Cell organelles and their functions is a topic of biology studied during higher education and a graduate degree in science.
These cells are almost similar in all the organisms ranging from microbes to plants and animals.
A cell is a basic unit of life that carries out most of the physiological processes on its own. Except in higher animals and plants, cells of microbes like bacteria, protozoa are independent even in terms of the search for food, reproduction, excretion, etc.
But we can still say that a cell is an independent entity and makes up the whole living system in the world.
A group of cells forms a tissue, groups of tissues form an organ, groups of organs form an organism. So the cell is a basic element of all the living organisms.
In microbes like the amoeba, paramecium, bacteria, etc. a single cell even carries out complex functions like eating, digestion, moving, sex, reproduction, excretion, etc. through a few extra or modified cell organelles.
In larger animals and plants, this is not present and cells have the same set of cell organelles inside.
Check Out: List Of Cells in Human Body
List of cell organelles in a typical cell:
- The cell membrane (plasma membrane)
- Golgi bodies
- Endoplasmic reticulum
- Centrosome (Centrioles)
A typical cell as shown in the image below
Plasma membrane: Cell membrane is the outer covering of the cell. In-plant cells it is present just below the cell wall while in an animal cell, it forms the outermost cover.
It is a lipid bilayer that encloses the entire cell and its organelles. It is a selectively permeable, flexible layer of the cell. It is one of the largest organelles in a cell structure.
Mitochondria: These are sac-like organelles inside the cells. They have their own single-stranded DNA. Because of this DNA presence, mitochondria have the ability to self replicate.
Hence mitochondria multiply within the cell even before a cell divides. This is because they are worn out during the process of respiration. So, they form new ones to carry out the function non-stop. Check for its structure Mitochondria structure.
Golgi bodies: These are the vacuoles or sac-like structures. They occupy a considerable amount of cytoplasm. They are formed from the endoplasmic reticulum. They have two sets of vesicles as Cis and Trans Golgi networks. Cis-set is at the center while the trans set is at the periphery of the apparatus. From these vesicles, lysosomes are formed.
Endoplasmic reticulum: This is also a sac-like structure attached to the nucleus and extends thereof like being suspended in the cytoplasm. It is of two types. Rough endoplasmic reticulum (RER) and smooth endoplasmic reticulum (SER).
Lysosome: Lysosomes are cell organelles found mostly bound to the cell membrane. This organelle is found in all the cells and contains hydrolytic enzymes.
Peroxisome: These are vesicles that store enzymes of energy metabolism.
Centrosomes: These contain centrioles which form spindles and help in the separation of genetic material in cell division.
Nucleus: This is the innermost and most centrally located organelle. Nucleus function is to regulate the activities if the entire cell. Hence it is called the control center of the cell. They contain the cell’s genetic material.
Flagella: These are the organelles of locomotion. They are found in a few cells like protozoans and in human cells sperms.
Cilia: These are the organelles that help in the movement of a particle near the membrane on the outer surface.
Genetic material: This compromises DNA, chromosomes which assist in cell multiplication. This is not an organelle but is present in the nucleus and involves cell multiplication.
Vesicles: These are small-sized sac-like structures. They are of different types of lysosomes, peroxisomes.
Vacuole: Vacuoles are pouches in the cell that store materials such as water, salts, proteins, and carbohydrates.
Micro-tubules: These are filamentous extensions in the cytoplasm. They form the cytoskeleton.
Cytoplasm: This is the fluid matrix of the cell. It encompasses cell organelles, other solid substances, enzymes, water, etc. Its volume is fixed and has a definite pH, tonicity depends on the ionic concentration
Cell wall: This is a non-living outer envelope of the cell. This is very characteristic and seen only in plant cells. Even bacteria possess cell walls and hence are sometimes classified under plants. It is a rigid, firm, thick external covering of the cell. It is made of cellulose, mucopolysaccharides and muco-peptides.
Functions of Cell Organelles
Each cell organelle has a specific role to play in the cell’s physiology and growth.
Cell wall: Since plants are mostly non-motile, cell wall presence imparts rigidity, capacity to tolerate harsh conditions like wind, heat, wear and tear, etc. It imparts a definite shape to the cell.
Cell membrane: This is a selectively permeable membrane and hence helps transport desired substances into and outside the cell. In animal cells, the membrane is flexible and helps tolerate mechanical movements. It is made of glycoproteins, glycolipids, etc.
Nucleus function: This is the key organelle that has the genetic material and is involved in the multiplication of cells, growth and maintenance of cells. This nucleus is absent in prokaryotic cells. The nucleus has a nucleolus that produces ribosomes. These ribosomes pass out of the nucleus and settle over the endoplasmic reticulum to aid protein synthesis by translation.
Golgi bodies: They are helpful in the storage and transport of substances in the cell.
Lysosomes: They in cellular digestion, removal of dead cells and other waste matter. They have a larger role in cell physiology and organisms’ life. See the importance of lysosomes for more details.
Vesicles: These help in the storage and release of substances as required by the cell. For example, lysosomes help in cell digestion when the cell dies. Vacuoles’ function is to store water.
Micro-tubules: These micro-tubules provide structural strength. Because of these microtubules, the cell has a fixed structure and does not collapse.
Also one comes across these cell organelles in botany. There are small differences in cell organelles and their function in between animal and plant cells. But largely similar. On the other hand, most of the organelles are absent in red blood cells.
Specialized cell organelles: These are the cell organelles present in cells of special purpose. They are not common to all the cells. These include
1. Chloroplast: These are specialized cell organelles present in leaf cells and green algae. They contain chlorophyll pigment. They help in photosynthesis wherein energy from sunlight is captured as carbohydrates.
2. Pilus: These are the organs present in bacteria. The small tubular structures anchoring out of the cell. They are meant for sexual reproduction.
3. Flagella: These are the organelles that see only a few types of bacteria. They are hair-like structures helping in motion.
4. Eyespot: Seen in euglena (protozoa) and few algae. It helps detect the sunlight and move the cell towards the light.
Reference: Essential Cell biology-Bruce Alberts.