Types of Cells - Prokaryotic Cell and Eukaryotic Cell
Cells, which are the basic building blocks of all living species, are the basic building blocks of all living organisms. The human body has thousands of cells. They help support the body's structure, absorb nutrition, convert them to energy, and perform specialized functions. Cells also contain the body's genetic material and have the potential to multiply.
Cells are made up of various portions that have a specific function. Organelles, for example, are specialized structures within the cell that perform specific functions. Cells exist in various sizes, shapes, and types in the human body. The concept of a "generalized cell" is proposed for descriptive purposes. It incorporates characteristics from a variety of cells. The cell membrane, the nucleus, and the cytoplasm, which sit in between the two, make up a cell. Dozens, if not thousands, of tiny yet distinct structures known as organelles can be found in the cytoplasm.
Cytoplasm
It aids biochemical processes by acting as a catalyst. It acts as a platform for the cell's other organelles to function. A cell's cytoplasm is responsible for all aspects of cell proliferation, growth, and replication. Diffusion is a physical phenomenon that permits objects to move across tiny distances within the cytoplasm.
Cytoskeleton
The cytoskeleton is a system of long fibers that sustain the cell's structural integrity. The cytoskeleton is responsible for various functions, including establishing cell shape, facilitating cell division, and allowing cells to move. It also features a track-like system for controlling the movement of organelles and other substances within cells.
The cytoplasm contains organelles.
Cytoplasmic organelles are "mini organelles" that float around in the cell's cytoplasm. Organelles each have their own structure and function in the cell's operation. Organelles are, by definition, membrane-bound structures in a cell. The nucleus is a nice example.
Types of Cells
Cells are categorized into two types – prokaryotic cell and eukaryotic cell depending on the presence or absence of a true nucleus in the cell.
A usual cell contains cytoplasm which is surrounded by a thin membrane known as the cell membrane. The key function of a cell membrane is to protect the constituents of the cell from the outside environment. Selective materials are only permitted to enter the cell through the cell membrane. It involves other cell organelles like mitochondria, nucleus, etc.
Cells are joined together to form tissues, tissues form organs, organs form organ systems such as the circulatory system, digestive system, central nervous system, etc. They combine together to form different forms of life in different shapes and sizes. Most of the organisms are multicellular like humans. There are unicellular organisms like bacteria and protozoa and multicellular organisms like human beings.
Cell Structure
There are several cells in an individual, and the different kinds of cells include - prokaryotic cells, plant and animal cells. The size and the shape of the cell vary from millimeter to microns, which are usually based on the type of function that it performs. Cells usually vary in their shapes. They could either be rod-shaped, flat, curved, concave, spherical, rectangular, oval, etc. These cells will only be visible under a microscope.
Prokaryotic Cell Structure
They are the first organisms to be existing on our planet earth. Organisms with this cell type, are called prokaryotic organisms (or) prokaryotes. Prokaryotic cells are single-celled organisms, with the deficiency of nucleus and comprise of a capsule, cytoplasm, cell wall, cell membrane, ribosome, nucleoid, plasmids, pili, and flagella.
Prokaryotic Cell General Features
The size of a cell varies from 1-10 microns. Few prokaryotic cells vary in their size.
They are unicellular, which forms a colony.
The shape of the cell contains rod spherical and flat-shaped organisms.
Mode of nutrition - A few organisms are photosynthetic, and get nourished on living things and dead things.
They reproduce asexually by binary fission, transformation, conjugation, transduction.
Structure and Functions of a Prokaryotic Cell
Capsule: It is the greasy outer coating of the cell wall. The key function of the capsule is to protect the cell from getting dry and also helps in protecting cells from outside pressures.
Cell Wall: It is the stronger and rigid structure, which provides the shape and protects the inside organelles of a cell. It is the middle layer, which lies between the capsule and the cell membrane.
Cell Membrane: It is the inner delicate structure, which plays an important role in regulating the entry and exit of any materials in the cell. It acts as a permeable membrane. It is of about 5-10nm in width, which helps in the oozing of proteins and elimination of waste products.
Cytoplasm: It is the viscous membrane, which is lying in between the cell membrane and nucleoid.
Nucleoid: It is the cytoplasm region covering genetic material. The DNA of a prokaryotic organism is one big loop, which is situated inside the nucleoid. It plays an important role in cell division.
Ribosome: It consists of both RNA and proteins. It supports protein synthesis in the cell. They are the tiniest membrane present inside the cytoplasm.
Plasmids: They are the minute membrane of a cell with double-stranded DNA. Plasmids are hardly present in prokaryotic organisms.
Pili: It is the thinnest tissue of a prokaryotic cell. They consist of a protein complex named pilin and are mostly involved in sticking to the objects particularly during sexual reproduction.
Flagella: It is a membrane that is in a helical shape, and its sizes vary from 19-20nm in diameter and play an important role in the mobility of an organism from one place to another place.
Eukaryotic Cell Structure
They are cells with a true nucleus. Organisms, with this cell kind, are identified by the term eukaryotes. Animals, plants, and other organisms apart from bacteria, blue-green algae, and E. coli have been grouped into this group. Eukaryotic cells are more complex in comparison to prokaryotic cells. These organisms contain a membrane-bound nucleus with many cell organelles to make several cellular functions within the system.
Eukaryotic Cell General Features
The size of a eukaryotic cell varies from 10-100 microns.
They are multicellular and have membrane-bound organelles.
They reproduce either sexually or asexually.
Type of nutrition - Autotrophic and heterotrophic
KingdomsProtozoa, Fungi, Algae, Plantae, and Animalia are eukaryotic organisms.
Structure and Functions of a Eukaryotic Cell
Plasma Membrane: They are semi-permeable membranes that behave as a boundary of a cell, which protects and splits up the cell from the outside environment.
Nucleus: It is a double-layered wall of Phospholipid bilayer. They are the stockroom for the cell’s genetic materials in the form of DNA and keep all the essential information, which are vital for a cell to control.
Nuclear Membrane: It is the double membrane layer that surrounds the nucleus and it plays a part in the entry and exit of resources within the nucleus.
Nucleolus: It is the non-membrane-bound organelle, which is located within the nucleus.
Mitochondria: They are the double smooth membrane, which is in all eukaryotic cells. They are the powerhouse of the cell. It plays a vital part in the synthesis of ATP and transforms glucose into ATP.
Endoplasmic Reticulum: Double membrane organelle, which splits the cell into sections. It is linked to the nuclear membrane of the cell. It plays an important role in protein synthesis, biosynthesis of lipids and steroids, stores and controls calcium, and digestion of carbohydrates. The endoplasmic reticulum is of two type’s rough and smooth Endoplasmic reticula.
Ribosome: It is in the cytoplasm. They are the spot for cells protein synthesis, which is made of ribosomal RNA and proteins.
Golgi Bodies: It is the compacted membrane, which is mostly used to preserve the materials made by the cell. This membrane also helps in storing, carrying materials within the cell. Therefore, it is also named the post office of a cell.
Lysosomes: They are membrane-bound organelles, which have digestive enzymes to break down macromolecules. Lysosome plays a vital part in protecting the cell by destroying foreign bodies entering the cell.
Cytoplasm: Jelly types of organelles, which are in the inner region of a cell. It plays a vital part in keeping a cell stable and keeps the cell organelles distinct from each other.
Chromosomes: The rod-shaped structures, which are made of proteins and DNA. Chromosomes also play a vital part in determining the sex of an individual.
Plant Cell Structure
Plant cells are eukaryotic cells, with a true nucleus, multicellular large, and progressive membrane-bound organelles. These plant cells are relatively different from animal cells in shape and other several organelles which are only found in animal cells but are absent in plant cells. Depending on structure and functions, plant cells comprise of:
Cell Wall: It is the outer layer of a plant cell, which helps in providing the form and strength to the complete plant. A cell wall is made of cellulose that protects and helps the plant to grow.
Cell Membrane: A biological membrane that divides living cell organelles from nonliving structures. This membrane plays a vital part in helping a cell to communicate with the outside environment and in carrying proteins and other molecules throughout the cell.
Chloroplasts: Green-colored oval-shaped double-membrane organelles, which are the spots of photosynthesis. The green-colored pigment (chlorophyll) located in the leaves helps plants in absorbing solar energy to make food.
Golgi Bodies (or) Golgi Complex: The sac-like structures, which are in a cell to manufacture, store, packing, and shipping the substance throughout the cell.
Mitochondria: Mitochondria play an important part in liberating energy and they are the powerhouse of a cell. The metabolic processes of the cell are referred to as cellular respiration. Many of the actions that occur during aerobic respiration occur in the mitochondria. Mitochondria are the cell's energy-producing organelles, which keep it alive. Mitochondria are little organelles that float freely within cells. They're digestive organelles that take in nutrients, break them down, and transform them into energy-rich molecules for the cell. There are dozens of mitochondria in specific cells, whereas in others, there are none.
Vacuole: They are the fluid bags, which are in great numbers in plant cells. The chief function is this membrane is to preserve food and other waste substances. Vacuoles are the biggest organelles present in plant cells.
Animal Cell Structure
Animal cells are eukaryotic cells, with the existence of a true nucleus; multicellular big and advanced membrane-bound organelles. Similarly, like plant cells, animal cells have similar organelles except for the cell wall, chloroplasts, number of vacuoles, and many more. Due to the deficiency of the cell wall, the shape of an animal cell is uneven. Depending on structure and functions, animal cells comprise of:
Cell Membrane: They are semi-permeable membranes covering the cell. It supports holding the cell together and controls the entry and exit of nutrients into the cell.
Vacuole: They are the fluid bags, which are in fewer numbers in animal cells as compared to plant cells. The key function is this membrane is to preserve food and other waste substance.
Golgi Bodies (or) Golgi Complex: The bag-like assemblies, which are existing in a cell to manufacture, storage, packing and transport the selected particles throughout the cell.
Ribosome: It is situated in the cytoplasm. They are the place for protein synthesis, which is made of ribosomal RNA and proteins.
Mitochondria: They are bar-shaped organelles, play an important part in liberating energy, and are known as the powerhouse of a cell.
FAQs on Cell Structure and Function
1. What is a cell and what are the fundamental principles of the Cell Theory?
A cell is the basic structural, functional, and biological unit of all known organisms. The Cell Theory, a cornerstone of biology, provides a universal framework for understanding life. Its main principles are:
- All living organisms are composed of one or more cells.
- The cell is the most basic unit of life.
- All cells arise from pre-existing cells, as stated by Rudolf Virchow.
2. What are the key differences that distinguish a prokaryotic cell from an eukaryotic cell?
The primary distinction lies in their structural complexity. Eukaryotic cells possess a true, membrane-bound nucleus containing their genetic material, along with other membrane-bound organelles like mitochondria and the Golgi apparatus. In contrast, prokaryotic cells lack a true nucleus; their genetic material is located in a region called the nucleoid. They also lack membrane-bound organelles, and their ribosomes (70S) are smaller than those in eukaryotes (80S).
3. Why is the plasma membrane often described using the fluid mosaic model?
The fluid mosaic model is used because it accurately describes the structure and properties of the plasma membrane. It is considered:
- Fluid: The lipid bilayer is viscous, allowing individual lipid molecules and embedded proteins to move laterally, much like buoys in an ocean. This fluidity is crucial for cell movement, growth, and communication.
- Mosaic: It is composed of a collage of different components, including phospholipids, cholesterol, and various proteins that are scattered throughout the bilayer, creating a mosaic-like pattern. These proteins perform key functions like transport and signalling.
4. What are the main components of the endomembrane system and how do they function together?
The endomembrane system is a group of organelles that work together to modify, package, and transport lipids and proteins. The key components and their coordinated functions are:
- Endoplasmic Reticulum (ER): The Rough ER synthesises proteins, while the Smooth ER synthesises lipids.
- Transport Vesicles: These small sacs bud off from the ER and transport the synthesised molecules to the Golgi apparatus.
- Golgi Apparatus: It modifies, sorts, and packages the proteins and lipids into new vesicles.
- Lysosomes/Vacuoles: Vesicles from the Golgi can become lysosomes, which digest cellular waste, or fuse with the plasma membrane to release their contents outside the cell.
5. How does the unique structure of a mitochondrion directly support its role as the 'powerhouse of the cell'?
The mitochondrion's structure is perfectly optimised for cellular respiration and ATP production. The outer membrane encloses the organelle, while the inner membrane is extensively folded into structures called cristae. This folding dramatically increases the surface area available for the electron transport chain, a key process in ATP synthesis. The innermost compartment, the matrix, contains the enzymes required for the Krebs cycle. This compartmentalisation allows for the efficient, step-by-step breakdown of glucose to generate energy.
6. What is the function of chloroplasts in a plant cell, and how do they fundamentally differ from mitochondria?
The primary function of chloroplasts is to conduct photosynthesis, the process of converting light energy into chemical energy (glucose). They contain the green pigment chlorophyll to capture sunlight. The main difference lies in their energy conversion role: Chloroplasts build glucose to store energy, whereas Mitochondria break down glucose to release energy. While both have double membranes and their own DNA, chloroplasts are found only in plant cells and some protists, while mitochondria are found in almost all eukaryotic cells.
7. If a cell's ribosomes were to suddenly become non-functional, what would be the immediate and long-term consequences?
The consequences would be catastrophic for the cell. The immediate effect would be a complete halt in protein synthesis. Since ribosomes are the sites where proteins are made, the cell would be unable to produce any new enzymes, structural components, or signalling molecules. In the long term, this would lead to a breakdown of all cellular functions—metabolism would stop, cell repair would cease, and the cell would quickly die.
8. What is the primary role of the cell nucleus and what are its main structural components?
The nucleus serves as the cell's control centre, housing its genetic material and coordinating all cellular activities like growth, metabolism, and reproduction. Its structure includes:
- Nuclear Envelope: A double membrane with nuclear pores that regulate the passage of molecules.
- Nucleoplasm: The jelly-like substance within the nucleus.
- Chromatin: A complex of DNA and proteins (histones) that condenses to form chromosomes during cell division.
- Nucleolus: A dense structure responsible for synthesising ribosomes.
9. How do the cell walls of plants and fungi demonstrate convergent evolution in their function?
The cell walls of plants and fungi demonstrate convergent evolution as they serve the same primary function—providing structural support, maintaining cell shape, and preventing osmotic lysis—but are made of different biochemical materials. The plant cell wall is primarily composed of cellulose, a polysaccharide of glucose. In contrast, the fungal cell wall is made of chitin, a different polysaccharide also found in the exoskeletons of insects. This shows how different evolutionary paths can lead to a similar functional solution.
10. What is the cytoskeleton and what are its three main functions inside an animal cell?
The cytoskeleton is an intricate network of protein filaments and tubules extending throughout the cytoplasm of a cell. It is not a static scaffold but a dynamic structure. Its three main functions are:
- Mechanical Support: It provides structural integrity and helps maintain the cell's shape.
- Intracellular Transport: It acts as a system of 'highways' along which organelles and vesicles can be moved.
- Cell Motility: It is essential for cell movement, including the movement of cilia and flagella, and the process of cell division (cytokinesis).
