Cells make up all living things, from the tiniest bacteria (only one cell big) to an elephant (1000 trillion cells big). They do loads of different things in your body as well, from making you think to making your body move – your body has over 200 different types of cells each doing its own little job to keep you alive. Because there are so many different types of cells, we tend to put them into groups to help us organise them. The biggest groups of cells are called the Prokaryotes and the Eukaryotes. So, how do we know if a cell is a Prokaryote or a Eukaryote?
- DO NOT have a nucleus. Their DNA is just sort of floating around in a doughnut shape called a plasmid.
- DO have a thick cell wall to protect them from damage.
- Usually have a flagellum (tail) to help them to move around.
These are normally bacterial cells and other simple single-celled organisms. To find out more about these you take a look at our worksheet on communicable diseases.
- DO have a nucleus where they keep their DNA nice and safe.
There is a lot more variation in Eukaryotic cells, but they make up plants and animals. Plant cells and animal cells is another way we can divide up the cells (we'll look at this in more detail in a bit).
Eukaryotic cells have some common organelles (parts that make up the cells): nucleus, cell membrane and cytoplasm. Let's take a look at what they each do:
The nucleus contains the DNA, so controls what happens in the cell; it makes sure that the cell is doing the job that it's meant to be.
The cell membrane controls what goes in and out of the cell, like a security guard stopping the bad stuff (like bacteria and viruses) from coming in and kicking the bad stuff that gets made in the cell (like CO2) out.
The cytoplasm is the place where chemical reactions occur. They help the cell do its job by starting off some of the important chemical reactions we will take a look at in later worksheets, like respiration.
Finally, there is another very important cell organelle, the mitochondra. The important process of respiration is finished there so that cells can produce the energy to perform all their roles.
Plant cells contain additional organelles because they just 'have to be different'. Just because they evolved 470 million years ago, and animals only evolved 230 million years ago.
These are the chloroplasts that contain chlorophyll, a green pigment that collects light energy so they can do photosynthesis (again, something that we will look at in much more detail later).
Plant cells also have a cell wall around the cell membrane for additional strength and support, after all, they don't have bones, so they need to have string cells to stay upright. The cell wall is made of cellulose.
Finally, they have the vacuole which is filled with a liquid called cell sap. This provides support from the inside and helps with the movement of water into and out of the cell.
Right, understood all of that? Well - take a look at the images below and see if you can find where each of the organelles we mentioned above appears in. Then get your brains in gear to answer some questions on them.