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The cell theory was first put forth by Schleiden and Schwann and then altered by Rudolf Virchow. According to cell theory, the cell is the building block of all organisms.
- Cell populations collectively make up organs, tissues, and entire organisms.
- While some are made up of just one cell and are referred to as unicellular creatures, others are made up of numerous cells and are referred to as multicellular organisms.
- The concept of cell theory has evolved and advanced from the time of discovering the initial cells, inspiring a multitude of incredible experiments to highlight its different components.
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Key Terms: Cell, Cell Theory, Prokaryotes, Eukaryotes, Cell Organelles, Genes, Organs, Organisms
What is a Cell?
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All living organisms are constructed from cells, which are the fundamental units of the structure. All plants and animals have this smallest biological, structural, and functional unit. The essential constituents of life are cells, commonly denoted as the building blocks.
Multicellular organisms are made up of many cells, as opposed to unicellular organisms, which are made up of just one cell. Digestion, respiration, and reproduction are among the diverse functions conducted by cells within living organisms.
Cell Theory
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The cell theory was developed first jointly by Schleiden and Schwann. But there were several gaps in their idea. The concept of cells dividing and generating new cells from old ones was first introduced by Rudolf Virchow in 1855 (Omnis cellula-e cellula). To give the cell theory its final form, he amended Schleiden and Schwann's theory. According to the current understanding of the cell theory,
- All living things are made up of cells and cell products.
- All cells develop from earlier cells
History of Cell Theory
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Schleiden and Schwann worked together for the first time to establish the cell theory. However, their approach had a few flaws. Rudolf Virchow first proposed the idea of cells dividing and creating new cells from old ones in 1855 (Omnis cellula-e cellula). He modified Schleiden and Schwann's hypothesis to create the ultimate version of the cell theory.
Read More: Difference between Plasma Membrane and Cell Membrane
Parts of Cell theory
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The three basic principles of the theory are as follows:
- All living things are composed of cells.
- Cells serve as the fundamental building blocks for the growth of tissues, organs, and fully-grown living things.
- Cells can only develop from other cells.
Types of Cell
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Cells are broadly divided into two types, Prokaryotic cells, or Prokaryotes, and Eukaryotic cells, or eukaryotes. The details are given below:
Prokaryotes
Prokaryotes are very small cells with a plasma membrane creating an envelope around the cell. They have a characteristic cell wall that varies in composition depending on the species. Organelles that are attached to membranes and a nucleus are absent in prokaryotes.
- They have linear or circular DNA. Prokaryotic protoplasm contains the cytoplasm and the chromosomal region.
- Archaea and bacteria are the two domains that make up prokaryotes.
- Examples: E.coli, Streptococcus, Cyanobacteria, etc.
Eukaryotes
The distinct organelles within eukaryotic cells provide their distinctive features. The functions of every organelle contribute to the development and well-being of cells or organisms. These cellular structures encompass mitochondria, responsible for energy generation, endoplasmic reticulum, orchestrating protein packaging, and chloroplasts in plants, using sunlight and carbon dioxide for food synthesis, and more. Examples: plants, fungi, animals, etc.
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| Related Articles | ||
|---|---|---|
| Cell: Definition, Structure, Functions & Diagram | Parts of Cell | Endoplasmic Reticulum |
| Cell Organelles Types and Functions | What Are Tissues? | Discovery of Cells |
Things to Remember
- The cell constitutes the basic building block of life.
- The cell theory maintains that all living beings are comprised of cells, cells function as the fundamental components of life, and new cells arise from existing cells.
- The cell theory was first generated by Schleiden and Schwann, and later modified by Rudolf Virchow.
- The organelles are the various smaller components that constitute the cell.
- Cells are grouped into plant cells and animal cells, distinguished by the types of organisms they are present in.
- An organism can consist of a solitary cell, referred to as a Unicellular organism, or multiple cells, known as a Multicellular organism.
- Anton Von Leeuwenhoek, a groundbreaking scientist, was the first to discover and name the "cell," the fundamental building block.
- Cells can be divided into two types based on age, prokaryotes, and eukaryotes.
- All cells, prokaryotic or eukaryotic, have an enveloped membrane that controls what enters and exits the cell (selectively permeable) and preserves the electric potential of the cell.
Previous Year Questions
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Sample Questions
Ques. What is the cell theory? (2 Marks)
Ans. Rudolf Virchow first proposed the idea of cells dividing and creating new cells from old ones in 1855 (Omnis cellula-e cellula). The three central tenets of the theory of cells are as follows:
- Primarily, all living entities are constructed from cells.
- Moreover, cells act as the fundamental constituents that contribute to the development of tissues, organs, and fully-developed organisms.
- Cells can exclusively originate from existing cells, constituting the third and arguably pivotal aspect of this theory.
Ques. What is the history of the cell theory? (2 Marks)
Ans. Schleiden and Schwann worked together for the first time to establish the cell theory. However, their approach had a few flaws. Rudolf Virchow first proposed the idea of cells dividing and creating new cells from old ones in 1855 (Omnis cellula-e cellula). He modified Schleiden and Schwann's hypothesis to create the ultimate version of the cell theory.
Ques. Write the difference between prokaryotes and eukaryotes. (2 Marks)
Ans. Eukaryotic and prokaryotic structures have several contrasting aspects. Prokaryotes are minuscule life entities without the membrane-encased nucleus that is present in eukaryotic cells. Organelles bound to membranes are absent in prokaryotes. The DNA in prokaryotes is circular and double-stranded, while eukaryotic DNA consists of multiple linear double-stranded segments.
Ques. What is the function of a nucleus in the cell? (3 Marks)
Ans. The following is a list of the nucleus's functions:
- The nucleus holds chromosomes responsible for harboring and transporting the genetic material (DNA and RNA). Both gene expression and cell division hinge on the DNA and the genes it encompasses.
- The nuclear organizers, which contain the RNA required for ribosome synthesis, are found in the nucleus. Organelles called ribosomes are essential for the synthesis of proteins. Then, proteins serve as the foundation of all living things.
- The transcription process is also governed by the nucleus. They control how messenger RNA, or mRNA, is converted into proteins.
Ques. What are the components of a nucleus? (1 Mark)
Ans. The nucleus also contains paraspeckles, splicing speckles, promyelocytic leukemia (PML) bodies, Gemini of coiled bodies, Cajal bodies, and PIKA bodies.
Ques. List any three different types of cells in animals. (2 Marks)
Ans. Stem cells: Cells with pluripotency hold totipotency, granting them the capacity to morph into diverse cell types.
- Bone tissue: These categories include osteoblasts and osteoclasts. The creation of new bone cells is the role of osteoblastic cells, while osteoclastic cells induce cell breakdown.
- Blood cells: The blood contains red and white blood cells, serving purposes in oxygen transport and immune response.
Ques. What are nerve cells? (1 Mark)
Ans. The simplest component of the neurological system is a nerve cell or a neuron. Nerves transmit messages to the brain, spinal cord, and other organs through nerve impulses. A neuron is structurally made up of a cell body and nerve processes.
Ques. What is cell division? (2 Marks)
Ans. The process of cell multiplication leads to the formation of two daughter cells from one mother cell. The process that a cell follows in order to divide is known as the cell cycle. The cell cycle is the defined set of stages that a cell undergoes to divide.
- Interphase: the pause phase or the resting phase
- The M Phase is when cells divide.
Ques. What is mitosis and meiosis? (2 Marks)
Ans. Mitosis and meiosis are distinct cell-division processes. Mitosis produces two daughter cells with an equal chromosome count, while meiosis yields four daughter cells with half the chromosomes, transitioning from diploid to haploid. Meiosis involves two cell cycles and cell division sequences, whereas mitosis only involves one.
Ques. How does the nucleus affect the expression of genes? (2 Marks)
Ans. Genetic material (DNA and RNA) is transported and stored by the nucleus in the form of chromosomes. DNA contains the necessary information for cell division and replication in the form of genes. A gene is a small portion of the DNA strand that holds the instructions required for producing both RNA and the final protein responsible for various functions. This process is referred to as gene expression.
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