The second most vital organelle is the cell membrane. It is constructed by a lipid bilayers array for the plasma membrane. This structure is an oily margin that avoids the free channel of water-soluble substances, which is also continuous. There are two ways of this flow, into and out of the cell. The nuclear envelope is an example of a membrane. The cell wall is another organelle that has a similar function as the membrane. It is fully permeable, also called porous, while the cell membrane is partially permeable. The cell wall also protects and structurally supports the cell.
The next organelle is the mitochondrion, which is universal in eukaryotic cells. The function of this organelle is to produce energy in the form of ATP (adenosine triphosphate), which is formed when organic compounds are completely broken down to carbon dioxide and water. One of the main requirements for this process to occur is the presence of plentiful supply of oxygen. Each mitochondrion has a double-membrane system. The inner membrane is folded repeatedly and it is also known as cristae. The outer membrane faces the cytoplasm. This complex system creates two divisions. In the outer division, enzymes and other proteins stockpile hydrogen ions. These ions then flow into the inner compartment. The energy inherent creates ATP-formation. Hydrogen binds with oxygen to produce the end product, water.
There is another section of organelles. It is known as the endomembrane system. Endoplasmic reticulum (ER) is one of the main constituents in this section. ER is usually described as stacks of flattened cells. There are two types of ER, smooth and rough. The main difference between these two types is that in the rough ER structure, ribosomes are attached on the surface, and there is absence of it in the smooth ER. In animal cells, the ER is continuous with the nuclear envelope, and it lengthens to the cytoplasm. The main task of the smooth and rough ER is to assemble many types of proteins and lipids.
Another component in the endomembrane is the Golgi body. It is also made up from a chain of flattened, membrane-bound cells. The function is almost similar to the ER. This structure is known as the manufacturing site for the lipids and proteins that are transported from the ER. With the aid of certain specific enzymes, this organelle parcels the lipids and proteins to be sent to a structure that we will discuss in the next paragraph, which is the vesicle. Sometimes, these enzymes add phosphate groups or even amine groups to a protein. This will help the shipping scheme to a particular destination.
Even tough vesicles are tiny structures; they play a significant role in the activity of the whole cell. It consists of membranes which surround them. They either have a fixed position in the cytoplasm or move around randomly in it. The most common type of vesicles is the lysosomes. They aid in intracellular digestion. They seize enzymes that break down complex proteins, carbohydrates, nucleic acids and a number of forms of lipids. Another function of lysosomes is to digest part of cells and also the whole cell, in certain cases.
There is another type of organelle that is found only in plant cells. It is found in eukaryotic cells that are photosynthetic. It is identified as chloroplast. These organelles build adenosine triphosphate (ATP) and phosphorylated nucleotide coenzyme (NADPH), which they consume sunlight energy for this production. This is then assembled to sugars and other organic compounds. This entire process is called photosynthesis. The shape of a chloroplast is often a disc or an oval shape. There are two outer membrane layers in the semifluid interior, which is also known as stroma. Thylakoid membrane is the inner membrane in the stroma which forms a single compartment.
There are other additional organelles that are found in certain kind of cells. The main function of these organelles is movement of the whole cell. Some cells have flagella (singular, flagellum) or cilia (singular, cilium). Flagella are longer and less abundant on cells if compared to cilium. Both this structures beat by a sliding mechanism that occurs at the minus end of a microtubule. A microtubule helps in internal arrangement that reposition cell structures and organelles into distinct locations. The ‘false feet’ also known as pseudopods that is found in amoebas, macrophages and many other free-living cells. The last example is the centriole. A centriole is a barrel-shaped microtubule organizing centre (MTOC), which aids in cell division. It has an array of nine pairs of microtubules plus a central pair that are internal and cylindrical.
