Cells were first discovered by Robert Hook in 1665, who described the building blocks of life as little rooms in which monks lived. Robert Hook witnessed dead plant cells present in cork; it took many years and numerous studies to describe the internal structures of the cell and define Cell Theory. Cell Theory states all living organisms are composed of one or more cells, the cell is the basic unit of structure and organization in organisms and that cells arise from pre-existing cells.
The origins of the cell can be traced back 3.8 billion years ago. Evidence of these prehistoric life forms can be found on Stromatolite rocks in Greenland, these Stromatolies are formed by layer upon layer of Cynobacteria and serve as a fossil record book. Stanley Miller recreated the earths early atmosphere in order to mimic the spontaneous formation of organic molecules, the Miller-Urey experiment demonstrated how the foundations of life arose from the chaos of early earth. The first cell comprised of self-replicating material, RNA, enclosed by a phospholipid bi-layer; cells later synthesized DNA from RNA and used DNA as an informational storage molecule. The Proto-cell evolved to form Prokaryotes which in later evolved into Eukaryotes, Eukaryotes underwent endosymbiosis which involves the engulfment of other independent organisms- like mitochondria and chloroplasts- to form a symbiotic relationship, this was a vital step in the evolution of the modern-day Eukaryote. The first signs of multi-cellular organism formations can be seen in colonies of algae, it is thought that these colonies are the ancient precursors of modern-day plants.
DNA was discovered by Francis Crick and James Watson with the help of a X-ray made by Rosalind Franklin in the 1950’s. DNA is located in the nucleus and contains the code used to transcribe all the proteins necessary for propagation of cell-function. DNA is structured as a double helix ladder with ‘rungs’ of the ladder being comprised of the nucleotide’s Cytosine, Thymidine, Guanine and Adenine. The different sequences of these four nucleotide’s ,known as genes, and are transcribed into mRNA and translated into proteins. The process of DNA to RNA to proteins is known as central dogma.
Cells comprised of structures which carry out specified functions vital for survival of the cell and/or organism, these structures are called organelles. Organelle functions include metabolism, storage, waste management, replication, protein synthesis, protein modification, motility and more. The main differences between animal and plant cells is that plant cells include a cell wall and contain a large vacuole and chloroplasts. The human body contains more than 200 different kinds of cells which can be grouped into 5 types namely epithelial tissue, neuronal tissue, connective tissue and blood. These different cell types deal with all the functions necessary for survival.
Fig 1 shows the wing of a Mucosa domestica. We are able to see clear venation as well as the closely packed cells spanning the surface area of the wing. Fig 2 and 3 shows the flower of a Tecoma capensis and a
Jasminum polyanthum respectfully, the cells forming the flower look like small circular bumps.