This course satisfies a high school mathematics graduation requirement. Practicum in Agriculture, Food, and Natural Resources. Regional floras commonly are divided into categories such as native flora and agricultural and garden flora , the lastly mentioned of which are intentionally grown and cultivated. Classification of a substance or mixture as posing a carcinogenic hazard is based on its inherent properties and does not provide information on the level of the human cancer risk which the use of the substance or mixture may represent. How does this exemplify the role of collaboration and effective communication in scientific research?
Systems Biology in Toxicology and Environmental Health
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Study Jams - Inertia. NASA - 1st Law. Weather Around the World. Dioramas Coming to Life. Ben's Guide 2 Gov't. Branches of Gov't Worksheet. Questions from Crime Lab. The act of taking the food material into the buccopharyngeal cavity is called ingestion. During ingestion the mouth is opened and the muscular sticky tongue is shot out with much speed to catch the prey. The prey gets adhered to the sticky tongue. The tongue along with the prey is withdrawn with great rapidity into the buccopharyngeal cavity and the mouth is firmly closed.
The prey is held, injured or killed by the maxillary and vomerine teeth. The bulging of eye balls and raising up the throat help in pushing down the food towards the oesophagus. The movement of the epithelial cilia of the buccopharyngeal cavity and peristalsis further aid in the downward movement of the food into the oesophagus. During this, the contents of the tube are pushed onwards.
Digestion is a process by which the non-diffusible food material is converted into diffusible form by the action of various digestive enzymes. The buccopharyngeal cavity and the oesophagus do not secrete any enzymes. Digestion that takes place in the stomach is known as gastric digestion. The walls of the stomach secrete a hormone, the gastrin, which stimulates the gastric glands to release the gastric juice.
The gastric juice contains hydrochloric acid and a pro-enzyme pepsinogen and mucus. Hydrochloric acid converts inactive pepsinogen into active pepsin. The acid also provides the acidic medium, which is essential for the action of pepsin. The pepsin converts proteins into proteoses and peptones. The carbohydrates and fats remain unaffected by the proteolytic enzymes. In the stomach the food is stored for quite a long time.
Due to the massive peristalsis of the stomach wall, the food is broken into smaller pieces and thoroughly mixed with the gastric secretions including the mucus. The food is now in a semi-liquid state known as chyme. The latter passes into the duodenum through pyloric sphincter at regular intervals. Digestion that takes place in the intestine is called intestinal digestion.
In the duodenum, the acidity of the chyme is neutralized by the salts of bile and now the chyme becomes alkaline in nature.
With the entry of bile, pancreatic juice, the intestinal juice and more of mucus, the food is now in a more liquid form and is called chyle. A hormone, the cholecystokinin, produced by the duodenum reaches the gall bladder through blood circulation where it stimulates the gall bladder to release the bile. The bill contains no enzymes, but its salts provide the alkaline medium necessary for the action of the pancreatic and intestinal enzymes.
The duodenum also secretes secretin hormone which reaches the pancreas through blood circulation, where it stimulates the pancreas to release the pancreatic juice. The pancreatic juice contains pro-enzymes trypsinogen, chymotrypsinogen and enzymes peptidase, amylase, maltase and lipase.
The inactive trypsinogen is converted into trypsin by the action of an activator enzyme, the enterokinase of the intestinal juice. The trypsin converts inactive chymotrypsinogen into chymotrypsin. All these three enzymes— trypsin, chymotrypsin and peptidase change proteoses and peptones into peptides. Amylase converts starch into maltose. Maltase converts some maltose into glucose. Lipase changes fat into fatty acid and glycerol. Intestinal juice contains peptidases, maltase and lipase enzymes.
The enzyme enterokinase present in this juice converts inactive trypsinogen of pancreatic juice into trypsin. Many peptidases tri and dipeptidases , change peptides into amino acids. Maltase changes the rest of the maltose into glucose and the lipase converts the remaining fat in fatty acids and glycerol. It is a process by which the digested food diffuses into the circulatory system blood and lymph through the wall of the alimentary canal.
The absorption starts from the stomach. Most of the absorption is done by small intestine. The wall of the alimentary canal is richly traversed by blood and lymph capillaries. The lymph capillaries of the intestine are known as lacteals. Amino acids, glucose, vitamins and water are absorbed into blood capillaries, while fatty acids and glycerol enter the lymph-capillaries lacteals.
The indigestible food comes to rectum by peristaltic action, where water is mainly absorbed. After that, the faecal matters are transferred to the cloaca and from there they are egested via cloacal aperture. The skin of frog provides an extensive surface for the exchange of gases. It is thin, richly supplied with blood and kept moist by the mucus and water. The cutaneous respiration is always carried out. During hibernation winter sleep and aestivation summer sleep , it is the only method of respiration in frog.
It occurs when the animal is on the land or partially immersed in water. There are present two external nares situated at the tip of the snout. Each external naris nostril leads into a nasal chamber which opens into the buccopharyngeal cavity by an internal naris.
During this mode of respiration, the mouth and glottis are tightly closed while the nares are kept open. There are two sets of muscles which operate the mechanism of buccopharyngeal respiration. These muscles are stemohyal muscles and petrohyal muscles.
It is less frequent than the cutaneous and buccopharyngeal respiration. It occurs when need for oxygen is increased.
Respiratory path includes external nares, nasal chambers, internal nares, buccopharyngeal cavity and glottis. This chamber leads posteriorly to the lungs through a pair of apertures. The lungs are two delicate, elastic, pinkish, ovoid, thin walled hollow sacs lying on either side of the oesophagus. Each lung looks like a honey-comb. The inner surface of the lungs is divided by a series of partitions, the septa into many small cavities known as alveoli.
Exchange of gases takes place through alveoli. During pulmonary respiration, the mouth is tightly closed.
The sternohyal and petrohyal muscles play very important role in the mechanism. A thin walled laryngotracheal chamber is the sound producing organ in the frog. It corresponds to the larynx and trachea of higher animals. There is also present a pair of elastic bands, the vocal cords which extend longitudinally across the laryngotracheal chamber. The vocal cords are the true sound producing organs. A narrow slit like gap, the rima-glottis is present between the free inner edges of the vocal cords, which helps in the production of sound.
The inner edges of the vocal cords, which lie freely, get vibrated when air from the lungs is expelled out forcibly to produce a characteristic sound croak. The male frogs produce louder and prolonged sound than the females because males have a pair of vocal sacs. These sacs are the pouches of the skin on the throat, opening into the buccopharyngeal cavity and acting as resonators.
When the air is expelled out from the lungs the vocal sacs are inflated with air to raise the pitch of the sound in the male frog. The circulatory system of frog consists of blood vascular system and lymphatic system.
It is of closed type as the blood flows in the blood vessels. It represents single circulation. It means both the oxygenated and the deoxygenated blood enters the heart and get mixed in the ventricle. Blood vascular system comprises blood, heart and blood vessels. The blood is a mobile connective tissue, composed of a fluid, the plasma and the cells, the blood corpuscles. These are large, oval and biconvex nucleated cells. The cytoplasm contains a respiratory red pigment, known as haemoglobin, which is made up of a blood protein, the globin and haematin.
They are small, numerous and spindle shaped nucleated cells. They are produced by the bone marrow. They help in the clotting of blood, by producing the thrombin enzyme. The heart is situated mid-ventrally in the thorax in between the two lungs, just anterior to the liver. The heart is protected by the pectoral girdle ventrolaterally and by vertebral column dorsally. The outer layer of the sac is called parietal pericardium and inner layer is known as visceral pericardium.
In between the two layers, a space, the pericardial cavity is present, which is filled with a pericardial fluid. The pericardium protects the heart from the shocks, and mechanical injuries and also allows its free movements. After removing the pericardium, the external characters of the heart are clearly seen.
The heart of frog is three chambered, viz. The two thin walled auricles are separated from each other by the inter auricular septum. The sinus venosus opens into right larger auricle through sinuauricular aperture which is guarded by a pair of sinuauricular valves. It only allows the blood to flow towards the right auricle. The common opening of pulmonary veins is present in the smaller left auricle. The opening is not guarded by any valve.
Both the auricles open into a single ventricle by a common wide auriculo-ventricular aperture, which is guarded by a valve, the auriculoventricular valve bearing four flaps— one dorsal, one ventral and two lateral in position.
The free edges of these flaps project into the ventricle and are connected to the wall of the ventricle with fine contractile but tough thread-like structures known as chordae tendineae. The chordae tendineae regulate the movement of the auriculo-ventricular valve so as to allow the blood to pass from the auricles into the ventricle and further prevent the backward flow of the blood into the auricles. The ventricle is a muscular and thick walled chamber, the inner surface of which is projected into ridges, the columnae carneae.
The latter divide the cavity of the ventricle into smaller spaces, known as fissures. The right side of the ventricle opens into truncus arteriosus on the ventral side. At the place from where the truncus arteriosus arises from the ventricle, a row of three pocket shaped semilunar valves is present.
These valves allow blood flow from the ventricle to the truncus arteriosus. The latter consists of a proximal muscular part, the pylangium and the distal part, the synangium. A row of the three semilunar valves separates the pylangium from the synangium.
The pylangium part is further divided vertically into two incomplete chambers by a spiral twisted valve. The right chamber is called cavum aorticum and the left cavum pulmocutaneum. The spiral valve is a flap of tissue running vertically in the pylangium and is attached with the middle valve of the anterior row of the three semilunar valves. The spiral valve is free ventrally and posteriorly. The cavity of the synangium is further divided into a dorsal and ventral chamber by a horizontal partition called primary septum or septum principle.
The synangium bifurcates into two branches as aortic trunks. A small opening of the pulmocutaneous arch is present in the cavum pulmocutaneum just behind the anterior row of semilunar valves. This opening is guarded by a small valve. Thus, the cavum pulmocutaneum leads into the dorsal chamber of synangium and then dorsal chamber opens into pulmocutaneous arch. While the cavum aorticum leads into the ventral chamber of synangium and then the ventral chamber opens into both systemic and carotid arches.
In addition to the above mentioned structures, there is present one sinus venosus. Histologically, the wall of the heart consists of three layers: Heart of frog is myogenic heart beat originates from a muscle, however, it is regulated by the nerves.
Wave of contraction originates from the sinus venosus and spreads over the wall of the sinus venosus and both the auricles. It compels the heart to beat. The contraction of the heart is termed as systole while its expansion is called diastole and both constitute one heart beat. The sinus venosus contracts, whose contraction drives the mixed blood from the sinus venosus to the right auricle.
At the same time, the left auricle receives oxygenated blood through the opening of the pulmonary veins from the lungs. When the two auricles are full of blood, they contract simultaneously.
The backward flow of the blood into the sinus venosus is prevented by the sinuauricular valves. Thus, the blood from both the auricles is forced into the single ventricle through auriculoventricular aperture. The auriculoventricular node is stimulated by the auricular contraction and passes a fresh wave of the contraction over the wall of the ventricle. Thus both oxygenated and deoxygenated bloods are mixed in the ventricle. The mixed blood of the ventricle enters the truncus arteriosus.
From the truncus arteriosus mixed blood goes to three arches carotid, systemic and pulmocutaneous and ultimately reaches all the parts of the body. The contraction of heart systole and the relaxation of heart diastole constitute the heart beat. The rate of heart beat is controlled by the medulla oblongata of the brain and by certain hormones such as adrenalin and thyroxine. Increase in carbon dioxide and temperature also affects the sinus venosus and thereby it increases the rate of heart beat.
In frog cardiac cycle is completed in about 0. Arteries, arterioles, veins, venules and blood capillaries are called blood vessels. Arteries carry blood from the heart to different body parts.
Veins bring blood from different body parts to the heart. Arteries divide to form arterioles. The arterioles divide to form blood capillaries which unite to form venules. The venules join to form veins. The veins have valves to prevent backward flow of blood. Exchange of nutrients, hormones, gases, etc.
The renal portal system collects the blood from the hind parts on the body from which the urea and uric acid present in the blood are first got filtered in the kidneys before the blood goes into postcaval and then to the heart. Thus, the blood going to the heart contains comparatively less impurities after passing through the renal portal system.
The excess of glucose is converted into glycogen which is stored in the liver for later use. When an individual feels deficiency of food, the glycogen is converted into glucose and is transferred to the blood stream via hepatic veins,. Thus the blood is detoxified purified of harmful nitrogenous waste;. It is the second part of the circulatory system, through which a mobile connective tissue, the lymph, is circulated. Lymphatic system comprises a Lymph, b Lymph capillaries, c Lymph sinuses and d Lymph hearts.
It is similar to blood plasma but has got less number of proteins. Mainly globulin proteins are present. Other components of the lymph plasma are very much like that of blood plasma, i. Red blood corpuscles Erythrocytes are completely absent. Thrombocytes spindle shaped cells are few in number due to which the clotting of the lymph is very slow. Lymph capillaries lie very close to the blood capillaries but differ from them, as they end blindly in contact with the body cells or the tissue spaces.
The lymph always flows from the tissues towards the lymph hearts. Their walls are extremely thin and permeable to colloids, crystalloids and water.
They do not have a constant shape. The lymph capillaries of the intestine transport the digested fat, which does not pass through blood stream directly.
In the frogs, lymph vessels are not found. Instead of these vessels, there are present thin walled spaces or lymph sinuses around the tissues and between the organs. The important lymph sinuses are subcutaneous sinuses and sub-vertebral sinus. There are present two pairs of thin walled, muscular lymph hearts, one pair is located behind the transverse processes of third vertebra and the other is situated in the region of urostyle.
It is a dark, red oval structure lying near the anterior end of the rectum. It includes the nerves and ganglia that control and coordinate such organs which are not under voluntary control.
It comprises sympathetic nervous system and parasympathetic nervous system. It is lodged in the cranial cavity of the skull. The brain is covered by two membranes or meanings sing meninx. The outer tough, thick membrane is duramater, and the inner thin, more delicate and vascular membrane is pia arachnoid membrane.
The brain is divisible into three parts: Fore brain, mid brain and Hind brain. It comprises two olfactory lobes, two cerebral hemispheres and a diencephalon. Dorsal surface of the diencephalon has anterior choroid plexus to supply nourishment to the anterior parts of the brain. From the dorsal side of the diencephalon also arises a short cylindrical pineal stalk, which carries knob like pineal body. The pineal body is an endocrine gland. The position of pineal body is indicated externally by the brow spot.
A pair of thick optic nerves crosses and forms optic chiasma on the ventral side of the diencephalon. Further, behind the infundibulum and attached to it a flattened ovoid sac, the hypophysis pituitary gland is present. It produces very important hormones. It consists of optic lobes and crura cerebri. Behind the diencephalon two ovals, large slightly pressed to the outside, optic lobes are present. These are well seen in dorsal view. On the ventral side, the brain is thickened to form two fibrous strands of nervous tissue, the crura cerebri sing, crus cerebrum , which carry the stimuli between the cerebral hemispheres and medulla oblongata.
It comprises cerebellum and medulla oblongata. Immediately behind the optic lobes, there is present a sort of transverse ridge on the dorsal surface known as cerebellum, which is poorly developed in frog. It maintains balance of the body. The last part of the brain is medulla oblongata, which is stout and somewhat triangular in shape and continues as spinal cord posteriorly.
The dorsal side of the medulla oblongata is non-nervous but highly vascular and forms posterior choroid plexus. The cranial nerves from 5th to 10th are connected with the medulla oblongata. The brain is hollow containing cavities, which are filled with the cerebro spinal fluid secreted by anterior and posterior-choroid plexuses. The cavities of the brain are known as ventricles. Each olfactory lobe encloses a ventricle termed as rhinocoel which leads into the ventricles of the cerebral hemisphere, the lateral ventricles or paracoels or first and second ventricles.
Two lateral ventricles open into the ventricles of the diencephalon, the diocoel or third ventricle through an aperture, the foramen of Monro. The ventricle of the cerebellum is called the metacoel. The myelocoel communicates with the central canal of spinal cord. They also control the voluntary activities of the animals. It also regulates the autonomic nervous system. Diencephalon also controls the metabolism of fat, water and carbohydrates. The secretion of pituitary body influences a number of activities of the animal.
Originally Aristotle divided all living things between plants, which generally do not move fast enough for humans to notice, and animals. In Linnaeus ' system, these became the kingdoms Vegetabilia later Plantae and Animalia. Since then, it has become clear that the Plantae as originally defined included several unrelated groups, and the fungi and several groups of algae were removed to new kingdoms. However, these are still often considered plants in many contexts. Bacterial life is sometimes included in flora,   and some classifications use the term bacterial flora separately from plant flora.
Among the many ways of classifying plants are by regional floras , which, depending on the purpose of study, can also include fossil flora , remnants of plant life from a previous era. People in many regions and countries take great pride in their individual arrays of characteristic flora, which can vary widely across the globe due to differences in climate and terrain.
Regional floras commonly are divided into categories such as native flora and agricultural and garden flora , the lastly mentioned of which are intentionally grown and cultivated. Some types of "native flora" actually have been introduced centuries ago by people migrating from one region or continent to another, and become an integral part of the native, or natural flora of the place to which they were introduced. This is an example of how human interaction with nature can blur the boundary of what is considered nature.
Another category of plant has historically been carved out for weeds. Though the term has fallen into disfavor among botanists as a formal way to categorize "useless" plants, the informal use of the word "weeds" to describe those plants that are deemed worthy of elimination is illustrative of the general tendency of people and societies to seek to alter or shape the course of nature.
Similarly, animals are often categorized in ways such as domestic , farm animals , wild animals , pests , etc. Animals as a category have several characteristics that generally set them apart from other living things. Animals are eukaryotic and usually multicellular although see Myxozoa , which separates them from bacteria, archaea , and most protists. They are heterotrophic , generally digesting food in an internal chamber, which separates them from plants and algae.
They are also distinguished from plants, algae, and fungi by lacking cell walls. With a few exceptions—most notably the two phyla consisting of sponges and placozoans —animals have bodies that are differentiated into tissues.
These include muscles , which are able to contract and control locomotion, and a nervous system , which sends and processes signals.
There is also typically an internal digestive chamber. The eukaryotic cells possessed by all animals are surrounded by a characteristic extracellular matrix composed of collagen and elastic glycoproteins. This may be calcified to form structures like shells , bones , and spicules , a framework upon which cells can move about and be reorganized during development and maturation, and which supports the complex anatomy required for mobility. Although humans comprise only a minuscule proportion of the total living biomass on Earth, the human effect on nature is disproportionately large.
Because of the extent of human influence, the boundaries between what humans regard as nature and "made environments" is not clear cut except at the extremes. Even at the extremes, the amount of natural environment that is free of discernible human influence is diminishing at an increasingly rapid pace. The development of technology by the human race has allowed the greater exploitation of natural resources and has helped to alleviate some of the risk from natural hazards.
In spite of this progress, however, the fate of human civilization remains closely linked to changes in the environment. There exists a highly complex feedback loop between the use of advanced technology and changes to the environment that are only slowly becoming understood. Humans have contributed to the extinction of many plants and animals. Humans employ nature for both leisure and economic activities.
The acquisition of natural resources for industrial use remains a sizable component of the world's economic system. Agriculture was first adopted around the 9th millennium BCE. Ranging from food production to energy, nature influences economic wealth. Although early humans gathered uncultivated plant materials for food and employed the medicinal properties of vegetation for healing,  most modern human use of plants is through agriculture.
The clearance of large tracts of land for crop growth has led to a significant reduction in the amount available of forestation and wetlands, resulting in the loss of habitat for many plant and animal species as well as increased erosion. Beauty in nature has historically been a prevalent theme in art and books, filling large sections of libraries and bookstores.
That nature has been depicted and celebrated by so much art, photography, poetry, and other literature shows the strength with which many people associate nature and beauty. Reasons why this association exists, and what the association consists of, are studied by the branch of philosophy called aesthetics.
Beyond certain basic characteristics that many philosophers agree about to explain what is seen as beautiful, the opinions are virtually endless. An early tradition of landscape art began in China during the Tang Dynasty — The tradition of representing nature as it is became one of the aims of Chinese painting and was a significant influence in Asian art.
Although natural wonders are celebrated in the Psalms and the Book of Job , wilderness portrayals in art became more prevalent in the s, especially in the works of the Romantic movement. British artists John Constable and J. Turner turned their attention to capturing the beauty of the natural world in their paintings.
Before that, paintings had been primarily of religious scenes or of human beings. William Wordsworth 's poetry described the wonder of the natural world, which had formerly been viewed as a threatening place. Increasingly the valuing of nature became an aspect of Western culture. A common classical idea of beautiful art involves the word mimesis , the imitation of nature. Also in the realm of ideas about beauty in nature is that the perfect is implied through perfect mathematical forms and more generally by patterns in nature.
As David Rothenburg writes, "The beautiful is the root of science and the goal of art, the highest possibility that humanity can ever hope to see". Some fields of science see nature as matter in motion, obeying certain laws of nature which science seeks to understand. Matter is commonly defined as the substance of which physical objects are composed. It constitutes the observable universe. The visible components of the universe are now believed to compose only 4.
The remainder is believed to consist of The behavior of matter and energy throughout the observable universe appears to follow well-defined physical laws. These laws have been employed to produce cosmological models that successfully explain the structure and the evolution of the universe we can observe.
The mathematical expressions of the laws of physics employ a set of twenty physical constants  that appear to be static across the observable universe. Outer space, also simply called space , refers to the relatively empty regions of the universe outside the atmospheres of celestial bodies.
Outer space is used to distinguish it from airspace and terrestrial locations. There is no discrete boundary between the Earth's atmosphere and space, as the atmosphere gradually attenuates with increasing altitude. Outer space within the Solar System is called interplanetary space , which passes over into interstellar space at what is known as the heliopause. Outer space is sparsely filled with several dozen types of organic molecules discovered to date by microwave spectroscopy , blackbody radiation left over from the big bang and the origin of the universe, and cosmic rays , which include ionized atomic nuclei and various subatomic particles.
There is also some gas, plasma and dust , and small meteors. Additionally, there are signs of human life in outer space today, such as material left over from previous manned and unmanned launches which are a potential hazard to spacecraft.
Some of this debris re-enters the atmosphere periodically. Although the Earth is the only body within the solar system known to support life, evidence suggests that in the distant past the planet Mars possessed bodies of liquid water on the surface. At present though, most of the water remaining on Mars is frozen. If life exists at all on Mars, it is most likely to be located underground where liquid water can still exist.
Conditions on the other terrestrial planets, Mercury and Venus , appear to be too harsh to support life as we know it. But it has been conjectured that Europa , the fourth-largest moon of Jupiter , may possess a sub-surface ocean of liquid water and could potentially host life. Astronomers have started to discover extrasolar Earth analogs — planets that lie in the habitable zone of space surrounding a star , and therefore could possibly host life as we know it.
From Wikipedia, the free encyclopedia. For other uses, see Nature disambiguation. For other uses, see Natural disambiguation. Hopetoun Falls , Australia. Bachalpsee in the Swiss Alps. Lightning strikes during the eruption of the Galunggung volcano , West Java , in Human timeline and Life timeline. Earth and Earth science. History of the Earth and Evolution.
Atmosphere of Earth , Climate , and Weather. Human timeline and Nature timeline. Life , Biology , and Biosphere. Life timeline and Nature timeline. Outer space , Universe , and Extraterrestrial life.
Retrieved September 23, Generally, these senses match rather well the current senses in which the English word nature is used, as confirmed by Guthrie, W. The word is dealt with thoroughly in Liddell and Scott's Greek Lexicon. For later but still very early Greek uses of the term, see earlier note. Retrieved September 20, Retrieved September 21, Retrieved January 6, Retrieved January 7, Archived from the original on January 23, American Institute of Physics.
The Age of the Earth. Archived from the original on September 28, Retrieved May 24, Palaeobotanical records and forest simulations".
Vegetation History and Archaeobotany.