March 28, at am. Scientists — and people in general — love to divide things into categories. In some ways, life on Earth has done the same. Right now, scientists can divide cells into major categories — prokaryotes or procaryotes; both spellings are okay and eukaryotes. Prokaryotes PRO-kaer-ee-oats are individualists. These organisms are small and single-celled. They might form into loose clumps of cells.
But prokaryotes will never come together to take on different jobs within a single organism, such as a liver cell or a brain cell.
Eukaryotic cells are generally bigger — up to 10 times bigger, on average, than prokaryotes. Their cells also hold much more DNA than prokaryotic cells do. Made from a network of protein threads, it forms a scaffold inside the cell to give it strength and help it move.
Prokaryotes make up two of the three big domains of life — those super kingdoms that scientists use to organize all living things. The domains of bacteria and archaea Ar-KEY-uh consist of prokaryotes only.
These single cells are small, and usually round or rod shaped. They might have one or more flagella Fla-JEL-uh — powered tails — hanging off the outside to move around. Prokaryotes often but not always have a cell wall for protection.
Inside, these cells throw together all they need to survive. They let all their cell parts hang out together. A eukaryotic cell is a cell that has a membrane-bound nucleus and other membrane-bound compartments or sacs, called organelles , which have specialized functions. The small size of prokaryotes allows ions and organic molecules that enter them to quickly spread to other parts of the cell.
Similarly, any wastes produced within a prokaryotic cell can quickly move out. However, larger eukaryotic cells have evolved different structural adaptations to enhance cellular transport. Indeed, the large size of these cells would not be possible without these adaptations. In general, cell size is limited because volume increases much more quickly than does cell surface area. As a cell becomes larger, it becomes more and more difficult for the cell to acquire sufficient materials to support the processes inside the cell, because the relative size of the surface area across which materials must be transported declines.
Figure 2. This figure shows the relative sizes of different kinds of cells and cellular components. An adult human is shown for comparison. Prokaryotes are single-celled organisms of the domains Bacteria and Archaea. All prokaryotes have plasma membranes, cytoplasm, ribosomes, a cell wall, DNA, and lack membrane-bound organelles. Many also have polysaccharide capsules. Prokaryotic cells range in diameter from 0.
The host cell profited from the chemical energy the mitochondrion produced, and the mitochondrion benefited from the protected, nutrient-rich environment surrounding it. When two become one. Evidence for endosymbiosis. Subscribe to our newsletter. Email Facebook Twitter. Previous When two become one.
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