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• Sex CHROMOSOMES are also CALLED ALLOSOMES (the other chromosomes that are not sex chromosomes are called autosomes).
• Sex chromosomes get such name because they have genes that determine the sex (male or FEMALE) of an individual. Sex chromosomes also have genes related to other biological FUNCTIONS.

Except for clones (individuals created from nucleus transplantation, like the Dolly sheep) and MONOZYGOTIC twins, it is very improbable the genomes of TWO individuals of the same species and generated by sexual reproduction to be identical. NEVERTHELESS the karyotypes of two normal individuals of the same species and of the same sex are ALWAYS identical. The human normal karyotype is represented by the formula 44+XX for women and 44+XY for men.

Except for clones (individuals created from nucleus transplantation, like the Dolly sheep) and monozygotic twins, it is very improbable the genomes of two individuals of the same species and generated by sexual reproduction to be identical. Nevertheless the karyotypes of two normal individuals of the same species and of the same sex are always identical. The human normal karyotype is represented by the formula 44+XX for women and 44+XY for men.

Genome is the set of DNA molecules that CHARACTERIZES each living being or each species. The concept then includes the specific nucleotide sequence of the DNA molecules of each INDIVIDUAL or species. KARYOTYPE is the set of chromosomes of individuals of a given individual or species concerning morphology and number of each CHROMOSOME or pair of HOMOLOGOUS.

Genome is the set of DNA molecules that characterizes each living being or each species. The concept then includes the specific nucleotide sequence of the DNA molecules of each individual or species. Karyotype is the set of chromosomes of individuals of a given individual or species concerning morphology and number of each chromosome or pair of homologous.

Chromosomes contain genes (GENETIC information in the FORM of nucleotide SEQUENCES) that command the protein synthesis thus regulating and controlling the activities of the cell. In the nucleus of somatic cells of diploid beings every chromosome has its correspondent homologous chromosome, both CONTAINING alleles of the same genes related to same functions. This occurs because one chromosome of one pair comes from the father and the other comes from the mother of the individual. The chromosomes that form a pair with alleles of the same genes are called homologous chromosomes. In humans, there are 22 pairs of homologous chromosomes PLUS the pair of sex chromosomes (the sex chromosomes are partially homologous).

The only human cells that do not have homologous chromosomes are the gametes since during meiosis the homologous chromosomes are separated.

Chromosomes contain genes (genetic information in the form of nucleotide sequences) that command the protein synthesis thus regulating and controlling the activities of the cell. In the nucleus of somatic cells of diploid beings every chromosome has its correspondent homologous chromosome, both containing alleles of the same genes related to same functions. This occurs because one chromosome of one pair comes from the father and the other comes from the mother of the individual. The chromosomes that form a pair with alleles of the same genes are called homologous chromosomes. In humans, there are 22 pairs of homologous chromosomes plus the pair of sex chromosomes (the sex chromosomes are partially homologous).

The only human cells that do not have homologous chromosomes are the gametes since during meiosis the homologous chromosomes are separated.

Primary constriction is the narrower region of a condensed chromosome where the centromere, the structure that unites identical chromatids, is located. SECONDARY constriction is a region similar to the primary constriction, narrower than the NORMAL thickness of the chromosome too, and in general it is related to genes that coordinate the formation of the nucleolus and control the ribosomic RNA (rRNA) synthesis. For this reason the secondary contrictions (that can be one or more in chromosome) is called nucleolus ORGANIZER region (NOR).

Primary constriction is the narrower region of a condensed chromosome where the centromere, the structure that unites identical chromatids, is located. Secondary constriction is a region similar to the primary constriction, narrower than the normal thickness of the chromosome too, and in general it is related to genes that coordinate the formation of the nucleolus and control the ribosomic RNA (rRNA) synthesis. For this reason the secondary contrictions (that can be one or more in chromosome) is called nucleolus organizer region (NOR).

• The chromosome region where the centromere is LOCATED is called primary CONSTRICTION. In microscopic view this region is NARROWER (a stricture) than most part of the chromosome.
• ACCORDING to the position of the primary constriction the chromosomes are classified as telocentric, acrocentric, submetacentric or METACENTRIC.

The STRUCTURE that MAINTAINS IDENTICAL CHROMATIDS bound is the centromere.

The structure that maintains identical chromatids bound is the centromere.

Chromatin is a set of filamentous DNA molecules dispersed in the karyoplasm forming euchromatin and heterochromatin portions. Each chromatin filament is a complete chromosome (a DNA MOLECULE, or double helix). The chromatin of the human somatic cell is formed by 46 DNA molecules (22 HOMOLOGOUS CHROMOSOMES and 1 pair of sex chromosomes).

In interphase the cell prepares itself for division and duplication of DNA molecules occurs. The duplication of every DNA molecule forms two identical DNA double helix BOUND by a structure called centromere. In this phase each identical chromosome of these pairs is called chromatid. It is also during the interphase that the chromatids begin to condensate assuming the thicker and shorter shape typical of chromosome illustrations. So the phase of the cell cycle in which DNA duplicates is the interphase.

Some Biology textbooks call chromosome an unique filament of chromatin as well as the condensed structure made of two identical chromatids after the DNA duplication. Rigorously the pair of identical chromatids bound in the centromere are two copies of the same chromosome and therefore they are two identical chromosomes (and not only one).

Chromatin is a set of filamentous DNA molecules dispersed in the karyoplasm forming euchromatin and heterochromatin portions. Each chromatin filament is a complete chromosome (a DNA molecule, or double helix). The chromatin of the human somatic cell is formed by 46 DNA molecules (22 homologous chromosomes and 1 pair of sex chromosomes).

In interphase the cell prepares itself for division and duplication of DNA molecules occurs. The duplication of every DNA molecule forms two identical DNA double helix bound by a structure called centromere. In this phase each identical chromosome of these pairs is called chromatid. It is also during the interphase that the chromatids begin to condensate assuming the thicker and shorter shape typical of chromosome illustrations. So the phase of the cell cycle in which DNA duplicates is the interphase.

Some Biology textbooks call chromosome an unique filament of chromatin as well as the condensed structure made of two identical chromatids after the DNA duplication. Rigorously the pair of identical chromatids bound in the centromere are two copies of the same chromosome and therefore they are two identical chromosomes (and not only one).

In the INTERPHASE there is INTENSE metabolic activity in the cell NUCLEUS: DNA is DUPLICATING, euchromatin is being TRANSCRIPT and RNA is produced.

In the interphase there is intense metabolic activity in the cell nucleus: DNA is duplicating, euchromatin is being transcript and RNA is produced.

Every FILAMENT of chromatin is a complete DNA molecule (a complete double HELIX), i.e., a complete chromosome. A DNA molecule MAY form euchromatin and HETEROCHROMATIN portions thus both are part of CHROMOSOMES.

Every filament of chromatin is a complete DNA molecule (a complete double helix), i.e., a complete chromosome. A DNA molecule may form euchromatin and heterochromatin portions thus both are part of chromosomes.

CHROMATIN is uncondensed nuclear DNA, the typical DNA morphology in interphase (the phase of the cell cycle in which the cells is not dividing itself). In this phase of the cell cycle chromatin can be FOUND as HETEROCHROMATIN, more condensed and dark (in electronic microscopy) portions of DNA molecules, and as euchromatin, less condensed and lighter portions of DNA molecules.

Since it is uncondensed the euchromatin is the biologically active portion of the DNA, i.e, the region that has active genes to be transcripted into RNA. The heterochromatin REPRESENTS the INACTIVE portions of the DNA molecule.

Chromatin is uncondensed nuclear DNA, the typical DNA morphology in interphase (the phase of the cell cycle in which the cells is not dividing itself). In this phase of the cell cycle chromatin can be found as heterochromatin, more condensed and dark (in electronic microscopy) portions of DNA molecules, and as euchromatin, less condensed and lighter portions of DNA molecules.

Since it is uncondensed the euchromatin is the biologically active portion of the DNA, i.e, the region that has active genes to be transcripted into RNA. The heterochromatin represents the inactive portions of the DNA molecule.

There are eukaryotic cells without nucleus and others with more than one nucleus. OSTEOCLASTS, the cells responsible for resorption of the osseous MATRIX, for example, are multinucleate cells; striated muscle fibers are multinucleate too. RED blood cells are example of ENUCLEATED SPECIALIZED cells.

There are eukaryotic cells without nucleus and others with more than one nucleus. Osteoclasts, the cells responsible for resorption of the osseous matrix, for example, are multinucleate cells; striated muscle fibers are multinucleate too. Red blood cells are example of enucleated specialized cells.

CELLS with delimited nucleus are CALLED EUKARYOTIC cells. Organisms composed of one or more eukaryotic cells are called eukaryotes.

The mains elements of the nucleus are the chromatin (made of DNA MOLECULES), the nucleolus, the karyolymph, or nucleoplasm, and the nuclear membrane (or karyotheca).

Cells with delimited nucleus are called eukaryotic cells. Organisms composed of one or more eukaryotic cells are called eukaryotes.

The mains elements of the nucleus are the chromatin (made of DNA molecules), the nucleolus, the karyolymph, or nucleoplasm, and the nuclear membrane (or karyotheca).

The remodelation of the osseous tissue, the function of acrosomes in sperm cells and the elimination of the tadpole tail are examples of biological processes in which lysosomic enzymes are key factors.

The bone is a tissue made of osteoblast-containing matrix (osteoblasts are the SECRETORY cells of the osseous matrix), osteocytes (mature bone cells) and osteoclasts (the remodeling cells). Osteoclasts are responsible for the the continual renovation of the osseous tissue since their lysosomic enzymes digest the osseous matrix.

The sperm acrosome, for carrying digestive enzymes within, is responsible for the perfuration of the egg cell membrane in the fertilization process. The acrosome, located in the anterior END of the sperm cell, is a SPECIALIZED region of the Golgi apparatus that accumulates great amount of digestive enzymes.

In tadpoles the tail regresses while the organism develops into an adult frog. This tissue destruction is a digestion of the tail own cells and extracellular materials and it is made by lysosomes and their enzymes. The complete digestion of a cell by its own mechanisms is CALLED AUTOLYSIS, a type of apoptosis (celll suicide).

The remodelation of the osseous tissue, the function of acrosomes in sperm cells and the elimination of the tadpole tail are examples of biological processes in which lysosomic enzymes are key factors.

The bone is a tissue made of osteoblast-containing matrix (osteoblasts are the secretory cells of the osseous matrix), osteocytes (mature bone cells) and osteoclasts (the remodeling cells). Osteoclasts are responsible for the the continual renovation of the osseous tissue since their lysosomic enzymes digest the osseous matrix.

The sperm acrosome, for carrying digestive enzymes within, is responsible for the perfuration of the egg cell membrane in the fertilization process. The acrosome, located in the anterior end of the sperm cell, is a specialized region of the Golgi apparatus that accumulates great amount of digestive enzymes.

In tadpoles the tail regresses while the organism develops into an adult frog. This tissue destruction is a digestion of the tail own cells and extracellular materials and it is made by lysosomes and their enzymes. The complete digestion of a cell by its own mechanisms is called autolysis, a type of apoptosis (celll suicide).

AUTOPHAGIC intracellular digestion is the cellular internal digestion of waste and RESIDUAL materials. In GENERAL it is DONE by lysosomes.

Autophagic intracellular digestion is intensified in situations of starvation because in such condition the cell tries to obtain from its own constituent materials the NUTRIENTS necessary to stay alive.

Autophagic intracellular digestion is the cellular internal digestion of waste and residual materials. In general it is done by lysosomes.

Autophagic intracellular digestion is intensified in situations of starvation because in such condition the cell tries to obtain from its own constituent materials the nutrients necessary to stay alive.

Heterophagic intracellular digestion is the breaking into smaller substances of external substances engulfed in the cell by pinocytosis or phagocytosis. Phagosomes or pinosomes fuse with lysosomes making the DIGESTIVE vacuoles. WITHIN the digestive vacuoles the molecules to be digested are hydrolyzed and the products of the digestion cross through the membrane and reach the CYTOPLASM or they are kept inside the vacuoles. The VACUOLE with residues from digestion is called residual body and by exocytosis it fuses with the plasma membrane and liberates its “waste” in the EXTERIOR space.

Heterophagic intracellular digestion is the breaking into smaller substances of external substances engulfed in the cell by pinocytosis or phagocytosis. Phagosomes or pinosomes fuse with lysosomes making the digestive vacuoles. Within the digestive vacuoles the molecules to be digested are hydrolyzed and the products of the digestion cross through the membrane and reach the cytoplasm or they are kept inside the vacuoles. The vacuole with residues from digestion is called residual body and by exocytosis it fuses with the plasma membrane and liberates its “waste” in the exterior space.

The ORGANELLES responsible for intracellular digestion are the LYSOSOMES. Lysosomes are vesicles that contain digestive ENZYMES CAPABLE of breaking big molecules into smaller ones. These vesicles fuse with others that carry the material to be digested and then digestion takes place.

The organelles responsible for intracellular digestion are the lysosomes. Lysosomes are vesicles that contain digestive enzymes capable of breaking big molecules into smaller ones. These vesicles fuse with others that carry the material to be digested and then digestion takes place.

Intracellular DIGESTION, or cellular digestion, is the breaking in the interior of the cell of BIG molecules coming from outside or even from the own cell METABOLISM into smaller molecules. Products and residues of the intracellular digestion are used by the cell or EXCRETED.

Intracellular digestion is classified into two types:

1. heterophagic intracellular digestion
2. autophagic intracellular digestion.

Intracellular digestion, or cellular digestion, is the breaking in the interior of the cell of big molecules coming from outside or even from the own cell metabolism into smaller molecules. Products and residues of the intracellular digestion are used by the cell or excreted.

Intracellular digestion is classified into two types:

Extracellular digestion is that in which food breaking into utile molecules that can be internalized by the cell is done in the extracellular SPACE, i.e., outside the cell. In extracellular digestion the cells SECRET substances that break big molecules into SMALLER ONES in the external environment. Later the cell can benefit from these products of the digestion.

Extracellular digestion is that in which food breaking into utile molecules that can be internalized by the cell is done in the extracellular space, i.e., outside the cell. In extracellular digestion the cells secret substances that break big molecules into smaller ones in the external environment. Later the cell can benefit from these products of the digestion.

Endocrine and exocrine PANCREATIC cells, thyroid and parathyroid endocrine cells, adenohypophysis, adrenal and pineal endocrine cells, the many types of gastric exocrine and endocrine cells, the MUCOUS secretory cells of the lungs and of the bowels, the salivary gland cells, the LACRIMAL gland cells, the sebaceous gland cells, the secretory cells of the ovaries and testicles, ETC., are all examples of secretory cells.

Endocrine and exocrine pancreatic cells, thyroid and parathyroid endocrine cells, adenohypophysis, adrenal and pineal endocrine cells, the many types of gastric exocrine and endocrine cells, the mucous secretory cells of the lungs and of the bowels, the salivary gland cells, the lacrimal gland cells, the sebaceous gland cells, the secretory cells of the ovaries and testicles, etc., are all examples of secretory cells.

The rough endoplasmic reticulum has in its outer membrane numerous ribosomes, structures where translation of messenger RNA and protein SYNTHESIS occur. These PROTEINS are stored in the rough endoplasmic reticulum and later they go to the Golgi apparatus. Within the Golgi apparatus proteins are chemically transformed and when ready they are PUT INSIDE VESICLES that detach from the organelle. These vesicles fuse with the plasma membrane (exocytosis) in the right place and its content is liberated outside the cell.

The rough endoplasmic reticulum has in its outer membrane numerous ribosomes, structures where translation of messenger RNA and protein synthesis occur. These proteins are stored in the rough endoplasmic reticulum and later they go to the Golgi apparatus. Within the Golgi apparatus proteins are chemically transformed and when ready they are put inside vesicles that detach from the organelle. These vesicles fuse with the plasma membrane (exocytosis) in the right place and its content is liberated outside the cell.

In secretory cells, LIKE the secretory cells of endocrine glands, organelles related to production, processing and “exportation” of SUBSTANCES are widely PRESENT and well-developed. These organelles are the rough endoplasmic reticulum and the Golgi apparatus.

The NUCLEAR membrane of the secretory cells generally has more pores to allow the intense traffic of MOLECULES related to protein synthesis between the cytoplasm and the nucleus.

Rough endoplasmic reticulum Golgi apparatus

In secretory cells, like the secretory cells of endocrine glands, organelles related to production, processing and “exportation” of substances are widely present and well-developed. These organelles are the rough endoplasmic reticulum and the Golgi apparatus.

The nuclear membrane of the secretory cells generally has more pores to allow the intense traffic of molecules related to protein synthesis between the cytoplasm and the nucleus.

Rough endoplasmic reticulum Golgi apparatus

CELL SECRETION is the elimination to the EXTERIOR of SUBSTANCES produced by the cell (for example, hormones, mucous, sweat, etc.)

Cell secretion is the elimination to the exterior of substances produced by the cell (for example, hormones, mucous, sweat, etc.)

Cyclosis is a TYPE of internal cell movement in which an oriented flow of circulating material is CREATED and maintained in the cytoplasm by the action of MICROFILAMENTS. Cyclosis is more easily observed in PLANT CELLS.

Cyclosis is a type of internal cell movement in which an oriented flow of circulating material is created and maintained in the cytoplasm by the action of microfilaments. Cyclosis is more easily observed in plant cells.

The handling of a CUP of coffee, the peristaltic movements of the BOWELS, the cardiac beats and even a SMILE are examples of movement created by contraction of the sarcomeres of the muscle cells. This contraction is a type of CELL movement.

The handling of a cup of coffee, the peristaltic movements of the bowels, the cardiac beats and even a smile are examples of movement created by contraction of the sarcomeres of the muscle cells. This contraction is a type of cell movement.

Amoeboid movements are created by cytoplasmic movements and PLASMA membrane projections called pseudopods. Their formation actively CHANGES the external shape of some portions of the cell surface making it to move along a substratum. Pseudopods appear from differences of viscosity among neighboring REGIONS of cytoplasm near the plasma membrane and from the contractile action of microfilaments.

Amoeboid movements occur, for example, in amoebas (a protozoan), organisms that USE their movement to find food. The leukocytes, cells of the immune system, when attracted by chemical substances (immune mediators) use amoeboid movements to get out from capillaries in regions of tissue damage to participate in the INFLAMMATORY process.

Amoeboid movements are created by cytoplasmic movements and plasma membrane projections called pseudopods. Their formation actively changes the external shape of some portions of the cell surface making it to move along a substratum. Pseudopods appear from differences of viscosity among neighboring regions of cytoplasm near the plasma membrane and from the contractile action of microfilaments.

Amoeboid movements occur, for example, in amoebas (a protozoan), organisms that use their movement to find food. The leukocytes, cells of the immune system, when attracted by chemical substances (immune mediators) use amoeboid movements to get out from capillaries in regions of tissue damage to participate in the inflammatory process.

Cilia and flagella are structures found in some prokaryotes as well in some eukaryotic cells. They play defense, nutrition and movement roles for the cell. In eukaryotic cells of PROTISTS and animals they originate from centrioles that migrate towards the plasma membrane and differentiate into structures projected outside the cell. Each cilium or flagellum is MADE of nine peripheral pairs of microtubules and one central pair all covered by membrane. (In bacteria, flagella are made of a protein named FLAGELLIN and there can also be fimbria made of pilin.)

In the fixation base of each cilium or flagellum in the plasma membrane there are proteins that work as molecular MOTORS providing movement for these structures with energy spending. Due to this energy spending ciliated or flagellated eukaryotic cells have a large number of MITOCHONDRIA.

In humans ciliated cells can be found, for example, in the bronchial and tracheal epithelium. In these tissues the cilia have the defensive function of sweeping mucous and foreign substances that enter the airways. Sperm cells are typical example of flagellated cells their flagellum is the propulsion equipment for the movement towards the ovule.

Cilia and flagella are structures found in some prokaryotes as well in some eukaryotic cells. They play defense, nutrition and movement roles for the cell. In eukaryotic cells of protists and animals they originate from centrioles that migrate towards the plasma membrane and differentiate into structures projected outside the cell. Each cilium or flagellum is made of nine peripheral pairs of microtubules and one central pair all covered by membrane. (In bacteria, flagella are made of a protein named flagellin and there can also be fimbria made of pilin.)

In the fixation base of each cilium or flagellum in the plasma membrane there are proteins that work as molecular motors providing movement for these structures with energy spending. Due to this energy spending ciliated or flagellated eukaryotic cells have a large number of mitochondria.

In humans ciliated cells can be found, for example, in the bronchial and tracheal epithelium. In these tissues the cilia have the defensive function of sweeping mucous and foreign substances that enter the airways. Sperm cells are typical example of flagellated cells their flagellum is the propulsion equipment for the movement towards the ovule.

Cell movements are movements PERFORMED by cell structures, like the movements of cilia and FLAGELLA, the pseudopod movements (in amoeba, macrophages, etc.), the cyclosis of the cytoplasm and the sarcomere contraction in MUSCLE cells.

Cell movements can be created by the citoskeleton ACTION, by differences of viscosity among cytoplasmic regions and by intracellular contraction systems.

Cell movements are movements performed by cell structures, like the movements of cilia and flagella, the pseudopod movements (in amoeba, macrophages, etc.), the cyclosis of the cytoplasm and the sarcomere contraction in muscle cells.

Cell movements can be created by the citoskeleton action, by differences of viscosity among cytoplasmic regions and by intracellular contraction systems.

Microtubules are made of consecutive DIMERS of the PROTEIN tubulin (each dimer has an ALPHA and a beta tubulin associated). Microtubules participate in cell division, they are constituents of cilia and flagella and they also form the CENTRIOLES.

Microtubules are made of consecutive dimers of the protein tubulin (each dimer has an alpha and a beta tubulin associated). Microtubules participate in cell division, they are constituents of cilia and flagella and they also form the centrioles.

Cytoskeleton is the CYTOPLASMIC structure that SUPPORTS the cell, keeps its shape and fixates and moves the cell organelles. It is made of an extensive NETWORK of fibers dispersed in the cytoplasm and anchored in the plasma membrane. Its components are microtubules, MICROFILAMENTS and intermediate filaments.

Cytoskeleton is the cytoplasmic structure that supports the cell, keeps its shape and fixates and moves the cell organelles. It is made of an extensive network of fibers dispersed in the cytoplasm and anchored in the plasma membrane. Its components are microtubules, microfilaments and intermediate filaments.

Substances that maintain highly hypertonic environment, like sugar and salt, are used in the production of dried MEAT, fish or FRUITS (for example, cod) because the material to be conserved is then dehydrated and the resulting DRYNESS prevents the growth of populations of decomposer beings (since these beings also LOSE WATER and die).

Substances that maintain highly hypertonic environment, like sugar and salt, are used in the production of dried meat, fish or fruits (for example, cod) because the material to be conserved is then dehydrated and the resulting dryness prevents the growth of populations of decomposer beings (since these beings also lose water and die).

The plant cell when PLACED under HYPERTONIC medium loses a great amount of WATER and its cell membrane detaches from the cell wall. In that situation the cell is CALLED plasmolysed cell. When the plasmolysed cell is placed under hypertonic medium it absorbs water and BECOMES a turgid cell. This phenomenon is called deplasmolysis.

The plant cell when placed under hypertonic medium loses a great amount of water and its cell membrane detaches from the cell wall. In that situation the cell is called plasmolysed cell. When the plasmolysed cell is placed under hypertonic medium it absorbs water and becomes a turgid cell. This phenomenon is called deplasmolysis.

Withered plant cells are those that shrank due to loss of WATER by evaporation without ENOUGH replacement. In this situation the cell MEMBRANE retracts and detaches from the cell wall. The cell wall moreover expands in length to stimulate the entrance of water making TP < 0. Since DPD = SF – TP and TP is negative (< 0) its formula becomes DPD = SF + |TP|.

Withered plant cells are those that shrank due to loss of water by evaporation without enough replacement. In this situation the cell membrane retracts and detaches from the cell wall. The cell wall moreover expands in length to stimulate the entrance of water making TP < 0. Since DPD = SF – TP and TP is negative (< 0) its formula becomes DPD = SF + |TP|.

In plant cells under hypertonic medium there is loss of water for the exterior, SF > 0 (the vacuolar pressure is high because it is concentrated) and TP = 0 (there is no distension of the cell wall since the cellular volume is reduced) so DPD = SF. These cells are called plasmolysed cells, situation characterized by the retraction of the cell membrane that detach from the cell wall.

In plant cells under isotonic medium there is no increase of the internal water volume, SF > 0 and TP = 0 (since the cell wall is not distended). The cell membrane slightly touches the cell wall and in this situation the cell is called flaccid cell.

In plant cells under hypotonic medium there is TENDENCY of water to enter, SF = TP (since the osmotic pressure is TOTALLY compensated by the distension of the cell wall) and DPD = 0. The cell that EXPANDED itself to this point is called turgid cell.

In plant cells under hypertonic medium there is loss of water for the exterior, SF > 0 (the vacuolar pressure is high because it is concentrated) and TP = 0 (there is no distension of the cell wall since the cellular volume is reduced) so DPD = SF. These cells are called plasmolysed cells, situation characterized by the retraction of the cell membrane that detach from the cell wall.

In plant cells under isotonic medium there is no increase of the internal water volume, SF > 0 and TP = 0 (since the cell wall is not distended). The cell membrane slightly touches the cell wall and in this situation the cell is called flaccid cell.

In plant cells under hypotonic medium there is tendency of water to enter, SF = TP (since the osmotic pressure is totally compensated by the distension of the cell wall) and DPD = 0. The cell that expanded itself to this point is called turgid cell.

DPD is the abbreviation of diffusion pressure DEFICIT, SF (suction FORCE) is the vacuolar osmotic pressure and TP is the turgor pressure.

The difference between SF and TP DETERMINES whether water tends or not to enter the cell. If SF > TP, DPD > 0 and water tends to enter the cell by osmosis. If TP > SF, DPD < 0 and water cannot enter the cell by osmosis.

DPD is the abbreviation of diffusion pressure deficit, SF (suction force) is the vacuolar osmotic pressure and TP is the turgor pressure.

The difference between SF and TP determines whether water tends or not to enter the cell. If SF > TP, DPD > 0 and water tends to enter the cell by osmosis. If TP > SF, DPD < 0 and water cannot enter the cell by osmosis.

Wall resistance, or turgor pressure (TP), is the pressure made by the distension of the plant CELL wall in OPPOSITION to the INCREASE of the cell volume. The wall resistance works against the ENTRANCE of water in the cell, i.e., it acts forcing the exiting of water and compensating the entrance of the solvent by osmosis.

Wall resistance, or turgor pressure (TP), is the pressure made by the distension of the plant cell wall in opposition to the increase of the cell volume. The wall resistance works against the entrance of water in the cell, i.e., it acts forcing the exiting of water and compensating the entrance of the solvent by osmosis.

The suction force (SF) is the osmotic PRESSURE of the plant cell VACUOLE, i.e., of the vacuolar internal solution.

Since the vacuolar solution is hypertonic in comparison to cytosol it attracts water then increasing the cytosol concentration. With the osmotic action of the vacuole the cytosol BECOMES hypertonic in RELATION to the exterior and more water enters the cell.

The suction force (SF) is the osmotic pressure of the plant cell vacuole, i.e., of the vacuolar internal solution.

Since the vacuolar solution is hypertonic in comparison to cytosol it attracts water then increasing the cytosol concentration. With the osmotic action of the vacuole the cytosol becomes hypertonic in relation to the exterior and more water enters the cell.

The PLANT CELL WALL (the covering of the cell external to the cell membrane) is made of CELLULOSE, a polymer of glucose.

When the cell is put under hypotonic medium it absorbs too much water through OSMOSIS. In that situation the cell wall pressure acts to compensate the osmotic pressure thus forbiding excessive increase of the cellular volume and the cell lysis.

The plant cell wall (the covering of the cell external to the cell membrane) is made of cellulose, a polymer of glucose.

When the cell is put under hypotonic medium it absorbs too much water through osmosis. In that situation the cell wall pressure acts to compensate the osmotic pressure thus forbiding excessive increase of the cellular volume and the cell lysis.

Endocytosis is the ENTRANCE of materia in the cell ENGULFED by portions of the cell membrane.

Endocytosis can be classified as pinocytosis or phagocytosis. In pinocytosis small particles on the external surface of the membrane stimulate the invagination of the membrane inwards and vesicles full of that particles then detach from the membrane and ENTER the cytoplasm. In phagocytosis bigger particles on the external surface of the membrane induce the PROJECTION of pseudopods outwards enclosing the particles; the vesicle then detachs from the membrane and enter the cytoplasm receiving the name phagosome.

Endocytosis is the entrance of materia in the cell engulfed by portions of the cell membrane.

Endocytosis can be classified as pinocytosis or phagocytosis. In pinocytosis small particles on the external surface of the membrane stimulate the invagination of the membrane inwards and vesicles full of that particles then detach from the membrane and enter the cytoplasm. In phagocytosis bigger particles on the external surface of the membrane induce the projection of pseudopods outwards enclosing the particles; the vesicle then detachs from the membrane and enter the cytoplasm receiving the name phagosome.

MASS TRANSPORTATION is the entrance or the exiting of substances in or from the cell engulfed by PORTIONS of membrane. The fusion of internal substance-containing MEMBRANOUS vesicles with the cell membrane is CALLED exocytosis. The entrance of substances in the cell after they have been engulfed by projections of the membrane is called endocytosis.

Mass transportation is the entrance or the exiting of substances in or from the cell engulfed by portions of membrane. The fusion of internal substance-containing membranous vesicles with the cell membrane is called exocytosis. The entrance of substances in the cell after they have been engulfed by projections of the membrane is called endocytosis.

The sodium-potassium pump is the transport protein that maintains the concentration gradient of these ions between the intra and the extracellular spaces. This protein is phosphorylated in each PUMPING cycle and then it pumps three sodium ions outside the cell and puts two potassium ions inwards. The phosphorylation is made by the binding of a phosphate donated by one ATP MOLECULE that then is CONVERTED into ADP (adenosine diphosphate).

The job of the sodium-potassium pump, also known as sodium-potassium ATPase, is fundamental to keep the characteristic negative electric charge in the intracellular side of the membrane of the resting cell and to create adequate CONDITIONS of sodium and potassium concentrations inside and outside the cell to maintain the cellular metabolism.

The sodium-potassium pump is the transport protein that maintains the concentration gradient of these ions between the intra and the extracellular spaces. This protein is phosphorylated in each pumping cycle and then it pumps three sodium ions outside the cell and puts two potassium ions inwards. The phosphorylation is made by the binding of a phosphate donated by one ATP molecule that then is converted into ADP (adenosine diphosphate).

The job of the sodium-potassium pump, also known as sodium-potassium ATPase, is fundamental to keep the characteristic negative electric charge in the intracellular side of the membrane of the resting cell and to create adequate conditions of sodium and potassium concentrations inside and outside the cell to maintain the cellular metabolism.

ACTIVE transport is made by specific membrane PROTEINS. These proteins are called “PUMPS” because they “pump” the moving substance through the membrane USING energy from ATP molecules.

Active transport is made by specific membrane proteins. These proteins are called “pumps” because they “pump” the moving substance through the membrane using energy from ATP molecules.

Facilitated diffusion can be confused with active transport because in both processes there is participation of MEMBRANE PROTEINS.

In active transport however the transported substance moves against its concentration gradient and with energy SPENDING. Facilitated diffusion is a PASSIVE transport in favor of the concentration gradient and it does not require energy.

Facilitated diffusion can be confused with active transport because in both processes there is participation of membrane proteins.

In active transport however the transported substance moves against its concentration gradient and with energy spending. Facilitated diffusion is a passive transport in favor of the concentration gradient and it does not require energy.

Hemolysis (destruction of red blood cells) by entrance of water, the hydric regulation in plants and the entrance of water in the xylem of VASCULAR plants are all examples of biological phenomena CAUSED by osmosis.

Excessive dilution of the blood plasma makes, by osmosis, the entrance of too MUCH water in red blood cells and then the destruction of these cells (hemolysis). Osmosis also is the MAIN process for maintenance of the flaccid, turgid or plasmolytic states of plant cells. Osmosis is one of the FORCES responsible for the entrance of water in plant roots since root cells are hypertonic in comparison to the soil.

Hemolysis (destruction of red blood cells) by entrance of water, the hydric regulation in plants and the entrance of water in the xylem of vascular plants are all examples of biological phenomena caused by osmosis.

Excessive dilution of the blood plasma makes, by osmosis, the entrance of too much water in red blood cells and then the destruction of these cells (hemolysis). Osmosis also is the main process for maintenance of the flaccid, turgid or plasmolytic states of plant cells. Osmosis is one of the forces responsible for the entrance of water in plant roots since root cells are hypertonic in comparison to the soil.

ONE of the main examples of facilitated transport is the entrance of glucose from the BLOOD into cells. Glucose from blood binds to specific permeases (hexose-transporting permeases) present in the cell membrane and by diffusion facilitated by these proteins it enters the cell to play its metabolic functions.

Facilitated diffusion RESEMBLES CHEMICAL catalysis because the transported substances bind to permeases like substrates bind to enzymes and in addition after one transport job is concluded the permease is not consumed and can perform successive other TRANSPORTS.

One of the main examples of facilitated transport is the entrance of glucose from the blood into cells. Glucose from blood binds to specific permeases (hexose-transporting permeases) present in the cell membrane and by diffusion facilitated by these proteins it enters the cell to play its metabolic functions.

Facilitated diffusion resembles chemical catalysis because the transported substances bind to permeases like substrates bind to enzymes and in addition after one transport job is concluded the permease is not consumed and can perform successive other transports.

The action of FACILITATOR proteins in FACILITATED diffusion MAKES this type of diffusion FASTER than simple diffusion under EQUAL concentration gradients of the moved substance.

The action of facilitator proteins in facilitated diffusion makes this type of diffusion faster than simple diffusion under equal concentration gradients of the moved substance.

Likewise SIMPLE DIFFUSION facilitated diffusion is more intense when the concentration gradient of the SUBSTANCE increases and less intense when the gradient lessens. In facilitated diffusion however there is a limiting FACTOR: the quantity of the PERMEASES that facilitate the transport through the membrane. Even in a situation in which the concentration gradient of the diffusing substance increases, if there are not enough permeases to perform the transport there will be no increase in the intensity of the diffusion. This situation is called saturation of the transport proteins and it represents the point in which the maximum transport capacity of the substance across the membrane is achieved.

Likewise simple diffusion facilitated diffusion is more intense when the concentration gradient of the substance increases and less intense when the gradient lessens. In facilitated diffusion however there is a limiting factor: the quantity of the permeases that facilitate the transport through the membrane. Even in a situation in which the concentration gradient of the diffusing substance increases, if there are not enough permeases to perform the transport there will be no increase in the intensity of the diffusion. This situation is called saturation of the transport proteins and it represents the point in which the maximum transport capacity of the substance across the membrane is achieved.

The higher the CONCENTRATION gradient of a substance the more intense its SIMPLE diffusion will be. If the concentration gradient DIMINISHES the INTENSITY of simple diffusion diminishes too.

The higher the concentration gradient of a substance the more intense its simple diffusion will be. If the concentration gradient diminishes the intensity of simple diffusion diminishes too.

Simple diffusion is the direct passage of substances across the membrane in favor of their CONCENTRATION gradient. In facilitated diffusion the MOVEMENT of substances is ALSO in favor of their concentration gradient but the substances move BOUND to specific MOLECULES that act as “permeabilizers”, i.e., facilitators of their passage through the membrane.

Simple diffusion is the direct passage of substances across the membrane in favor of their concentration gradient. In facilitated diffusion the movement of substances is also in favor of their concentration gradient but the substances move bound to specific molecules that act as “permeabilizers”, i.e., facilitators of their passage through the membrane.

The ENERGY NECESSARY for active transport (against the concentration gradient of the transported substance) to occur comes from ATP MOLECULES. The active transportation uses chemical energy from ATP.

The energy necessary for active transport (against the concentration gradient of the transported substance) to occur comes from ATP molecules. The active transportation uses chemical energy from ATP.