Różnorodność świata komórek [ang]

DIFFERENCES AND DIVERSITY
OF THE CELLWORLD


What is the cell?

Cell is the basic microscopic unit of all living beings. The usual size of human cell is mostly 0.001 of an inch centimeter in diameter. The cell produces energy and uses it to build all the substances necessary for its life.
Cells can nourish themselves, produce energy, exchange information with their neighbors, multiply (mitosis and meiosis), and, eventually, die, when their time comes. But sometimes happens, that they can ‘commit a suicide’, which is called apoptosis.

The organisms are consisted of many cells, e.g. an average sized man contains from 60 to 100 trillion cells, but, what is very rare, there are some of them, which are made up of only one cell, and such organisms are called unicellular - that includes bacteria or protozoa.

**As a curiosity, it is good to know, that scientists used to think, that human cells contained 24 pairs of chromosomes. In 1957, with a better microscope, it was shown, that we only have 23 pairs.**


Origin of the cell

The cells were firstly seen over 300 years ago in England. In 1665, an English scientist Robert Hooke, designed and put together one of the first optical microscope. Observing and examining different objects, he had noticed once, ‘a thin sections of cork’, and then, that those sections were consisted of many, tiny, regular compartments, which he had later named cells.
The person, who emerged the previous work of Hooke, was Dutch - Anton van Leeuwenhoek. In 1676 he observed the life of unicellular organisms in the drops of water.

There is also the theory, concerning cells, called ‘the cell theory’.
It states, that all organisms are composed of similar units of organization, called cells.
Originally, the theory was formally enunciated in Rudolph Virchow’s powerful dictum, ‘Omnis cellula e cellula’… meaning ‘all cells only arise from pre- existing cells’.
The concept was formally articulated in 1839 by Matthias Schleiden and Theodor Schwann, and has remained as the foundation of modern biology. On the beginning, they summarized their surveys in three points:

1) The cell is the unit of structure, physiology, and organization in living
things.

2) The cell retains and dual existence as a distinct entity and building block in the construction of organisms.

3) Cells form by free – cell formation, similar to the formation of crystals.

Obviously, the last point is incorrect.
Later the others, including Virchow, had corrected this, so then, the modern tenets say:

1. all known living organisms are made up of cells

2. the cell is structural and functional unit of all living things

3. all cells come from pre- existing cells by division

4. cells contain hereditary information, which is passed from cell to
cell during cell division

5. all cells are basically the same in chemical composition

6. all energy flow [metabolism and biochemistry] of life occurs within the cells


Cells’ lives

Like all living things, cell die. If you watched a clock for one minute, about three billion cells in your body die. In the same minute, about three billion cells divided, so that all the cells, that died were replaced. Dead skin cells flake off and dead cells from internal organs will pass through and out of the body, with waste products.
The length of time of cells’ lives can vary. For instance, white blood cells live only for 13 days, red blood cells live for about 120 days, liver cells live about 18 months, and nerve cell can live up to 100 years.


Different kinds of cells

The proof of that thesis, may be the fact, that the human body is composed of more that 200 different kinds of cells.

If possible, we could differ plenty of cells’ kinds, but concentrate on those most basic and well-known, as well as structures, showing the variety of the cell world.



A. EUKARYOT [animal cell] and PROKARYOT [bacteria]
- these pictures are drawn by me, according to the descriptions
(this is NOT under the microscope observations)











The comparison of eukaryotic and prokaryotic cells:

1. type of genetic
material A naked loop of DNA Chromosomes, consisting of strands of DNA, associated with proteins
2. main location of
genetic material In the cytoplasm, in a region called the nucleoid In the nucleus, inside a nuclear envelope
3. mitochondria Not present. The cell surface membrane and mesosomes are instead Always present
4. Ribosomes Small sized Larger sized
5. Organelles bounded
by a single membrane Few or none present Many are present



B. ANIMAL (pig’s liver) and PLANT (apple – tree’s leaf) cells.

- as you can see in the pictures below, there are a few significant differences, which can be noticed there, between such cells.
magnification – 40x









1. The cell surrounding is thicker in plants, which means, that in the plant cells, there is a cellwall, when in animal it is not present.
2. Then, we can see some darker points, in plant cells, which are chloroplasts, absent in animal.
3. The shape of the cells is a little different from each other – plants’ cells have rather regular shape, and animals usually rounded.

Apart from those, there are other differences, which cannot be seen in the pictures:


PLANTS ANIMAL
4. large, fluid – filled vacuoles -vacuoles not usually present.
they are small and temporary,
divided in functions


5.the carbohydrate storage- starch -the carbohydrate storage- glycogen


** the view of pig’s liver under the microscope**









C. UNICELLULAR organism and MULTICELLULAR one

- as it was said on the beginning, the unicellular organism is consisted only of one cell, and it is possible for that cases e.g. bacteria and protozoa.





magnification – 40x


Unicellular – paramecium multicellular – dog’s blood














The paramecium cells, as shown, are larger than the blood cells, and, what is more have quite oval shape, when in blood, they are more round.
The paramecium cells do not adhere to each other, what proves they are single, and blood cells do adhere, so then, they create blood.



** the very prcised photo of paramecium, alas, not made by me**










D. HUMAN blood and FROG’S blood














The main difference, which can be seen above, is that frog’s cells are bigger than human, and have nuclei.

…besides:

- they also divide, unlike ours
- in frog’s blood there are no platelets
- frogs do not produce fragments, like we do
- but their white blood cells are very much the same as our, and serve
the same function





** here is a photos of microscopic human blood**







E. SMOOTH and SKELETAL muscles

magnification – 20 x



Comparison:

Smooth muscle cells are spindle – shaped and contain a single nucleus, when the skeletal muscle cells are long, fiber – like and multinucleated. Besides skeletal the difference is also in the place, when they can occur.
The first ones ( smooth) is found in internal organs, and is involuntary.
The skeletal, instead, are attached to the skeleton with tendons, and is controlled consciously.

** this is how smooth muscle really looks like:**





To summarize, we can see, that the cellworld is very diverse and complex. Unfortunately, I could not prove it at all, using a microscope, because, most of the pictures, if not all are not precise. Nevertheless, I think, I managed to give the proper and enough examples, telling about the cells’ variety, though, there could be found many others