The cell is regarded as a fundamental structural and functional unit of life because the basic structure of all the living organisms is made up of cells. Hence cell is known as the structural unit of life. Let us learn about cell study and cell theory.
Landmarks in Cell Study
- Discovery of Cell: Cell was discovered by an English scientist Robert Hook in the year 1665. He published this information in his book ‘Micrographia’. He observed that dead cells in a thin cork slice in a self-made microscope. And this was the beginning of cell study and discovery.
- Why were they named cells? Because the cells looked like the small rooms of a Buddhist monastery which were called cellullae. Hence the name cell was given.
- Anton Von Leeuwenhoek designed an improved microscope and observed first free-living cells (Bacteria) in the year.
- Robert Brown A Scottish Botanist discovered nucleus in the year 1831.
- A French Zoologist Dujardin discovered the semifluid living material inside a cell and named it Sarcode.
- Purkinje in the year 1840 renamed it as ‘Protoplasm – The First Substance’.
- A cell can be viewed as an enclosed vessel, within which innumerable chemical reactions take place simultaneously. These reactions are under very precise control so that they contribute to the life and formation of new cells.
A German botanist M.J. Schleiden in the year 1838 found out that all plants are made of cells. A German Zoologist T. Schwann in the year 1839 also said that all the animals are made up of cells. They commonly presented their findings as Cell Theory.
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Postulates of Cell Theory are
- All living organisms are composed of cells.
- All cells are basically alike in structure and functions.
- The function of an organism as a whole is the result of the activities and interactions of constituents of the cell.
Modern Cell Theory
In the year 1858 scientist Rudolf Virchow presented the idea ‘Omnis Cellula e Cellula’, which means that all living cells arise from pre-existing cells. After addition of this postulate in the cell theory, it was called Modern Cell Theory.
- Cells vary in shape and size.
- The nerve cell is the longest cell in our body. It can be about 1m long.
- Ostrich egg is the largest cell.
- Red Blood Corpuscles are the smallest cell in the human body and female ovum is the largest cell in the human.
- Some organisms may be made up of a single cell (Unicellular Organisms), eg; Amoeba. Others are multicellular.
- Proper division of labour is seen in multicellular organisms as different organs perform different functions but in unicellular organisms, the single cell performs all the functions.
Types of Cells
Cells are of two types depending on the presence or absence of a well-defined nucleus.
- Prokaryotic cell
- Eukaryotic cell
|S. No.||Prokaryotic cell||Eukaryotic cell|
|1||Pro-Primitive; Karyon- Nucleus||Eu-True; Karyon- Nucleus|
|2||The nuclear membrane is absent. Content of nucleus present in the cytoplasm known as a nucleoid.||Nucleus distinct with the nuclear membrane.|
|3||Size: 1µm to 10 µm||Size: 5 µm to 100 µm|
|4||Membrane-bound cell organelles are absent.||Membrane-bound cell organelles like Golgi bodies, mitochondria etc are present.|
|5||Ribosome -70 S||Ribosome – 80 S|
|6||A single circular chromosome is present.||Many chromosomes are present which are linear.|
|7||A respiratory enzyme is present in mesosoma.||Respiratory enzymes are formed in mitochondria.|
Solved Questions for You
Question 1: Bacteria do not have chloroplast but some bacteria are photoautotrophic in nature and perform photosynthesis. Which part of bacterial cell performs this?
Answer: They have chlorophyll which helps in absorption of light for photosynthesis.
Question 2: Which is smaller- Cell or an atom. Also, justify your answer.
Answer: Cell study shows us that atoms are smaller than cells. Thousands of atoms make a single cell. Atoms like carbon, oxygen, hydrogen etc unite to form molecules like glucose, fat, amino acid etc. these molecules further unite to form macromolecules like starch, lipids and proteins. These molecules combine together to form cells.