Here are two cells on your screen. Can you tell me which one is a plant cell and which is an animal cell by merely glancing at them? Don't worry, it's not that difficult.
Plant and animal cells can be distinguished from each other by merely looking at them. The presence and the absence of a few characters are enough to let us know the differences. Let's go through the differences one by one.
If we travel from the outside of the cell to the inner core then the first difference that we find is the presence and the absence of the cell wall. Plant cells have a proper well-defined cell wall. On the other hand, animal cells do not have a cell wall at all. They just have the cell membrane which is also part of the plant cells. It's due to the cell wall that the plant cells obtain their proper defined shape.
On the other hand, animal cells do not have a proper shape because they lack cell wall. The next obvious difference is the presence of chloroplast in the plant cell. This, as we have already studied, is the exclusive organelle for plant cell. It's absent in the animal cells.
Now can you help me with the third difference? That's right, the presence of vacuoles. Both plant and animal cells contain vacuoles.
However, in plant cells the vacuole is a large one located at the center. While in animal cells there are numerous small sized vacuoles. This central vacuole can occupy majority of the cell space pushing other organelles to the periphery.
The case of animal cells is slightly different. Here the vacuoles are much smaller in size and they are scattered throughout the cell. the cytoplasm.
Apart from these, there are several other differences in these two cells. But we will have a look at them in our higher grades. For now, you tell me, is classification of cells done only on these bases? Are they only two types of cells? Plant cells and animal cells?
Think for a moment. The answer is a definite no. This was just the difference between plant and animal cells.
This is not the way cells are classified. Then how do we classify the cells? Cells are broadly classified into two major types.
Prokaryotic cells and Eukaryotic cells. Here are the two types we are referring to. This is a typical prokaryotic cell and this is a eukaryotic cell. Let's begin understanding the difference between the two.
To begin with, the name prokaryotic helps us to know its structure. The term pro indicates primitive and the term carrion refers to kernel which means nucleus in this case. So these cells have a primitive type of nucleus.
Well, these cells do not actually have a proper well-defined nucleus. Can you see these thread-like structures scattered in the cytoplasm? This is nothing but the genetic material named nucleoid. The nucleoid is analogous to the nucleus in our cells. It has strands of DNA, RNA and it contains the genetic information of the cell.
The only difference is that the nucleoid does not have a compact shape and mainly lacks a proper membrane. The next obvious difference is that the organelles are also not membrane bound. That means the prokaryotic cells does not have well-defined membranes for the different organelles.
On the other hand, the eukaryotic cell which means cell with the true nucleus has well-defined membranes for nucleus as well as the other organelles. There are several other features but we'll not get into the details for now. Now tell me one thing, doesn't this look like an animal cell?
Yes it does! And that's because this is an animal cell! So is animal cell an example of a eukaryotic cell?
Yes it is! Both plant and animal cells can be included in the category of eukaryotic cells. So which cells will be in the prokaryotic types?
Cells of lower organisms like various bacteria have prokaryotic cells.