bb+Biology

The cell Every living being, animal or plants, observed by light microscopy is formed by small particles, the cell, placed closed to each other. Each cell is constituted by even smaller elements, each able to carry out by itself of the activities of the cell, for this reason the cell is considered “the basic unit of life”. The organism, according to number of cells they are composed , of may be unicellular (bacteria, protozoa) or multicellular (animals, plants, fungi).Cells have morphologic features only in the simplest organism; in others the cell vary in shape, size and tasks. The cell shape is usually spherical although it may have other shapes according to its function. The size is variable, usually from 5 to 50 microns; anyway there are exceptions, such as the chicken egg is the only cell which may have a diameter up to 4 centimeters. There are two types of cells: ü Prokaryote : is the simplest because it has no nuclear membrane and intracellular organelles except for ribosome.



ü Eukaryote : is a that contains a nucleus surrounded by a nuclear membrane and organelles separated. This cell may in turn be divided into two groups, the eukaryote animal cell and the eukaryote plant cell.





The cell membrane surrounds all the cell, isolating it from the outside. It consists of a phospholipids bilayer and contains many protein molecules which are used for active transport. Instead the water enters and exits rather easily through the gradient, that is, the water goes from where it is more concentrated to where it is less concentrated.
 * || Typical animal cell || Typical plant cell ||
 * Organelles || * Nucleus
 * Nucleolus (within the nucleus)
 * Rough endoplasmic reticulum
 * Smooth endoplasmic reticulum
 * Ribosomes
 * Cytoskeleton
 * Golgi apparatus
 * Cytoplasm
 * Mitochondria
 * Lysosomes
 * Centrosomes
 * Centrioles
 * Vacuoles || * Nucleus
 * Nucleolus (within the nucleus)
 * Rough endoplasmic reticulum
 * Smooth endoplasmic reticulum
 * Ribosomes
 * Cytoskeleton
 * Golgi apparatus (dittiosomi)
 * Cytoplasm
 * Mitochondria
 * Chloroplasts and other plastids
 * Central vacuole (large)
 * Tonoplast (membrane central vacuole)
 * Peroxisomes (glyoxysomes)
 * Vacuoles
 * Cell wall ||
 * Additional structures || * Plasma membrane
 * Flagella
 * Eyelashes || * Plasma membrane
 * Flagella (only in gametes)
 * Cell wall
 * Plasmodesmata ||
 * 1) Thecellular membrane



2.Cytoplasm The cytoplasm is a solid but not homo geneus mass of gelatin. Inside it there are several small groups called organelles (small organs) formed of a nucleus, mitochondria, ribosomes, an endoplasmic reticulum, Golgi apparatus, lysosomes. Within the cytoplasm most of the cellular activities occur and the necessary energy for the life of the cell is produced here. 3.Nucleolus

The nucleus is constituted by the most important part of a cell controlling all its activities. It also decides when it is the right time of cell reproduction and supervises all phases of it.



The nucleus is surrounded by a nuclear membrane that separates it from the cytoplasm. The nuclear membrane is covered with numerous nuclear pores, through which occurs the passage of various substances from the cytoplasm into the nucleus.

The nucleus contains the DNA combined with proteins (chromatin). When the cell divides itself, the chromosomes are formed from the chromatin. Inside the nucleus you can trace a very dense body called the nucleolus. 4. Mitochondrion They appear as round or elongated rod-granulation, they vary in size and each is bounded by a double membrane. They are detached from the inner membrane of the protuberances said ridges. On them there are mitochondrial enzymes intended to recover the energy contained in food. The number of mitochondrion for cell is variable and depends on the type of work performed by the cell itself.



5.Endoplasmatic reticulum The endoplasmic reticulum can be of two types: endoplasmic smooth reticulum (without ribosomes) or endoplasmic rough reticulum (with ribosomes).The endoplasmic reticulum is composed of a set of interconnected tanks bordered by a membrane that separates them from cytoplasm.

6. Ribosomes Ribosomes can be free in cytoplasm or related to tanks of the endoplasmic reticulum. Their task consists of producing proteins.



7. Golgi apparatus Golgi apparatus was discovered in 1898 by Camillus Golgi by staining some nerve cells in a particular way. It Appears as a stack of flattened membranous vesicles at the ends of which there are spherical vesicles capable of transporting substances produced by the endoplasmic reticulum, up to the plasma membrane with which they combine, pouring all their content outside.



8. Lysosomes Lysosomes are rounded vesicles wrapped by a membrane rich in digestive enzymes that digest cell's own substances or those coming from outside. Each cell contains about 300 lysosomes. They are particularly abundant in cells able to ingest and digest foreign bodies such as the white blood cells whose job is to defend our body from microbes by "eating them" 9. Chloroplasts

The chloroplast is the type of organelle found in plant cells and eukaryotic algae. Within these organelles the process of photosynthesis takes place: the light energy is captured by the pigments of chlorophyll and is converted into chemical energy (ATP and NADPH). The chloroplast is delimited by two membranes: the outer membrane is permeable for the majority of molecules, while the interior is far more selective and is crossed by specific transport proteins. The two double layers are separated by an inner membrane space.



10. Cell wall The cell wall (formed by cellulose) is an organelle characteristic of the plant cell, which confers rigidity and shape retention capacity; it has the function of regulating the osmotic pressure when the cell is in anon-osmotic environment. It Also represents a physical, chemical barrier to the pathogen agents and is the first contact of the plant cell with the outside.The contacts with adjacent cells are guaranteed by the presence of plasmodesmata. 11. Central vacuole

vacuoles are cavities typical of plant cells, delimited by a membrane of its own, derived by the Golgi apparatus, which is called tonoplast and encloses a solution, the vacuolar juice. It has several functions including the storage of water and other substances, the demolition of waste products and hydrolysis of macromolecules.