Question

Who discovered free living cells in pond water for the first time?
State the cell theory presented by Schleiden and Schwann.

Answer 1

Hint: Cell theory emphasizes unity in diversity. It is an organization of life forms. All living organisms have a basic unit called a cell. All organisms are composed of cells. Some are composed of a single cell and are called unicellular organisms while others are composed of multicellular organisms. Cells carry out physiological processes like digestion, excretion, memory, defense, recognition etc.

Complete Explanation:
Anton Van Leeuwenhoek was the first person to see and describe a living cell. He was the scientist who first discovered free-living algae Spirogyra cells in pond water in \[1674\]. He observed the cells in an improved electron microscope which revealed all the structural details of the cell.
Matthias Schleiden was a German botanist who studied a huge number of plants in \[1838\] and discovered that all plants are made up of several types of cells that create the plant's tissues. At about the same time, Theodore Schwann who was a British Zoologist, studied different types of animal cells and he noticed that cells had a thin outer layer which is today known as the plasma membrane. Schleiden and Schwann together formulated the cell theory.
So, the cell theory which is introduced into the world is- all living organisms are composed of cells and products of cells and all cells arise from the pre-existing cells. In organisms, the cell is the fundamental unit of structure and organization. There is no such universally accepted definition of life. Some biologists consider non-cellular entities such as viruses living organisms, thus reasonably disagree with the first tenet.
There are also many limitations to the cell theory opposed by other scientists. There have been many opposing concepts in cell theory. The cell was first discovered by Robert Hooke in \[1665\] using a microscope. In cell theory, the internal components of cells were referred to as protoplasm and characterized as a jelly-like substance, which was also referred to as living jelly. So many other theories like- Brownian motion, semipermeable membrane.

Note:
As we discussed, the theory of cells was proposed by two well-known scientists. They have discovered many things and their contribution is major in cell theory and they got many awards for their contribution. They got recognition in this field of cell biology as their papers got published. It is still one of the greatest discoveries in the biological world. As cells possess the center of life. A life can be evolved, multiplied from a tiny single cell. Hence it is the greatest discovery so far known.