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Lunes, Marso 12, 2012
Multi grade Teaching
Teaching and Learning in the Multigrade Classroom: Student Performance and Instructional Routines. ERIC Digest.
The multigrade classroom is an organizational pattern widely used in schools in the United States. Typically a feature of small-scale schooling, multigrade classrooms are today getting a closer look. This Digest, written for practitioners, parents, and policymakers, brings together recent information on the topic. It considers the history of the multigrade classroom, its effects on achievement and attitude, and the requirements of teaching and learning in multigrade classrooms.
HISTORY AND BACKGROUND
In 1918, there were 196,037 one-room schools, representing 70.8 percent of all public schools in the United States. By 1980, less than 1,000 of these schools remained (Muse, Smith, & Barker, 1987). But the multigrade classroom persists. For example, in a study consisting of multigrade classrooms of only two grades, Rule (1983) used a sample from a suburban district outside Phoenix, Arizona. Of the 21,000 elementary students in the district, approximately 17 percent were in classrooms that combined grades. In rural, small elementary schools the incidence of students served in multigrade classrooms may well be much higher.
Although rural, small schools may combine grades to save money, in the guise of the "ungraded classroom," multigrade organization has also been a feature of urban and suburban districts. In the 1960s and 1970s, "open education" and individualized instruction became influential curriculum and instructional models. Such models were commonly implemented with multigrade classrooms. Energized by developmental theories of learning, a large influx in federal money, and student-centered models of instruction, open education became a major educational innovation. As a result, multigrade classrooms received new attention.
Numerous studies compared the effectiveness of "open" classrooms (multigrade organization with student-centered ethos and methods) and "regular" classrooms (single-grade organization with traditional ethos and methods). We have learned a great deal from these innovative efforts. Working in an open, multigrade school requires serious, ongoing teacher training and a commitment to hard work.
Most teachers have been trained to work in single-grade classrooms. Their knowledge of teaching method is based on whole-class instruction and small-group instruction (with groups often formed on the basis of ability or achievement level). When placed in a multigrade setting, teachers of the 60s and 70s discovered that the time requirements and skills needed to be effective were simply not part of their prior training and experience. Although the premises of "open" and "regular" (traditional) education can differ sharply, this finding still applies to multigrade classrooms in traditional schools.
THE NORM OF THE GRADED SCHOOL
The large-scale innovations of the 60s and 70s have virtually ended. But the multigrade classroom persists, especially in small, rural schools. Yet, here, as elsewhere, most people view graded schools as the natural way to organize education. This norm can be a handicap for anyone (whether out of necessity or by theoretical design) who wants to--or who must--work with multigrade classrooms or schools. Teachers of multigraded classrooms who face the biggest challenge may be those working in school systems in which single-grade classrooms are the norm.
For many rural educators, multigrade instruction is not an experiment or a new educational trend, but a necessity imposed, in part, by economic and geographic conditions. In an environment dominated by graded schools, the decision to combine grades can be quite difficult--especially if constituents feel shortchanged by the decision. Nonetheless, recent proposals for school restructuring reflect renewed interest in multigrade organization (Cohen, 1989) and in small-scale organization generally. Such work may eventually contest the norm of the graded school.
EFFECTS ON STUDENT PERFORMANCE
Many teachers, administrators, and parents continue to wonder whether or not multigrade organization has negative effects on student performance. Research evidence indicates that being a student in a multigrade classroom does not negatively affect academic performance, social relationships, or attitudes.
Miller (1990) reviewed 13 experimental studies assessing academic achievement in single-grade and multigrade classrooms and found there to be no significant differences between them. The data clearly support the multigrade classroom as a viable and equally effective organizational alternative to single-grade instruction. The limited evidence suggests there may be significant differences depending on subject or grade level. Primarily, these studies reflect the complex and variable nature of school life. Moreover, there are not enough such studies to make safe generalizations about which subjects or grade levels are best for multigrade instruction.
When it comes to student affect, however, the case for multigrade organization appears much stronger. Of the 21 separate measures used to assess student affect in the studies reviewed, 81 percent favored the multigrade classroom (Miller, 1990).
If this is the case, why then do we not have more schools organized into multigrade classrooms? One response is that history and convention dictate the prevalence of graded classrooms. However, there is a related, but more compelling, answer to be found in the classrooms themselves and in information drawn from classroom practitioners.
INSTRUCTIONAL AND ORGANIZATIONAL ROUTINES
The multigrade classroom can be more of a challenge than the single-grade classroom. Skills and behavior required of the teacher may be different, and coordinating activities can be more difficult. In fact, such a realization is one reason graded schools came into being in the first place (Callahan, 1962).
At first look, the skills needed to teach well in the multigrade and the single-grade (multilevel) classroom appear to be quite similar. The differences between the two sorts of classrooms may be more a product of socialization and expectation than of fact. Clearly, if a teacher in either sort of classroom fails to address differences among students, the effectiveness of instruction suffers. Likewise, teachers are harmed when they have not been adequately prepared to teach students with varying ages and abilities--no matter what sort of classroom they work in.
But what does the research tell us regarding the skills required of the multigrade teacher? When student diversity increases, whether it be in a multigrade or single-grade classroom, greater demand is placed on teacher resources, both cognitive and emotional.
Six key instructional dimensions affecting successful multigrade teaching have been identified from multigrade classroom research (Miller, 1991). Note that each of these points has some bearing on the related issues of independence and interdependence. It is important to cultivate among students the habits of responsibility for their own learning, but also their willingness to help one another learn.
1. Classroom organization: Instructional resources and the physical environment to facilitate learning.
2. Classroom management and discipline: Classroom schedules and routines that promote clear, predictable instructional patterns, especially those that enhance student responsibility for their own learning.
3. Instructional organization and curriculum: Instructional strategies and routines for a maximum of cooperative and self-directed student learning based on diagnosed student needs. Also includes the effective use of time.
4. Instructional delivery and grouping: Methods that improve the quality of instruction, including strategies for organizing group learning activities across and within grade levels.
5. Self-directed learning: Students' skills and strategies for a high level of independence and efficiency in learning individually or in combination with other students.
6. Peer tutoring: Classroom routines and students' skills in serving as "teachers" to other students within and across differing grade levels.
In the multigrade classroom, more time must be spent in organizing and planning for instruction. Extra materials and strategies must be developed so that students will be meaningfully engaged. This additional coordination lets the teacher meet with small groups or individuals, while other work continues.
Since the teacher cannot be everywhere or with each student simultaneously, the teacher shares instructional responsibilities with students. A context of clear rules and routines makes such shared responsibility productive. Students know what the teacher expects. They know what assignments to work on, when they are due, how to get them graded, how to get extra help, and where to turn assignments in.
Students learn how to help one another and themselves. At an early age, students are expected to develop independence. The effective multigrade teacher establishes a climate to promote and develop this independence. For example, when young students enter the classroom for the first time, they receive help and guidance not only from the teacher, but from older students. In this way, they also learn that the teacher is not the only source of knowledge.
Instructional grouping practices also play an important role in a good multigrade classroom. The teacher emphasizes the similarities among the different grades and teaches to them, thus conserving valuable teacher time. For example, whole-class (cross-grade) instruction is often used since the teacher can have contact with more students. However, whole-class instruction in the effective multigrade classroom differs from what one generally finds in a single-grade class.
Multigrade teachers recognize that whole-class instruction must revolve around open task activities if all students are to be engaged. For example, a teacher can introduce a writing assignment through topic development where all students "brainstorm" ideas. In this context, students from all grades can discuss different perspectives. They can learn to consider and respect the opinions of others (Miller, 1989).
Cooperation is a necessary condition of life in the multigrade classroom. All ages become classmates, and this closeness extends beyond the walls of the school to include the community.
REWARDS AND CHALLENGES
There are many rewards for teaching in the multigrade classroom, but there are challenges, too. Instruction, classroom organization, and management are complex and demanding. A teacher cannot ignore developmental differences in students nor be ill-prepared for a day's instruction. Demands on teacher time require well-developed organizational skills.
The multigrade classroom is not for the timid, inexperienced, or untrained teacher. Clearly, the implications for teacher educators, rural school board members, administrators, and parents are far-reaching.
Multigrade teaching involves the teaching of children from two or more grade levels in one classroom.
Such contexts requires the employment of particular teaching methodologies and classroom administration.
Since Multigrade classes are smaller and can be established more cheaply than complete schools, they can be more numerous, therefore more dispersed and thus located closer to the settlements where the children live. This means both that younger children can attend and that the time children spend travelling between school and home can be reduced to an acceptable level. This in turn means that there is sufficient time outside school hours for the children to continue to contribute to the family's economic activity . Attending school is therefore likely to be more acceptable to the families concerned, and thus both increase the number of children receiving education and reduce the failure rate.
Multigrade schools, being smaller and more dispersed, would enjoy much closer links with the smaller communities that they would be set up to serve.
This would have a very positive effect on local attitudes and access to education.
The professional teacher is a key resource person in the Multigrade context. The local content is a significant part of the curriculum, it is particularly important to resolve the issue of appointing well-trained and locally-oriented teachers.
Special Topic Course 1
Multi-grade teaching: Concept and status
Multi-grade teaching refers to the teaching of students of different ages, grades and abilities in the same group. It is referred to variously in the literature as 'multilevel', 'multiple class', 'composite class', 'vertical group', 'family class', and, in the case of one-teacher schools, 'unitary schools'. It is to be distinguished from 'mono-grade' teaching in which students within the same grade are assumed to be more similar in terms of age and ability. Substantial variation in ability within a mono-grade class often leads to "mixed-ability" teaching. Multi-grade teaching should also be distinguished from "multi-age-within-grade" teaching which occurs when there are wide variations in age within the same grade. This is common in developing countries, where the age of entry to school varies and where grade repetition is common. However, in North America, where age and grade are more congruent, the terms "multi-age" and "multi-grade" are often used synonymously.
Several writers have pointed out that the first state-supported elementary schools in North America and Europe were un-graded. The school often consisted of a single room in which one teacher taught basic literacy and numeracy to children from six to fifteen years of age. In the US the "death knell of the one room school was sounded" after a visit to Prussia by Horace Mann, the Secretary of the Massachusetts Board of Education, in 1843.
the first element of superiority in a Prussian school...consists in the proper classification of scholars. In all places where the numbers are sufficiently large to allow it, the children are divided according to ages and attainments, and a single teacher has the charge of only a single class... There is no obstacle whatever... to the introduction at once of this mode of dividing and classifying scholars in all our large towns (Mann quoted in Pratt 1986)
Urban education administrators in the US were soon to recommend that schools be divided on the lines of age and grade, a development which was consistent with the division of labour in industry. The "principle of the division of labour holds good in schools, as in mechanical industry" (Bruck quoted in Pratt 1986). The mono-grade model was to become a universal ideal in the late nineteenth and twentieth centuries and came to dominate the basis of school, class and curriculum organisation used by central authorities.
The persistence of the multi-grade reality towards the close of the twentieth century
Yet despite the ideal, the multi-grade reality has characterised hundreds of thousands of schools throughout the twentieth century and will continue to do so well into the twenty first. Although information about the extent of multi-grade teaching tends not to be collected on a regular basis, 1959 data were collected by UNESCO's International Bureau of Education (Table 1). Table 1 indicates the large number and proportion of teachers who were teaching in one-teacher schools in the late 1950s - some 2040% in countries of South and Central America, 16% in India, 25% in Turkey and 15% in the USSR. The percentage of teachers teaching in one-teacher schools in some of the European countries was also extremely high - 47% in Spain, 23% in Luxembourg, 20% in France, 10% in Switzerland. Figures in the US and UK were lower - 2.9% in the USA, 3.6% in Scotland, 2.3% in Northern Ireland and 0.7% in England and Wales (UNESCO/IBE 1961).
Comparable data for the late 1980s early 1990s are not available. Data on multi-grade teachers and schools do not appear to be collected systematically by national and international agencies. Table 2 synthesises available information from a wide variety of sources on the current status of multi-grade teaching. It expresses the incidence of multi-grade teaching at the primary school level in different countries in the years for which the most recent data are available. The several columns in Table 2 reflect the non-standard nature of available data. In some countries data on the number and percentage of one and two teacher schools are available. In others only the number and or the percentage of schools which have multi-grade classes are available; or the number of classes within a system which are multi-grade; or the number of teachers per school; or the percentage of teachers who teach multi-grade; or the percentage of students who study in multi-grade classes.
Table 2 suggests that in 1986 India had over 300,000 one or two teacher schools, representing more than 60% of all schools. In Sri Lanka the percentage is lower. However the seven hundred schools in Sri Lanka which have either one or two teachers are located in the most difficult environments in a country which has achieved near universal enrolment in primary school. In Malaysia too the multi-grade schools are located in those areas which are disadvantaged in several ways Malay and Chinese schools in small villages and settlements and in the remote, secluded areas of Sabah; Tamil schools in rubber estates and the aboriginal schools in the interior and remote areas of Peninsular Malaysia.
A multi grade class is defined as a class composed of two or more grades less than one teacher in a complete or incomplete elementary school. But when was this system introduced in the Philippines setting?
The Multi Grade System has been implemented since 1920’s. it has always been covered by policies on monograde class organization which resulted in multi grade classes. The multi grade system has been with us for quite some time but it is very obvious that we have not regarded it as a very viable alternative delivery system to provide access to basic education as well as quality education by providing complete grade levels in all public elementary schools.
While DECS (now DepEd) officials then had always recognized the existence of multi grade classes, it was only under the leadership of Secretary Armand Fabella (1993-1994) that the multi grade program was launched as a systematic and viable means of meeting the goal and providing education for all.
The existence of the multi grade classes in our country is also embodied under the provision of the Philippine Constitution. Considering the present thrusts of the government to make at least elementary education truly accessible to all particularly to children in remote barangays, a policy has been made and declared to build a school in all school-less barangays where enrolment and population growth trends warrant the establishment of a new school, and develop and /or implement the Multi grade System of Delivery, so as to enable children to complete their elementary schooling particularly in areas where it is uneconomical to put up a six-classroom building.
From then on, multi grade classes became truly a part of our educational system. at present, some of these multi grade classes were already converted to monograde classes due to increase of enrolment while other areas of the country are just starting to put up multi grade classes
The Multi Grade System has been implemented since 1920’s. it has always been covered by policies on monograde class organization which resulted in multi grade classes. The multi grade system has been with us for quite some time but it is very obvious that we have not regarded it as a very viable alternative delivery system to provide access to basic education as well as quality education by providing complete grade levels in all public elementary schools.
While DECS (now DepEd) officials then had always recognized the existence of multi grade classes, it was only under the leadership of Secretary Armand Fabella (1993-1994) that the multi grade program was launched as a systematic and viable means of meeting the goal and providing education for all.
The existence of the multi grade classes in our country is also embodied under the provision of the Philippine Constitution. Considering the present thrusts of the government to make at least elementary education truly accessible to all particularly to children in remote barangays, a policy has been made and declared to build a school in all school-less barangays where enrolment and population growth trends warrant the establishment of a new school, and develop and /or implement the Multi grade System of Delivery, so as to enable children to complete their elementary schooling particularly in areas where it is uneconomical to put up a six-classroom building.
From then on, multi grade classes became truly a part of our educational system. at present, some of these multi grade classes were already converted to monograde classes due to increase of enrolment while other areas of the country are just starting to put up multi grade classes
BASIC LESSONS IN GENETICS
· Genetics is the field of biology devoted to understanding how characteristics are transmitted from parents to offspring.
· Genetics was founded with the work of Gregor Johann Mendel. His work is with Pisum sativum. The pea characteristics that Mendel observed were plant height, flower position along stem, pod color, pod appearance, seed texture, seed color, and flower color.
· Heredity is the transmission of characteristics from parents to offspring.
· P generation refers to the true-breeding parents. F1 generation or filial generation is the offspring of the P generation. If you cross the F1 the second filial generation or F2 is the result.· Dominant is the trait appearing while recessive is the trait that is masked
· Law of Segregation states that a pair of factors is segregated or separated during the formation of gametes
· Law of Independent Assortment states that factors separate independently of one another during the formation of gametes.
· Most of Mendel’s findings agree with what biologists now know about molecular genetics.
· Molecular genetics is the study of the structure and function of chromosomes and genes.
· Chromosome is a threadlike structure made up of DNA.
· Gene is the segment of DNA on a chromosome that controls a particular hereditary trait
· Both chromosomes and genes occur in pairs. Each of two or more alternative forms of a gene is called an allele. Mendel’s factors are now called alleles. Letters are used to represent alleles. Capital letters refer to dominant alleles, and lowercase letters refer to recessive alleles.
Mendel’s law of independent assortment is supported by the independent segregation of chromosomes to gametes during meiosis. Therefore, the law of independent assortment is observed only for genes located on separate chromosomes or located far apart on the same chromosome.
Transplantation of a human kidney, heart, liver, pancreas, lung, and other organs is now possible due to two major breakthroughs.
First, solutions have been developed that preserve donor organs for several hours. This made it possible for one young boy to undergo surgery for 16 hours, during which time he received five different organs.
Second, rejection of transplanted organs is now prevented by immunosuppressive drugs; therefore, organs can be donated by unrelated individuals, living or dead. Even so, rejection is less likely to happen if the donor’s tissues “match” those of the recipient—that is, their cell surface molecules should be similar to one another. Living individuals can donate one kidney, a portion of their liver, and certainly bone marrow, which quickly regenerates.
After death, it is still possible to give the “gift of life” to someone else—over 25 organs and tissues from the same person can be used for transplants at that time. A liver transplant, for example, can save the life of a child born with biliary atresia, a congenital defect in which the bile ducts do not form. Dr. Thomas Starzl, a pioneer in this field, reports a 90% chance of complete rehabilitation among children who survive a liver transplant. (He has also tried animal-to-human liver transplants, but so far, these have not been successful.) So many heart recipients are now alive and healthy that they have formed basketball and softball teams, demonstrating the normalcy of their lives after surgery.
One problem persists: The number of Americans waiting for organs now stands at over 80,000 and is getting larger by the day. Although it is possible for people to signify their willingness to donate organs at the time of their death, only a small percentage do so. Organ and tissue donors need only sign a donor card and carry it at all times. In many states, the back of the driver’s license acts as a donor card. Age is no drawback, but the donor should have been in good health prior to death. Organ and tissue donation does not interfere with funeral arrangements, and most religions do not object to the donation.
Family members should know ahead of time about the desire to become a donor because they will be asked to sign permission papers at the time of death.
Especially because so many Americans are waiting for organs and a chance for a normal life, researchers are trying to develop organs in the laboratory. Just a few years ago, scientists believed that transplant organs had to come from humans or other animals. Now, however, tissue engineering is demonstrating that it is possible to make some bio-artificial organs—hybrids created from a combination of living cells and biodegradable polymers. Presently, lab grown hybrid tissues are on the market. For example, a product composed of skin cells growing on a polymer are used to temporarily cover the wounds of burn patients. Similarly, damage cartilage can be replaced with a hybrid tissue produced after chondrocytes are harvested from a patient. Another connective tissue product made from fibroblasts and collagen is available to help heal deep wounds without scarring. Soon to come are a host of other products, including replacement corneas, heart valves, bladder valves, and breast tissue.
The ultimate goal of tissue engineering is to produce fully functioning transplant organs in the laboratory. After nine years, a Harvard Medical School team headed by Anthony Atala has produced a working urinary bladder. After testing the bladder in laboratory animals, the Harvard group is ready to test it in humans, whose own bladders have been damaged by accident or disease,
or will not function properly due to a congenital birth defect. Another group of scientists has been able to grow arterial blood vessels in the laboratory. Tissue engineers are hopeful that they will one day produce more complex organs such as a liver or kidney.
· Cellular respiration is the complex process in which cells make ATP by breaking down organic compounds. Energy in ATP is used by cells to do work.
· Cellular respiration can be divided into two stages:
1. Glycolysis – organic compounds are converted into three C molecules of pyruvic acd, producing a small amount of ATP and NADH (an electron carrier molecule). It is an anaerobic process because it does not require the presence of oxygen.
2. Aerobic Respiration – if oxygen is present in the cell’s environment, pyruvic acid is broken down and NADH is used to make a large amount of ATP through the process known as aerobic respiration.
· If oxygen is not present in the cell’s environment, pyruvic acid can enter in to another anaerobic pathway called fermentation.
GLYCOLYSIS
· Glycolysis is a biochemical pathway in which one 6-C molecule of glucose is oxidized to produce two 3-C molecules of pyruvic acid. It is a series of chemical reactions catalyzed by specific enzymes.
· The major steps in Glycolysis are:
1. Two phosphate groups are attached to one molecule of glucose, forming new 6-C compound that has two phosphate groups. The phosphate groups are supplied by two molecules of ATP, which are converted into two molecules of ADP.
2. The 6-C compound is split into 3-C molecules of glyceraldehydes-3-phosphate (G3P). Recall that G3P is also produced by the Calvin cycle in photosynthesis.
3. The two G3P molecules are oxidized, and each receives a phosphate group. The product of this step is two molecules of a new 3-C compound. This is also accompanied by reduction of two molecules of NAD+ to NADH. (Counter part of NADP in light reaction). NAD+ is an organic molecule that accepts electrons during redox reactions.
4. The phosphate groups added in steps 1 and 3 re removed from the 3-C compounds which produce two molecules of pyruvic acid. Each phosphate group Is combined with a molecule of ADP to make a molecule of ATP. Since there were four phosphate groups added, four molecules of ATP are produced.
· Notice that two ATP molecules were used in step 1 but four were produced in step 4. Therefore, Glycolysis has a net yield of two ATP molecules for every molecule of glucose that is converted into pyruvic acid.
· Fermentation is the combination of Glycolysis and additional pathways which regenerate NAD+. The additional pathways in fermentation do not produce ATP; however, recycled NAD+ from NADH. Thus allow for the continued production of ATP.
FERMENTATION
· There are many fermentation pathways, and they differ in terms of enzymes that are used and the compounds that are made from pyruvic acid. Two common fermentation pathways result n the production of lactic acid and ethyl alcohol.
· Lactic acid fermentation, an enzyme converts pyruvic acid made during Glycolysis into another 3-C compound called lactic acid. It involves the transfer of one hydrogen atom from NADH and addition of one free proton, H+ to pyruvic acid. Thus, the regeneration of NAD+ in lactic acid fermentation helps to keep Glycolysis operating.
· Lactic acid fermentation by microorganisms plays an essential role in manufacture of many dairy products – cheese, buttermilk, yogurt, sour cream. In muscle, lactic acid makes the cells’ cytosol more acidic that reduce the capacity of the muscle cells to contract resulting to muscle fatigue, pain and cramps. Eventually, the lactic acid diffuses into the blood and is transported to the liver, where it can be converted back to pyruvic acid.
· Alcoholic fermentation converts pyruvic acid into ethyl alcohol which requires two steps
1. Carbon dioxide molecule is removed from pyruvic acid, leaving a 2-C compound
2. Two hydrogen atoms are added to the 2-C compound to form ethyl alcohol
· Like lactic acid fermentation, NAD+ is also regenerated in this process.
· Alcoholic fermentation by yeast cells is the basis of the wine and beer industry.
· The efficiency of Glycolysis in providing energy or ATP can be determined if one compared the amount of energy available in glucose with the amount of energy contained in the ATP that is produced by Glycolysis.
· Scientists have calculated that the complete oxidation of a standard amount of glucose releases 686 kcal. The production of a standard amount of ATP from ADP absorbs a minimum of about 7 kcal, depending on the conditions inside the cell.
· Efficiency of Glycolysis = Energy required to make ATP
Energy released by oxidation of glucose
= (2 X 7 kcal/686 kcal) x 100% = 2%
CITRIC ACID/KREB’S CYCLE
· The Krebs cycle is a biochemical pathway that breaks down acetyl CoA, producing CO2, hydrogen atoms, and ATP.
· The cycle has five main steps:
1. A 2-C molecule of acetyl CoA combines with a 4-C compound, oxaloacetic acid to produce a 6-C compound, citric acid. Notice that this reaction regenerates coenzyme A.
2. Citric acid releases a CO2 molecule and a hydrogen atom to form a 5-C compound. By losing a hydrogen atom with its electron, citric acid is oxidized. The electron in the hydrogen atom is transferred to NAD+, reducing it to NADH.
3. The 5-C compound formed also releases a CO2 molecule and a hydrogen atom, forming a 4-C compound. Again NAD+ is reduced to NADH. Notice that in this step a molecule of ATP is also synthesized from ADP.
4. The 4-C compound formed releases a hydrogen atom to form another 4-C compound. This time, the hydrogen atom is used to reduce FAD to FADH2. FAD or flavin adenine dinculeotide, is a molecule very similar to NAD+. Like NAD+, FAD accepts electrons during redox reactions.
5. The 4-C compound formed releases a hydrogen atom to regenerate oxaloacetic acid, which keeps the Krebs cycle operating. The electron in the hydrogen atom reduces NAD+ to NADH.
ELECTRON TRANSPORT SYSTEM
· In the electron transport chain, these electrons are passed along a series of molecules embedded in the inner mitochondrial membrane.
1. NADH and FADH2 give up electrons to the electron transport chain. NADH donates electrons at the beginning, and FADH2 donates them farther down the chain. These molecules also give up protons (hydrogen ions, H+.
2. The electrons are passed down the chain. As they move from molecules to molecules, they lose energy.
3. The energy lost from the electrons is used to pump protons from the matrix, building a high concentration of protons between the inner and outer membranes. Thus, a concentration gradient is also created, as the protons carry a positive charge.
4. The concentration and electrical gradients of protons drive the synthesis of ATP by chemiosmosis, the same process that generates ATP in photosynthesis. ATP synthase molecules are embedded in the inner membrane, near the electron transport chain molecules. As protons move through ATP synthase and down their concentration and electrical gradients, ATP is made from ADP and phosphate.
5. Oxygen is the final acceptor of electrons that have passed down the chain. Oxygen also accepts protons that were part of the hydrogen atoms supplied by NADH and FADH2. The protons, electrons and oxygen all combine to form water.
· Cellular respiration can produce up to 38 ATP molecules from the oxidation of single molecules of glucose. Thus, up to 39 percent of the energy released by the oxidation of glucose can be transferred to ATP. However, most eukaryotic cells produce only about 36 ATP molecules per molecule of glucose.
Cellular respiration uses the processes of Glycolysis and aerobic respiration to obtain energy from organic compounds.
· Autotrophs use photosynthesis to make organic compounds from carbon dioxide and water. Heterotrophs cannot make their own organic compounds from inorganic compounds and therefore depends on autotrophs
· Photosynthesis converts light energy into chemical energy through series of reactions known as biochemical pathways. Almost all life depends on photosynthesis.
· Photosynthesis occurs in two stages. In the light reactions, energy is absorbed from the sunlight and converted into chemical energy; in the Calvin cycle, carbon dioxide and chemical energy are used to form organic compounds.
· The light reactions of photosynthesis begin with the absorption of light by chlorophyll a and accessory pigments in the thylakoids.
· Excited electrons that leave chlorophyll a travel along two electron transport chains, resulting in the production of NADPH. The electrons are replaced when water is split into electrons, protons and oxygen in the thylakoid. Oxygen is released as a by-product of photosynthesis.
· As electrons travel along the electron transport chains, protons move into the thylakoid and built up a concentration gradient. The movement of protons down this gradient of protons and through ATP synthase results in the synthesis of ATP through chemiosmosis.
· The dark reaction of photosynthesis or also known as Calvin Cycle happens without the presence of light energy.
· The ATP and NADPH produced in the light reactions drive this second stage of photosynthesis. Carbon dioxide is incorporated in this cycle through the process of carbon fixation.
· The Calvin Cycle produces a compound called G3P. Most of the G3P molecules are converted into RuBP to keep the Calvin cycle operating. However, some G3P molecules are used to make other organic compounds, including amino acids, lipids and carbohydrates.
· Plants that fix carbon using only the Calvin cycle are known as C3 plants. Some plants that evolved in hot, dry climates fix carbon through alternative pathways – the C4 and CAM pathways. These plants carry out carbon fixation and the Calvin cycle either in different cells or at different times.
· The rate of photosynthesis increases and then reaches a plateau as light intensity or carbon dioxide concentration increases. Below a certain temperature, the rate of photosynthesis increases as temperature increases. Above that temperature, the rate of photosynthesis decreases as temperature increases.
· As energy and matter flow through an ecosystem, matter must be recycled and reused. Substances such as water, carbon, nitrogen, sulphur and phosphorus each pass between the living and non living words through biogeochemical cycles.
· The energy from the sub causes water to move into the atmosphere. This is called evaporation. Water moving from the atmosphere to the earth is called precipitation.
· In the carbon-oxygen cycle there are two basic life processes involved – respiration and photosynthesis.
- During cellular respiration, glucose is oxidized and carbon dioxide is released.
- During photosynthesis, green plants use the carbon dioxide and energy from the sun to make oxygen, glucose and water.
· When plants and animals die, the organic compounds of their bodies are broken down by microorganisms. One of the end products that eventually form is carbon dioxide.
· In spite of the abundance of nitrogen in the atmosphere, plants cannot change the element nitrogen into compounds they need. The nitrogen must be in the form of nitrate. Synbiotic bacteria can change atmospheric nitrogen into ammonium compound
· Bacteria of decay break down the protein of dead organisms to ammonia or ammonium compounds. Some bacteria cause nitrogen to return to the atmosphere by breaking down ammonia in the soil.
· Phosphorus is present in the soil in the form of phosphate. Through weathering, phosphate rocks contribute to the amount of phosphate in the soil. Phosphate is taken in by plants and passed on to the food chain when plants and animals die. The bacteria converts the dead bodies into phosphates and return them into the soil. Guano deposits are also sources of phosphate.
Sulfur and phosphorus cycles are both lithosphoric cycles. Sulfur comes from several sources – volcanoes, the action of soil microorganisms – combustion of fossil fuels such as oil, gas, and coal. When fuel is burned, oxygen combines to form oxides. When oxides reach the atmosphere, they combine with rain and form sulphuric acid, which in turn falls to the ground as acid precipitation.
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