Cell_Theory_and_Difference_Between_Prokaryotic_and_Eukaryotic_Cells

The cell theory states that: • All living organisms are composed of cells. Multicellular organisms (example: humans) are composed of many cells while unicellular organisms (example: bacteria) are composed of only one cell. • Cells are the smallest unit of life. They are the smallest structures capable of surviving on their own. • Cells come from pre-exsisting cells and cannot be created from non-living material. For example, new cells arise from cell division and a zygote (the very first cell formed when an organism is produced) arises from the fusion of an egg cell and a sperm cell. Comparison between Prokaryotic and Eukaryotic cells 1. Prokaryotic cells have naked DNA which is found in the cytoplasm in a region named the nucleoid. On the other hand, eukaryotes have chromosomes that are made up of DNA and wound around proteins called histones. These chromosomes are found in the nucleus enclosed in a nuclear membrane. 2. Prokaryotes do not have any mitochondria whereas eukaryotes do. 3. Prokaryotes have small ribosomes (70S) compared to eukaryotes which have large ribosomes (80S). 4. In prokaryotes there are either no or very few organelles bounded by a single membrane in comparison to eukaryotes which have many of them including the Golgi apparatus, Endoplasmic Reticulum, Mitochondria. Animal and Plant cells are both examples of Eukaryotic cells. However, there are several basic differences between animal and plant cells outlined below: 1. Animal cells only have a plasma membrane and no cell wall. Whereas plant cells have a plasma membrane and a cell wall. 2. Animal cells do not have chloroplasts whereas plant cells do for the process of photosynthesis. 3. Animal cells store glycogen as their carbohydrate resource whereas plants store starch. 4. Animal cells do not usually contain any vacuoles and if present they are small or temporary. On the other hand plants have a large vacuole that is always present. 5. Animal cells can change shape due to the lack of a cell wall and are usually rounded whereas plant cells have a fixed shape kept by the presence of the cell wall.