Dear Students ,if you get something from my blog then share it,to help other students...........Thanks..
INTRODUCTION
- Cell is the fundamental structural and functional unit of all living organisms.
- Antony Von Leeuwenhoek first saw and described a live cell.
- All organisms are composed of cells.
- Some organisms are composed of a single cell and are called unicellular organisms, while others composed of many cells are called multicellular organism.
CELL THEORY
- Schleiden and Schwann together formulated the cell theory
- Rudolf Virchow (1855) first explained that cells divided and new cells are formed from pre-existing cells.
- Cell theory states that-----
- All living organisms are composed of cells and products of cells.
- All cells arise from pre-existing cells.
AN OVERVIEW OF CELL
- Cells are surrounded by a cell membrane and in plants cell membrane is surrounded by a cell wall.
- Inside each cell is a dense membrane bound structure called nucleus, which contains the chromosome and in turn DNA.
- Cells that have membrane bound nuclei are called Eukaryotic where as cells that lack a membrane bound nucleus are prokaryotic.
- In both prokaryotic and eukaryotic cells, a semi-fluid matrix called cytoplasm occupies the volume of the cell.
- Besides the nucleus, the eukaryotic cells have other membrane bound distinct structures called organelles like
- Endoplasmic reticulum (ER)
- Golgi complex
- Lysosomes
- Mitochondria
- Microbodies and
- Vacuoles
- Mycoplasmas, the smallest cells, are only 0.3 micro meter in length while bacteria could be 3 to 5micro meter.
- The largest isolated single cell is the egg of an ostrich.
- Human red blood cells are about 7.0 μm in diameter.
- Nerve cells are some of the longest cells.
Fig. Egg of ostrich
Fig. Red blood cells
Fig. Nerve cell
Fig. All cells arise from pre-existing cells
No comments:
Post a Comment