What is Cell?

The word cell originates from a Latin word which means a small room. Cell is the basic fundamental unit of life, present in living organism. Cell has various organelles within multi-celled organism and single-celled in unicellular organism to perform various function. It can replicate on its own. A cell can be a prokaryotic as well as eukaryotic.

Type of Cell

Cells can be classified in two ways such as unicellular, multicellular and acellular. Another classification type as a prokaryote and eukaryote.

Prokaryotic vs Eukaryotic Cell

An organism is said to be prokaryotic if it lacks nucleus and various other organelles. A eukaryotic cell contains nucleus and organelles such as endoplasmic reticulum, mitochondria, chloroplast, vacuoles, lysosomes, Golgi apparatus and others. Nuclear membrane is another layer surrounding the nucleus and separating the inner contents from the outside. However there exist similarities between the two like the storage of genetic materials which gets copied and then reaches the ribosomes where it gets translated into proteins.

Unicellular vs Multicellular vs Acellular

Organism can be classified as unicellular or multicellular on the basis of the number of cell it contains. Single-celled organisms are called Unicellular. Organisms with multi-celled are multicellular. Unicellular organism examples are prokaryotes. In prokaryotes the example is protist. Example of multicellular organisms are plants and animals.

When various cells comes together it forms tissue. Epithelial tissue, Meristematic tissue, Vascular tissue, Nerve tissue, Muscle tissue, Connective tissue and Sporogenous tissues are the types of tissue. Fundamental and complex are the types of tissue. Example of fundamental tissue are parenchyma, sclerenchyma and others. Complex tissue are phloem and xylem. Cells forms tissue and tissue forms organ when many tissue come together and work.

Acellular refers to something that is not formed from cell. example hyphae.

Structure of Cell

Cell contains various structures which are compartmentalized in it and each one of them has several functions to perform. The very first outer layer is cell membrane which is made up of phospholipids. The function of cell membrane is to keep the outer and inner content separate.

On the surface of the cell membrane are molecules present, which play a role in cell recognition. Cell wall is also present in plants, animal, fungi, algae and few prokaryotes, which is present outside the cell membrane. It keeps the cell rigid, protects it from outer environment. The cytoplasm present in the cell, inhabiting near the organelles, consist of cytosol, a liquid solution made up of ion such as chloride, sodium, water and biomolecules such as carbohydrate, protein and others. Cell signaling, action potential and other reactions take place in the cytosol.

Bacterial Cell Diagram

Eukaryotes are quite organized, due to the presence of various organelles. Eukaryotic cells various organelles are Mitochondria, Endosomes, Golgi apparatus, Endoplasmic Reticulum, Vacuoles, Lysosomes and Cytoskeleton. The function of Endoplasmic reticulum is to clear the drug, metabolism of carbohydrate and synthesis of biomolecules. Glycosylation, lipid transportation within cell, lysosomes arrival and packaging various molecules are functions of Golgi apparatus.

Animal Cell Diagram

The powerhouse of cell is the mitochondria which will provide energy for various process. Plastid example chloroplast which produces and stores food, as they contain chlorophyll which helps in carrying out photosynthesis. The shape of the cell is maintained by the cytoskeleton. The unwanted components are thrown and the reusable ones are recycled by lysosomes.

Plant Cell Diagram

For digestion, excretion, secretion and storage inside the cell vacuoles are important. Cytoplasm contains cytosol made up of proteins, ions and water. Apart from the DNA present in the nucleus, there are DNA found in the mitochondria as well as chloroplast. They carry out various metabolic functions. Both of them are semi-autonomous. Chloroplast DNA is not found in all types of eukaryotic cell as only plants and algae possess chloroplast. Plants possess cell wall which protect them from the outer environment and provides rigidity and shape. The cell wall is surrounded by cell membrane, which is a barrier separating outer contents from the inside. As animal cells do not contain cell wall, they are more flexible.

Although, a prokaryotic cell does not have organelles it has other structures such as Carboxysome which fixes carbon content. Magnetosomes which are seen in magneto tactic bacteria. They also have chlorosomes which are green sulphur bacteria, which harvests light. The DNA is present in a nucleoid region in the prokaryotes.

Features of Cells

i. Cell Cycle

In cell cycle, the DNA get copied, replicated and there is cell division of parent cell to form daughter cell. Thus, it involves division and the growth of the daughter cell. there are various phases in cell cycle such as the interphase, resting phase and others. Cell grows in size, makes copy of its DNA for the division to take place. Before the interphase is the resting phase where the cell is in a dormant stage. G1, S and G2 are the phases of interphases. Thus, leading to completion of cell cycle.

ii. Cell Division

In this process, offspring i.e., the daughter cells are obtained from the parent cell. Mitosis and Meiosis are the cell division process in eukaryotes. Cell division is a very important step as it helps to reproduce, after which the cells grow. The end-product of meiosis is four un-identical cell. the end-product of mitosis is two similar cells.

iii. Cell Growth and Metabolism

While the cells grow, they undergo metabolism. Metabolism is of two types; Catabolism and Anabolism. The process where larger molecules are broken down into smaller molecules is called as Catabolism. With the help of smaller molecules, preparing a larger molecule and requires energy in the form of ATP is called as Anabolism.

Molecules present inside the cell are stored and degraded such as proteins, lipid, carbohydrate and others. The DNA and RNA synthesis site is nucleus. Ribosomes synthesize proteins, whereas in endoplasmic reticulum, lipid is synthesized.

iv. Motility

Motility basically means movement. For the movement of organism, they possess flagella. In structure they are thin long extensions. It is not always necessary that they are used for movement only. They could be used as a signal source as well as for sensation. E.g., olfactory receptor neurons present in the nose, in the eye rod photoreceptor cells.

On the surface, presence of hair like projections are cilia. They are of two types; motile and non-motile. Non- motile play a role in sensory and motile cilia play a role in locomotion. Example are protozoans. Another example is the lining of the lung to throw-off dust particles contain cilia.