The Different Cell Membrane Transport Mechanisms Essay Example for Free

The Different Cell Membrane Transport Mechanisms Essay The different cell membrane transport mechanisms The cell membrane is referred to as a ‘fluid mosaic model’ because the protein part within the cell membrane used to be though of as an even layer spread over the outside and the inside of the phospholipid. Now we are starting to think that it is spread unevenly, more like a mosaic than a layer. The phospholipid part of the cell membrane is fluid; this means that its molecules are constantly moving about. Through the molecules constantly moving about it allows for things such as ‘transient gaps’ to occur, these are gaps within the phospholipids which allow molecules to pass through; they are only temporary. Here is a picture of the fluid mosaic model: [pic] Both water-soluble (hydrophilic) and lipid soluble (hydrophobic) substances are able to pass across the cell membrane. It is easier for lipid-soluble compounds to pass relatively quickly through by dissolving in the lipid layer. Water needs to pass through via osmosis where as water-soluble substances cross the membrane through simple diffusion, facilitated diffusion and active transport. Osmosis is thought of as the diffusion of water from an area of high concentration of water molecules to an area of low concentration, across a partially permeable membrane. To define osmosis more accurately we define it in terms of water potential. Water potential is a measure of how easy it is for water molecules to move. Diffusion occurs because substances attract a ‘cloud’ of polar water molecules around them. The cloud is held by weak chemical bonds, including hydrogen bonds; this means that these water molecules cannot move freely. This is a picture of osmosis: [pic] Inside cells some solutes have a higher concentration inside than outside of the cell, this means in order to make it equal they need to move across the cell membrane against the concentration gradient. This means that they cannot get in by passive transport; passive transport is the diffusion of substances across a membrane, this is a spontaneous process and cellular nergy is not expended. Molecules will move from where the substance is more concentrated to where it is less concentrated. The rate of diffusion for different substances is not always the same even if the process is spontaneous; this is because membranes are selectively permeable. They must enter by way of a process known as active transport. It is called active transport because unlike passive transport it requires cellular energy. Active transport involves sp ecial molecules of the membrane called ‘pumps’. Pump molecules can pick up molecules and transport them to the other side of the molecule; where they are released by the pump. Pump molecules are globular proteins which span the lipid bilayer. The energy needed for active transport is used here; a reaction with ATP is required by the pump molecules to supply the metabolic energy to the process. Membrane pumps are specific to the particular molecules they work within; this is what makes selective transport. Here is a picture of active transport: [pic] Simple diffusion can take place in some of the carrier proteins found in the plasma membrane. Carrier proteins have binding sites which pick up specific molecules. They can only function in one direction and they require energy to change shape and move a solute. Simple diffusion is a passive process; this means that substances move down a concentration gradient and they do not need any input of energy from the cell, the rate of diffusion can be affected by a few things. Such as the difference in concentration between the area of high and the area of low concentration. The distance over which concentration occurs has an affect on the rate of diffusion; for example the thickness of the membrane which separates the areas of high and low concentration. The surface area which separates the area of high concentration from the area of low concentration affects the rate of diffusion. The higher the temperature is the more kinetic energy the particles possess and the faster they move; therefore this affects rate of diffusion. [pic] Facilitated diffusion is when diffusion is speeded up by specific proteins in cell membranes. These proteins are able to pass substances across the membrane faster than usual. Facilitated diffusion occurs along a concentration gradient and requires no metabolic energy, unlike active transport. There are only two types of proteins involved in facilitated diffusion; specific carrier proteins take particular substances, e. g. glucose, from one side of the membrane to the other. Ion channels are protein pores that can open or close to control the passage of selected ions, e. g. sodium and potassium. Facilitated diffusion occurs when molecules such as those that are soluble in water cannot pass through the phospholipids in the bilayer. When this happens they are transported across via the carrier proteins. Solute molecules moving about on either side of the membrane will randomly come into contact with their specific binding site. Once they bind, the protein changes shape and the molecules come off the binding site on the other side of the membrane. [pic] Both carrier proteins and ion channels are used during facilitated diffusion. Carrier proteins transport polar molecules across the membrane. The carrier protein is specific to the diffusing molecule. The molecule binds to the receptor on the carrier protein, and the protein changes shape (after an input of energy). The diffusing molecule ends up on the other side of the cell, where it is released. Ion channels are used for the transport of inorganic ions. They facilitate the diffusion of charged particles. The channels are lined with polar molecules. The charge particles move towards regions of opposite charge. The ion channels are usually specific to one particular ion.

Catholic scandal :: essays research papers

Bishops Acknowledge Role in Crisis DALLAS (AP) - America's Roman Catholic bishops opened their historic meeting on clerical sex abuse Thursday by bluntly acknowledging that their mistakes helped cause the crisis, then yielding the floor to victims who described how pain permeated their lives. Photos AP Photo Slideshows AP Photo Catholic Church Abuse Controversy Audio/Video Victims Demand Zero Tolerance, More Accountability for Church Leaders (WFAA, Dallas) Bishops Open Priest Sex Abuse Talks (AP) The bishops followed the morning session by going behind closed doors to take up proposals aimed at reforming the way the church handles abuse claims. Whether to adopt a zero tolerance policy — ousting any priest found guilty of a single case of abuse — was among the decisions facing them. The closed-door talks could continue into the evening. Public debate and action was scheduled Friday. Outside the hotel where the meeting was being held, about 50 people protested the church's handling of abuse cases. There were no arrests. Bishop Wilton Gregory, president of the United States Conference of Catholic Bishops, opened the meeting with a remarkably direct address, calling the crisis "perhaps the gravest we have faced." Abuse victim Michael Bland, of Chicago, told the bishops how he joined the priesthood but then left after trying to convince church leaders to take action against his molester. He urged the prelates to get rid of all those who abuse children. "The priesthood lost me but kept the perpetrator," Bland said. "The church has taken care of him." Gregory pledged to take action to restore parishioners' badly shaken faith in the church hierarchy. "The crisis, in truth, is about a profound loss of confidence by the faithful in our leadership," he said. That's "because of our failures in addressing the crime of the sexual abuse of children and young people by priests and church personnel." He admitted "we did not go far enough to ensure that every child and minor was safe from sexual abuse. Rightfully, the faithful are questioning why we failed to take the necessary steps." The bishops rarely allow lay Catholics to speak at their meetings, but three Catholic thinkers who have been following the abuse crisis were given the chance to address the church leaders after Gregory. They were followed by the abuse victims. Bland said he came forward with his molestation claim while he was still a priest. Suddenly, he felt he "was no longer one of the good guys but one of the victims to be dealt with.

Logitech Case Essay

1.In a world without trade, what would happen to the costs that American consumers would have to pay for Logitech’s Products? World trade refers to buying and selling across national borders. It would be difficult to predict or estimate the prices of the product of one company like Logitech in one market like America. 2.Explain how trade lowers the costs of making computer peripherals such as mice and keyboards. 1. Components are procured from any part of the world where they can be produced and manufactured at the best cost. (Motorola plant in Malaysia makes the mouse’s chip; Agilent Technologies supplies optical sensors). 2. The intellectual capital going into any product is created at the place where the right talent is available. (Ergonomics design is done in Ireland, software programming is done in Switzerland and Fremont). 3. The actual assembling/manufacturing is done at the place where is can be done most cost effectively. (Assembling is done in Taiwan and China). 4. The products reach the customers the most efficient way by taking the service s of the most efficient logistics company. (Marketing and operations from Fremont). 3.Use the theory of comparative advantage to explain the way in which Logitech has configured its global operation. Why does the company manufacture in China and Taiwan, undertake basic R&D in California and Switzerland, design products in Ireland, and coordinate marketing and operations from California? Comparative advantage, as proposed by Ricardo, says that it is beneficial for nations to involve in trade even when there is absolute advantage for them to produce all the goods. So nations will invest a major portion of their resources to produce what they can produce with advantage. This theory is being applied to the case in the following way 4.Who creates more value for Logitech – the 650 people it employs in California and Switzerland, or the  4,000 employees at its Chinese factory? What are the implications of this observation for the argument that free trade is beneficial? Logitech make $8 for every mouse being sold. Let us assume that $3 of this is spent on R&D and software programming. Free trade is beneficial because, it is the free trade which is allowing Logitech to take advantage of the low cost manpower available in China. If free trade w ere not available, Logitech would be forced to manufacture it’s mice in U.S. at a much higher cost. 5.Why do you think the company decided to shift its corporate headquarters from Switzerland to Fremont? It helps Logitech to stay close to its customers. It can respond to the demands of the customers more promptly. Fremont is also the place where a lot of technological innovations are happening. Logitech being in the high-tech industry, continuous innovation is a key success factor for its business. Fremont is also an important in terms of managerial talent. All these reasons make it convenient for Logitech to move to Fremont. 6. To what extent can Porter’s diamond help explain the choice of Taiwan as a major manufacturing site for Logitech? Porter’s diamond considers four important attributes which will create an environment that helps the domestic industries. The four attributes can be applied to Taiwan becoming a manufacturing hub for electronics goods as shown below:Taiwan has well qualified people for manufacturing electronic goods. It has good infrastructure and transport facility. There is demand throughout the world for electronic products produced in Taiwan. All major global companies source their electronic components from Taiwan. Taiwan has a well-developed supply base for parts and rapidly expanding local computer industry. There is tough competition and rivalry among local companies which help in better efficiency. The government has created Science-based industrial parks through which they encourage companies to invest in Taiwan. Land is given at very subsidized rates in these parks. 7. Why do you think China is now a favored location for so much high-technology manufacturing activity? How will China’s increasing involvement in global trade help that country? How will it help the world’s developed economies? What potential problem are associated with moving to China? All the factors in Porter’s diamond are at play in China very efficiently. It has huge human resources, land, water and other natural resources. It has good infrastructure for transportation, ports and communication. It has created special zones for promoting exports, thus ensuring a good demand for the goods they manufacture. The rivalry among the domestic firms is also very strong. Government supports export oriented firms through funds. The cost of labor is very low. Technical human skills are available. These factors make China a favored location for high-technology manufacturing. China’s increase in global trade will ensure that investment flows into China for manufacturing. Its balance of payment position will become very strong. It can use the trade as a lever for political mileage. As more investment happens it w ill help China to reap the advantages of economics of scale. It can provide better living conditions for its citizens. It will also generate funds for planned investments. The world’s developed economics will be able to take advantage of the low cost manufacturing available in China. The global companies can improve the efficiency of their supply chain by manufacturing in China. The following are the potential problems associated with moving work to China: The political changes, when they happen, can lead to disruption of work. Decision making at the government level is opaque, which can cause problems if unfavorable decisions are taken. When there is trouble in the political relationship between the home country and China. The companies may lose an opportunity to develop an alternate to China as a manufacturing hub.

Theme, Theme And Themes InBattle Royal, By Ralph Ellison

An author uses setting, character, plot, theme, language, and point-of-view to express their thoughts into their writing, and as a reader, one perceives what they write. Each characteristic of a story further develops the ideas differently. The setting of a story can develop the idea further with the time frame of the story, giving the reader a historic background; whereas the language can distinguish the mood and tone of the story. By looking at all these elements of a story, people are able to find a central idea of a piece. In â€Å"Battle Royal,† Ellison expresses the idea of segregation throughout the story, mainly focusing on the social responsibility of the whites and blacks with the conflicts that take place, externally and internally.†¦show more content†¦The protagonist is finally seeing an environment around him where his grandfather is right. The protagonist uses the grandfather’s advice to then write a speech. In the short story â€Å"Battle Royal,† the narrator is then invited to read his speech to the leading white citizens at the hotel ballroom. It is at this event where everything changes. As the narrator arrives, he expects to give his speech, but in reality, he shows up to a battle royal. At the battle royal, the white men trick the blacks with fake coins. The protagonist had a decision to make: follow what he is told by the white citizens, or stand up for his rights. In the short story: â€Å"[The protagonist] lunged for a yellow coin lying on the blue design of the carpet, touching it and sending a surprised shriek to join those around me. [He] tried frantically to remove my hand but could not let go. A hot, violent force tore through [his] body, shaking [him] like a wet rat. The rug was electrified. The hair bristled up on [his] head as [he] shook [himself] free. [The narrator’s] muscles jumped, [his] nerves jangled, writhed† (Ellison 1217). This quote represents the chaos that went on in the hotel ballroom. The black men were tricked by the white people with coins on an electrocuted rug. As they picked up a coin, they would get electrocuted. The blacks were not expecting the torture they had went through. As the blacks were being tortured, the whites just sat there laughing; it was all just a