Cell Theory: Introduction, History, Modern cell theory, Practice problems and FAQs

Everytime we learn about living organisms, the first thing that we are told is that all living organisms are made up of cells and cells are the basic units of life. Now the question is how do we know this?

If there is any scientific proof that cells are the building blocks of our body?

Some scientists started searching for the reasons why and how the cell is important and in the process laid down some theories which were accepted universally. Cell theory is one of the most fundamental concepts in biology. It was initially proposed by Schleiden and Schwann and later modified by Virchow.

The original cell theory was later revised and a modern cell theory was laid down. In this article we will discuss cell theory in detail.

Table of contents

History of Cell Theory
Modern Cell Theory
Practice problems
FAQs

History of Cell Theory

Cell theory was proposed by Schleiden and Schwann in the year 1839 in their paper “Microscopical Researches on the Similarity in Structure and Growth of Animals and Plants.” It is a significant unifying principle of biology. These scientists also found certain key differences between the plant and animal cells.

Contributions of Matthias Schleiden

In 1838, a German botanist, M. J. Schleiden stated that all the plants are composed of cells. He observed that plants are composed of different types of cells which form tissues in them. He also stated that each plant cell has a broadly similar structure involving an outermost cell wall, cell membrane, cytoplasm and nucleus.

Fig: Matthias Schleiden

Contributions of Theodore Schwann

In 1839, German zoologist Theodore Schwann stated that all animals are made of cells. He concluded that the plant cells differ from animal cells in having a cell wall. Finally he put forward his hypothesis that stated that bodies of animals and plants are composed of cells and their products. The hypothesis was proposed after discussion between Schleiden and Schwann.

Fig: Theodore Schwann

Demerit of the Cell theory

Although the cell theory proposed that the bodies of plants and animals are composed of cells and their products, it could not explain the origin of cells.

Contributions of Rudolf Virchow

In 1858, a German physiologist, Rudolf Virchow, filled the bridging gap of the cell theory. He observed and stated that all the living cells arise from the pre-existing cells. This was called as

Omnis cellula-e-cellula. Hence, he modified the cell theory.

Fig: Rudolf Virchow

Modern Cell Theory

After the laying down of the original Cell Theory by Schleiden and Schwanna and its further modification by Rudolf Virchow, there were additional findings which told us that cells contain a number of organelles which cannot exist independently. In order to include all the new findings regarding cells, the cell theory was further modified and a modern cell theory was proposed which was raised to the status of a cell principle or cell doctrine.

Fundamentals of Modern Cell Theory

All living things are made up of smaller fundamental units called cells and their products. Cell is the smallest entity which can be called ‘living’. All the cells are basic structural and functional units of living organisms. These are also basic units of heredity and reproduction. The new cells arise from the pre-existing cells by cell division. They don’t arise de novo. Cell is a small compartment containing cytoplasm and cell organelles enclosed in a cell membrane. Cell organelles can not survive alone. All the cells are fundamentally similar in physical, chemical and metabolic aspects. Functions and activities of an entire organism is attributed to the sum total of the interactions and activities of the individual cells. Cells maintain homeostasis to keep any living being alive.

Merits of Modern Cell Theory

The Modern cell theory given by Rudolf Virchow in 1858 provided insight into the origin of cells. It suggested that all the cells originated from a common ancestor. Division of ancestral cells over generations constituted several lines of cells. According to this, cells could be considered as the vehicle of transmission of hereditary traits over generations.

Since the Modern Cell Theory was proposed after a few years of Cell Theory, it involved all the modern findings done by contemporary scientists. Thus it is a better version of the Cell Theory.

Objections to the Modern Cell Theory

Viruses are an exception to cell theory. Viruses are microscopic pathogens that are considered neither dead nor alive. This is because they can only replicate inside a specific host organism. Hence, viruses are called acellular.
Some organisms have parts which are in a multinucleated condition and do not have constituent cells. For example, coenocytes of certain fungi.
Bacteria and cyanobacteria do not have membrane-bound cell organelles.
Protoplasm is replaced by the non-living materials in certain cells such as cork cells and cells of the outer layer of skin.

Practice problems

Q1. Who observed the different types of cells in plant tissue?

(a) Rudolf Virchow
(b) Antony Von Leeuwenhoek
(c) Theodore Schwann
(d) Matthias Schleiden

Solution : In 1838, a German botanist, M. J. Schleiden stated that all the plants are composed of cells. He observed that plants are composed of different types of cells which form tissues in them.

Thus, the correct option is d.

Q2. Which of these scientists concluded that the cell wall was a unique feature of plant cells?

(a) Matthias Schleiden
(b) Theodore Schwann
(c) Robert Koch
(d) Rudolf Virchow

Solution: Theodore Schwann, a British zoologist, concluded from his studies that plant cells were unique in having an additional cell wall surrounding the cell membrane, which is not the case for animal cells. The outermost covering in animal cells is the cell membrane.

Thus, the correct option is b.

Q3. Which of these statements is false regarding Theodore Schwann?

(a) He was a British zoologist
(b) He studied various types of animal cells and observed the plasma membrane.
(c) He concluded that animal and plant cells have cell walls
(d) He hypothesised that animals and plants were made of cells and cellular products.

Solution: In 1839, German zoologist, Theodore Schwann stated that all animals are made of cells. He concluded that the plant cells are unique as they possess a cell wall. Finally he put forward his hypothesis that stated that bodies of animals and plants are composed of cells and their products.

Thus, the correct option is c.

Q4. Which of these is not a postulate of the cell theory?

(a) Cells are the basic units of life.
(b) All cells contain membrane bound organelles.
(c) Living things are composed of one or more cells.
(d) Cells arise from existing cells.

Solution: Matthias Schleiden and Theodore Schwann together formulated the cell theory. It states that living things are composed of cells, that the cell is the basic unit of life, and that new cells arise from existing cells.

The modern cell theory does speak of cells being made up of organelles but it does not state that all cellular organelles are membrane bound.

Thus, the correct option is b.

FAQs

Question 1. What is the importance of the study of cell theory?
Answer: Cell theory was proposed by Schleiden and Schwann in the year 1839. These scientists also found certain key differences between the plant and animal cells.

All living things are made up of smaller fundamental units called cells and their products. Cell is the smallest entity which can be called ‘living’. All the cells are basic structural and functional units of living organisms. That information helps us understand how new life is created, why organisms take the form they do, how cancer spreads, how diseases progress at a cellular level and how they can be treated, and more.

Question 2. When was the first cell discovered?
Answer: Robert Hooke in 1665 discovered the dead cells in a thin slice of a cork by viewing it under a microscope.

Question 3. Who was the first person to coin the term ‘protoplasm’?
Answer: Protoplasm refers to the total living matter of the cell that is enclosed by the cell membrane. This term was first coined by J.E. Purkinje in 1839.

Question 4. Are all living cells totipotent?
Answer: Totipotency is the ability of a cell to give rise to an entire organism. All undifferentiated cells are totipotent but as cells of a multicellular organism become more and more specialised and differentiate into cells of specific tissues, certain genes in their genome become active while certain genes get suppressed. Hence they lose totipotency.

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