Index
A cell is the smallest unit of work of all living organisms on our planet earth, which is capable of carrying out the functioning of life.
Therefore, it can also be defined as a fundamental unit of life. The term cell was first observed and identified by an English physicist Robert Hook in the year 1665.
There were many theories developed for the cell. Later, in the year 1839, two German scientists, Schwann and Schleiden, provided some basic principles of the cell.
Cell structures
There are many cells in an individual, which perform various functions throughout life. The different types of cells include prokaryotic, plant, and animal cells.
The size and shape of the cell vary from millimeter to micron, which is generally based on the type of function it performs.
A cell generally varies in its shapes. Some cells are spherical, rod, flat, concave, curved, rectangular, oval, etc. These cells can only be seen under a microscope.
Cell theory
- Each living organism is made up of a single cell ( unicellular ) (or) many cells (multicellular) and all types of cells have certain structures in common such as: genetic material and plasma membrane.
- The cell is the smallest living thing.
- Each cell arises only from pre-existing cells.
Cell structure and function
Cell wall: helps protect the plasma membrane and plays a vital role in supporting and protecting cells. It is a thick outer layer made of cellulose.
Cell membrane : it is a thin double layer barrier that surrounds the cell to control the entry and exit of certain substances.
Cytoplasm: it is a membrane that protects the cell by keeping the cell organelles separated from each other. This helps maintain a stable cell. The cytoplasm is the site where many vital biochemical reactions occur.
Nucleus: they are the membrane bound organelles, which are found in all eukaryotic cells. It is the most important organelle in a cell as it controls the entire activity of a cell and also plays a vital role in reproduction.
Nuclear membrane: the bilayer membrane, which protects the nucleus by surrounding it and acts as a barrier between the cell nucleus and other organs of a cell.
Nucleolus: it is an important membrane found within the nucleus. It plays a vital role in the production of the cell’s ribosome.
Chromosomes: It is made of DNA and is stored in the nucleus, which contains the instructions for traits and characteristics.
Endoplasmic reticulum: helps in the movement of materials around the cell. It contains an enzyme that helps build molecules and make proteins. The main function of this organelle is storage and secretion.
Ribosome: plays a vital role in protein synthesis.
Mitochondria: they are double membrane filamentous organelles, which play a vital role in the generation and transformation of energy. Mitochondria play a vital role in various functions of cellular metabolism, including oxidative phosphorylation.
Golgi bodies: helps in the movement of materials within the cell.
Lysosomes: It is also known as suicide bags as it helps in cell renewal and breaks down old cell parts.
Vacuoles – Helps plants maintain their shape and also stores water, food, waste, etc.
Chloroplast: they are the site of photosynthesis, which is present in chlorophyll bacteria, blue-green algae, etc.
Prokaryotic cell structure
They are the first organisms to be present on our planet earth. Organisms with this type of cell are known by the term prokaryotic organisms.
Bacteria, blue-green algae, and E. coli are few examples in this category. Prokaryotic cells are unicellular organisms, lacking a nucleus and comprise capsule, cell wall, cell membrane, cytoplasm , nucleiod, ribosome, plasmids, pili and flagella.
General characteristics of the prokaryotic cell
- The size of a cell varies between 1-10 microns. Few prokaryotic cells vary in size.
- They are unicellular, forming a colony or filamentous.
- Cell shape includes spherical, rod-shaped, and flat-shaped organisms.
- Nutrient mode: few organisms are photosynthetic (they make food with the help of sunlight), they feed on living things and dead things.
- They reproduce asexually by the process called binary fission, transformation, conjugation, transduction.
Structure and functions of a prokaryotic cell
Capsule: it is the viscous outer layer of the cell wall. It is composed of the polypeptide. The main function of the capsule is to protect the cell from dryness and it also helps to protect the cells from external pressures.
Cell wall: it is the most rigid structure, which provides the shape and protects the internal organelles of a cell. It is the intermediate layer, which is present between the capsule and the cell membrane.
Cell membrane: it is the internal delicate structure, which plays a vital role in regulating the entry and exit of materials into the cell.
It acts as a permeable membrane and separates the cell from its environment. It is approximately 5-10 nm thick, which aids in the secretion of proteins and the removal of waste products. It is also called by a name plasma membrane.
Cytoplasm: it is the liquid membrane, which is present between the cell membrane and the nucleus. It plays a vital role in the storage of all kinds of materials, which are necessary for an organism to maintain life.
Nucleiod: is the region of the cytoplasm that contains genetic material. The DNA of a prokaryotic organism is a large loop, or a circular one, found within the nucleus. It plays a vital role in cell division.
Ribosome: comprises both RNA and proteins. Helps in the synthesis of proteins in the cell. They are the smallest membranes present within the cytoplasm.
Plasmids: they are the smallest membrane of a cell with double-stranded DNA. Plasmids are rarely present in prokaryotic organisms. The main role of plasmids is that they help in the exchange of DNA between bacterial cells.
Pilli: it is the thinnest membrane of a prokaryotic cell. They are made up of a protein complex called pilin and are primarily involved in sticking to objects, especially during sexual reproduction.
Flagella: it is the helical-shaped membrane, whose sizes vary between 19-20 nm in diameter and plays a vital role in the motility of an organism from one place to another. It also helps to swim, slide, twist and turn clockwise and counterclockwise.
Structure of eukaryotic cells
They are cells with the presence of a true nucleus. Organisms with this type of cell are known by the term eukaryotic organisms.
Animals, plants, and other organisms, excluding bacteria, blue-green algae, and E. coli have been grouped into this category. Eukaryotic cells are more complex than prokaryotic cells.
These organisms have a membrane-bound nucleus with many cellular organelles to perform various cellular functions within the system.
General characteristics of the eukaryotic cell
- The size of a eukaryotic cell ranges from 10-100 microns. Few eukaryotic cells vary in size.
- They are large, advanced, multicellular, and have membrane-bound organelles.
- They reproduce both sexually and asexually.
- Nutrient mode: autotrophic and heterotrophic.
- The protozoa, algae, fungi, plants and animals of the Kingdom are organisms with eukaryotic cells.
Structure and functions of a eukaryotic cell
Plasma membrane: they are semi-permeable membranes that act as a boundary of a cell, which protects and separates the cell from the external environment.
Nucleus: it is surrounded by a double layer of phospho-lipid bilayer called the nuclear envelope. They are the storehouse of the cell’s genetic materials in the form of DNA and store all the necessary information, which is required for a cell to control all kinds of activities.
Nuclear membrane: it is the double membrane layer that surrounds the nucleus and plays a role in the entry and exit of materials within the nucleus.
Nucleus: Mainly involved in the control of all kinds of cellular activities, including cellular reproduction.
Mitochondria: they are the smooth double membrane, which are present in all eukaryotic cells. They are the engine of the cell. It plays a vital role in the synthesis of ATP and converts glucose to ATP.
Endoplasmic reticulum: they are the double membrane organelle, which divides the cell into compartments. It is connected to the nuclear membrane of the cell.
It plays a vital role in protein synthesis, lipid and steroid biosynthesis, stores and regulates calcium and carbohydrate metabolism. The endoplasmic reticulum is of two types: rough and smooth endoplasmic reticulum.
Ribosome: it is present in the cytoplasm. They are the site for the synthesis of proteins in cells, which are made up of RNA and ribosomal proteins.
Golgi bodies: it is the flattened membrane, which is used mainly to store the substances produced by the cell. This membrane also helps preserve and transport materials within the cell. Therefore it is also called as the post office of a cell.
Lysosomes: are membrane bound organelles, which contain digestive enzymes to break down macromolecules. Lysosomes play a vital role in protecting cells by absorbing or destroying foreign bodies that enter the cell.
Cytoplasm: they are the gelatin types of organelles, which are present in the inner region of a cell. It plays a vital role in keeping a cell in a stable and keeps cell organelles separate from each other.
Chromosomes: the rod-shaped structures, which are made up of proteins and DNA. Chromosomes also play a vital role in determining the sex of an individual. All human cells contain 46 numbers of chromosomes.
Plant cell structure
The cells of a plant are eukaryotic cells, with the presence of a true nucleus, large and advanced multicellular organelles attached to the membrane.
These plant cells are quite different from animal cells in shape and a few other organelles that are only found in animal cells but are absent in plant cells.
Depending on the structure and functions, plant cells are part of:
Cell wall: it is the outer layer of a plant cell, which helps to provide shape and strength to the entire plant. A cell wall is made of cellulose that protects and supports the plant to grow.
Cell membrane: it is a biological membrane that separates the organelles of living cells from non-living structures. This membrane plays a vital role in helping a cell communicate with the external environment and also in the transport of proteins and other molecules throughout the cell.
Chloroplasts: they are oval-shaped double membrane organelles of green color, which are the sites of photosynthesis. The green color pigment (chlorophyll) present in the leaves helps plants absorb solar energy to prepare food.
Cytoplasm: a type of double-membrane gelatin organelles, which are present in the inner region of a cell. It helps keep a cell stable and protects cell organelles by separating them from each other.
Lysosomes: they are round organelles with a single membrane, which help to digest proteins, fats and carbohydrates. It also helps in the excretion of undigested materials from plant cells. It also aids in cell renewal and the breakdown of large cells into smaller, older, dead cells.
Golgi bodies: the sac-like structures, which are present in a cell to manufacture, store, package, and ship materials through the cell.
Endoplasmic reticulum: the membrane network, which helps transport materials around the cell. It forms a connection between the nuclear envelope and the cell membrane of a cell.
Mitochondria: they are rod-shaped organelles, they play an important role in the release of energy and are the source of energy for a cell. In the plant cell, they are the sites of cellular respiration.
Nucleus: They are large, oval-shaped organelles that contain one or more nucleoli with DNA. The main role of the nucleus in the plant cell is that it controls all types of cellular activities.
Nucleus: they are the spherical membranes, present within the nucleus. This membrane contains RNA, which is used to build proteins. They are the sites of RNA synthesis.
Vacuole: are the fluid sacs, which are present in large quantities in plant cells. The main function is this membrane is to store food and other waste materials. Vacuoles are the largest organelles present in plant cells.
Structure of animal cells
Animal cells are eukaryotic cells, with the presence of a true nucleus; Large and advanced multicellular organelles attached to the membrane.
Like plant cells, animal cells have the same organelles except for the cell wall, chloroplasts, the number of vacuoles, and many more. Due to the absence of a cell wall, the shape of an animal cell is irregular.
Depending on the structure and functions, animal cells are part of:
Cell membrane: they are semi-permeable membranes that surround the cell. It helps to hold the cell together and allows nutrients to enter and leave the cell.
Nucleus – The largest organelle in the cell, which contains hereditary information from DNA and other cells. The main role of the nucleus in the animal cell is that it controls all cellular activities.
Vacuole: are the fluid sacs, which are present in less quantity in animal cells compared to plant cells. The main function is this membrane is to store food and other waste materials.
Golgi bodies: the sac-like structures, which are present in a cell to manufacture, store, package and ship the selected particles throughout the cell.
Ribosome: it is present in the cytoplasm. They are the site of protein synthesis, which are made up of RNA and ribosomal proteins.
Endoplasmic reticulum: the membrane network, which helps transport materials around the cell and also aids in the synthesis of lipids and proteins. It forms a connection between the nuclear envelope and the cell membrane of a cell.
Mitochondria: they are rod-shaped organelles, they play an important role in the release of energy and are the source of energy for a cell.
Cytoplasm: a type of double-membrane gelatin organelles, which are present in the inner region of a cell. It helps keep a cell stable and protects cell organelles by separating them from each other.
Lysosomes: they are round organelles with a single membrane, which help to recycle cell organelles. The lysosome of an animal cell contains some digestive enzymes that help digest cell debris.
