What is a cell?
Remember when we talked about atoms? Atoms are the basic building blocks for all matter in the universe. When it comes to living things, cells are the building blocks. Cells are tiny little living organisms themselves, and all life on Earth is built from cells, from bacteria all the way up to humans. Cells are small structures that hold all of the equipment an organism needs to function successfully. Sometimes organisms are made of just one single cell, and sometimes they are made of many cells.
Just as more complicated organisms have organs that help take care of various functions inside their bodies, cells have organelles that help take care of various functions within the cell. The types and organization of organelles within a cell help determine the type of cell it is.
Just as more complicated organisms have organs that help take care of various functions inside their bodies, cells have organelles that help take care of various functions within the cell. The types and organization of organelles within a cell help determine the type of cell it is.
Where life began...
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A long time ago, after the earth had been created, atoms began to come together in specific patterns. These atoms began forming proteins and eventually formed the very first cell. These first cells came into being around 3.5 billion years ago and were called prokaryotic cells. In Latin (the original language of science), "Pro-" means before and "Karyo-" means nucleus, so prokaryotic cells were cells that developed without a nucleus. Their genetic material (the instruction booklet for their existence) was just floating around unprotected in the middle of the cell. These cells were very simple. As I said before, they had no nucleus, and they also had no other organelles. They had a cell membrane, some cytoplasm and some ribosomes floating around with DNA but that was pretty much it.
Those very first cells made up a group of organisms that we call Archaea, meaning ancient ones. Prokaryotic cells are still very simple today, making up the most simple of organisms: Bacteria. Some have developed a Cell Wall and a Flagellum, but for the most part, they are still simple, unorganized cells. They are all single-celled organisms, meaning they can only be made of one cell. This is because they lack the structures needed to coordinate with other cells.
Those very first cells made up a group of organisms that we call Archaea, meaning ancient ones. Prokaryotic cells are still very simple today, making up the most simple of organisms: Bacteria. Some have developed a Cell Wall and a Flagellum, but for the most part, they are still simple, unorganized cells. They are all single-celled organisms, meaning they can only be made of one cell. This is because they lack the structures needed to coordinate with other cells.
Bigger, Better, Faster, Stronger...
Somewhere on the evolutionary line, some of those Prokaryotic cells we were talking about decided they weren't really happy with their lot in life and that they wanted more. In order to get more out of life, they had to get better at living life, so to speak. So, around 2 billion years ago, some of those Prokaryotic cells started to develop a membrane like structure around their DNA to protect it. Eventually this membrane became a nucleus, the centrla structure that protected and controlled the DNA, thus controlling the cell. Now the cell could coordinate, but it still didn't have all the structures it needed. The nucleus couldn't do everything by itself. So those same cells began to develop other organelles. Scientists called these new cells Eukaryotic. In Latin, "Eu-" means true and remember "Karyo-" meant nucleus, so these new cells have a "true nucleus" and also have membrane bound organelles that take care of various other functions within the cell.
Since the development of the nucleus and other organelles, Eukaryotic cells have branched into several different categories. Some Eukaryotic cells remain as single celled organisms, called protists. Other Eukaryotic cells became multi-celled organisms now that they had all the structures they needed to work together. These Eukaryotic cells became the cells that make up animals, plants, and fungi.
Animal vs. Plant Cells
Animal and plant cells have many things in common, but there are some key differences that separate the two. Think of the differences between plants and animals. Many of the differences between the two organisms can be traced back to their cells.
The biggest difference between animals and plants is that plants can make their own food while animals have to find theirs and eat it. This is because plants cells have a special organelle called a chloroplast. A chloroplast contains a chemical called chlorophyll that traps sunlight and converts it to energy in a process called photosynthesis. Only plant cells contain chloroplasts. Animals cells don't have them, so they can't make their own food.
If you look at the cross sections of the two types of cells above, you may also notice that the plant cell has a giant blue bubble labelled as a vacuole while the animal cell only has very little bubbles labelled as vacuoles. Plants tend to need more water than animals do. This is because plants use their large central vacuole as a form of support. When plants do not have enough water, they wilt, or fall over. This is because there is not enough water to fill up the vacuole in each cell so the cell doesn't have enough support to stand upright.
Animals have something specific to them as well. Only animal cells have lysosomes, which are used to digest food and get rid of waste. Because plant cells make their own food, they don't need lysosomes to clean up after them. Animal cells, on the other hand, have to have lysosomes in order to make sure food gets digested and that the leftovers and waste don't clutter up the cell.
The last major difference between plants and animals also has to do with structure. Animals have bones and muscle cells that all work together to keep them strong and sturdy. Plants don't have these things because more of their energy is devoted to making food than into making different types of cells. Instead, plant cells have a cell wall that surrounds each cell. The cell wall helps provide support and protection to the soft parts of the cell. It is like the bones for the plant that helps it stay upright.
Now that we have discussed the major differences between the cells, you just need to know what the other organelles are for. Take a look at the table below to see a brief description and the function of each organelle.
The biggest difference between animals and plants is that plants can make their own food while animals have to find theirs and eat it. This is because plants cells have a special organelle called a chloroplast. A chloroplast contains a chemical called chlorophyll that traps sunlight and converts it to energy in a process called photosynthesis. Only plant cells contain chloroplasts. Animals cells don't have them, so they can't make their own food.
If you look at the cross sections of the two types of cells above, you may also notice that the plant cell has a giant blue bubble labelled as a vacuole while the animal cell only has very little bubbles labelled as vacuoles. Plants tend to need more water than animals do. This is because plants use their large central vacuole as a form of support. When plants do not have enough water, they wilt, or fall over. This is because there is not enough water to fill up the vacuole in each cell so the cell doesn't have enough support to stand upright.
Animals have something specific to them as well. Only animal cells have lysosomes, which are used to digest food and get rid of waste. Because plant cells make their own food, they don't need lysosomes to clean up after them. Animal cells, on the other hand, have to have lysosomes in order to make sure food gets digested and that the leftovers and waste don't clutter up the cell.
The last major difference between plants and animals also has to do with structure. Animals have bones and muscle cells that all work together to keep them strong and sturdy. Plants don't have these things because more of their energy is devoted to making food than into making different types of cells. Instead, plant cells have a cell wall that surrounds each cell. The cell wall helps provide support and protection to the soft parts of the cell. It is like the bones for the plant that helps it stay upright.
Now that we have discussed the major differences between the cells, you just need to know what the other organelles are for. Take a look at the table below to see a brief description and the function of each organelle.
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Cell Organelle Chart | |
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