Cell Theory
- Matthias Schleiden (1838):
A German botanist observed that all plants are composed of various types of cells, which together form the tissues of the plant.
- Theodore Schwann (1839):
- A British zoologist, he studied animal cells and noted the presence of a thin outer layer, now known as the plasma membrane.
- He also recognized the unique characteristics of cell walls in plant cells.
- Schwann proposed that both plants and animals are composed of cells and their products, contributing to the formulation of Cell Theory.
- Rudolf Virchow (1855):
- He added a crucial aspect to Cell Theory by explaining that new cells are formed through the division of pre-existing cells.
- His famous phrase "Omnis cellula-e cellula" means that every cell originates from another cell.
- Virchow's contribution finalized the Modern Cell Theory, consisting of two main principles:
1. All living organisms are composed of cells and their products.
2. All cells arise from pre-existing cells through cell division.
Overview of Cell
- Cells are the fundamental structural and functional units of all living organisms.
- Unicellular organisms can independently exist and perform essential life functions. Anything less than a complete cell structure cannot ensure independent living.
- Anton Von Leeuwenhoek was the first to observe and describe live cells, and Robert Brown later discovered the nucleus.
- The invention and improvement of microscopes, including electron microscopes, have revealed the intricate structural details of cells, advancing our understanding of life at the cellular level.
- Cells come in various forms, but two main types are plant cells and animal cells.
-Plant cells have a distinctive cell wall as the outer boundary, followed by the cell membrane.
-In contrast, animal cells have a cell membrane as their outer boundary.
- Both plant and animal cells contain a nucleus, a dense membrane-bound structure.
- The nucleus houses chromosomes, which carry genetic material in the form of DNA.
- Cells with membrane-bound nuclei are known as eukaryotic, while those lacking such a nucleus are prokaryotic.
Cytoplasm:
- Within cells, a semi-fluid matrix known as cytoplasm fills the interior.
- It serves as the primary site for various cellular activities, including essential chemical reactions.
Organelles:
- Eukaryotic cells have membrane-bound organelles such as the endoplasmic reticulum (ER), Golgi complex, lysosomes, mitochondria, microbodies, and vacuoles.
- Prokaryotic cells lack these structures.
Ribosomes:
- Non-membrane-bound organelles called ribosomes are present in all cells, both eukaryotic and prokaryotic.
- They can be found in the cytoplasm, as well as within organelles like chloroplasts (in plants) and mitochondria, or attached to rough ER.
Centrosome:
- Animal cells have another non-membrane-bound organelle known as the centrosome, which plays a role in cell division.
Cell Variation:
- Cells differ in size, shape, and function.
- For example, the smallest cells like Mycoplasmas are only 0.3 µm in length, while bacteria can range from 3 to 5 µm.
- The largest isolated single cell is the ostrich egg.
- Among multicellular organisms, human red blood cells have a diameter of about 7.0 µm.
- Nerve cells are among the longest.
- The shape of cells may vary according to their specific functions.
