Biology: What is a Cell?
The cell is the smallest unit of living matter that exhibits the characteristics of life.
Cell theory:
Every organism is composed of one or more cells. Each new cell arises from a preexisting cell.
Understanding cells:
There are millions of different types of cells. There are cells that are organisms onto themselves, such as microscopic amoeba and bacteria cells. There are cells that only function when part of a larger organism, such as the cells that make up your body.
Cells contain hereditary material called DNA, which is passed from parent to daughter cell. All metabolic processes take place with in cells. Its structure is highly organized, and it can sense and respond to changes in the environment. Cells are extremely small structures, so small that you need a microscope to see them. You could fit a line of 2,000 red blood cells across your thumbnail.
Some organisms like bacteria are unicellular. Other organisms like humans are multicellular. Before we understand the cell, we need to briefly review the origin of organisms.
There are two types of cells Prokaryotic and Eukaryotic.
Prokaryotic Cells
These cells are simple cells without a nucleus. The best example is bacteria. Prokaryotic cells have three regions:
- Appendages called flagella and pili—proteins present on the cell surface
- A cell envelope consisting of a capsule, a cell wall, and a plasma membrane
- A cytoplasmic region that contains the cell genome, ribosomes and various sorts of inclusions.
Eukaryotic Cells
The eukaryotic cells are fungi, animals, plants and some unicellular organisms. They have nucleus, as well as DNA; which is the hereditary material. Finding eukaryotic cell was a milestone in science. Without eukaryotes the world would not have mammals, birds, fish, invertebrates, mushrooms, plants etc.
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