Theories of group formation

Be able to recognize a nail as a fastening device from a non-fastening devices. Cognitive structures are used to provide meaning and organization to experiences and allows the individual to go beyond the information given. According to Bruner, the instructor should try and encourage students to construct hypotheses, makes decisions, and discover principles by themselves Kearsley b.

Theories of group formation

Short half-life corresponds to high reactivity.

Theories of group formation

The one nanosecond half-life of the hydroxyl radical indicates that it is so reactive that it reacts with the first molecule it bumps into. Ascorbate forms H2O2 on autoxidation direct Theories of group formation with oxygen.

Lipid peroxidation of polyunsaturated fatty acids exposed to oxygen leads to rancidity in foods. In living animal cells peroxidized membranes lose their permeability, becoming rigid, reactive and nonfunctional.

Lipid peroxidation can produce singlet oxygen, hydroperoxides and lipid epoxides. MDA is a major metabolite of arachidonic acid Aldehyde-bridge formation leads to the protein-protein cross-linking associated with lipofuscin formation.

Polyunsaturated fatty acids are more vulnerable to free radical oxidation than any other macromolecules in the body — and the sensitivity to free radical damage increases exponentially with the number of double bonds. Animal cells contain three important enzymes to deal with the superoxide and hydrogen peroxide: A dismutase is an enzyme that catalyzes the reaction of two identical molecules to produce molecules in different oxidative states.

In the absense of SOD, two superoxide ions can spontaneously dismutate to produce hydrogen peroxide and singlet oxygen. SOD catalyzes a reaction between two superoxide ions to produce hydrogen peroxide and triplet oxygen. CAT is present in membrane-limited organelles known as peroxisomes.

Glutathione is a tripeptide composed of the amino acids cysteine, glycine and glutamic acid. Glutathione is the major antioxidant in the non-lipid portion of cells most of the cytoplasm.

Reduced glutathione hydrogen donation can neutralize a hydroxyl radical: The elimination of hydrogen peroxide by glutathione can be written as the reaction: The liver, in particular, is very high in SOD. Cellular concentration of SOD relative to metabolic activity is a very good lifespan predictor of animal species.

Most mammals experience a lifetime energy expenditure ofcalories per gram, but humans have an amazingcalories per gram. Humans have the highest levels of SOD — relative to metabolic rate — of all species studied. Oxidative damage to DNA is ten times greater in rats than in humans.

Superoxide dismutase without glutathione peroxidase or catalase CAT to remove hydrogen peroxide is of little value.

Insects lack glutathione peroxidase, but experiments have been performed on fruit flies made transgenic by having extra genes for SOD, CAT or both. Radiation produces the hydroxyl radical, but most of the oxygen free radicals are byproducts of cell metabolism — particularly in the mitochondria, the lysosomes and the peroxisomes.

One of the reasons these organelles are surrounded by membranes may be to protect the cell from the free-radicals they generate.

DNA may be sequestered in the nucleus, in part, as additional protection against free radicals. Nonetheless, free radicals contribute to DNA damage and mutation. In addition to enzymes, the animal cell uses many other chemicals to protect against oxygen free-radicals. Melatonina hormone produced by the pineal gland in decreasing quantities with aging, efficiently crosses membranes including the nucleus and is effective against hydroxyl radicals.

Uric acid also protects against free-radical catalysis by binding iron.Miscellaneous Sites. ACT Research Home Page- The ACT group is led by John Anderson at Carnegie Mellon University and is concerned with the ACT theory and architecture of goal of this research is to understand how people acquire and organize knowledge and produce intelligent behavior.

This article throws light on the four important theories of group formation, i.e, (1) Propinquity Theory, (2) Homan’s Theory, (3) Balance Theory, and (4) Exchange Theory. Theories of Group Formation: 1. Propinquity Theory: The most basic theory explaining affiliation is propinquity.

Edwin Powell Hubble

Doubt cast on new theories of star formation New findings reveal surprising distribution of star-forming cores outside of our galaxy Date: April 30, Refining and extending Erik Erikson’s work, James Marcia came up with four Identity Statuses of psychological identity development.

The main idea is that one’s sense of identity is determined largely by the choices and commitments made regarding certain personal and social traits. Theories of Group Formation Below is an explanation of the different models of group formation processes by Lewin, Tuckman, McGrath, and Gersick including the major features, steps, and characteristics.

The vast range of maximum lifespan differences between species provides convincing evidence that longevity is genetically influenced. An elephant lives about 10−20 times longer than a mouse, yet both animals have roughly the same number of lifetime heartbeats — the elephant at 30 per minute and the mouse at per minute.

Group development - Wikipedia