By Alastair Noon
To spot the difference between different types of cells it is important to first understand what makes a cell different from a pool of chemicals with high hopes.
A House With Walls
Imagine a house, it can be a big house with 7 bedrooms, 8 bathrooms and a pool or a small two up two down. It really doesn’t matter. What houses have in common are walls. Walls separate the outside (the garden, the street, and the rest of the town) from the inside (the lounge, the kitchen, and the bedrooms). Houses also come with doors; they aren’t prisons after all. These let the people you want in, normally the people who own the house and their friends, while attempting to keep people you don’t like out (nosy neighbours, relatives, and burglars etc.).
Cells don’t have doors, or a structure made of bricks, but what they do have is a membrane. The membrane separates everything within it, the cell, from the outside world. The membrane is the place where the cell ends, and the rest of the world begins. Despite a cell membranes disappointing lack of doors, substances useful to a cell can pass through the membrane, think glucose and oxygen. More harmful visitors such as viruses the membrane tries very hard to keep out.
A Room With a View
Returning to the house. Even modern open plan houses have rooms with different functions. For example, there is not a combined bathroom, kitchen, and garage. A room that tried to do all these functions would be very poor at each of them. This also true in cells. Different structures inside the cell (called organelles, from the Latin for instrument if you are interested) have different jobs. For example, the nucleus controls the cells activities while mitochondria release energy for these activities to happen. We can summarise this to say a cell has a membrane to separate itself from the outside world and organelles which perform specific jobs within the cell.
Part of Something Bigger
Some cells live sad lonely lives, independent of all other living things. They don’t require help or support and contain all the organelles needed to grow and survive. Other cells, however, form part of a larger living thing. Imagine these like the bricks of the house. A single brick is not very interesting. But 15,000 bricks arranged in the shape of a house can be very useful when it is cold and rainy out. We do not walk down a street and think that is a nice collection of 15,00 bricks. We view them as a house and hardly notice the bricks. The number of bricks depends on the size of the house, larger houses need more bricks. Cells can be arranged in the shape of a human. We refer to this as a human, not the 37.2 trillion cells that are needed to make them. An elephant by comparison needs 3 to 4 quadrillion cells as it is much larger than most people. A bacterium needs only 1 cell being much smaller.
All the Bills Add Up
In a house there are a range of very useful systems which overlap each other. For example, the water is heated using a gas boiler, water comes out using an electric power shower, the gas boiler it turned on using electric thermostat. This overlap of systems regulates the houses temperature, makes sure there is enough hot water and generally makes life easier for the residents. If you added all result of the gas, electric and water up the result would be the homeowner’s utility bill (this does not make life easier for the residents). In a cell there are many chemical reactions which take place. For example, in a plant cell photosynthesis uses the suns energy to combine carbon dioxide and water into glucose. The plant then uses this glucose to release energy in a process called respiration. Plants can also combine this glucose with nitrates from the soil to make new proteins. If you add up all the chemical reactions that take place the result is called metabolism. Some cells, or groups of cells, perform chemical reactions quickly. They have a quicker metabolism. Others do their chemical reactions more slowly, they have a slower metabolism. Slow or fast, a cell can be recognised by having a series of chemical reactions called metabolism.
Growing Up and Moving Out
Most people are never happy with their houses. People are always working on their next big idea, it might be the perfect new kitchen or the conservatory that will be the highlight of the street. Houses, therefore, are always changing. They are generally getting larger as people regularly add extensions to them (it’s very important to add value to your house). They are also always being repaired because they have an unfortunate habit of falling apart. Cells are similar to this but not exactly the same. A cell might be hit by UV radiation from the sun or damaged by toxins from a bacteria. A cell is able to able to repair this damage and continue living. Cells, like houses, are always growing. They make new copies of the organelles inside them, more mitochondria, another nucleus etc. When they have enough copies of organelles to make another cell, that is exactly what they do. Cells divide. They go from being one cell into two identical cells. This is where, it can be argued, that cells differ from houses. Cell division allows singled celled life to reproduce and life made of more than one cell to grow in size and heal over cuts.
A Checklist For Cells
The cell checklist. If you spot a cell it should have the following properties: a cell membrane, with organelles inside, a series of chemical reactions called a metabolism and the ability to grow and divide into new cells.
Kommentarer