Tuesday, August 4, 2009
The dissolution of salt in water: This seems like a physical change because we know we can recover the salt from the water. However, if we look at the microscopic level, we see that the two types of atoms in salt, sodium and chlorine, separate from one another. In this example, we don’t have a new substance, therefore this salt in solution doesn’t fit the microscopic definition of a chemical change; but we also don’t have the substance in its original form — a stack of alternating sodium and chlorine atoms. Does this mean the change is half chemical and half physical? Though it has aspects of a chemical change, scientists would still classify the dissolution of salt as a physical change.
The creation of a metal alloy: If we melt two types of metal together, we create an alloy metal that has different properties than either of its components (e.g., heat conductivity, electrical conductivity, density, etc.). This might lead us to think that we’ve witnessed a chemical change. In fact, a new particle is not created by melting two metals together. This indicates they did not undergo a chemical reaction. Brass, for example, is about 60% copper and 40% zinc, and is composed of individual copper and zinc atoms (i.e., there is no “smallest unit” that is still brass). There is no such thing as a brass molecule.
The heating and cooling of certain rubbers and plastics: One might think that exposing certain rubbers and plastics to heat or cold would cause a chemical reaction because the properties change (e.g., the materials become more rigid and brittle). While chemical reactions do take place, they simply bind together different parts of the large molecules that compose rubber and plastic. These new bonds add to the rigidity of the material, but the particles of the substances remain the same.
So, to find which change is a physical change and which change is a chemical change, we have to make sure that we put the factors of the changes into account to make sure that they are not mixed-up.
Monday, August 3, 2009
Physical properties can be observed without changing the type of matter. Examples of physical properties include: texture, shape, size, colour, odour, volume, mass, weight, and density. An example of a physical change occurs when making a baseball bat. Wood is carefully crafted into a shape which will allow a batter to best apply force on the ball. Even though the wood has changed shape and therefore physical properties, the chemical nature of the wood has not been altered. The bat and the original piece of wood are still the same chemical substance. In my next post, i will tell you on different examples of chemical changes and physical changes.
Sunday, August 2, 2009
A primary example of a chemical change is the combustion of methane to produce carbon dioxide and water.
• iron rusting (iron oxide forms)
• gasoline burning (water vapor and carbon dioxide form)
• eggs cooking (fluid protein molecules uncoil and crosslink to form a network)
• bread rising (yeast converts carbohydrates into carbon dioxide gas)
• milk souring (sour-tasting lactic acid is produced)
• suntanning (vitamin D and melanin is produced)
Physical change rearranges molecules but doesn't affect their internal structures. Some examples of physical change are:
• whipping egg whites (air is forced into the fluid, but no new substance is produced)
• magnetizing a compass needle (there is realignment of groups ("domains") of iron atoms, but no real change within the iron atoms themselves).
• boiling water (water molecules are forced away from each other when the liquid changes to vapor, but the molecules are still H2O.)
• dissolving sugar in water (sugar molecules are dispersed within the water, but the individual sugar molecules are unchanged.)
• dicing potatoes (cutting usually separates molecules without changing them.)
Thursday, July 30, 2009
Energy changes, whether released or absorbed, like fireworks, as it releases energy in the form of light that can be seen.
Odour changes, when food spoils, they undergo chemical changes. Like the egg, if it is rotten they smell differently from fresh eggs. Production of gases or solids from the chemical changes, when wood is burned, they turn into ashes and gases, and it can’t be reversed, thus it is a chemical change.
And chemical changes are not easily reversed, unlike physical reactions. Think about ice for a moment. After ice melts into liquid water, you can refreeze it into solid ice if the temperature drops. Freezing and melting are physical changes. The substances produced during chemical changes however cannot easily change back into the original substances. The most important thing for you to remember is that in a physical change the composition of a substance does not change and in a chemical change the composition of a substance does change.
Wednesday, July 29, 2009
First, i will tell you what is a chemical change and the factors that shows that is is a chemical change.
A chemical change is a change in matter that occurs on the molecular level. Mostly, this change is irreversible, meaning you can’t go back after the change has been done. Say you have a nail made of iron. Now you cut that piece in half. Is it still iron?
Take an identical nail made of iron and throw it into a blazing hot campfire. Assume that the campfire is so hot that the iron begins to melt. Is it still iron?
Again, take another nail made of iron and let it sit outside and rust. Is it still iron?
In the example with the iron nail, the first two changes are physical changes, because the end product is still iron. You cut it in half, it is still iron. You melt it, even though it is shaped differently, it is still iron. However, if the iron rusts you can’t take rust and make it into iron again. Therefore, the rusting of iron is a chemical change. It also turns out that you can change rust back into iron, but it takes so much energy that it almost never happens. How can you tell whether a change is a chemical change? It is actually very easy here are the factors: Colour changes, whether the item releases or absorbs energy, odour changes and production of gases or solids.
Saturday, July 11, 2009
Many of these adaptations can be seen in the mouth of snakes. Since snakes are terrestrial, many changes occur in the salivary glands in the transition from an amphibian to a reptile. These changes in salivary glands and venom glands aid in the immobilizing and swallowing of their prey. The salivary glands found in snakes include the palatine, lingual, sublingual and labial gland. These glands help moisten the prey for swallowing. In venomous and poisonous snakes, such as the Water Moccasin, poison glands are modifications of the labial glands, lying on either side of the head and neck and lead to ducts in the modified front teeth. The teeth of snakes also underwent changes. Venomous snakes have grooved or tubular teeth for the injection or shooting of venom, while vipers have large retractable, tubular teeth.
Directly inside the mouth of snakes is the buccal cavity. This leads to the oesophagus of the snake. In snakes, the oesophagus is very long and may be as long as half the length of the body. The oesophagus of snakes has more internal folds than other reptiles, which allows for the swallowing of large, whole prey. Peristaltic movement by the walls of the oesophagus moves the food downward towards the stomach.
The stomach is a j-shaped organ in which most of the digestion occurs in snakes. The cells of the stomach secrete digestive enzymes and gastric juices that breakdown proteins. The food then passes through the pyloric valve and into the small intestines.
The small intestines are a long narrow coiled tube where absorbance of nutrients takes place. The small intestines is divided into three regions: the duodenum, the ileum, and jejunum.(Same as a human) The liver, which primarily functions in excreting nitrogenous wastes, storing nutrients, and producing bile, excretes digestive enzymes into the duodenum of the small intestines. Also, the pancreas, which produces insulin and glycogen as well, produces digestive enzymes such as lipases, proteases and carbohydrases and secretes them into the duodenum.(Also the same as in a human)
The food moves from the small intestines to the large intestines, through the caecum. The large intestines are the least muscular and most thin-walled structure of the snake digestive system. It passes into the cloacae chamber. This chamber is divided into a copradaeum for receiving faeces and an urodaeum for urine and products of the genital organs, it also absorbs excess water from the faeces, before it is passed out. The rate of their digestion is most dependent on body temperature because they are cold-blooded animals, if their body is heated up, then their digestion will be faster than a snake which is not heated up.
Friday, July 10, 2009
The digestive system consists of a foregut formed from the mouth region (stomodaeum), a hindgut formed similarly from the anal region (proctodaeum), and a midgut (mesenteron). The foregut and hindgut are lined by cuticle continuous with that on the body surface. The mouth is followed by the muscular pharynx, which functions in sucking and swallowing, and the esophagus, which may be enlarged to form a crop. The crop discharges into the midgut, sometimes, as in cockroaches, by way of a muscular gizzard or proventriculus. The termination of the midgut is marked by the attachment of the malpighian tubules, the chief organs of excretion. The hindgut commonly consists of a narrow ileum followed by a larger and often thick-walled rectum, which discharges at the anus.
Digestive enzymes, secreted not only by the salivary glands but also by the cells of the midgut and its diverticula, vary with the diet of the insect. The most important enzyme secreted by the salivary glands is amylase; the midgut secretes several enzymes including protease, lipase, amylase, and invertase. The products of digestion are absorbed chiefly in the midgut.
The hindgut receives food residues from the midgut as well as waste products from the malpighian tubules. The end products of nitrogen metabolism are uric acid, small amounts of amino acids, and urea; in aquatic insects, ammonium salts may be a major form for nitrogen excretion. In the rectum, the epithelial cells lining the gut wall often are enlarged, particularly in restricted areas where they form rectal glands. The epithelial cells of these glands are supplied richly with tracheae and function in the reabsorption of water and ions. The rectal contents of insects that inhabit dry environments commonly are reduced to dry fecal pellets prior to discharge. In many insects, particularly those which feed on relatively dry foods (e.g., beetles infesting stored grain), the upper segments of the malpighian tubules are bound by a sheath to the rectal surface and form a cryptonephridial system that serves to increase the capacity of the rectum for reabsorbing water and salts. The products of digestion, discharged into the hemocoele, or general body cavity, are transported by the circulatory fluid, or hemolymph, to the organs.
In my next post, i will be posting about the digestive system of reptiles.
Wednesday, July 8, 2009
The digestive system of birds is complex for the size of most birds. A small bird can eat up to twenty percent of its body weight daily. Birds have an extremely high metabolism so to keep up with the requirements bird must eat a large amount of food.
The digestive system of the bird begins with the beak and tongue. Evolution has eliminated the teeth in birds. Birds have a very strong beak. The beak and the tongue are modified according to the diet and the environment of the bird. The curved beak and thick tongue of a macaw are well adapted to breaking large nuts and climbing. The long curved beak of a hummingbird is suitable for drinking nectar. The beak grows constantly and must be worn down by climbing and cracking nuts. When a bird eats it uses its beak and tongue to gather food. Since a bird has no teeth, chewing time is eliminated. Since a bird does not have to chew its food they can often eat a large quantity of food at one time. Saliva lubricates the food much like in a human so that it can pass to the esophagus. The oesophagusis a tube-like structure which passes food in waves better known as peristalsis, to an organ known as the crop.
The crop separates birds from many animals because it is an organ that is exclusive to these animals. A crop’s main function is to store food. It is like an extra fuel tank for the bird. The crop is located at the base of the neck and can be easily seen after a bird has just eaten. If you have a pet bird a sure way to tell if a bird is full is to look at the size of the crop. If the crop is large in size the bird is probably full. If the crop is deflated and has a flat appearance the bird has not eaten yet. The crop continuously supplies small amounts of the food to the stomach.
The food passes from the crop to the stomach, the most active part of the digestive system of a bird. There are two parts to the stomach of a bird. The first part is known as the proventriculus. This is the glandular portion of the stomach. This portion secretes digestive juices which break down the food. In a popular breed of pet bird, the budgie stomach can produce what is known as crop milk which the budgies can feed to their young. The proventriculus joins a large muscular portion of the stomach known as the ventriculus, or more commonly known as the gizzard.
The gizzard grinds up food even more. The gizzard contains gravel, or girt, which works alongside with muscles in grinding up food. Some birds have gizzards that are so powerful they could grind up needles of steel in a matter of hours. In birds that ingest whole seeds a gizzard is very important. In these birds digestive enzymes alone cannot effectively break the seed hull. This is where the gizzard comes in to help. These birds require a large amount of grit in their diet. Larger birds such as the parrot that tend to de-hull their seeds do not require such a continuous supply of grit in their diets.
After leaving the gizzard the food is passed on to the small intestine where it mixes with bile and enzymes. The enzymes help with the breakdown of sugars, fats and proteins. Bile from the liver breaks down the larger fat molecules. The nutrients are then absorbed and passed on to the blood stream.
The liver of the bird has two equal lobes and is nestled next to the heart under the rib cage. Like in humans, the liver acts as a detoxifier, purifying toxins that enter the bloodstream and it recycles red blood cells some which are used to create bile. In some birds the bile is stored in the gallbladder. In birds such as the budgie, and some members of the parrot family lack a gallbladder.
The pancreas in birds is located near the small intestine. The first function of the pancreas is to neutralize acids that are found in the mixture passed on from the stomach. If this does not occur serious damage could occur to the intestine of the bird. Another major function of the pancreas is to produce insulin so that all the bird’s cells are supplied with glucose.
Some birds have an appendix or cecum which helps in the digestion of grains and fibers. This is not present is some members of the parrot family.
Whatever does not get digested is passed through the single opening in the urogenital system known as the cloaca or vent. The waste is excreted in the form of bird droppings. Birds tend to make droppings often because they have such a high metabolism and eat often. If your bird is a seed eater its droppings should have a firm greenish or brown part, this is the feces, and the dropping should have a white pasty part, this is the urine. A normal healthy bird should have anywhere from 25 to 50 eliminations a day. There are several reasons why a bird can have loose droppings. It is recommended that you should never drastically change your bird’s diet. If this has occurred it might cause diarrhea in your bird and should be taken to the vet immediately. Stress can also cause this condition in birds. It is rare for a bird to have constipation and if you find this happening in your pet bird you should consult a veterinarian.
A bird’s digestive system is extremely efficient because it has to be to keep up with the metabolic reactions the bird has. Birds that are fruit eaters can digest berries in thirty minutes, and seed eaters usually digest their food within three hours.
In my next post i will be posting about the digestive system of the insects.
Tuesday, July 7, 2009
In the human body, the mouth is a specialized organ for receiving food and breaking up large organic masses. In the mouth, food is changed mechanically by biting,chewing and grinding. In the mouth, food is moistened by saliva, a sticky fluid that is produced from the salivary glands. The saliva contains an enzyme called amylase, which digests starch molecules into smaller molecules of maltose.
During chewing, the tongue moves food about and manipulates it into a mass called a bolus. The bolus is pushed back into the throat and is forced through the opening to the oesophagus or in other words, the gullet.
The oesophagus is a long, narrow, muscular tube located behind the windpipe that extends through the neck and chest to the stomach. The bolus of food moves through the esophagus by peristalsis: a rhythmic series of muscular contractions that propels the bolus along. The contractions are assisted by the pull of gravity.
At the junction of the esophagus and stomach, there is a ringlike muscle, called the lower esophageal sphincter, closing the passage between the two organs. As food approaches the closed sphincter, the sphincter relaxes and allows the food to pass through to the stomach.
The stomach has three mechanical tasks. First, it stores the swallowed food and liquid. To do this, the muscle of the upper part of the stomach relaxes to accept large volumes of swallowed material. The second job is to mix up the food, liquid, and digestive juice produced by the stomach. The lower part of the stomach mixes these materials by its muscle action. The third task of the stomach is to empty its contents slowly into the small intestine.
In the stomach, gastric juice is produced by the linings of the stomach and it contains hydrochloric acid and proteases. Proteases in the stomach digest the proteins in the food eaten into shorter chains of amino acids, while the hydrochloric acid provides the acidic condition needed for the proteases to work. The hyfrochloric acid also kills bacteria which may have been swallowed in together with food. The cells lining the stomach also produces a thick layer of mucus which coats the inner stomach walls and prevents the stomach from digesting itself and from the corrosive effects of the hydrochloric acid.
The small intestine is about 6 meters (20 feet) long. It is coiled in the center of the abdominal cavity . The small intestine is divided into 3 sections: upper, jejunum, and ileum. The lining of the small intestine secretes a hormone called secretin, which stimulates the pancreas to produce digestive enzymes.The small intestine is where the most extensive part of digestion occurs. Most food products are absorbed in the small intestine.
The large intestine has a larger width but is only 1.5 meters (5 feet) long. The large intestine is divided into 6 parts: cecum, ascending colon, transverse colon, descending colon, sigmoid/transverse colon, and rectum.The large intestine is responsible for absorption of water and excretion of solid waste material. Food and waste material are moved along the length of the intestine by rhythmic contractions of intestinal muscles; these contractions are called peristaltic movements. Waste is solid because most of the water has been removed by the intestines as it travels through them.
In the next post, I will be posting about the digestive systems of birds.