Ultrastructure of cells
There are two groups of cells:
Eukaryotic and Prokaryotic cells.
Cells of bacteria which divide by binary fission; they feature:
1. The cell wall; outer part of the cell which protects and gives shape to the cell.
2. Plasma Membrane; it is inside the cell wall and it controls what goes in and out of the cells
3. Flagella; it allows the locomotion of the cell
4. Pili; hair-like growths outside of the cell wall that are used for attachment.
5. Ribosomes; sites inside the cell where protein synthesis takes place
6. Nucleoid: non-compartmentalized (free) region containing the DNA
7. Plasmids: Circular DNA mollecules floating around the plasma membrane, their function is to help adapt the cell to unknown or weird circumstances
- Binary Fission: Process of reproduction of prokaryotic cells in which the daughter chromosome attach to the plasma membrane and the cell then divides into two identical daughter cells.
- Prokaryotic cells are characterized for:
1. Being less complex than eukaryotic celss
2. No compartmentalization in the cytoplasm ( substance that occupies the whole inside of the cell)
3. They are 1-10 micrometers
Eukaryotic and Prokaryotic cells.
- Prokaryotic Cells
Cells of bacteria which divide by binary fission; they feature:
1. The cell wall; outer part of the cell which protects and gives shape to the cell.
2. Plasma Membrane; it is inside the cell wall and it controls what goes in and out of the cells
3. Flagella; it allows the locomotion of the cell
4. Pili; hair-like growths outside of the cell wall that are used for attachment.
5. Ribosomes; sites inside the cell where protein synthesis takes place
6. Nucleoid: non-compartmentalized (free) region containing the DNA
7. Plasmids: Circular DNA mollecules floating around the plasma membrane, their function is to help adapt the cell to unknown or weird circumstances
- Binary Fission: Process of reproduction of prokaryotic cells in which the daughter chromosome attach to the plasma membrane and the cell then divides into two identical daughter cells.
- Prokaryotic cells are characterized for:
1. Being less complex than eukaryotic celss
2. No compartmentalization in the cytoplasm ( substance that occupies the whole inside of the cell)
3. They are 1-10 micrometers
- Eukaryotic Cells
Animal and plant cells; they feature:
1. Cell Wall (Only plant cells)
2. Plasma membrane
3. Endoplasmic recticulum: it is involved with the transportation of materials within the cell due to its structure. It can be classified in rough E.R - posses ribosomes on the exterior- and smooth E.R -does not posses ribosomes on its outside.
4. Ribosomes: same function as in prokaryotic cells, however, in eukaryotic cells they may be attached to the endoplasmic recticulum, they are larger and denser, and are composed of two subunits: 80S and 70S
5. Lysosomes (animal cells): digestive centres in which breakdowns of proteins, nucleid acids, lipids and carbohydrates occur
6. Golgi Apparatus: it collects, packages, modificates and distributes materials synthesized in the cell
7. Mitochondria: site of the production of ATP (cell energy). They have their own DNA and thus have autonomy within the cell. They have a double membrane
8. Nucleus: region where DNA takes place, it has a double membrane and allows a compartmentalization of the DNA where it can carry out its functions without problems
9. Chloroplasts (plant cells): organelle in charge of the absorption of light for photosynthesis. It counts with a double membrane, its own DNA and 70S ribosomes.
10. Centrosomes: consists of an alignment of centrioles which are related to assembling microtubules to provide mobility and structure to the cell
11. Vacuoles: Storage organelles that store food, metabolic wastes and toxins, and water.
Prokaryotic:
- DNA in a ring form without protein - DNA free in the cytoplasm - No mitochondria - 70S ribosomes - No internal compartmentalization present - Size less than 10 micrometers |
Eukaryotic:
- DNA with proteins as chromosomes - DNA enclosed within the nucleus - Mitochondria present - 80S ribosomes - Internal compartmentalization present - Size more than 10 micrometers |
Applications and skills:
- Application: Structure and function of organelles within exocrine gland cells of the pancreas and within palisade mesophyll cells of the leaf.
- Application: Prokaryotes divide by binary fission.
- Skill: Drawing of the ultrastructure of prokaryotic cells based on electron micrographs.
- Skill: Drawing of the ultrastructure of eukaryotic cells based on electron micrographs.
- Skill: Interpretation of electron micrographs to identify organelles and deduce the function of specialized cells.
- The world that we inhabit is limited by the world that we see. Is there any distinction to be drawn between knowledge claims dependent upon observations made by sense perception and knowledge claims dependent upon observations assisted by technology?
Observtions made by sense perception can be very limited compared to ones made by technology; for instance, the microscope allows us to see structures of less then 10 micrometers, unlike our own sight which would not be capable of seeing such small things if not by using technology. Also, the knowledge given to us by our senses and experiences can change over time, our senses give us basic and ¨easy-to-get¨ concept of what things may be, however, most of the times they do not give us in dept information of any topic. We perceive what our senses allow us to, we do not know if there is more to what we see, feel, touch, smell our taste, which is why we cannot simply rely our sanses and state that we know something simply because we have experienced it.
By way of contrast, knowledge assisted by technology is more of a reliable source. Today, we are able to test things as many times we want due to technology, and it could be said that it allows us to have accurate results of what is being tested. For example, a DNA test is ran with technological supplies, and due to the advanced features these possess, scientists are able to make conclusions in regard to genetics. However, technology can also be fallible at times, therefore it is not a 100% reliable either. Say a microscope is being used to observe cells in onion roots with a magnification of 40, one trusts that the maginification is actually 40, but how can one be able to tell if it is the other way around? If instead of being 40 it is 10 and the microscope is biased? To prove whether what is being, in a way, ¨told¨ by the microscope one would have to go to the place where it was fabricated and run some tests, which is something that would most likely take a lot of time.
In short, knowledge from sense perception is a way to gain easy and quick information but is reliable to an extent. Knowledge assisted by technology is to be more of a reliable source but it also has its limitations.