The Algae - Chlorophycae - Siphonales - Vaucheria

Phylum Thallophyta - The Algae - Chlorophycae - Siphonales - Vaucheria 
This Alga is largely terrestrial, occurring frequently on damp soils, as, for example, on the soil in flower pots, where it forms a green felt-like covering. It may also be found in fresh water, and it is under these conditions that asexual reproduction most frequently occurs.
Vaucheria consists of a non-septate, tubular coenocyte with lateral branches. It is dark green in colour and is very sensitive to changes of environment. The coenocyte is frequently attached to the substratum by
means of a branched holdfast or hapteron, which may be brown or white in colour and is devoid of chloroplasts. The remainder of the coenocyte contains a lining layer of protoplasm closely applied to the cell wall, and in it are embedded numerous nuclei and chloroplasts. The central part of the coenocyte consists of a vacuole containing cell sap. The chloroplasts are small and discoid, but in some species they become spherical when exposed to intense light.
In Vaucheria the reserve material is oil, which is stored in countless tiny droplets in the cytoplasm. Under normal circumstances no starch is formed, but under constant intense illumination it can be produced, which seems to indicate that the appropriate enzymes are present.
Injury to the thallus results in the formation of a septum sufficing to isolate the injured part, but otherwise, with the exception of those formed in relation to the sex organs, no septa occur.
Asexual Reproduction in Vaucheria
Asexual reproduction takes place by the formation of zoospores (Fig. 77), which are produced singly in club-shaped zoosporangia. The sporangia develop singly from the swollen ends of the branches by the accumulation of a large amount of cytoplasm with many nuclei and chloroplasts in the swollen tip, which, as a result, diminishes the size of the central vacuole, and thus these tips appear dark green in colour. Inside the zoosporangium a single large mass is formed which is termed the zoospore. It contains many nuclei which are arranged in a single layer near the surface and opposite each nucleus a pair of flagella is developed. The zoospore is liberated by the breakdown of the apical part of the wall of the sporangium to form a small pore through Which the large zoospore forces Its way. This zoospore IS generally mter­preted as a compound structure, resulting from the failure of the protoplast within the sporangium to divide into a number of uninucleate biflagellate zoospores. Zoospores are formed only by aquatic species or by terrestrial ones which have become flooded. They are usually developed during the night, or they may be induced by a sudden transference from light to darkness, or from running to quiet water. On liberation the zoospores are sluggish and only swim for a short time. On coming to rest the flagella are immedi­ately withdrawn and a thin membrane is secreted around the zoospore. Germination begins with the protrusion of two or more tubular outgrowths, one of which attaches itself to the substratum and forms the holdfast, whilst the other produces the filament.
Not all species of Vaucheria produce zoospores. Some develop what are termed aplanospores. These are simple non-flagellate structures which are produced in special sporangia called aplanosporangia. These aplano­sporangia develop as swellings either on the main or lateral branches of the thallus. When mature the aplanospores simply drop out of the aplano­sporangium through a perforation in the wall. This second method of asexual reproduction occurs most commonly among terrestrial species.
Sexual Reproduction in Vaucheria
In Vaucheria the sexual reproduction is oogamous and occurs most frequently in plants growing on damp soil or in quiet water, but is rarely found in plants growing in streams. The antheridia and oogonia are borne close to one another, either together on the same filament or on a common lateral branch or on adjoining lateral ones. Development of the oogonium begins (Fig. 78) with the formation of a swelling, which becomes filled with nuclei, oil and chloroplasts, though ultimately only a single central nucleus remains, which reaches a considerable size. The rest migrate back into the filament. The whole oogonium then becomes cut off from the rest of the coenocyte by a transverse wall or septum. Later a beak, or lateral swelling, is developed at one side of the oogonium, and in this region the wall becomes gelatinous and dissolves, leaving a pore. It is at this point that, subsequently, the antherozoids enter the oogonium. When mature the chloroplasts and oil take up a central position, leaving either a clear peripheral area of protoplasm or at least a clear area under the beak, the receptive spot, and the contents as a whole contract and become the oosphere.
The antheridia are formed at the ends of short lateral branches and develop simultaneously with the oogonia. Each antheridium is an elongated, strongly curved structure and is cut off from the thallus by a septum. The nuclei within the antheridium divide up and ultimately each becomes surrounded by a small mass of cytoplasm and constitutes an antherozoid. These antherozoids form a mass in the centre of the antheridium, whilst the periphery is filled with chloroplasts and residual cytoplasm. The antherozoids are liberated apically shortly before daybreak, as very minute, colourless, oval bodies with two laterally inserted flagella.
At the time of fertilization the oosphere exudes a droplet of gelatinous cytoplasm through the pore in the oogonium wall, and the antherozoids accumulate in numbers around the droplet. Several antherozoids may enter the oogonium, but only one enters the oosphere. The small male nucleus migrates to that of the oosphere, which is considerably larger, but does not immediately fuse \yith it. Whilst lying side by side the male nucleus increases in size, and when its volume equals that of the female nucleus the two fuse together.
After fertilization a membrane develops across the oogonial aperture, and subsequently a thick, several-layered envelope is formed around the zygote, thus producing an oospore. At the same time the oil globules unite to form one or more large central globules, and the zygote enters a resting period of several months before germination. It germinates directly to produce a new filament without the intervention of zoospores.

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Posted in Botany

The Algae - Chlorophycae - Siphonales - Bryopsis plumosa

Phylum Thallophyta - The Algae - Chlorophycae - Siphonales - Bryopsis plumosa
The Siphonales are Chlorophyceae in which the thallus consists of a single multinucleate cell or coenocyte, which often grows to form a structure of macroscopic size. Asexual reproduction occurs in a few genera by the formation of zoospores. The sexual reproduction in many of the marine genera is by the fusion of unlike motile gametes; that in the fresh-water genera IS oogamous.
Some of these coenocytic Green Algae show great complexity. For example, in the genus Caulerpa, there is a complex development of coenocyte branches to form a thallus, which may be as much as 10 em. in height, with a definite external form. The thallus in Caulerpa is especially remarkable, since the branches of the single coenocyte build up thalli that simulate in appearance the differentiation into roots, stems and leaves found in the higher land plants.
Bryopsis plumosa
The genus Bryopsis is distributed mainly in tropical seas, but one species, B.plumosa, is commonly found in spring and early summer on the British coasts. The thallus consists of a single coenocyte, but this enormous ce shows differentiation into a main axis, from which arise, towards the up end, two rows of lateral branches or pinnae. From the lower end of the axis there is formed a little-branched horizontal rhizome anchored by rhizoids. This rhizome may produce numerous upright axes, so that each plant actually consists of a little tuft of vertically growing filaments. The pinnae vary in length, those nearest the base being the longest and decreasin regularly towards the apex. Each pinna is an elongated sac, and there is a constriction at the base where it joins the main axis. No true septa are formed in the coenocyte prior to the reproductive phase and the entire plant has one continuous vacuole lined by cytoplasm and containing numerous minute, round chloroplasts and nuclei.
Vegetative propagation may be effected by the detachment of pinnae which become plugged at the point of abstriction. These are able to develop new rhizoids and grow into fresh plants. It is interesting to note that in conditions of dull light or when plants are placed upside down the apices of the pinnae develop rhizoids.
The only known method of reproduction is by means of gametes. There is no asexual method of reproduction.
SEXUAL REPRODUCTION
The gametes are not alike and are usually produced on separate plants.
The first stage consists of the cutting off of a pinna from the main axis by means of a septum which arises as a ring-like thickening. The whole of the pinna thus forms a 'gametangium whose protoplasmic contents increase and the chloroplasts multiply by division. In the male gametangium the pyrenoids disappear from the chloroplasts, but they remain in those of the female gametangium. Later the contents divide up by simultaneous cleavages to form gametes, which are liberated by the gelatinization of the apex of the pinna. The gametes are pyriform with two equal, apical flagella. The female gamete is about three times as large as the male and is provided with a deep-green chloroplast. In the male the cWoroplast is yellowish in colour and probably not functional. Gametes fuse in pairs and produce a zygote which may, for a time, retain all four flagella. Later it rounds off and germinates directly to produce a new plant. The plants are diploid and reduction division occurs in the formation of the gametes

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Posted in Botany

What is the organization of the body?

Organization of Body Parts 
The structure of the body can be studied at different levels of organization. First, all substances, including body parts, are composed of chemicals made up of submicro­scopic particles called atoms. The atoms most frequently found in the body are carbon, hydrogen, oxygen, and ni­trogen. Atoms join together to form a molecule, which can join with other molecules to form macromolecules. The macromolecules in cells are called biomolecules in this text. For example, the molecules called amino acids join to­gether to form a biomolecule called protein. Muscles con­tain a significant amount of protein; therefore, meat is a rich source of this basic nutrient.
Proteins and also fats contribute to the makeup of the cell, the basic unit of all living things. Cells are the smallest living portion of any organism, and it is at the cellular level that health and disease are best understood. Within cells are organelles, tiny membranous structures that perform cell functions. For example, the or­ganelle called the nucleus is especially concerned with cell reproduction; another organelle called the mitochondrion supplies the cell with energy.
Cells are found in tissues, and tissues make up organs. A tissue is composed of similar types of cells and performs a specific function. An organ is composed of several types of tissues and performs a particular function within an organ system. For example, the stomach is an organ and is a part of the digestive system. It has a specific role in this system, in which the overall function is to supply the body 'dth the nutrients needed for growth and repair. The other systems of the body also have specific functions.
All of the body systems together make up the organism -in this case, the human being. Human beings are com­plex animals, but this complexity can be broken down and
studied at ever simpler levels. Each simpler level is organ­ized and constructed in a particular way.
The body has levels of organization that progress from atoms to molecules. macromolecules (biomolecules), cells, tissues. organs. organ systems. and finally, the organism.

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Posted in Human Anatomy and Physiology

Anatomy and Physiology a complete defination

Anatomy and Physiology 
Anatomy is the study of the structure of body parts. For example, the stomach is a J-shaped, pouchlike organ. The stomach wall has thick folds, which disappear as the stomach expands to increase its capacity. Physiology is the study of the function of body parts. For example, the stomach temporarily stores food, secretes digestive juices, and passes on partially digested food to the small intestine.
Anatomy and physiology are closely connected in that the structure of an organ suits its function. For example, the stomach's pouchlike shape and ability to expand are suit­able to its function of storing food. In addition, the micro­scopic structure of the stomach wall is suitable to its secretion of digestive juices, as we shall see later in the text.
Anatomy is the study of the structure of body parts, and physiology is the study of the function of these parts. Structure is suited to the function of a part.

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Posted in Human Anatomy and Physiology

Classification and stages of xerophthalmia

Classification of stages of xerophthalmia 
The ocular signs of vitamin A deficiencies include nightblindness, conjunctival xerosis, Bitot's spots, corneal xerosis, and keratomalacia. The classification proposed for general use is as follows:
Classification X1A 
Signs -primary
Conjunctival xerosis-dryness or lack ofluster, loss of ability to re­tain moisture no matter whether tears are present or absent, loss of transparency, thickening, wrin­kling, pigmentation, accumula­tion of debris.
Classification X1B
Signs -primary
Bitot's spot with conjunctival xe­rosis-a small plaque with a sil­very gray hue and a foamy surface; it is quite superficial and is raised above the general level of the conjunctiva
Classification X2
Signs -primary
Corneal xerosis-follows con­junctival xerosis. The corneal sur­face has a rough, fine pebbly appearance and lacks luster. Later, cellular infiltration of the corneal stroma contributes to the intense haziness of the cornea, which frequently has a bluish, milky appearance
Classification X3A
Signs -primary
Corneal ulceration wi th xerosis­involving loss of substance of a part or of the whole of the corneal thickness
Classification X3B
Signs -primary
Keratomalacia - consists of a characteristic softening of the en­tire thickness of a part or, more often, the whole of the cornea, leading to deformation or destruc­tion of the eyeball. The process is a rapid one, the corneal structure melting into a cloudy gelatinous mass which may be dead white or dirty yellow in color
Classification XN
Signs -secondary
Night blindness-impairment of the ability to adapt to the dark
Classification XF
Signs -secondary
Xerophthalmia fundus-multiple lesions, sometimes glaring white, scattered profusely along the course of the vessels
Classification XS
Signs -secondary
Corneal scars-resulting from the healing of irreversible corneal changes
Classification XB
Signs -secondary
Bitot's spot with conjunctival xe­rosis-a small plaque with a sil­very gray hue and a foamy surface; it is quite superficial and is raised above the general level of the conjunctiva
Stage XN, or night blindness, indicates a functional impairment ofthe retina and is difficult to diagnose in the young child (1-4 yr) unless the mother is aware that the child cannot see well at night. As a method of screening, the child may be asked to walk into a darkened room.
The first sign of xerophthalmia is xerosis of the con­junctiva (stage X1A). This dryness and dullness associated with the stability of the precorneal film is considered complete alteration of the reflection of light from the conjunctiva. Night blindness (XN) and Bitot's spots (ac­cumulation of debris and fatty material near the edge of the eye) are frequently present at stage X1B. At stage X2, when there is xerosis of the cornea itself, the pre corneal film fails to cover the cornea, which now appears dry and opaque. Small erosions or perforations begin to occur if treatment with massive doses of vitamin A (100,000 IU/day, orally or intramuscularly) is not provided within 1 to 3 days of inception, and irreversible damage will soon result. However, if treated, the corneal xerosis will clear up within a short period of time.
Irreversible damage occurs once deeper layers of the cornea are involved, as in stage X3A. The cornea may liquety and melt away, resulting in large perforations and extrusion of the iris, the lens, and the vitreous (X3B). The permanent scarring effects (stage X5) may differ depend­ing on whether or not intraocular pressure was restored at stage X3B. It is essential that medical and paramedical personnel be alert to the signs of xerophthalmia and that treatment be instituted immediately when symptoms are recognized in order to prevent blindness.

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Posted in Diseases

Transportation in Plasma Membrane

Plasma Membrane Transport 
The plasma membrane allows only certain molecules to enter and exit the cytoplasm freely; therefore, the plasma membrane is said to be selectively permeable. Transport of molecules across the membrane can be active or passive. Active transport requires the use of ATP energy; passive trans­port does not. Passive transport mechanisms include diffu­sion, osmosis, and filtration.
Passive Diffusion
Diffusion is the passive movement of molecules from an area of higher concentration to an area of lower concentra­tion. For example, if a perfume bottle is opened in one cor­ner of a room, the perfume's scent will soon be apparent throughout the room because the perfume molecules have diffused from an area of high concentration (the corner) to areas oflower concentration. Another example of diffusion is putting a tablet of dye into water. The water eventually takes on the color of the dye as the tablet dissolves.
In the body, oxygen enters the blood from the alveoli (air sacs) ofthe lungs by diffusion. During kidney dialysis, waste molecules diffuse across a membrane from the area of higher concentration (the blood) to the area of lower concentration (the dialysate). Cells do not expend any energy when sub­stances can simply diffuse across the plasma membrane.
Some molecules that cannot cross the phospholipid bilayer of the plasma membrane diffuse through plasma membrane protein channels. Passive transport of this sort is a form of facilitated diffusion.
Osmosis 
Osmosis (oz-mo'sis) is the diffusion of water across a plasma membrane. It occurs whenever the concentrations of water on either side of a selectively permeable mem­brane are unequal. Normally, body fluids are isotonic (i"so-ton'ik) to cells, that is, the concentrations of substances (solutes) and water (solvent) on either side of the plasma membrane are equal and cells, therefore, maintain their usual size and shape. For this reason, most intravenous solutions are also isotonic to cells.
If red blood cells are placed in a hypotonic (hi "po­ton'ik) solution, which has a higher concentration of water (lower concentration of solute) than do the cells, water will enter the cells, and they will swell to bursting. Bursting of red blood cells is called hemolysis. On the other hand, if red blood cells are placed in a hypertonic (hi"per-ton'ik) solution, which has a lower concentration of water (higher concentration of solute) than do the cells, water will leave the cells, and they will shrink. The shrinking of red blood cells is called crenation.
Filtration 
Because capillary walls are only one cell thick, small mole­cules (water, small solutes) tend to passively diffuse across these walls, from areas of higher concentration to those of lower concentration. However, blood pressure aids matters by pushing water and dissolved solutes out of the capillary. This process is called filtration.
Filtration is easily observed in the laboratory when a so­lution is poured past filter paper into a flask. Large substances stay behind, but small molecules and water pass through.
Filtration of water and substances in the region of cap­illaries is largely responsible for the formation of tissue fluid, the fluid that surrounds the cells. Filtration is also at work in the kidneys when water and small molecules move from the blood to the inside of the kidney tubules.
Active Transport 
In active transport, substances accumulate either inside or outside the cell in the region of higher concentration. For ex­ample, iodine collects in the cells of the thyroid gland; sugar is completely absorbed from the gut by the cells lining the digestive tract; and sodium is sometimes almost completely withdrawn from uri ne by cells lining the kidney tubules.
Carrier proteins and an expenditure of energy are both needed to transport substances from an area of lower concentration to an area of higher concentration. A carrier is a plasma membrane protein that specializes in combining with and transporting substances across the plasma membrane. Because ATP energy is needed to cause a carrier to combine with the substance to be transported, cells primarily involved in active transport, such as kidney cells, have a large number of mitochondria near the mem­brane where active transport is occurring.
During active transport. vvhich requires plasma membrane carriers and ATP energy. substances move against a concentration gradient and accumulate in the area of higher concentration.
Endocytosis and Exocytosis
At times, substances are taken into cells by vesicle forma­tion. This is called endocytosis (en"do-si-to'sis). When the material taken in is quite large, the process is called phagocytosis (fag" o-si-to' sis) (cell eating). Phagocy­tosis is common to amoeboid-type cells, such as macro­phages. These white blood cells are called the body's scavengers because they engulf worn-out red blood cells and other types of debris. When cells take in material that is small enough to be dissolved or suspended in water, the process is called pinocytosis (pi" no-si- to' sis) (cell drinking).
Vesicles within the cytoplasm of the cell can fuse with the plasma membrane and release their contents to the outside of the cell. This is called exocytosis (ex" o-si-to'sis). Some cells of the nervous system release substances in­volved in the transfer of nerve impulses between adjacent cells via exocytosis.

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Posted in Human Anatomy and Physiology

Composition and Functions of Nucliec Acids

Nucleic Acids 
Nucleic acids (nu-kla'ik as'idz) are huge biomolecules with very specific functions in cells. Genes, the hereditary factors that we receive from our parents and that control the characteristics of the cell and organism, are composed of a nucleic acid called DNA (deoxyribonucleic acid) (de­ok'sf-ri"bo-nu-kla"ik as'id). DNA is a molecule that stores coded information. Another important nucleic acid-RNA (ribonucleic acid)-works in conjunction with DNA to bring about protein synthesis in cells.
Both DNA and RNA are polymers of nucleotides joined together. Every nucleotide is a molecular complex of three types of unit molecules: a phosphate, a 5-carbon sugar, and a nitrogen base. The sugar in DNA is deoxyribose, while that in RNA is ribose, which accounts for the difference in their names. The nitrogen bases in DNA are adenine (A), guanine (G), thymine (T), and cytoine (C). The bases in RNA are the same, except that uracil (U) is substituted for thymine.
When nucleotides join together, they form a linear molecule called a strand, composed of a sugar-phosphate backbone, with the nitrogen bases projecting to one side. RNA is single-stranded, but DNA is double-
tranded. The two strands of DNA are twisted in the form of a double helix and are held together by hydrogen bonds between the bases. An unwound DNA helix re­embles a ladder: The steps of the ladder are the hydrogen­bonded nitrogen bases.
The sequence of nitrogen bases in DNA serves as a code for directing the sequence of bases in RNA and then the sequence of amino acids in a protein. In other words, the genes we inheri t determine the types of proteins we can produce in our cells.
Both DNA and RNA are polymers of nucleotides; only DNA is double-stranded. DNA makes up the genes. and along with RNA. controls protein synthesis.

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Posted in Human Anatomy and Physiology