Tag: cell as structural and functional unit

Robert Hook discovered cells in 1655 with the help of compound microscope. He was observing insects, sand, bird feathers, fossils and plants. Once he was observing a thin slice of cork under the microscope he found a framework similar to honeycomb-like structure. He named those structures as cells but those were actually non living cell walls. So option A is correct.

Robert cook first discovered the cells in a cork. He saw small spaces under a microscope and called them cells meaning "little rooms".

• Schleiden and Schwann in 1839 formulated cell theory. 
• There are several exceptions to cell theory, e.g., viruses do not have a cellular structure. 
• They replicate but are non-living particles made up of proteins and nucleic acids. 
• Only one nucleic acid is found in a virus particle either RNA or DNA.

In 1838, German botanist, Matthias Schleiden found that all plant tissues are made up of cells which have been essentially similar structure. German zoologist, Theodor Schwann in 1839 working independently observed that animal cells do not have cell walls but are otherwise similar amongst themselves. He put forward cell hypothesis which states that bodies of animal and plants are made up of cells. Schleiden and Schwann in 1839 compared their findings and formulated cell theory.

• By carefully observing the process of cell division, Rudolph Virchow in 1858, argued that cells only arose from the division of pre-existing cells.