The cell theory was jointly put forward by Schleiden and Schwann in their paper, "Microscope investigations on the similarity of structure and growth of animals and plants''. The theory stated that 'the cell are the units of both structure and function of the organisms'. 

Cell theory is a scientific theory,  which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction. Cell theory was eventually formulated in 1838. This is usually credited to Mattias Schleiden and Theodor Schwann. The cell theory, was further expanded by Virchow. Cell theory, has become the foundation of biology and is the most widely accepted explanation of the function of cells.
So, the correct answer is option D.

The cell theory is one of the basic principles of biology. The credit for the formulation of this theory is given to German scientists, Theodor Schwann, Mattias Schleiden. Cell theory, stated that cells arise from pre-existing cells. They donot have the potential to replicate independently. They depend upon the parent cell,  for the enzymes which are used for replication.
So, the correct answer is option B.

Cell theory was proposed by a German botanist, Matthias Schleiden and English zoologist, Theodor Schwann in the year 1839. The cell theory states
1) Cells are the building blocks of living organisms.
2) All living organisms are composed of cells and a cell is the basic structural and functional unit
3) All cells arise from pre-existing cells.

• The cell is the smallest structural and functional unit of living organisms, which can exist on its own. Therefore, it is sometimes called the building block of life. Cell theory has 3 basic points.

• All living things are made of cells.
• The cell is the smallest living thing that can perform all the functions of life.
• All cells must come from pre-existing cells. Hence option B is correct.

Cell theory was proposed by a German botanist, Matthias Schleiden and English zoologist, Theodor Schwann in the year 1839. Cell theory was considered as most acceptable theory which, elucidated the functioning of cell. The cell theory includes the following points -
1) All living things are made up of cells.
2) The cell is the smallest living thing that can perform all the functions of life.   
3) All cells must come from pre-existing cells.
So, the correct answer is option D.

All the given characteristics are peculiar and prominent for the living things.
Living things cannot change their external environment, as because the external environment depends upon the several biogeographical factors. Living things adjust themselves according to external environment, as they have immense potential of homeostasis, which helps them to acclimatize according to the changing environment.  Skin and the hormonal response helps to sense the changing condition which is further analyzed by the brain in parietal lobe.

Cell theory was proposed by a German botanist, Matthias Schleiden and English zoologist, Theodor Schwann in the year 1839. The cell theory states 
1) Cells are the building blocks of living organisms.
2) All living organisms are composed of cells and a cell is the basic structural and functional unit
Later on, Rudolf Virchow added a new point in cell theory that 'all cells arise from pre-existing cells'.
So, the correct answer is option B.

The term hypothesis means a proposition or a set of propositions set forth as an explanation for the occurrence of some specific phenomenon. In this case, the phenomenon was smallest constituent entity of living organisms. In 1838, German Botanist Matthias Schleiden found that all plant tissues are made up of cells which have essentially similar structure. German zoologist Theodor Schwann, 1839, working independently observed that animal cells do not have cell wall but are otherwise similar among themselves. Thus, the original idea of both the workers was a hypothesis based on their observation which had to be experimentally verified by other workers.

Schleiden was the son of a well-to-do municipal physician of Hamburg. He first studied law at the University of Hamburg from 1824 to 1827 and obtained a doctorate. He subsequently practiced law in Hamburg, but was unhappy with his career choice and choose to develop his hobby of botany into a full-time pursuit.

A tissue is a group of similar cells performing similar functions. Each tissue has a specific function.

In 1838, Matthias Jakob Schleiden, who is a German botanist, was born in Hamburg located in Germany. He was a co-founder of the cell theory. He hypothesized that the body of plants and animals are composed of cells and product of cells.

The cell theory that all the plants and animals are composed of cells and the cell is the basic unit of life, was presented by two biologists, Schleiden (1838) and Schwann (1839). In 1855, a German physiologist, Rudolf Virchow added a third principle to the cell theory. He gave the phrase, 'Omnis cellula-e-cellula', i.e., all cells arise from pre-existing cells. Later, discoveries led to the modification of cell theory. Modified cell theory is termed as cell principle or modern cell theory which postulates that all living organisms are composed of cells or cell products and arise from pre-existing cells. All cells are basically alike in chemical composition and metabolic processes.
So, the correct answer is option D.

• Cell theory was proposed by a German botanist, Matthias Schleiden 1838 and English zoologist, Theodor Schwann in the year 1839. Cell theory was considered as the most acceptable theory which, elucidated the functioning of a cell.
•  The cell theory includes the following points -

Robert Brown discovered the cell is false because cells were first discovered by Robert Hooke.

In 1855 Rudolf Virchow, after an exciting study of the growth of cells in human tissues, stated clearly that all arise only by the division of pre-existing cells. Virchow's famous statement of this concept, 'Omnis cellula e cellula', completed the cell theory. 

Theodor Schwann and Matthias Jakob Schleiden proposed the cell theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction.

Matthias Jakob Schleiden, a German botanist who gave the cell theory, proposes that all plant tissues are composed of cells and that cells are the basic building blocks of all plants and generalized as all the tissue is made up of individual cells.

Cell theory was applied to plants by Schleiden. Theodor Schwann and Matthias Jakob Schleiden, proposed the cell theory which describes the properties of cells. These cells are the basic unit of structure in all organisms and also the basic unit of reproduction. The work on the plants was done by Matthias Jakob Schleiden.

Two German biologists M.J.Schleiden (1838) and Theodore Schwann (1839) proposed the cell theory. According to the theory, all living organisms are composed of cells, which are the smallest entities that can be called as living.

Cell theory was proposed by a German botanist, Matthias Schleiden and English zoologist, Theodor Schwann in the year 1839. It states that cells are structural and functional unit of plants and animals. The cell theory includes the following points -
1) All living things are made up of cells.
2) The cell is the smallest living thing that can perform all the functions of life.   
3) All cells must come from pre-existing cells.

The cell theory was developed from three German scientist's discoveries. They are Matthias Schleiden, Theodor Schwann, and Rudolph Virchow. In 1838, the German botanist Matthias Schleiden discovered that all plants were composed of cells.

Cell theory was proposed by a German botanist, Matthias Schleiden and English zoologist, Theodor Schwann in the year 1839. Cell theory was considered as most acceptable theory which, elucidated the functioning of a cell. The cell theory includes the following points -
1) All living things are made up of cells.
2) The cell is the smallest living thing that can perform all the functions of life.   
Later on, in year 1855 Rudolf Virchow added a new point in cell theory that all cells must come from pre-existing cells, which was also known as "Omnis cellula e cellula".
So, the correct answer is option B.

The cell theory is one of the basic principles of biology. Credit for the formulation of this theory is given to German scientists Theodor Schwann, Matthias Schleiden and Rudolph Virchow.
The cell theory states-

Cell theory has 3 basic points: All living things are made of one or more cells. The cell is the smallest living thing that can perform all the functions of life. All cells must come from pre-existing cells through cellular division.

• The generally accepted parts of the cell theory include: All known living things are made up of one or more cells. 
• All living cells arise from pre-existing cells by the division and cell is the basic unit of life.

Nehmiah Grew initiate cell concept when he found that plant tissues contain minute elementary structures or cells. Thus, it was a 'basic generalization' extended to all the plants by Schleiden. Schleiden by himself neither discovered cell nor described their structure but extended the cell concept to all plants.

Rudolf Virchow explained that cells divided and new cells are formed from pre-existing cells. "Omnis cellula e cellula" is also attributed to the Cell Theory, that works on a similar principle. The cell theory asserts that every organism is formed of the same units of the organisation, known as cells.

Leeuwenhoek was the first to see 'free-living cells' under his microscope. In 1809, Lamarck concluded that all living beings are formed of cells. Living substance was first observed by Corti in 1772 and was named sarcode by Dujardin in 1835. Dutrochet believed in the individuality of cells, i.e., living organisms are made up of a number of individual cells. The nucleus was discovered by Robert Brown and Schleiden and Schwann are credited with the formulation of the cell theory. 

New cells generate from pre-existing cells. Rudolf Virchow (1985) first explained that cells divide and new cells are formed from pre-existing cells (omnis cellula-e cellula). He modified the hypothesis of Schleiden and Schwann to give cell theory a final shape.
Cell theory now is understood as:

1. All living organisms are composed of cells and the product of cells.
2. All cells arise from pre-existing cells.
   

According to the cell theory all organisms (unicellular or multicellular) are formed of cells. It also states that all cells arise from pre-existing cells by cell division and do not originate spontaneously. Bacteria and other organisms therefore cannot arise spontaneously. So, the correct answer is 'It states that bacteria and other small organisms can arise spontaneously'.

• Reproduction is based on the phenomenon that new cells arise from preexisting cells. 
• Spontaneous generation is not possible.

Cell theory is the idea that the cell is the fundamental structural and functional unit of all living organisms and that new cells are formed from other existing cells. This theory is one of the foundations of modern biology. First formulated in the early 1800s in landmark publications by Mathias Jacob Schleiden and Theodor Schwann, the foundations of this theory began in mid-1600s through advances in microscopy. Today, it is held that all organisms are composed of one or more cells, all vital functions of an organism occur within cells, and cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.

Rudolf Virchow modified the cell theory and gave the concept of 'Omnis cellule e cellulae'- which means new cells develop by the division of the pre-existing cells. This is called the theory of cell lineage or common ancestry.

Antonie Philips van Leeuwenhoek was first to observe the living cell. He is commonly known as "the Father of Microbiology", and considered to be the first microbiologist. He is best known for his work on the improvement of the microscope and for his contributions towards the establishment of microbiology.
The cell was first discovered by Robert Hooke in 1665, which can be found to be described in his book Micrographia. In this book, he gave 60 observations in detail of various objects under a coarse, compound microscope. One observation was from very thin slices of bottle cork. Hooke discovered a multitude of tiny pores that he named "cells". 
Cell theory was eventually formulated in 1838. This is usually credited to Matthias Schleiden and Theodor Schwann.  Cell theory has become the foundation of biology and is the most widely accepted explanation of the function of cells.
Virchow is credited with many important discoveries. His most widely known scientific contribution is his cell theory, which built on the work of Theodor Schwann. He was one of the first to accept the work of Robert Remak, who showed the origins of cells was the division of pre-existing cells.