The word cell comes from Latin cella, meaning "small room" and it's used to define the basic structural, functional, and biological unit of all known living organisms.
Cells were firstly observed by Robert Hooke in 1665, although the cell theory was firstly developed in 1839 by German biologists Matthias Jakob Schleiden, Theodor Schwann and Rudolf Virchow. Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometers. THE CELL THEORY Classical interpretation
The generally accepted parts of modern cell theory include:
Exceptions to cell theory The cell theory was developed because biologists observed a trend for living organisms to be composed of cells. Scientific theories can be tested by looking for discrepancies, in fact there are some tissues and organisms that are not made of typical cells: 1 | Skeletal muscle is made up of muscle fibres. Like cells these fibres are inclosed in a membrane but their length is triple the length of normal cells ( 300 or more mm ) and contain hundreds of nuclei. 2 | Giant algae can grow to a length of around 100 mm, but although their big dimensions they only contain a single nucleus . 3 | Aseptate fungi consist of thread-like structures called hyphae, which are not divided up into sub-units containing a single nucleus; instead there are long undivided sections of hypha which contain many nuclei. TWO TYPES OF CELLS There is another basic cell structure that is present in many but not all living cells: the nucleus. The nucleus of a cell is a structure in the cytoplasm that is surrounded by a membrane (the nuclear membrane) and contains, and protects, most of the cell's DNA. Based on whether they have a nucleus, there are two basic types of cells: prokaryotic cells and eukaryotic cells. You can watch animations of both types of cells at the link below. Prokaryotic Cells Prokaryotic cells are cells without a nucleus. The DNA in prokaryotic cells is in the cytoplasm rather than enclosed within a nuclear membrane. Prokaryotic cells are found in single-celled organisms, such as bacteria. Organisms with prokaryotic cells are called prokaryotes. They were the first type of organisms to evolve and are still the most common organisms today. Eukaryotic Cells Eukaryotic cells are cells that contain a nucleus. Eukaryotic cells are usually larger than prokaryotic cells, and they are found mainly in multicellular organisms. Organisms with eukaryotic cells are called eukaryotes, and they range from fungi to human beings. COMPARING ANIMAL AND PLANT CELLS Plant and animal cells are known as Eukaryotic cells which contain a nucleus and other genetic material enclosed within membranes. The primary difference between the two cell types is: plant cells produce their own food through a photosynthetic process and can support their own weight, while animal cells cannot produce their own food and require support from a skeletal structure. Listed below are some similarities and difference found between animal and plant cells: Similarities:
1 Comment
Mr Lovat
9/27/2016 07:47:27 am
Brilliant revision notes that have tackled an area of understanding that you struggled with on the recent test. Great demonstration of independent learning and a determination to improve. Very promising start to the course.
Reply
Leave a Reply. |
ABOUT
IB Biology student at Ardingly College |