Fermentation

June 23, 2011 by · Leave a Comment 

scan0009Fermentation, process by which the living cell is able to obtain energy through the breakdown of glucose and other simple sugar molecules without requiring oxygen. Fermentation is achieved by somewhat different chemical sequences in different species of organisms. Two closely related paths of fermentation predominate for glucose. When muscle tissue receives sufficient oxygen supply, it fully metabolizes its fuel glucose to water and carbon dioxide. However, at times of strenuous activity, muscle tissue uses oxygen faster than the blood can supply it. During this anaerobic condition, the six-carbon glucose molecule is only partly broken down to two molecules of the three-carbon sugar called lactic acid. This process, called lactic acid fermentation, also occurs in many microorganisms and in the cells of most higher animals. In alcoholic fermentation, such as occurs in brewer’s yeast and some bacteria, the production of lactic acid is bypassed, and the glucose molecule is degraded to two molecules of the two-carbon alcohol, ethanol, and to two molecules of carbon dioxide. Many of the enzymes of lactic acid and alcoholic fermentation are identical to the enzymes that bring about the metabolic conversion known as glycolysis. Alcoholic fermentation is a process that was known to antiquity. Before 2000 B.C. the Egyptians apparently knew that crushed fruits stored in a warm place would produce a substance with a pleasant intoxicating power. By 1500 B.C. the production of beer from germinating cereals (malt) and the preparation of wines from crushed grapes were established arts in most of the Middle East. Aristotle believed that grape juice was an infantile form of wine and that fermentation was, therefore, the maturation of the grape extract. Interest in the process of fermentation has continued through the ages, and much of modern biochemistry, especially enzyme studies, has emerged directly from early studies on the fermentation process. One of the earliest laboratories established for the study of biological chemistry was that founded in Copenhagen in 1875 and financed by the brewing family of Jacob Christian Jacobsen.

Fermentation is one of the oldest known food preservation techniques. Along with drying and salting, fermentation was a key method of extending the life of foods, allowing them to be available, and eaten safely, in times of scarcity or seasonal nonavailability. These methods helped allow the transition from hunting and gathering to organized food cultivation and storage, which took place some ten to fifteen thousand years ago in the Middle East.

Fermentation involves the action of desirable microorganisms, or their enzymes, on food ingredients to make biochemical changes, which cause significant modification to the food. Often lactic-acid bacteria convert the carbohydrate energy source of food, such as lactose in milk, to lactic acid; examples are yogurt and cheeses from milk, and pickles from fruits and vegetables. Alternatively, yeasts, often of the Saccharomyces species, may convert the glucose to ethanol and carbon dioxide in leavened breads, or the sugars in grain or fruit beverages to beers and wines. Molds also can be active in certain fermentations, such as Stilton cheese and soy sauce. It is estimated that about one-third of all the food we consume is fermented. World estimates for beer consumption are about 22 million gallons, and a total of 15 million tons of some one thousand varieties of cheese are eaten annually.

13-26

Leaves

September 3, 2009 by · Leave a Comment 

tufail

1. A usually green, flattened, lateral structure attached to a stem and functioning as a principal organ of photosynthesis and transpiration in most plants.

2. A leaflike organ or structure.

         1. Leaves considered as a group; foliage.

         2. The state or time of having or showing leaves: trees in full leaf.

3. The leaves of a plant used or processed for a specific purpose: large supplies of tobacco leaf.

4. Any of the sheets of paper bound in a book, each side of which constitutes a page.

         1. A very thin sheet of material, especially metal.

         2. Such leaves considered as a group: covered in gold leaf.

5. A hinged or removable section for a table top.

6. A hinged or otherwise movable section of a folding door, shutter, or gate.

7. One of several metal strips forming a leaf spring

The foliage leaf is the chief photosynthetic organ of most vascular plants. Although leaves vary greatly in size and form, they share the same basic organization of internal tissues and have similar developmental pathways. Like the stem and root, leaves consist of three basic tissue systems: thedermal tissue system, the vascular tissue system, and the ground tissue system. However, unlike stems and roots which usually have radial symmetry, the leaf blade usually shows dorsiventral symmetry, with vascular and other tissues being arranged in a flat plane.

Stems and roots have apical meristems and are thus characterized by indeterminate growth; leaves lack apical meristems, and therefore have determinate growth. Because leaves are more or lessephemeral organs and do not function in the structural support of the plant, they usually lack secondary growth and are composed largely of primary tissue only. See also Apical meristem; Root (botany); Stem.

The internal organization of the leaf is well adapted for its major functions of photosynthesis, gas exchange, and transpiration. The photosynthetic cells, or chlorenchyma tissue, are normally arranged in horizontal layers, which facilitates maximum interception of the Sun’s radiation. The vascular tissues form an extensive network throughout the leaf so that no photosynthetic cell is far from a source of water, and carbohydrates produced by the chlorenchyma cells need travel only a short distance to reach the phloem in order to be transported out of the leaf (Fig. 7). The epidermal tissue forms a continuous covering over the leaf so that undue water loss is reduced, while at the same time the exchange of carbon dioxide and oxygen is controlled.

11-37

Bumps on the Head

July 23, 2009 by · Leave a Comment 

tufail

Bumps that go away when you bump your head and others don’t has to do with the severity of the damage to the underlying tissue. When you bump your head, you get a bruise because you break small blood vessels under the skin and the blood pools causing discoloration and swelling in the surrounding tissue. As the blood clot (hematoma) breaks down it gets reabsorbed and disappears. If you whack your head hard enough you could damge the skull, the bone may be injured but not broken.  You can hurt your skull without causing a fracture. As the bone heals, it could get thicker in the damaged area. The same way your skin might form a scar. You could wind up with a knot that doesn’t go away.

Bumps on the head, even large ones, don’t always warrant a trip to the ER or even a call to your doctor. However a hard hit may shake up the brain – called a concussion, also blood can slowly leak out from a damaged blood vessel beneath the skull, called a hematoma–that push into the brain tissue. Larger hematomas can push into the brain tissue. This can either happen very quickly within an hour, or it can take two or three days. This is an emergency and requires a CAT scan of the head to diagnose. Remember, considering the many times children hit their head, injury to the brain is unusual. Most bumps on the head, even large ones, are not serious.

Loss of consciousness. If your child blacks out, even for a few seconds, this can mean that the force of the bump was strong enough to cause a hematoma. A reassuring sign is that you either hear or see your child start to cry immediately after the bump. This means he did not lose consciousness. If your child is unconscious, but breathing and pink (no blue lips), lay her on a flat surface and call emergency medical services. If you have cause to suspect a neck injury, don’t move the child but let the trained experts in neck injuries transport her.

Be very careful if your child has a head injury.

11-31