A vesicle is a small fluid sac surrounded by a membrane found in the cytoplasm that holds an important role for cell activity. Vesicles participate in the process of exocytosis and endocytosis by transporting substances in and out of the cell via the cell surface membrane. Vesicles also allow the movement of substances with a cell to different organelles. So, where are they formed? Vesicles can be formed at the Golgi Apparatus (which we will next learn about) or the Rough Endoplasmic Reticulum (which we previously explored) or at the cell surface. An example of a vesicle is lysosomes. Did you know that vesicles form naturally because of the properties of liquid membranes?
The Golgi apparatus is a group of fluid-filled, membrane-bound, flattened sacs. Fun fact, it was discovered by the Italian physicist Camillo Golgi in 1897. A way to distinguish them is to look out for the vesicles on the edges of the sacs. Its role is to gather simple molecules, combine them, and make them into more complex molecules. Additionally, it breaks down proteins into small, active fragments. It processes and packages new proteins and lipids. An example of something the Golgi Apparatus produces is the organelle lysosome. It also prevents apoptosis (fortunately) as that is cell death, and we want cell death to be controlled don’t we?
Next we have Cilia. Cilia are small hair-like organelles that are found on the surface of some animal cells, for example, inside our trachea, you will find Cilia. Their purpose is to move substances along the cell surface, and their structure is important as it allows them to do so. A cross section is at a right angle to the longitudinal axis. If you were to look at the cross section of Cilia, you would see that they have an outer membrane and a ring of nine pairs of protein microtubules. Furthermore there are two more microtubules found in the centre. This is known as the 9+2 formation (an easy way to remember their structure.) The microtubules allow movement of the Cilia. So for example, in the trachea, if there was mucus present, the cilia will move to move the mucus to the throat.
Similar to the Cilia is the Flagellum, the difference being that they are longer. They also have a 9+2 formation of microtubules. Flagella stick out of the cell as they have the role of moving the cell. The microtubules contract to make the flagellum move. It is found in a variety of cells such as the sperm cell. The sperm cell needs to move in order to leave the male genitalia and enter the vagina to reach the egg.
Lastly, there are two very important organelles which are immensely complex, mitochondria and chloroplasts. Mitochondria are found in both plants and animals but chloroplasts are only found in plants. As mitochondria are for respiration (which both plants and animals do) and chloroplasts are for photosynthesis (and we all should know that animals do not photosynthesise.) However, given how much there is to say, they shall be explored separately in large detail.
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