Cell – Structure and Function

Last Updated : 21 Apr, 2025

The cell is the fundamental and structural unit of all forms of life. Every cell is made up of cytoplasm that is enclosed in a membrane and includes many small molecules of nutrients and metabolites as well as many macromolecules including proteins, DNA, and RNA. The term “cell” is derived from the Latin word cellula, which means “small room.” In this article, we will learn about cell theory, types of cells, the structure and function of cells, and the diagram of cells.

Cell Definition

Cell is the smallest, fundamental unit of life and is responsible for all life’s functions. It is the basic biological, structural, and functional components of all living things.

What is Cell in Biology?

A cell is the basic unit of life. The cell is the lowest level of organization of any living organism. It was first discovered by Robert Hooke. The study of cells is known as cell biology. The organisms can be classified into two types on the basis of number of cells, i.e., unicellular and multicellular organisms. The size and shape of the cell are according to the function of that cell. The cell is a combination of different cell organelles which perform different functions.

Labeled Diagram of a Cell

The labeled diagram of plant and animal cell shown below:

Plant-Cell-and-Animal-Cell-Diagram

Discovery of Cell

Rober Hooke observed a cell for the first time in 1665. He was observing a dried piece of cork with a compound microscope. During the observation, he noticed various little chambers which he named the ‘cells’. Compound microscopes have limited magnification and cannot see the cell properly. Hence, with all his observations he stated that those chambers are non-living. After some time, another scientist Anton Van Leeuwenhoek observed cork under a compound microscope with more magnification power. During his observation, he saw that cells were showing some movements. Hence, he stated that cells are living.

Magnification technology progressed enough to find cells, as microscopes experienced continuous improvement over time. Robert Hooke is usually acknowledged with making this discovery, which established cell biology as a field of study. He could see pores when looking through the microscope at a piece of cork. At the time, this was remarkable because it was thought that nobody else had seen these. Matthias Schleiden and Theodor Schwann both investigated plant and animal cells to support their respective theories. They found that the two varieties of cells differed significantly from one another. This promoted the concept that cells were essential to both plants and animals.

Cell Theory

Cell theory was proposed by Schleiden (1838) and Schwann (1839). The cell theory postulates are given below:

All living things are composed of cells.
Cells serve as the fundamental building blocks for the growth of tissues and organs.
Cells can only develop from other cells, which is the third and possibly most important characteristic of the theory.

Every living being started with a single cell which split through the process of mitosis to generate multiple identical cells. These cells can specialize to create various tissues and organs. This method is used to create a complete complex organisms. A single-celled organism, on the other hand, splits when its cells separate into two different species. This method is known as asexual reproduction.

Types of Cells

There are 2 main types of cells – Eukaryotes and prokaryotes cells.

Characteristic	Prokaryotic Cell	Eukaryotic Cell
Development	Less developed	More developed
Nucleus	Absent	Present
Genetic Material	Nucleoid containing DNA or RNA	True nucleus containing DNA
Organelles	Absent	Membrane-bound organelles present
Size	0.1 to 0.5 mm	10-100 μm
Reproduction	Binary fission, fragmentation, conjugation	Sexual and asexual reproduction
Examples	Bacteria, Archaea	Animals, Plants, Fungi, Protists

Prokaryotic and Eukaryotic Cell Diagram

Given below is the detailed well-labeled diagram of prokaryotic and eukaryotic cell.

Prokaryotic-and-Eukaryotic-cell

Structure of Cell

The cell structure consists of various components and cell organelles with distinct functions. They are:

Cell Wall

Cell wall is a characteristic feature of plant cell. It comprises the outermost layer of the cell. Cell wall is made up of gelatin, cellulose, and hemicellulose. It protects the plasma membrane. It is a rigid and immovable structure enclosing the cell membrane. It protects the cells from mechanical shocks and damage while providing them form and support. Cell wall is absent in animal cells.

Cell Membrane

A cell membrane surrounds the cell. The cell membrane divides cells into the internal and external components of the cell. It protects a cell’s integrity and regulates the flow of materials into and out of the cell as it is semi-permeable. Two layers of phospholipid molecules form the cell membrane. The cell membrane proteins provides structural support, faciliate material transport, act as receptor sites for signaling molecules and transport substances across the membrane.

Cytoplasm

The gel-like substance that fills a cell is called cytoplasm. Cytoplasm functions as the site where various cellular processes occur, including metabolism, protein synthesis, and intracellular transport. It serves as a catalyst for chemical reactions. The cytoplasm of a cell performs every task necessary for cell division, growth, and replication. Diffusion moves materials within the cytoplasm.

Nucleus and Nucleolus

The nucleus is a crucial organelle found in eukaryotic cells, serving as the control center of the cell. It contains the genetic material (DNA) organized into chromosomes. The nuclear membrane surrounding the cell acts as a barrier, separating the nucleus from other cell parts.Within the nucleus, the nucleolus stands out as a distinct region responsible for ribosome assembly. It synthesizes ribosomal RNA (rRNA) and combines it with proteins to form ribosomes, essential for protein synthesis. Together, the nucleus and nucleolus play vital roles in controlling cellular activities, maintaining genetic integrity, and regulating gene expression.

Cell Organelles

Organelles are cell components that have been modified and/or specialized to perform one or more important functions. Cell organelles are found in both eukaryotic and prokaryotic cells; however, bacterial organelles are more basic and not membrane-bound. A cell contains different kinds of organelles. The cell organlles structure and function is given below:

Cell Organelles	Structure	Function
Chromosomes	Thread-like structures made of DNA and protein	Carries genetic information
Endoplasmic Reticulum	Network of membranous tubules and sacs; rough ER has ribosomes attached, while smooth ER does not.	Involved in protein and lipid synthesis, as well as transportation of molecules within the cell.
Golgi Bodies	Stack of flattened membrane-bound sacs (cisternae) with associated vesicles	Modifies, sorts, and packages proteins and lipids for transportation or secretion.
Ribosomes	Made of RNA and protein; can be free in the cytoplasm or attached to the ER.	Site of protein synthesis.
Mitochondria	Double membrane-bound organelle with inner cristae folds; contains mitochondrial DNA (mtDNA).	Generates ATP through cellular respiration; known as the “powerhouse” of the cell
Chloroplast	Double membrane-bound organelles with internal thylakoid membranes	Site of photosynthesis in plant cells; contains chlorophyll for capturing light energy.
Vacuoles	Membrane-bound sacs filled with fluid or sap; larger in plant cells.	Store water, nutrients, and waste; maintain turgor pressure in plant cells.
Lysosomes	Membrane-bound vesicles containing digestive enzymes.	contain digestive enzymes for breaking down waste materials and foreign invaders.

Characteristics of Cells

Below are the following characteristics of a cell.

Cells help in formation of the structure of an organism.
A cell is a membrane-bound organelle having other cell organelles which perform different functions.
Nucleus present in the between of a cell carries all the genetic information of a cell.
Lysosomes help in cellular digestion.
Cytoplasm is present in the interior of a cell in which all cell organelles are present.

Functions of a Cell

The below mentioned are some of the functions of a cell:

Structure and Support: Cells provide the structural basis of all organisms.
Growth: Cells are responsible for the growth of the organism.
Transport: Cells transport the nutrients that are used in the different chemical processes which take place inside them. As a result of these processes, a waste product is produced. Cells then work to get rid of this waste. In this manner, small molecules like oxygen, carbon dioxide, and ethanol pass through the cell membrane by diffusion. This method is known as passive transport. On the other hand, the larger molecules like the proteins and polysaccharides, go in and out of the cell via active transport.
Energy Production: Organisms need energy to perform different chemical reactions. In plants, the energy comes from the process of photosynthesis while in animals the energy comes via respiration.
Metabolism: The cell is responsible for the metabolism which includes all the chemical reactions that take place inside an organism to keep it alive.
Reproduction: A cell helps in reproduction through the processes of mitosis and meiosis.

Conclusion – Cell Structure and Function

In conclusion, the cell is the basic unit of life, consisting of cytoplasm enclosed within a membrane and containing various cell organelles essential for life processes. Through cell theory, we explore the cell structure, functions, and types, understanding its significance in both unicellular and multicellular organisms. Cells are classified into prokaryotic and eukaryotic, each with distinct characteristics and organelles, contributing to essential cellular functions like growth, transport, energy production, and reproduction. The different cell organelles play crucial roles in maintaining cellular integrity.

Also Read:

Cytoplasm – Structure and Function

Animal Cell

Plant Cell

Diagram of Animal Cell

Neuron Structure and Function

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