The differences between the prokaryota and eukaryota are significant. Eukaryotes possess a nucleus and various subcellular organs called organelles, and prokaryotes do not.
Almost all unicellular organisms are microorganisms but you can observe eukaryotes and many prokaryotes by using a compound microscope. Bacteria just appear as dark dots. To gather unicellular organisms for observation, one can place a cover slip on the surface of pond water, and leave it overnight. By the next morning, numerous unicellular organisms will have grown entire colonies on the bottom of the slip. They multiply fast: colonies can double their size in between 30 minutes and a few hours.
Unicellular organisms can be found everywhere. The oldest forms of life existed 3.8 billion years ago, if not longer. They pursue a variety of strategies for survival: photosynthesis (cyanobacteria), chemotrophy (many archaea), and heterotrophy (amoeba). Some unicellular organisms have flagella, little tails they use for locomotion, or lobopods, extensions of the cellular skeleton (cytoskeleton), which appear as bloblike arms. The flagella of our unicellular ancestors occurs all the way up into the animals, where it makes an appearance as flagellated sperm.
Of all the six eukaryote supergroups, four are exclusively composed of unicellular organisms. Unicellular organisms vary in size, with the smallest bacteria measuring only a third of a micron (300 nanometers) across, ranging up to the titanic plasmodial slime molds, which can grow to 20 cm (8 in) across. The largest unicellular organisms may have millions of nuclei scattered throughout the cellular envelope. To observe some of the smallest unicellular organisms requires an electron microscope, while the very largest can be seen with a microscope or anything that enhances images.
Multicellular organism
Multi-cellular organisms are organisms with more than one cell. This is the case for animals, plants and most fungi. In such organisms, cells are usually specialised. All the cells with the same function work together. Such a group of cells is then called a tissue.
Multi-cellular organisms have a set of cells that specialize in reproduction. Reproduction in such organisms is usually sexual. The sex cells are either sperm or ovum (also named "egg") cells. If they are sperm cells, the organism is male, if they are egg cells it is female. If both are present, the organism is a hermaphrodite.
We know, from their cell structure, that multicellularity has evolved independently many times in Earth history, for example in plants and animals.
The earliest forms of life in the fossil record are cyanobacteria from the Archaean era at 3.5 billion years ago. They grew as single cells but lived in colonies as stromatolites.
The first multicellular fossils have been found in 2.1 billion years old Palaeoproterozoic rocks from the Gabon in Africa. These are eukaryotic cells which live colonially. The fossils are visible to the naked eye, and hence much larger than bacteria. The authors comment that one advantage of multicellularity is larger size, and that an adequate level of oxygen is required to support this kind of life.
To reproduce, multicellular organisms must solve the problem of regenerating a whole organism from germ cells (i.e. sperm and egg cells), an issue that is studied in developmental biology.
Multicellular organisms, especially long-living animals, also face the challenge of cancer, which occurs when cells fail to regulate their growth within the normal program of development.
Hexahedron
A hexahedron (plural: hexahedra) is any polyhedron with six faces. A cube, for example, is a regular hexahedron with all its faces square, and three squares around each vertex.
There are seven topologically distinct "convex" hexahedra, one of which exists in two mirror image forms. (Two polyhedra are "topologically distinct" if they have intrinsically different arrangements of faces and vertices, such that it is impossible to distort one into the other simply by changing the lengths of edges or the angles between edges or faces.)
There are three further topologically distinct hexahedra that can only be realised as "concave" figures:
Kazan State University
Kazan (Volga region) Federal University (, "Kazanskiy (Privolzhskiy) federalnyy universitet"; ) is a university in Kazan, Tatarstan, Russia. It was founded in 1804. The famous Russian mathematician Lobachevsky was its headmaster from 1827 till 1846. The post is now being held by Myakzyum Salakhov (Mäğzüm Säläxev).
Kazan University is also known as "the birthplace of organic chemistry" because of the works of Aleksandr Butlerov, Vladimir Markovnikov, Aleksandr Arbuzov, and others.
New World
The New World is a name used for the Western Hemisphere. It specifically refers to the Americas. It can also refer to certain Atlantic and Pacific islands (like Bermuda) and sometimes Oceania, (Australasia). The name started in the early 16th century, shortly after America was colonized. The people of the European Middle Ages thought the world was only Europe, Asia, and Africa. These continents are called the Old World. The Americas were also referred to as the "fourth part of the world".
The continent (North and South America) was named America after Amerigo Vespucci.
Oceania, which was colonized some centuries later, is refered to as "The Newest World".
Rabbit
Rabbits are mammals of the order Lagomorpha. There are about fifty different species of rabbits and hares. The order Lagomorpha is made of rabbits, pikas and hares. Rabbits can be found in many parts of the world. They live in families and eat vegetables and hay. In the wild, rabbits live in burrows, that they dig themselves. A group of rabbits living together in a burrow is called a warren. Rabbits are famous for hopping and eating carrots.
A male rabbit is called a buck, and a female is called a doe. A baby rabbit is called a kit, which is short for kitten. Rabbits have a gestation period of around 31 days. The female can have up to 12-13 kits, very rarely litters as big as 18 and as small as one. When the doe gives birth her babies are collectively refered to as a litter. Some people have rabbits as pets. Rabbits are also raised for their meat. Rabbits are of a different biological classification than hares.
Since rabbits are prey animals, they are careful in open spaces. If they sense danger, they freeze and watch. Rabbit vision has a very wide field, including overhead scanning. Their enemies are foxes and dogs; also bears, raccoons, minks, weasels and snakes. Birds of prey sometimes take rabbits. People are also known to shoot rabbits, because they eat crops. Their escape method is to run for their burrow, where they are usually safe.
Rabbits have a complex social structure and, like dogs, they have a hierarchy. Rabbit ears probably have several functions. The main function is to give warning of predators, but they may be used for signalling, and temperature regulation.
In the wild, rabbits have plenty to keep them occupied, from foraging to reproduction to territorial defence. Captive rabbits, on the other hand, often lack stimulation. This can lead to behavioural problems and poor health. The expected lifespan of a rabbit in the wild is about three years.
Louis Pasteur
Louis Pasteur (December 27, 1822 – September 28, 1895) was a French microbiologist and chemist.
He and his wife, Marie, are best known for their experiments supporting the germ theory of disease, and he is also known for his vaccinations, most notably the first vaccine against rabies.
He made many discoveries in the field of chemistry, including the asymmetry (different shapes) of crystals. He is also well known for his way of keeping milk and wine from going sour for longer periods of time. That process is called pasteurization. It is when the milk and or wine is put under about 161 Fahrenheit (72 Celsius) for fifteen seconds