size is generally 1 to 10 m.
Differences between plant cells and animal cells: The main differencebetween plant cell and animal cell is difference in cell organelle.
Organelle of plant cells:
i. Lysosomes ii. Nuclus
iii. Chloroplast iv. Cytoplasm
v. Adjacent cell wall vi. Cell wall
vii. Smooth endoplasmic reticulm viii. Ribosomes
ix. Rough endoplasmic reticulum x. Golgi appartus
xi. Mitochondrion xii. Nuclear envelope
xiii. Plasma membrane
Organelle of animal cells:
i. Centroide ii. Nucleus
iii. Cytoplasm
iv. lysosome v. Smooth endoplasmic reticulm
vi. Ribosomes
vii. Rough endoplasmic reticulum viii. Golgi appartus
ix. Mitochondrion x. Nuclear envelope
In the year 1665, an English Scientist, name -Robert Hooke discovered a very small particle which entirly became the foundation of life. He observed a thin shaving of cork ( cork is the outer cover ing of a tree better known as bark of tree ) under a microscope and found that it was made up of thousands of little compartments which he imagined to resemble little rooms. He aptly named these compartments as "Cells". However, his research did not provide any more information insights on the structure of a cell.
After that a new Scientist came in light who give more information about cell.
And that was "Anton van Leeuwenhoek". Through his only own made microscope Robert Hooke could only see the outer thickend walls of of cork and could not provide any further information about cell.
Anton van Leeuwenhoek, a Dutch microscopist made a technically advance microscope. He observed spirogyara from a pond water and took it under his microscope. By doing this research he discoverd that these little animals were actually single cell organism. He considered as the "father of microscopy because of the advances he made in microscope design and use. He also discoverd bacteria, yeast and much more. His researchs, which were widely circulated, opened up an entire world of microscopic life to the awareness of scientists.
Cell Replication
The phenomenon of dividing number of times a normal human cell is called Hayflick limit or Hayflick Phenomenon .The Empirical evidence shows that the telomere which is associated with each cell's DNA will get slightly shorter with each new cell division until the cell goes shorter to a critical length. This concept of the Hayflick limit was advanced by American anatomist 'Leonard Hayflickin' in the year 1961. Leonard Hayflick demonstrated that a population of normal human fetal cells in a cell culture will divide between 40 and 60 times. The population will then enter a senescence phase , which refutes the contention by Nobel laureate Alexis Carrelthat normal cells are immortal in nature. Telomere shortening in humans eventually makes cell division impossible, and this aging of the cell population appears to correlate with the overall physical aging of the human body.
In a average human life, the cell replication is occurred around 10,000 trillion.
How cell came in existence
Scientists said that all organisms on Earth live today originated from a single cell that existed about
3.8 billion years ago. This original cell was likely few more than a sac of small organic molecules and RNA-like material that had both informational and catalytic functions, but they are not a fully functional cell. With the time, they make more stable DNA molecule evolved in the cell to take the information storage function, where as proteins, with a greater variety of structures than nucleic acids, they took the catalytic functions. The absence or presence of a nucleus, all membrane bound organelles is important enough to be a defining feature by which cells are categorized as either it is prokaryotics or eukaryotics. Scientists believe that the appearance of self contained nuclei andother organelles represents a major advance in the evolution of cells. But from where these structures came from? About one billion years ago, some cells "ate" by overwhelm objects that floated in the liquid environment in which they existed first. Then, according to the some theories of cellular evolution, one of the early eukaryotic cells engulfed a prokaryote, and together the two cells formed asymbiotic relationship, and formed a eukaryotic cell. In particular, the engulfed cell began to function as an organelle within the larger eukaryotic cell that consumed it. Both chloroplasts and mitochondria, which exist in modern eukaryotic cells and still retain their own genomes, are thought to have arisen in this way. A cell contain mainly four elements- Hydrogen, Oxygen, Nitrogen and Carbon some Cells also contain Sulpher.
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