treadle pump

A treadle pump is a human-powered suction pump that sits on top of a well and is used for irrigation.[1] It is designed to lift water from a depth of seven metres or less. The pumping is activated by stepping up and down on a treadle, which are levers, which drive pistons, creating cylinder suction […]

Treadle_pump_GB_drawing

A treadle pump is a human-powered suction pump that sits on top of a well and is used for irrigation.[1] It is designed to lift water from a depth of seven metres or less. The pumping is activated by stepping up and down on a treadle, which are levers, which drive pistons, creating cylinder suction that draws groundwater to the surface.

Evolution

Microevolution happens on a small scale (within a single population), while macroevolution happens on a scale that transcends the boundaries of a single species. Despite their differences, evolution at both of these levels relies on the same, establish…

Microevolution happens on a small scale (within a single population), while macroevolution happens on a scale that transcends the boundaries of a single species. Despite their differences, evolution at both of these levels relies on the same, established mechanisms of evolutionary change:

cells

A eukaryote (/juːˈkæri.oʊt/ or /juːˈkæriət/ yoo-karr-ee-oht or yoo-karr-ee-ət) is any organism whose cells contain a nucleus and other organelles enclosed within membranes. Eukaryotes belong to the taxon Eukarya or Eukaryota. The defining feature that sets eukaryotic cells apart from prokaryotic cells (Bacteria and Archaea) is that they have membrane-bound organelles, especially the nucleus, which contains the […]

A eukaryote (/ju??kæri.o?t/ or /ju??kæri?t/ yoo-karr-ee-oht or yoo-karr-ee-?t) is any organism whose cells contain a nucleus and other organelles enclosed within membranes.

Eukaryotes belong to the taxon Eukarya or Eukaryota. The defining feature that sets eukaryotic cells apart from prokaryotic cells (Bacteria and Archaea) is that they have membrane-bound organelles, especially the nucleus, which contains the genetic material, and is enclosed by the nuclear envelope.[2][3][4] The presence of a nucleus gives eukaryotes their name, which comes from the Greek?? (eu, “well”) and ?????? (karyon, “nut” or “kernel”).[5] Eukaryotic cells also contain other membrane-bound organelles such asmitochondria and the Golgi apparatus. In addition, plants and algae contain chloroplasts. Eukaryotic organisms may be unicellular, ormulticellular. Only eukaryotes have many kinds of tissue made up of different cell types.

Eukaryotes can reproduce both by asexual reproduction through mitosis and sexual reproduction through meiosis. In mitosis, one cell divides to produce two genetically identical cells. In meiosis, DNA replication is followed by two rounds of cell division to produce four daughter cells each with half the number of chromosomes as the original parent cell (haploid cells). These act as sex cells (gametes – each gamete has just one complement of chromosomes, each a unique mix of the corresponding pair of parental chromosomes) resulting from genetic recombination during meiosis.

The domain Eukaryota appears to be monophyletic, and so makes up one of the three domains of life. The two other domains,Bacteria and Archaea, are prokaryotes and have none of the above features. Eukaryotes represent a tiny minority of all living things;[6]even the cells in a human’s body are outnumbered ten to one by bacteria in the gut.[7][8] However, due to their much larger size, eukaryotes’ collective worldwide biomass is estimated at about equal to that of prokaryotes.[6] Eukaryotes first developed approximately 1.6–2.1 billion years ago.

A prokaryote is a single-celled organism that lacks a membrane-bound nucleus (karyon), mitochondria, or any other membrane-bound organelle.[1] The word prokaryote comes from the Greek ??? (pro) “before” and ?????? (karyon) “nut orkernel“.[2][3] Prokaryotes can be divided into two domains, Archaea and Bacteria. Species with nuclei and organelles are placed in the domain Eukaryota.[4]

In the prokaryotes all the intracellular water-soluble components (proteins, DNA and metabolites) are located together in thecytoplasm enclosed by the cell membrane, rather than in separate cellular compartments. Bacteria, however, do possess protein-based bacterial microcompartments, which are thought to act as primitive organelles enclosed in protein shells.[5][6]Some prokaryotes, such as cyanobacteria may form large colonies. Others, such as myxobacteria, have multicellular stages in their life cycles.[7]

Molecular studies have provided insight into the evolution and interrelationships of the three domains of biological species.[8]Eukaryotes are organisms, including humans, whose cells have a well defined membrane-bound nucleus (containing chromosomal DNA) and organelles. The division between prokaryotes and eukaryotes reflects the existence of two very different levels of cellular organization. Distinctive types of prokaryotes include extremophiles and methanogens; these are common in some extreme environments.[1]

Nuestro planeta

Johan Rockström
Director, Instituto del Medio Ambiente de Estocolmo

La presión que ejercen los seres humanos sobre el planeta está llegando a un punto de saturación y, si se lo supera, se puede socavar el desarrollo social y económico. Este fenómeno es nuevo, al igual que sus efectos en nuestros bienes comunes –la capa de ozono estratosférica, el sistema climático, la biosfera, la hidrosfera y la criosfera– que se han verificado mediante observaciones empíricas realizadas durante los últimos 20 años. Entre esas manifestaciones cabe mencionar el rápido agotamiento de la capa de ozono; la pérdida de diversidad biológica a un ritmo exponencial continuo; la degradación de la tierra, el agua dulce y la calidad del aire; la carga de aerosoles y contaminación química a escala regional; el cambio climático, y la apropiación no sostenible de recursos naturales finitos como el petróleo y el fósforo. Los efectos empiezan a manifestarse de maneras que afectan a las economías de todo el mundo.

La escala de la influencia humana es tal que es posible que hayamos entrado en una nueva época geológica, el Antropoceno, en la que la humanidad constituye una fuerza geológica planetaria. Por lo tanto, es posible que estemos saliendo de nuestra época actual, el Holoceno, los últimos 10.000 años del período interglaciar, que ha ofrecido condiciones ambientales sumamente estables y favorecido el desarrollo del mundo tal como lo conocemos.

Johan Rockström
Director, Instituto del Medio Ambiente de Estocolmo

La presión que ejercen los seres humanos sobre el planeta está llegando a un punto de saturación y, si se lo supera, se puede socavar el desarrollo social y económico. Este fenómeno es nuevo, al igual que sus efectos en nuestros bienes comunes –la capa de ozono estratosférica, el sistema climático, la biosfera, la hidrosfera y la criosfera– que se han verificado mediante observaciones empíricas realizadas durante los últimos 20 años. Entre esas manifestaciones cabe mencionar el rápido agotamiento de la capa de ozono; la pérdida de diversidad biológica a un ritmo exponencial continuo; la degradación de la tierra, el agua dulce y la calidad del aire; la carga de aerosoles y contaminación química a escala regional; el cambio climático, y la apropiación no sostenible de recursos naturales finitos como el petróleo y el fósforo. Los efectos empiezan a manifestarse de maneras que afectan a las economías de todo el mundo.

La escala de la influencia humana es tal que es posible que hayamos entrado en una nueva época geológica, el Antropoceno, en la que la humanidad constituye una fuerza geológica planetaria. Por lo tanto, es posible que estemos saliendo de nuestra época actual, el Holoceno, los últimos 10.000 años del período interglaciar, que ha ofrecido condiciones ambientales sumamente estables y favorecido el desarrollo del mundo tal como lo conocemos.

Group selection

Group selection is a proposed mechanism of evolution in which natural selection is imagined to act at the level of the group, instead of at the more conventional level of the individual. Early authors such as V. C. Wynne-Edwards and Konrad Lorenz argued that the behavior of animals could affect their survival and reproduction as […]

Group selection is a proposed mechanism of evolution in which natural selection is imagined to act at the level of the group, instead of at the more conventional level of the individual.

Early authors such as V. C. Wynne-Edwards and Konrad Lorenz argued that the behavior of animals could affect their survival and reproduction as groups.

From the mid 1960s, evolutionary biologists such as John Maynard Smith argued that natural selection acted primarily at the level of the individual. They argued on the basis of mathematical models that individuals would not altruistically sacrifice fitness for the sake of a group. They persuaded the majority of biologists that group selection did not occur, other than in special situations such as the haplodiploid social insects like honeybees (in the Hymenoptera), where kin selection was possible.

In 1994 David Sloan Wilson and Elliott Sober argued for multi-level selection, including group selection, on the grounds that groups, like individuals, could compete. In 2010 three authors including E. O. Wilson, known for his work on ants, again revisited the arguments for group selection, provoking a strong rebuttal from a large group of evolutionary biologists. As of yet, there is no clear consensus among biologists regarding the importance of group selection.

Kyoto Protocol

The Kyoto Protocol is an international agreement linked to the United Nations Framework Convention on Climate Change, which commits its Parties by setting internationally binding emission reduction targets. Recognizing that developed countries are principally responsible for the current high levels of GHG emissions in the atmosphere as a result of more than 150 years of […]

The Kyoto Protocol is an international agreement linked to the United Nations Framework Convention on Climate Change, which commits its Parties by setting internationally binding emission reduction targets.

Recognizing that developed countries are principally responsible for the current high levels of GHG emissions in the atmosphere as a result of more than 150 years of industrial activity, the Protocol places a heavier burden on developed nations under the principle of “common but differentiated responsibilities.”

The Kyoto Protocol was adopted in Kyoto, Japan, on 11 December 1997 and entered into force on 16 February 2005. The detailed rules for the implementation of the Protocol were adopted at COP 7 in Marrakesh, Morocco, in 2001, and are referred to as the “Marrakesh Accords.” Its first commitment period started in 2008 and ended in 2012.