Ribosomes : Protein Factories
Ribosomes are tiny, bead-like structures made up of rRNA and proteins. They may be free or attached to the endoplasmic reticulum in the cytoplasm.
Endoplasmic Reticulum : Channels
The endoplasmic reticulum or ER is a set of folded membranes found throughout the cell. These folded membranes divide the cell into compartments. They serve as channels through which materials are transported in the cell.
The ER also provides a great surface area on which enzymatic reactions and synthesis of carbohydrates and lipids take place. There are two types of ER: (a) the smooth ER and (b) rough ER. Smooth ER lacks ribosomes while rough ER is studded with ribosomes. It is where proteins intended for export are produced.
Golgi Complex : Packaging Factories
It is a flattened stack of membranes scattered throughout the cytoplasm. They serve as the “packaging factories” of the cell. They collect, package, and distribute the materials manufactured in the cell, such as lipids and proteins.
Lysosomes : Suicide Sacs
Lysosomes are spherical sacs or vesicles that contain powerful digestive enzymes. They originate from the Golgi complex. They play a great role in the normal development of organisms.
Lysosomes often acts as “suicide bags”, breaking open and spilling their digestive enzymes within the cell. As a result, the cell dies and the raw materials are further used in the production of new cells.
Lysosomes destroy bacteria and other micro organisms that invade the cells. They also help one-celled organisms like the paramecium and euglena digest food particles.
Mitochondria : Powerhouses
Mitochondria (singular: mitochondrion) convert food molecules into energy needed to power the cell. The mitochondrion is made up of two membranes: (a) a smooth outer membrane and an (b) inner membrane with numerous folds known as the cristae (singular: crista). On the surfaces of the cristae are various enzymes and proteins that help in aerobic respiration.
The mitochondrion is similar to the nucleus in that it contains its own DNA. It is capable of reproducing itself. Active cells such as muscle cells have numerous mitochondria. The large amount of mitochondria helps in harvesting more energy needed by these cells. It is important to note that only the mother passes on the mitochondria to the offspring. This is because the egg cell contains mitochondria. The mitochondria in the sperm are located in the tail which does not enter the egg during fertilization. Humans can trace their mitochondria back to their mothers, grandmothers, great grandmothers, and so on…
Plastids : Energy Converters
Plastids harvest solar energy and produce food in the process of photosynthesis. Plastids are oval-shaped structures in the cells of plants and some protists.
Three major types of plastids according to the pigments they contain:
1. Chloroplasts contain the green pigment, chlorophyll.
2. Chromoplasts, or colored plastids, contain red, yellow, and orange pigments. They give flowers and fruits their colors.
3. Starchy foods such as rice, corn, and potatoes, contains a number of leucoplasts, the colorless plastids
Leucoplasts store food in the form of starch.
Chloroplasts are larger than mitochondria. Like mitochondria, they have the outer and the inner membrane.
Photosynthesis takes place within the thylakoids, stacks of closed sacs formed by the inner membrane. The thylakoids pile one on top of the other to form a granum (plural: grana). The thylakoids are bathed with a semiliquid substance called strome.
Vacuole : Water Bag
It is a membrane-bound sac that stores water. The water stored in plant cells helps make the leaves, stems, and other plant parts plump and firm. Vacuoles can also store food and other substances such as plant toxins.
Microtubules and Microfilaments : Cellular Skeleton
These are hollow tubes that form a network within the cell, while microfilaments are long, fiberlike strands. Both are made up of proteins. They cause the movement of flagella, cilia, and pseudopodia—the basic locomotive structures of some protozoans.
These are made up of two sets of microtubules lying just outside the nuclear membrane. They are located within an area called the centrosome. The centrioles aid in cell division by causing the movements of chromosomes.