A cell is the most basic unit of an organism, and all organisms are made completely from cells. There are two different types of cells. The cell on the top right, is an animal cell. It has a round Cell Membrane that is semi-permeable. It is able to be sqaushed and 'flex'. This allows it to move, stretch and flex. Think about all the cells within you, they have to be able to move and bunch up in places, thus the round shape. The animal cell consists of the Cell Membrane, Mitochondria, Golgi Bodies, Cytoplasm etc. The plant cell on the bottom right, has a Cell Wall. This cell wall keeps the structure rigid and together. If you think about how a tree has to stand up for hundreds of years, the have to be structures that way. If you hold your arms out to the side like a tree, you can't do that for very long, and certainly not as long as a tree can. This is why they are structured this way. The only differences between plant and animal cells in terms of parts, are the Cell Wall, the chloroplasts and the amyloplasts.