Tuesday, 7 October 2014

JAPHET MASATU ALBUM NO. 3

Mwl. Japhet Masatu akiwa na Proffessa Gabriel , Mkurugenzi wa Vijana Tanzania Katika SEMINA YA VIJANA, "BADILISHA FIKRA " iliyofanyika " MLIMANI CITY " jijini Dar es salaam , Tanzania. AUGUST 2014.

Mwl. Japhet Masatu mwenye tai nyekundu akiwa na walimu wenzake katika SHULE YA SEKONDARI SALMA KIKWETE iliyopo MANISPAA YA KINONDONI, DAR ES SALAAM ,TANZANIA . Katika Mazoezi ya " TEACHING PRACTICE" April 2014. Mwl. Japhet Masatu akiwa kama MWANAFUNZI WA OPEN UNIVERSITY OF TANZANIA. KINONDONI CENTRE. DAR ES SALAAM, akisoma B.E.d {Adult Education }.

JAPHET MASATU ALBUM NO. 1

Mwl. Japhet Masatu Kulia nyuma akiwa pamoja na wanafunzi wenzake wa OPEN UNIVERSITY OF TANZANIA, KINONDONI CENTRE, DAR--ES--SALAAM---2014

Sunday, 10 August 2014

OEI 201 / 518 : TEACHING METHODS FOR ADULT LEARNERS ---- MAIN TIMED TEST ---- Friday , 14 February 2014

OCP 100 : INTRODUCTION TO MICROCOMPUTER STUDIES AND INFORMATION TECHNOLOGY ---SPECIAL / SUPPLEMENTARY EXAMINATION----Monday , 03 February 2014

OCP : INTRODUCTION TO MICROCOMPUTER STUDIES AND INFORMATION TECHNOLOGY ---- SPECIAL / SUPPLEMENTARY EXAMINATION-----Monday, 04 February 2013

Wednesday, 6 August 2014

OCP 100 : INTRODUCTION TO MICROCOMPUTER STUDIES AND INFORMATION TECHNOLOGY ---SPECIAL MAIN TIMED TEST---Tuesday , 26 June 2012

OSW 223 : MOFOLOJIA YA KISWAHILI ---- MTIHANI WA MWAKA---- Jumatano , 11 2012.

OEF 102 : HISTORY AND SOCIOLOGICAL ASPECTS IN EDUCATION --- SPECIAL / SUPPLEMENTARY EXAMINATION --- Monday , 27 January 2014

OEI 101 / 505 : CURRICULUM DEVELOPMENT AND EVALUATION -- SPECIAL / SUPPLEMENTARY EXAMINATION ---Friday , 01 February 2013

OEI 101 / 505 : CURRICULUM DEVELOPMENT AND EVALUATION --- MAIN TIMED TEST -- Monday , 13 February 2012

ODC O54: CURRICULUM DEVELOPMENT ----SPECIAL /SUPPLEMENTARY EXAMINATION ---- Thursday , 31 January.....Y 2013

Wednesday, 30 July 2014

OEA 305 : PLANNING AND MANAGEMENT OF ADULT AND COMMUNUTY EDUCATION

OEA 305 : COMMUNITY DEVELOPMENT

Community
Part of a series on

Concepts
Sense of community Social capital
Perspectives
Community psychology Community studies
Types
Community of interest Community of practice Community of place
Development
Community development Community organizing
See also
Outline Community portal
WikiProject Community
v t e

The United Nations defines Community development as "a process where community members come together to take collective action and generate solutions to common problems."^[1] It is a broad term given to the practices of civic leaders, activists, involved citizens and professionals to improve various aspects of communities, typically aiming to build stronger and more resilient local communities.
Community development seeks to empower individuals and groups of people by providing them with the skills they need to cause in their communities. These skills are often created through the formation of large social groups working for a common agenda. Community developers must understand both how to work with individuals and how to affect communities' positions within the context of larger social institutions.
Community development as a term has taken off widely in anglophone countries i.e. the USA, UK, Australia, Canada and New Zealand and other countries in the Commonwealth. It is also used in some countries in eastern Europe with active community development associations in Hungary and Romania. The Community Development Journal, published by Oxford University Press, since 1966 has aimed to be the major forum for research and dissemination of international community development theory and practice.^[2]
Community development approaches are recognised internationally. These methods and approaches have been acknowledged as significant for local social, economic, cultural, environmental and political development by such organisations as the UN, WHO, OECD, World Bank, Council of Europe and EU.

Definitions

There are complementary definitions of community development.
The United Nations defines Community development broadly as "a process where community members come together to take collective action and generate solutions to common problems."^[1]
The Community Development Challenge report, which was produced by a working party comprising leading UK organizations in the field (including (Foundation Builders) Community Development Foundation, the (now defunct)Community Development Exchange and the Federation for Community Development Learning) defines community development as:

A set of values and practices which plays a special role in overcoming poverty and disadvantage, knitting society together at the grass roots and deepening democracy. There is a community development profession, defined by national occupational standards and a body of theory and experience going back the best part of a century. There are active citizens who use community development techniques on a voluntary basis, and there are also other professions and agencies which use a community development approach or some aspects of it.^[3]

Community Development Exchange defines community development as:

both an occupation (such as a community development worker in a local authority) and a way of working with communities. Its key purpose is to build communities based on justice, equality and mutual respect.
Community development involves changing the relationships between ordinary people and people in positions of power, so that everyone can take part in the issues that affect their lives. It starts from the principle that within any community there is a wealth of knowledge and experience which, if used in creative ways, can be channeled into collective action to achieve the communities' desired goals.
Community development practitioners work alongside people in communities to help build relationships with key people and organizations and to identify common concerns. They create opportunities for the community to learn new skills and, by enabling people to act together, community development practitioners help to foster social inclusion and equality.^[4]

Different approaches to community development

There are numerous overlapping approaches to community development. Some focus on the processes, some on the outcomes/ objectives. They include:

Community capacity building; focusing on helping communities obtain, strengthen, and maintain the ability to set and achieve their own development objectives.^[5]
Social capital formation; focusing on benefits derived from the cooperation between individuals and groups.
Nonviolent direct action; when a group of people take action to reveal an existing problem, highlight an alternative, or demonstrate a possible solution to a social issue which is not being addressed through traditional societal institutions (governments, religious organizations or established trade unions) are not addressing to the satisfaction of the direct action participants.
Economic development, focusing on the "development" of developing countries as measured by their economies, although it includes the processes and policies by which a nation improves the economic, political, and social well-being of its people.
Community economic development (CED); an alternative to conventional economic development which encourages using local resources in a way that enhances economic outcomes while improving social conditions.
Sustainable development; which seeks to achieve, in a balanced manner, economic development, social development and environmental protection outcomes.^[6]
Community-driven development (CDD), an economic development model which shifts overreliance on central governments to local communities.
Asset-Based Community Development (ABCD); is a methodology that seeks to uncover and use the strengths within communities as a means for sustainable development.^[7]
Faith-based community development; which exploits faith based organisations to bring about community development outcomes.
Community-based participatory research (CBPR); a partnership approach to research that equitably involves, for example, community members, organizational representatives, and researchers in all aspects of the research process and in which all partners contribute expertise and share decision making and ownership, which aims to integrate this knowledge with community development outcomes.^[8]^[9]
Community organizing; a term used to describe an approach that generally assumes that social change necessarily involves conflict and social struggle in order to generate collective power for the powerless.
Participatory planning including community-based planning (CBP); involving the entire community in the strategic and management processes of urban planning; or, community-level planning processes, urban or rural.^[10]^[11]
Methodologies focusing on the educational component of community development, including the community-wide empowerment that increased educational opportunity creates.
Methodologies addressing the issues and challenges of the Digital divide, making affordable training and access to computers and the Internet, addressing the marginalisation of local communities that cannot connect and participate in the global Online community. In the United States, nonprofit organizations such as Per Scholas seek to “break the cycle of poverty by providing education, technology and economic opportunities to individuals, families and communities” as a path to development for the communities they serve.^[12]

There are a myriad of job titles for community development workers and their employers include public authorities and voluntary or non-governmental organisations, funded by the state and by independent grant making bodies. Since the nineteen seventies the prefix word ‘community’ has also been adopted by several other occupations from the police and health workers to planners and architects, who have been influenced by community development approaches.

History

Community development practitioners have over many years developed a range of approaches for working within local communities and in particular with disadvantaged people. Since the nineteen sixties and seventies through the various anti poverty programmes in both developed and developing countries, community development practitioners have been influenced by structural analyses as to the causes of disadvantage and poverty i.e. inequalities in the distribution of wealth, income, land etc. and especially political power and the need to mobilise people power to affect social change. Thus the influence of such educators as Paulo Freire and his focus upon this work. Other key people who have influenced this field are Saul Alinsky (Rules for Radicals) and EF Schumacher (Small is Beautiful).

In the global North

In the 19th century, the work of the Welsh early socialist thinker Robert Owen (1771–1851), sought to create a more perfect community. At New Lanark and at later communities such as Oneida in the USA and the New Australia Movement in Australia, groups of people came together to create utopian or intentional communities, with mixed success.

United States

In the United States in the 1960s, the term "community development" began to complement and generally replace the idea of urban renewal, which typically focused on physical development projects often at the expense of working-class communities. In the late 1960s, philanthropies such as the Ford Foundation and government officials such as Senator Robert F. Kennedy took an interest in local nonprofit organizations. A pioneer was the Bedford-Stuyvesant Restoration Corporation in Brooklyn, which attempted to apply business and management skills to the social mission of uplifting low-income residents and their neighborhoods. Eventually such groups became known as "Community Development Corporations" or CDCs. Federal laws beginning with the 1974 Housing and Community Development Act provided a way for state and municipal governments to channel funds to CDCs and other nonprofit organizations.
National organizations such as the Neighborhood Reinvestment Corporation (founded in 1978 and now known as NeighborWorks America), the Local Initiatives Support Corporation(LISC) (founded in 1980), and the Enterprise Foundation (founded in 1981) have built extensive networks of affiliated local nonprofit organizations to which they help provide financing for countless physical and social development programs in urban and rural communities. The CDCs and similar organizations have been credited with starting the process that stabilized and revived seemingly hopeless inner city areas such as the South Bronx in New York City.

UK

In the UK Community development has had two main traditions. The first was as an approach for preparing for the independence of countries from the former British Empire in the 50's and 60's. Domestically it first came into public prominence with the Labour Government's anti deprivation programmes of the latter sixties and seventies. The main example of this being the CDP (Community Development Programme), which piloted local area based community development. This influenced a number of largely urban local authorities, in particular in Scotland with Strathclyde Region's major community development programme (the largest at the time in Europe).
The Gulbenkian Foundation was a key funder of commissions and reports which influenced the development of community development in the UK from the latter sixties to the 80's. This included recommending that there be a national institute or centre for community development, able to support practice and to advise government and local authorities on policy. This was formally set up in 1991 as the Community Development Foundation. In 2004 the Carnegie UK Trust established a Commission of Inquiry into the future of rural community development examining such issues as land reform and climate change. Carnegie funded over sixty rural community development action research projects across the UK and Ireland and national and international communities of practice to exchange experiences. This included the International Association for Community Development.
In 1999 a UK wide organisation responsible for setting professional training standards for all education and development practitioners working within local communities was established and recognised by the Labour Government. This organisation was called PAULO - the National Training Organisation for Community Learning and Development. (It was named after Paulo Freire). It was formally recognised by David Blunket, the Secretary of State for Education and Employment. Its first chair was Charlie McConnell, the Chief Executive of the Scottish Community Education Council, who had played a lead role in bringing together a range of occupational interests under a single national training standards body, including community education, community development and development education. The inclusion of community development was significant as it was initially uncertain as to whether it would join the NTO for Social Care. The Community Learning and Development NTO represented all the main employers, trades unions, professional associations and national development agencies working in this area across the four nations of the UK.
The term ‘community learning and development’ was adopted to acknowledge that all of these occupations worked primarily within local communities, and that this work encompassed not just providing less formal learning support but also a concern for the wider holistic development of those communities – socio economically, environmentally, culturally and politically. By bringing together these occupational groups this created for the first time a single recognised employment sector of nearly 300,000 full and part-time paid staff within the UK, approximately 10% of these staff being full-time. The NTO continued to recognise the range of different occupations within it, for example specialists who work primarily with young people, but all agreed that they shared a core set of professional approaches to their work. In 2002 the NTO became part of a wider Sector Skills Council for lifelong learning.
The UK currently hosts the only global network of practitioners and activists working towards social justice through community development approach, the International Association for Community Development (IACD).^[13] IACD was formed in the USA in 1953, moved to Belgium in 1978 and was restructured and relaunched in Scotland in 1999.^[14]

Canada

Community development in Canada has roots in the development of co-operatives, credit unions and caisses populaires. The Antigonish Movement which started in the 1920s in Nova Scotia, through the work of Doctor Moses Coady and Father James Tompkins, has been particularly influential in the subsequent expansion of community economic development work across Canada...

In the global South

Community planning techniques drawing on the history of utopian movements became important in the 1920s and 1930s in East Africa, where Community Development proposals were seen as a way of helping local people improve their own lives with indirect assistance from colonial authorities.^{[citation needed]}
Mohandas K. Gandhi adopted African community development ideals as a basis of his South African Ashram, and then introduced it as a part of the Indian Swaraj movement, aiming at establishing economic interdependence at village level throughout India. With Indian independence, despite the continuing work of Vinoba Bhave in encouraging grassroots land reform, India under its first Prime Minister Jawaharlal Nehru adopted a mixed-economy approach, mixing elements of socialism and capitalism.During the fifties and sixties, India ran a massive community development programme with focus on rural development activities through government support. This was later expanded in scope and was called integrated rural development scheme [IRDP]. A large number of initiatives that can come under the community development umbrella have come up in recent years.
The main objective of Community Development in India remains to development the villages and to help the villagers to help themselves to fight against poverty, illiteracy, malnutrition etc. The beauty of Indian model of Community Development lies in the homogeneity of villagers and high level of participation.
Community Development became a part of the Ujamaa Villages established in Tanzania by Julius Nyerere, where it had some success in assisting with the delivery of education services throughout rural areas, but has elsewhere met with mixed success. In the 1970s and 1980s, Community Development became a part of "Integrated Rural Development", a strategy promoted by United Nations Agencies and the World Bank. Central to these policies of community development were

Adult Literacy Programs, drawing on the work of Brazilian educator Paulo Freire and the "Each One Teach One" adult literacy teaching method conceived by Frank Laubach.
Youth and Women's Groups, following the work of the Serowe Brigades of Botswana, of Patrick van Rensburg.
Development of Community Business Ventures and particularly cooperatives, in part drawn on the examples of José María Arizmendiarrieta and the Mondragon Cooperatives of the Basque Region of Spain
Compensatory Education for those missing out in the formal education system, drawing on the work of Open Education as pioneered by Michael Young.
Dissemination of Alternative Technologies, based upon the work of E. F. Schumacher as advocated in his book Small is Beautiful: Economics as if people really mattered
Village Nutrition Programs and Permaculture Projects, based upon the work of Australians Bill Mollison and David Holmgren.
Village Water Supply Programs

In the 1990s, following critiques of the mixed success of "top down" government programs, and drawing on the work of Robert Putnam, in the rediscovery of Social Capital, community development internationally became concerned with social capital formation. In particular the outstanding success of the work of Muhammad Yunus in Bangladesh with the Grameen Bank, has led to the attempts to spread microenterprise credit schemes around the world. This work was honoured by the 2006 Nobel Peace Prize.
The "Human Scale Development" work of Right Livelihood Award winning Chilean economist Manfred Max Neef promotes the idea of development based upon fundamental human needs, which are considered to be limited, universal and invariant to all human beings (being a part of our human condition). He considers that poverty results from the failure to satisfy a particular human need, it is not just an absence of money. Whilst human needs are limited, Max Neef shows that the ways of satisfying human needs is potentially unlimited. Satisfiers also have different characteristics: they can be violators or destroyers, pseudosatisfiers, inhibiting satisfiers, singular satisfiers, or synergic satisfiers. Max-Neef shows that certain satisfiers, promoted as satisfying a particular need, in fact inhibit or destroy the possibility of satisfying other needs: e.g., the arms race, while ostensibly satisfying the need for protection, in fact then destroys subsistence, participation, affection and freedom; formal democracy, which is supposed to meet the need for participation often disempowers and alienates; commercial television, while used to satisfy the need for recreation, interferes with understanding, creativity and identity. Synergic satisfiers, on the other hand, not only satisfy one particular need, but also lead to satisfaction in other areas: some examples are breast-feeding; self-managed production; popular education; democratic community organizations; preventative medicine; meditation; educational games.

References

"Community development". UNTERM. Retrieved 7 July 2014.
"Community Development Journal- about the journal". Oxford University Press. Retrieved 7 July 2014.
"Community Development Challenge Report". Produced by Community Development Foundation for Communities and Local Government. Retrieved 2009-02-13.
"Definition of CD". Community Development Exchange. Retrieved 2010-06-08.
United Nations Development Group. "United Nations Development System- A Collective Approach to Supporting Capacity Development". Retrieved 7 July 2014.
Sung, Hyung. "Sustainable development". General Assembly of the United Nations. General Assembly of the United Nations. Retrieved 12 July 2014.
Mathie, Alison & Cunningham, Gord (1 Jul 2010). "From clients to citizens: Asset-based Community Development as a strategy for community-driven development". Development in practice 13 (5): 474–486. doi:10.1080/0961452032000125857. Retrieved 12 July 2014.
Israel, B.A., Schulz, A.J., Parker, E.A., & Becker, A.B. (1998). Review of community-based research: Assessing partnership approaches to improve public health. Annual Review of Public Health, 19, 173-202.
Israel, B.A., Schulz, A.J., Parker, E.A., Becker, A.B., Allen, A., & Guzman, J.R. (2008). Critical issues in developing and following CBPR Principles. In M. Minkler & N. Wallerstein (Eds.), Community-based participatory research for health: From process to outcomes (2nd ed., pp. 47-66). San Francisco: Jossey-Bass.
Lefevre, Pierre; Kolsteren, Patrick; De Wael, Marie-Paule; Byekwaso, Francis; Beghin, Ivan (December 2000). "Comprehensive Participatory Planning and Evaluation" (PDF). Antwerp, Belgium: IFAD. Retrieved 2008-10-21.
[McTague, C. & Jakubowski, S. Marching to the beat of a silent drum: Wasted consensus-building and failed neighborhood participatory planning. Applied Geography 44, 182–191 (2013)]
"Per Scholas Website". Per Scholas Website. Retrieved July 6, 2014.
"International Association for Community Development". Retrieved 7 July 2014.
"IACD- a brief history". Retrieved 7 July 2014.

External links

The Citizen's Handbook
CDX: the Community Development Exchange, a UK-wide independent membership organisation for community development.
International Association for Community Development
Shelterforce: the magazine for community development, affordable housing, and community building.
Knowledgeplex: a news and information resource for the affordable housing and community development field.
Sustainable Urban Development Resource Guide

Categories:

Saturday, 28 June 2014

RESPIRATION --- BIOLOGY FORM FIVE .

RESPIRATORY SYSTEM --- BIOLOGY FORM FIVE.

The respiratory system, also called the gas exchange system is the body getting rid of carbon dioxide and taking in oxygen. Carbon dioxide, a waste product of cellular respiration is exhaled and oxygen is inhaled. The oxygen then goes into the blood due to a concentration gradient (a difference in concentration). The first process of this system is breathing in the air, or inhaling. The second process is gas exchange in the lungs where oxygen from the air is diffused into the blood in exchange for the carbon dioxide. The third process is cellular respiration, where oxygen and glucose in the blood is changed into energy during glycolysis, the Krebs cycle, and the electron transport chain. This produces the high concentration of carbon dioxide found in the blood. Finally, the carbon dioxide from cellular respiration is exhaled out the body from the lungs.^[1]

Ventilation

For respiration to happen, the body needs a constant supply of oxygen, which is done by breathing. Inhalation is the breathing in of air. To inhale, the lungs expand, decreasing the air pressure in the lungs. This is caused by the diaphragm (a sheet of muscular tissue that separates the lungs from the abdomen) and the muscles between the ribs contracting to expand the chest, which also expands the lungs. As the air pressure inside the lungs are lower when it has expanded, air from outside at higher pressure comes rushing into the area of low pressure in the lungs.^[2] Air first passes through the nose and mouth, then through the larynx (voice box), then down the trachea (windpipe), and into the lungs.
The lungs are made of many tubes or branches. As air enters the lungs, it first goes through branches called the bronchus, then through smaller branches called bronchioles, and finally into the air sacs. Gas exchange occurs in the air sacs where oxygen is exchanged with carbon dioxide. The carbon dioxide in the air sacs now need to be exhaled, or breathed out. In the reverse process to inhaling, the diaphragm and the rib muscles relax, causing the lungs to be smaller. As the air pressure in the lungs is greater when the lungs are smaller, air is forced out. The exhaled air has a high concentration of carbon dioxide and a low concentration of oxygen. The maximum volume of air that can be inhaled and exhaled is called the vital capacity of the lungs and is up to five liters.^[2]

Gas Exchange

The inhaled air goes down to the air sacs at the end of each bronchiole. The air sacs are called alveoli — they have a large surface area, and are moist, thin, and close to a blood supply. The inhaled air has a much greater concentration of oxygen than carbon dioxide whilst the blood flowing to the lungs has a more carbon dioxide than oxygen. This creates a concentration gradient between the air in the air sacs and the blood, meaning there is more oxygen in the air than the blood. As the membrane, oxygen can easily diffuse in and out. Oxygen at high concentration in the air sacs diffuses into the blood where oxygen concentration is low, and carbon dioxide at high concentration in the blood diffuses into the air sacs where carbon dioxide concentration is low. The oxygen in the blood enters the circulatory system and is used by the cells in the body. The carbon dioxide in the air sacs are exhaled out of the body.

Cellular Respiration

Cellular respiration is the process of the cells changing oxygen and glucose into carbon dioxide, water, and most importantly energy, in three stages known as glycolysis, the Krebs Cycle, and the electron transport chain. The energy is essential, as cells need it to do work. When there is not enough oxygen being supplied, the body undergoes anaerobic respiration, which doesn’t require oxygen. However, this process produces lactic acid (a poison) and is not as efficient as when oxygen is used. Aerobic respiration, the process that does use oxygen, produces much more energy and doesn’t produce lactic acid. It also produces carbon dioxide as a waste product, which then enters the circulatory system. The carbon dioxide is taken to the lungs, where it is exchanged for oxygen.

References

Pickering, W. Roy. Complete Biology. Oxford [etc.: Oxford UP, 2006. Print 116-127.
King, Rita Mary., Frances Chamberlain, Q. L. Pearce, and W. J. Pearce. Biology Made Simple. New York: Broadway, 2003. Print. 127-133.

Categories:

GASEOUS EXCHANGE AND RESPIRATION--- BIOLOGY FORM FIVE.

INTRODUCTION:

Gas exchange is a biological process through which different gases are transferred in opposite directions across a specialised respiratory surface. Gases are constantly required and produced as a by-product of cellular and metabolic reactions so an efficient system for their exchange is extremely important. It is linked with respiration in animals, and both respiration and photosynthesis in plants.^[1]
In respiration, oxygen (O₂) is required to enter cells whilst waste carbon dioxide (CO₂) must be removed – the opposite is true for photosynthesis, where CO₂ enters plants and O₂ is released.^[1] The exchange of gases essentially occurs as a result of diffusion down a concentration gradient – gas molecules moving from an area of high concentration to low concentration.

Diffusion

Diffusion follows Fick’s Law. It is a passive process (doesn’t require energy) affected by factors such as:

The surface area available
The distance the gas molecules must diffuse across
The concentration gradient

Gases must first dissolve in a fluid in order to diffuse across a membrane therefore all gas exchange systems require a moist environment.^[2]
In single-celled organisms diffusion can occur straight across the cell membrane; as organisms increase in size so does the distance gases must travel across. Their surface-area-to-volume ratio also decreases. Diffusion alone is not efficient enough and specialised respiratory systems are required. This is the case with humans and fish where circulatory systems have evolved: These are able to transport the gases to and from the respiratory surface and maintain a continuous concentration gradient.^[3]

In Humans

Gas exchange in humans - between a capillary and an alveolus

Both oxygen and carbon dioxide are transported around the body in the blood – through arteries, veins and capillaries. They bind to haemoglobin in red blood cells although this is more effective with oxygen. Carbon dioxide also dissolves in the plasma or combines with water to form bicarbonate ions (HCO−
3). This reaction is catalysed by the carbonic anhydrase enzyme in red blood cells:^[4]

The main respiratory surface in humans are the alveoli.^[5] Alveoli are small air sacs branching off from the bronchioles in the lungs. They are one-cell thick and provide a moist and extremely large surface area for gas exchange to occur. Capillaries carrying deoxygenated blood from the pulmonary artery run across the alveoli - they are also extremely thin so the total distance gases must diffuse across is only around 2-cells thick.
Inhaled oxygen is able to diffuse into the capillaries from the alveoli, while carbon dioxide from the blood diffuses in the opposite direction into the alveoli. The waste carbon dioxide can then be exhaled out of the body. Continuous blood flow in the capillaries as well as constant breathing maintains a steep concentration gradient.

Varying response

During physical exercise excess carbon dioxide is produced as a result of increased respiration: This must be removed and muscles and cells require increased oxygen. The body responds to this change by increasing the breathing rate, therefore maximizing the rate of possible gas exchange.^[6]

In Plants

Air diffuses directly into and out of plants through pores on the underside of leaves known as stomata. The stomata are controlled by guard cells (affected by osmosis and turgor pressure). When the guard cells are turgid, stomata are open. When they are flaccid, stomata close and gas exchange cannot take place. The main respiratory surface is the spongy mesophyll cells inside the leaf. They have large air spaces and therefore provide a large surface area for gas exchange. Leaves are also very thin so the diffusion distance is small.^[7]
During the day photosynthesis occurs at a faster rate than respiration so there is an overall uptake of CO₂ and release of O₂. At night (when there is no light available) this is reversed as photosynthesis stops and only respiration can take place.

In Fish

Fish must extract oxygen dissolved in water, not air, which has led to the evolution of gills and opercula. Gills are specialised organs containing filaments and lamellae – the lamellae contain capillaries and provide a large surface area and short diffusion distance as they are extremely thin.^[8]
Water is drawn in through the mouth and passes over the gills in one direction while blood flows through the lamellae in the opposite direction – this counter current maintains a steep concentration gradient. O₂ is able to continually diffuse down its gradient into the blood and CO₂ into the water.^[9]

Summary of main systems

	Large surface area	Short diffusion distance	Maintained concentration gradient
Human	Total alveoli = 70-100m² ^[10]	Alveolus + Capillary = 2-cells	Constant blood flow in capillaries; breathing
Fish	Many lamellae and filaments per gill	Usually 1-cell	Counter-current flow
Plant	High density of stomata; air spaces within leaf	1-cell	Constant air flow

Other examples

Insects such as crickets do not have an inner skeleton so exchange gases across structures known as trachea and tracheoles: These are tubes that run directly into the body of the insect. Air enters the trachea through valves known as spiracles and diffusion can then occur straight into the respiring tissues.^[11]
Amphibians are able to use their skin as a respiratory surface, as well as having lungs and sometimes gills.

References

"Gas exchange". Retrieved 19 March 2013.
Piiper J, Dejours P, Haab P & Rahn H (1971). "Oncepts and basic quantities in gas exchange physiology". Respiration Physiology 13: 292–304. doi:10.1016/0034-5687(71)90034-x.
Kety SS (1951). "The theory and applications of the exchange of inert gas at the lungs and tissues". Pharmacological Reviews 3: 1–41.
Raymond H & Swenson E (2000). "The distribution and physiological significance of carbonic anhydrase in vertebrate gas exchange organs". Respiration physiology 121: 1–12. doi:10.1016/s0034-5687(00)00110-9.
"Gas Exchange in humans". Retrieved 19 March 2013.
Wasserman K, Whipp B, Koyal S & Beaver W (1973). "Anaerobic threshold and respiratory gas exchange during exercise". Journal of Applied Physiology 35.
Casson S & Gray JE (2008). "Influence of environmental factors on stomatal development". New Phytologist 178: 9–23. doi:10.1111/j.1469-8137.2007.02351.x.
Newstead James D (1967). "Fine structure of the respiratory lamellae of teleostean gills". Cell and Tissue Research 79: 396–428. doi:10.1007/bf00335484.
Hughes GM (1972). "Morphometrics of fish gills". Respiration physiology 14: 1–25. doi:10.1016/0034-5687(72)90014-x.
Basset J, Crone C, Saumon G (1987). "Significance of active ion transport in transalveolar water absorption: a study on isolated rat lung". The journal of physiology 384: 311–324.
"Gas Exchange in Insects". Retrieved 19 March 2013.