Tag: cell as structural and functional unit

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 -

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 the 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".

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