document_title: World population

question_text: when will the worlds population reach 8 billion

text: World population

text: Population by region[edit]

text: Six of the Earth's seven continents are permanently inhabited on a large scale. Asia is the most populous continent, with its 4.54 billion inhabitants accounting for 60% of the world population. The world's two most populated countries, China and India, together constitute about 37% of the world's population. Africa is the second most populated continent, with around 1.28 billion people, or 16% of the world's population. Europe's 742 million people make up 10% of the world's population as of 2018, while the Latin American and Caribbean regions are home to around 651 million (9%). Northern America, primarily consisting of the United States and Canada, has a population of around 363 million (5%), and Oceania, the least-populated region, has about 41 million inhabitants (0.5%).[9] Though it is not permanently inhabited by any fixed population, Antarctica has a small, fluctuating international population based mainly in polar science stations. This population tends to rise in the summer months and decrease significantly in winter, as visiting researchers return to their home countries.[10]

text: Population by continent[edit]

text:
Population by continent (2016 estimates)

Continent
Density
(inhabitants/km2)
Population
(millions)
Most populous country
Most populous city (metropolitan area)

Asia
96.4
4,436
1,382,300,000[note 1] -  China
35,676,000/13,634,685 -  Greater Tokyo Area/Tokyo Metropolis

Africa
36.7
1,216
0186,987,000 -  Nigeria
21,000,000 -  Lagos

Europe
72.9
738
0145,939,000 -  Russia;
approx. 112 million in Europe)
17,100,000/12,228,685 -  Moscow urban area/Moscow[11]

North America[note 2]
22.9
579
0324,991,600 -  United States
23,723,696/8,537,673 -  New York Metropolitan Area/New York City

South America
22.8
422
0209,567,000 -  Brazil
27,640,577/11,316,149 -  Metro Area/São Paulo City

Oceania
4.5
39.9
0024,458,800 -  Australia
5,005,400 -  Sydney

Antarctica
0.0003
(varies)
0.004 in summer
(non-permanent, varies)[10]
N/A[note 3]
1,200 (non-permanent, varies) - McMurdo Station

text: History[edit]

text: Estimates of world population by their nature are an aspect of modernity, possible only since the Age of Discovery. Early estimates for the population of the world[12] date to the 17th century: William Petty in 1682 estimated world population at 320 million (modern estimates ranging close to twice this number); by the late 18th century, estimates ranged close to one billion (consistent with modern estimates).[13] More refined estimates, broken down by continents, were published in the first half of the 19th century, at 600 to 1000 million in the early 1800s and at 800 to 1000 million in the 1840s.[14]

text: Antiquity and Middle Ages[edit]

text: Estimates of the population of the world at the time agriculture emerged in around 10,000 BC have ranged between 1 million and 15 million.[15][16] Even earlier, genetic evidence suggests humans may have gone through a population bottleneck of between 1,000 and 10,000 people about 70,000 BC, according to the Toba catastrophe theory. By contrast, it is estimated that around 50–60 million people lived in the combined eastern and western Roman Empire in the 4th century AD.[17]

text: The Plague of Justinian, which first emerged during the reign of the Roman emperor Justinian, caused Europe's population to drop by around 50% between the 6th and 8th centuries AD.[18] The population of Europe was more than 70 million in 1340.[19] The Black Death pandemic of the 14th century may have reduced the world's population from an estimated 450 million in 1340 to between 350 and 375 million in 1400;[20] it took 200 years for population figures to recover.[21] The population of China decreased from 123 million in 1200 to 65 million in 1393,[22] presumably due to a combination of Mongol invasions, famine, and plague.[23]

text: Starting in AD 2, the Han Dynasty of ancient China kept consistent family registers in order to properly assess the poll taxes and labor service duties of each household.[24] In that year, the population of Western Han was recorded as 57,671,400 individuals in 12,366,470 households, decreasing to 47,566,772 individuals in 9,348,227 households by AD 146, towards the End of the Han Dynasty.[24] At the founding of the Ming Dynasty in 1368, China's population was reported to be close to 60 million; toward the end of the dynasty in 1644, it may have approached 150 million.[25] England's population reached an estimated 5.6 million in 1650, up from an estimated 2.6 million in 1500.[26] New crops that were brought to Asia and Europe from the Americas by Portuguese and Spanish colonists in the 16th century are believed to have contributed to population growth.[27][28][29] Since their introduction to Africa by Portuguese traders in the 16th century,[30] maize and cassava have similarly replaced traditional African crops as the most important staple food crops grown on the continent.[31]

text: The pre-Columbian North American population probably numbered somewhere between 2 million and 18 million.[32] Encounters between European explorers and populations in the rest of the world often introduced local epidemics of extraordinary virulence.[33] According to the most extreme scholarly claims, as many as 90% of the Native American population of the New World died due to Old World diseases such as smallpox, measles and influenza.[34] Over the centuries, the Europeans had developed high degrees of immunity to these diseases, while the indigenous peoples had no such immunity.[35]

text: Modern era[edit]

text: During the European Agricultural and Industrial Revolutions, the life expectancy of children increased dramatically.[38] The percentage of the children born in London who died before the age of five decreased from 74.5% in 1730–1749 to 31.8% in 1810–1829.[39][40] Between 1700 and 1900, Europe’s population increased from about 100 million to over 400 million.[41] Altogether, the areas populated by people of European descent comprised 36% of the world's population in 1900.[42]

text: Population growth in the West became more rapid after the introduction of vaccination and other improvements in medicine and sanitation.[43] Improved material conditions led to the population of Britain increasing from 10 million to 40 million in the 19th century.[44] The population of the United Kingdom reached 60 million in 2006.[45] The United States saw its population grow from around 5.3 million in 1800 to 106 million in 1920, exceeding 307 million in 2010.[46]

text: The first half of the 20th century in Imperial Russia and the Soviet Union was marked by a succession of major wars, famines and other disasters which caused large-scale population losses (approximately 60 million excess deaths).[47][48] After the collapse of the Soviet Union, Russia's population declined significantly – from 150 million in 1991 to 143 million in 2012[49] – but by 2013 this decline appeared to have halted.[50]

text: Many countries in the developing world have experienced extremely rapid population growth since the early 20th century, due to economic development and improvements in public health. China's population rose from approximately 430 million in 1850 to 580 million in 1953,[51] and now stands at over 1.3 billion. The population of the Indian subcontinent, which was about 125 million in 1750, increased to 389 million in 1941;[52] today, India, Pakistan and Bangladesh are collectively home to about 1.63 billion people.[53] Java had about 5 million inhabitants in 1815; its present-day successor, Indonesia, now has a population of over 140 million.[54] In just one hundred years, the population of Brazil decupled (x10), from about 17 million in 1900, or about 1% of the world population in that year, to about 176 million in 2000, or almost 3% of the global population in the very early 21st century. Mexico's population grew from 13.6 million in 1900 to about 112 million in 2010.[55][56] Between the 1920s and 2000s, Kenya's population grew from 2.9 million to 37 million.[57]

text: Milestones by the billions[edit]

text:
World population milestones in billions

Population
1
2
3
4
5
6
7
8
9

Year
1804
1927
1960
1974
1987
1999
2011
2024
2042

Years elapsed
––
123
33
14
13
12
12
13
18

text: It is estimated that the world population reached one billion for the first time in 1804. It was another 123 years before it reached two billion in 1927, but it took only 33 years to reach three billion in 1960.[58] Thereafter, the global population reached four billion in 1974, five billion in 1987, six billion in 1999 and, according to the United States Census Bureau, seven billion in March 2012.[59] The United Nations, however, estimated that the world population reached seven billion in October 2011.[60][61][62]

text: According to current projections, the global population will reach eight billion by 2024, and will likely reach around nine billion by 2042. Alternative scenarios for 2050 range from a low of 7.4 billion to a high of more than 10.6 billion.[63] Projected figures vary depending on underlying statistical assumptions and the variables used in projection calculations, especially the fertility variable. Long-range predictions to 2150 range from a population decline to 3.2 billion in the "low scenario", to "high scenarios" of 24.8 billion.[63] One extreme scenario predicted a massive increase to 256 billion by 2150, assuming the global fertility rate remained at its 1995 level of 3.04 children per woman; however, by 2010 the global fertility rate had declined to 2.52.[64][65]

text: There is no estimation for the exact day or month the world's population surpassed one or two billion. The points at which it reached three and four billion were not officially noted, but the International Database of the United States Census Bureau placed them in July 1959 and April 1974 respectively. The United Nations did determine, and commemorate, the "Day of 5 Billion" on July 11, 1987, and the "Day of 6 Billion" on October 12, 1999. The Population Division of the United Nations declared the "Day of 7 Billion" to be October 31, 2011.[66]

text: Global demographics[edit]

text:
80+
  77.5+
  75+
  72.5+
  70+
  67.5+
  65+

  60+
  55+
  50+
  45+
  40+
  less than 40

text: As of 2012, the global sex ratio is approximately 1.01 males to 1 female. The greater number of men is possibly due to the significant sex imbalances evident in the Indian and Chinese populations.[68][69] Approximately 26.3% of the global population is aged under 15, while 65.9% is aged 15–64 and 7.9% is aged 65 or over.[68] The median age of the world's population was estimated to be 29.7 years in 2014,[70] and is expected to rise to 37.9 years by 2050.[71]

text: According to the World Health Organization, the global average life expectancy is 70.5 years as of 2012, with women living an average of 73 years and men approximately 68 years.[67] In 2010, the global fertility rate was estimated at 2.52 children per woman.[65] In June 2012, British researchers calculated the total weight of Earth's human population as approximately 287 million tonnes, with the average person weighing around 62 kilograms (137 lb).[72]

text: The CIA estimated nominal 2013 gross world product at US$74.31 trillion, giving an annual global per capita figure of around US$10,500.[73] Around 1.29 billion people (18.4% of the world population) live in extreme poverty, subsisting on less than US$1.25 per day;[74] approximately 870 million people (12.25%) are undernourished.[75] 83% of the world's over-15s are considered literate.[68] In June 2014, there were around 3.03 billion global Internet users, constituting 42.3% of the world population.[76]

text: The Han Chinese are the world's largest single ethnic group, constituting over 19% of the global population in 2011.[77] The world's most-spoken first languages are Mandarin Chinese (spoken by 12.44% of the world's population), Spanish (4.85%), English (4.83%), Arabic (3.25%) and Hindustani (2.68%).[68] The world's largest religion is Christianity, whose adherents account for 31% of the global population; Islam is the second-largest religion, accounting for 24.1%, and Hinduism the third, accounting for 13.78%.[68] In 2005, around 16% of the global population were reported to be non-religious.[78]

text: Largest populations by country[edit]

text:
10 most populous countries

Rank
Country / Territory
Population
Date
Approx. % of world
population
Source

1
 China[note 4]
1,391,170,000
May 28, 2018
18.2%
[79]

2
 India
1,332,310,000
May 28, 2018
17.5%
[80]

3
 United States
327,210,000
May 28, 2018
4.29%
[81]

4
 Indonesia
261,600,000
October 31, 2016
3.43%
[82]

5
 Pakistan
211,719,000
May 28, 2018
2.78%
[83]

6
 Brazil
209,107,000
May 28, 2018
2.74%
[84]

7
 Nigeria
188,500,000
October 31, 2016
2.47%
[85]

8
 Bangladesh
164,574,000
May 28, 2018
2.16%
[86]

9
 Russia[note 5]
146,773,226
June 1, 2017
1.92%
[87]

10
 Japan
126,670,000
September 1, 2017
1.66%
[88]

text: Approximately 4.3 billion people live in these ten countries, representing around 58% of the world's population as of March 2016. Approximately 3.7 billion people, or half of the world population, live in the six most populous countries.[89]

text: Most densely populated countries[edit]

text: The tables below list the world's most densely populated countries, both in absolute terms and in comparison to their total populations.

text:
10 most densely populated countries (with population above 5 million)

Rank
Country
Population
Area (km2)
Density
(Pop. per km2)

1
 Singapore
5,612,300
710
7,905

2
 Bangladesh
164,570,000
143,998
1,143

3
 Taiwan
23,562,318
36,190
651

4
 South Korea
51,446,201
99,538
517

5
 Lebanon
6,082,000
10,452
582

6
 Rwanda
11,809,295
26,338
448

7
 Netherlands
17,220,000
41,526
415

8
 Haiti
10,911,819
27,065
403

9
 India
1,332,310,000
3,287,240
405

10
 Israel
8,860,000
22,072
401

text:
Countries ranking highly in both total population (more than 20 million people) and population density (more than 250 people per square kilometer):

Rank
Country
Population
Area (km2)
Density
(Pop. per km2)
Notes

1
 India
1,332,310,000
3,287,240
405
Growing population

2
 Pakistan
211,720,000
803,940
263
Rapidly growing population

3
 Bangladesh
164,570,000
143,998
1,143
Rapidly growing population

4
 Japan
126,670,000
377,873
335
Declining population[90]

5
 Philippines
105,940,000
300,000
353
Growing population

6
 Vietnam
93,700,000
331,689
282
Growing population

7
 United Kingdom
65,648,100
243,610
269
Slowly growing population

8
 South Korea
51,446,201
99,538
517
Slowly growing population

9
 Taiwan
23,562,318
36,190
651
Steady population

10
 Sri Lanka
21,444,000
65,610
327
Growing population

text: Fluctuation[edit]

text: Population size fluctuates at differing rates in differing regions. Nonetheless, population growth is the long-standing trend on all inhabited continents, as well as in most individual states. During the 20th century, the global population saw its greatest increase in known history, rising from about 1.6 billion in 1900 to over 6 billion in 2000. A number of factors contributed to this increase, including the lessening of the mortality rate in many countries by improved sanitation and medical advances, and a massive increase in agricultural productivity attributed to the Green Revolution.[91][92][93]

text: In 2000, the United Nations estimated that the world's population was growing at an annual rate of 1.14% (equivalent to around 75 million people),[94] down from a peak of 88 million per year in 1989. By 2000, there were approximately ten times as many people on Earth as there had been in 1700. Globally, the population growth rate has been steadily declining from its peak of 2.19% in 1963, but growth remains high in Latin America, the Middle East, and Sub-Saharan Africa.[95]

text:
7–8 children
  6–7 children

  5–6 children
  4–5 children

  3–4 children
  2–3 children

  1–2 children
  0–1 children

text: During the 2010s, Japan and some countries in Europe began to encounter negative population growth (i.e. a net decrease in population over time), due to sub-replacement fertility rates.[90]

text: In 2006, the United Nations stated that the rate of population growth was visibly diminishing due to the ongoing global demographic transition. If this trend continues, the rate of growth may diminish to zero by 2050, concurrent with a world population plateau of 9.2 billion.[96] However, this is only one of many estimates published by the UN; in 2009, UN population projections for 2050 ranged between around 8 billion and 10.5 billion.[97] An alternative scenario is given by the statistician Jorgen Randers, who argues that traditional projections insufficiently take into account the downward impact of global urbanization on fertility. Randers' "most likely scenario" reveals a peak in the world population in the early 2040s at about 8.1 billion people, followed by decline.[98] Adrian Raftery, a University of Washington professor of statistics and of sociology, states that "there’s a 70 percent probability the world population will not stabilize this century. Population, which had sort of fallen off the world’s agenda, remains a very important issue."[99]

text:
Estimated world population figures, 10,000 BC–AD 2000

Estimated world population figures, 10,000 BC–AD 2000 (in log y scale)

World population figures, 1950–2000

Estimated global growth rates, 1950–2050

Estimated and projected populations of the world and its continents (except Antarctica) from 1950 to 2100. The shaded regions correspond to the range of projections by the United Nations Department of Economic and Social Affairs.

text: Population growth by region[edit]

text: The table below shows historical and predicted regional population figures in millions.[100][101][102] The availability of historical population figures varies by region.

text:
World historical and predicted populations (in millions)[103][104][105]

Region
1500
1600
1700
1750
1800
1850
1900
1950
1999
2008
2010
2012
2050
2150

World
585
660
710
791
978
1,262
1,650
2,521
6,008
6,707
6,896
7,052
9,725
9,746

Africa
86
114
106
106
107
111
133
221
783
973
1,022
1,052
2,478
2,308

Asia
282
350
411
502
635
809
947
1,402
3,700
4,054
4,164
4,250
5,267
5,561

Europe
168
170
178
190
203
276
408
547
675
732
738
740
734
517

Latin America[Note 1]
40
20
10
16
24
38
74
167
508
577
590
603
784
912

North America[Note 1]
6
3
2
2
7
26
82
172
312
337
345
351
433
398

Oceania
3
3
3
2
2
2
6
13
30
34
37
38
57
51

text:
World historical and predicted populations by percentage distribution[103][104]

Region
1500
1600
1700
1750
1800
1850
1900
1950
1999
2008
2010
2012
2050
2150

World
100
100
100
100
100
100
100
100
100
100
100
100
100
100

Africa
14.7
17.3
14.9
13.4
10.9
8.8
8.1
8.8
13.0
14.5
14.8
15.2
25.48
23.7

Asia
48.2
53.0
57.9
63.5
64.9
64.1
57.4
55.6
61.6
60.4
60.4
60.3
54.16
57.1

Europe
28.7
25.8
25.1
20.6
20.8
21.9
24.7
21.7
11.2
10.9
10.7
10.5
7.55
5.3

Latin America[Note 1]
6.8
3.0
1.4
2.0
2.5
3.0
4.5
6.6
8.5
8.6
8.6
8.6
8.06
9.4

North America[Note 1]
1.0
0.5
0.3
0.3
0.7
2.1
5.0
6.8
5.2
5.0
5.0
5.0
4.45
4.1

Oceania
0.5
0.5
0.4
0.3
0.2
0.2
0.4
0.5
0.5
0.5
0.5
0.5
0.59
0.5

text: Past population[edit]

text: The following table gives estimates, in millions, of population in the past. The data for 1750 to 1900 are from the UN report "The World at Six Billion"[106] whereas the data from 1950 to 2015 are from a UN data sheet.[8]

text:
Year
World
Africa
Asia
Europe
Latin America & Carib.[Note 1]
North America[Note 1]
Oceania
Notes

70,000 BC
< 0.015

0
0

[107]

10,000 BC
4

[108]

8000 BC
5

6500 BC
5

5000 BC
5

4000 BC
7

3000 BC
14

2000 BC
27

1000 BC
50
7
33
9

[citation needed]

500 BC
100
14
66
16

AD 1
200
23
141
28

1000
400
70
269
50
8
1
2

1500
458
86
243
84
39
3
3

1600
580
114
339
111
10
3
3

1700
682
106
436
125
10
2
3

1750
791
106
502
163
16
2
2

1800
1,000
107
656
203
24
7
3

1850
1,262
111
809
276
38
26
2

1900
1,650
133
947
408
74
82
6

1950
2,525
229
1,394
549
169
172
12.7
[109]

1955
2,758
254
1,534
577
193
187
14.2

1960
3,018
285
1,687
606
221
204
15.8

1965
3,322
322
1,875
635
254
219
17.5

1970
3,682
366
2,120
657
288
231
19.7

1975
4,061
416
2,378
677
326
242
21.5

1980
4,440
478
2,626
694
365
254
23.0

1985
4,853
550
2,897
708
406
267
24.9

1990
5,310
632
3,202
721
447
281
27.0

1995
5,735
720
3,475
728
487
296
29.1

2000
6,127
814
3,714
726
527
314
31.1

2005
6,520
920
3,945
729
564
329
33.4

2010
6,930
1,044
4,170
735
600
344
36.4

2015
7,349
1,186
4,393
738
634
358
39.3

text: Using the above figures, the change in population from 2010 to 2015 was:

text:
World: +420 million
Africa: +142 million
Asia: +223 million
Europe: +3 million
Latin America and Caribbean: +35 million
Northern America: +14 million
Oceania: +2.9 million

text: ^ Jump up to: a b c d e f Northern America comprises the northern-most countries and territories of North America: Canada, the United States, Greenland, Bermuda, and St. Pierre and Miquelon. Latin America comprises Mexico, Central America, the Caribbean, and South America.

text: Projections[edit]

text: Long-term global population growth is difficult to predict. The United Nations and the US Census Bureau both give different estimates – according to the UN, the world population reached seven billion in late 2011,[100] while the USCB asserted that this occurred in March 2012.[111] The UN has issued multiple projections of future world population, based on different assumptions. From 2000 to 2005, the UN consistently revised these projections downward, until the 2006 revision, issued on March 14, 2007, revised the 2050 mid-range estimate upwards by 273 million.

text: Average global birth rates are declining fast, but vary greatly between developed countries (where birth rates are often at or below replacement levels) and developing countries (where birth rates typically remain high). Different ethnicities also display varying birth rates. Death rates can change rapidly due to disease epidemics, wars and other mass catastrophes, or advances in medicine.

text: 2012 United projections show a continued increase in population in the near future with a steady decline in population growth rate; the global population is expected to reach between 8.3 and 10.9 billion by 2050.[112][113] 2003 UN Population Division population projections for the year 2150 range between 3.2 and 24.8 billion.[64] One of many independent mathematical models supports the lower estimate,[114] while a 2014 estimate forecasts between 9.3 and 12.6 billion in 2100, and continued growth thereafter.[115][116] Some analysts have questioned the sustainability of further world population growth, highlighting the growing pressures on the environment, global food supplies, and energy resources.[117][118][119]

text:
UN (medium variant – 2012 revision) and US Census Bureau (June 2015) estimates[120][121]

Year
UN est.
(millions)
Difference
USCB est.
(millions)
Difference

2005
6,514
–
6,473
–

2010
6,916
402
6,866
393

2015
7,324
408
7,256
390

2020
7,717
393
7,643
380

2025
8,083
366
8,007
363

2030
8,425
342
8,341
334

2035
8,743
318
8,646
306

2040
9,039
296
8,926
280

2045
9,308
269
9,180
254

2050
9,551
243
9,408
228

text:
UN 2012 estimates and medium variant projections (in millions)[120]

Year
World
Asia
Africa
Europe
Latin America/Caribbean
Northern America
Oceania

2010
6,916
4,165 (60.2%)
1,031 (14.9%)
740 (10.7%)
596 (8.6%)
347 (5.0%)
37 (0.5%)

2015
7,324
4,385 (59.9%)
1,166 (15.9%)
743 (10.1%)
630 (8.6%)
361 (4.9%)
39 (0.5%)

2020
7,717
4,582 (59.4%)
1,312 (17.0%)
744 (9.6%)
662 (8.6%)
376 (4.9%)
42 (0.5%)

2025
8,083
4,749 (58.8%)
1,468 (18.2%)
741 (9.2%)
691 (8.5%)
390 (4.8%)
45 (0.6%)

2030
8,425
4,887 (58.0%)
1,634 (19.4%)
736 (8.7%)
717 (8.5%)
403 (4.8%)
47 (0.6%)

2035
8,743
4,997 (57.2%)
1,812 (20.7%)
730 (8.3%)
739 (8.5%)
415 (4.8%)
50 (0.6%)

2040
9,039
5,080 (56.2%)
1,999 (22.1%)
724 (8.0%)
757 (8.4%)
426 (4.8%)
52 (0.6%)

2045
9,308
5,136 (55.2%)
2,194 (23.6%)
717 (7.7%)
771 (8.3%)
436 (4.7%)
55 (0.6%)

2050
9,551
5,164 (54.1%)
2,393 (25.1%)
709 (7.4%)
782 (8.2%)
446 (4.7%)
57 (0.6%)

2055
9,766
5,168 (52.9%)
2,595 (26.6%)
700 (7.2%)
788 (8.1%)
456 (4.7%)
59 (0.6%)

2060
9,957
5,152 (51.7%)
2,797 (28.1%)
691 (6.9%)
791 (7.9%)
465 (4.7%)
61 (0.6%)

2065
10,127
5,120 (50.6%)
2,998 (29.6%)
681 (6.7%)
791 (7.8%)
474 (4.7%)
63 (0.6%)

2070
10,277
5,075 (49.4%)
3,195 (31.1%)
673 (6.5%)
788 (7.6%)
482 (4.7%)
64 (0.6%)

2075
10,409
5,019 (48.2%)
3,387 (32.5%)
665 (6.4%)
783 (7.5%)
490 (4.7%)
66 (0.6%)

2080
10,524
4,957 (47.1%)
3,570 (33.9%)
659 (6.3%)
776 (7.4%)
496 (4.7%)
67 (0.6%)

2085
10,626
4,894 (46.1%)
3,742 (35.2%)
653 (6.1%)
767 (7.2%)
502 (4.7%)
68 (0.6%)

2090
10,717
4,833 (45.1%)
3,903 (36.4%)
649 (6.1%)
757 (7.1%)
506 (4.7%)
69 (0.6%)

2095
10,794
4,773 (44.2%)
4,051 (37.6%)
644 (6.0%)
747 (6.9%)
510 (4.7%)
69 (0.6%)

2100
10,854
4,712 (43.4%)
4,185 (38.6%)
639 (5.9%)
736 (6.8%)
513 (4.7%)
70 (0.6%)

text: Mathematical approximations[edit]

text: In 1975, Sebastian von Hoerner proposed a formula for population growth which represented hyperbolic growth with an infinite population in 2025.[122] The hyperbolic growth of the world population observed until the 1970s was later correlated to a non-linear second order positive feedback between demographic growth and technological development. This feedback can be described as follows: technological advance → increase in the carrying capacity of land for people → demographic growth → more people → more potential inventors → acceleration of technological advance → accelerating growth of the carrying capacity → faster population growth → accelerating growth of the number of potential inventors → faster technological advance → hence, the faster growth of the Earth's carrying capacity for people, and so on.[123] The transition from hyperbolic growth to slower rates of growth is related to the demographic transition.

text: According to the Russian demographer Sergey Kapitsa,[124] the world population grew between 67,000 BC and 1965 according to the following formula:

text: where

text:
N is current population
T is the current year
C = (1.86±0.01)·1011
T0 = 2007±1

τ

{\displaystyle \tau }

 = 42±1

text: Years for world population to double[edit]

text: According to linear interpolation and extrapolation of UNDESA population estimates, the world population has doubled, or will double, in the years listed in the tables below (with two different starting points). During the 2nd millennium, each doubling took roughly half as long as the previous doubling, fitting the hyperbolic growth model mentioned above. However, after 2024, it is unlikely that there will be another doubling of the global population in the 21st century.[125]

text:
Starting at 500 million

Population
(in billions)
0.5
1
2
4
8

Year
1500
1804
1927
1974
2024

Years elapsed
304
123
47
50

text:
Starting at 375 million

Population
(in billions)
0.375
0.75
1.5
3
6

Year
1171
1715
1881
1960
1999

Years elapsed
544
166
79
39

text: Overpopulation[edit]

text: Predictions of scarcity[edit]

text: In his 1798 work An Essay on the Principle of Population, the British scholar Thomas Malthus incorrectly predicted that continued population growth would exhaust the global food supply by the mid-19th century. Malthus wrote the essay to refute what he considered the unattainable utopian ideas of William Godwin and Marquis de Condorcet, as presented in Political Justice and The Future Progress of the Human Mind. In 1968, Paul R. Ehrlich reprised Malthus' argument in The Population Bomb, predicting that mass global famine would occur in the 1970s and 1980s.[127]

text: The predictions of Ehrlich and other neo-Malthusians were vigorously challenged by a number of economists, notably Julian Lincoln Simon, and advances in agriculture, collectively known as the Green Revolution, forestalled any potential global famine in the late 20th century. Between 1950 and 1984, as the Green Revolution transformed agriculture around the world, grain production increased by over 250%.[128] The world population has grown by over four billion since the beginning of the Green Revolution, but food production has so far kept pace with population growth. Most scholars believe that, without the Revolution, there would be greater levels of famine and malnutrition than the UN presently documents.[129] However, neo-Malthusians point out that fossil fuels provided the energy for the Green Revolution, in the form of natural gas-derived fertilizers, oil-derived pesticides, and hydrocarbon-fueled irrigation, and that many crops have become so genetically uniform that a crop failure in any one country could potentially have global repercussions.[130]

text: In 2004, a meta-analysis of 70 quantitative studies estimating a sustainable limit to the world population generated a meta-estimate of 7.7 billion people.[131]

text: In May 2008, the price of grain was pushed up severely by the increased cultivation of biofuels, the increase of world oil prices to over $140 per barrel ($880/m3),[132] global population growth,[133] the effects of climate change,[134] the loss of agricultural land to residential and industrial development,[135][136] and growing consumer demand in the population centres of China and India.[137][138] Food riots subsequently occurred in some countries.[139][140] However, oil prices then fell sharply. Resource demands are expected to ease as population growth declines, but it is unclear whether mass food wastage and rising living standards in developing countries will once again create resource shortages.[141][142]

text: David Pimentel, professor of ecology and agriculture at Cornell University, estimates that the sustainable agricultural carrying capacity for the United States is about 200 million people; its population as of 2015 is over 300 million.[143] In 2009, the UK government's chief scientific advisor, Professor John Beddington, warned that growing populations, falling energy reserves and food shortages would create a "perfect storm" of shortages of food, water, and energy by 2030.[126][144] According to a 2009 report by the United Nations Food and Agriculture Organisation (FAO), the world will have to produce 70% more food by 2050 to feed a projected extra 2.3 billion people.[145]

text: The observed figures for 2007 showed an actual increase in absolute numbers of undernourished people in the world, with 923 million undernourished in 2007, versus 832 million in 1995.[146] The 2009 FAO estimates showed an even more dramatic increase, to 1.02 billion.[147]

text: Environmental impacts[edit]

text: A number of scientists have argued that the current global population expansion and accompanying increase in resource consumption threatens the world's ecosystem.[148][149] The InterAcademy Panel Statement on Population Growth, which was ratified by 58 member national academies in 1994, states that "unprecedented" population growth aggravates many environmental problems, including rising levels of atmospheric carbon dioxide, global warming, and pollution.[150] Indeed, some analysts claim that overpopulation's most serious impact is its effect on the environment.[118] The situation has continued to worsen, as at the time of the 1994 IAP statement, the world population stood at 5.5 billion and lower-bound scenarios predicted a peak of 7.8 billion by 2050, a number that current estimates state will be reached in the late 2020s.

text: Scientists contend that human overpopulation, continued human population growth and overconsumption, particularly by the wealthy, are the primary drivers of mass species extinction.[151][152][153][154] By 2050 population growth, along with profligate consumption, could result in oceans containing more plastic than fish by weight.[153] In November 2017, a statement by 15,364 scientists from 184 countries asserted that rapid human population growth is the "primary driver behind many ecological and even societal threats."[155]

text: A July 2017 study published in Environmental Research Letters argued that the most significant way individuals could mitigate their own carbon footprint is to have fewer children, followed by living without a vehicle, forgoing air travel and adopting a plant-based diet.[156]

text: Population control[edit]

text: Human population control is the practice of intervening to alter the rate of population growth. Historically, human population control has been implemented by limiting a region's birth rate, by voluntary contraception or by government mandate. It has been undertaken as a response to factors including high or increasing levels of poverty, environmental concerns, and religious reasons. The use of abortion in some population control strategies has caused controversy,[157] with religious organizations such as the Roman Catholic Church explicitly opposing any intervention in the human reproductive process.[158]

text: The University of Nebraska publication Green Illusions argues that population control to alleviate environmental pressures need not be coercive. It states that "Women who are educated, economically engaged, and in control of their own bodies can enjoy the freedom of bearing children at their own pace, which happens to be a rate that is appropriate for the aggregate ecological endowment of our planet."[159] The book Fatal Misconception by Matthew Connelly similarly points to the importance of supporting the rights of women in bringing population levels down over time.[160]


document_title: Gas exchange

question_text: where are gases exchanged in the respiratory system

root

text: Gas exchange

text: Physical principles of gas-exchange[edit]

text: Diffusion and surface area[edit]

text: The exchange of gases occurs as a result of diffusion down a concentration gradient. Gas molecules move from a region in which they are at high concentration to one in which they are at low concentration. Diffusion is a passive process, meaning that no energy is required to power the transport, and it follows Fick’s Law:[citation needed]

tag: p

text: In relation to a typical biological system, where two compartments ('inside' and 'outside'), are separated by a membrane barrier, and where a gas is allowed to spontaneously diffuse down its concentration gradient:[citation needed]

text:
J is the flux, the amount of gas diffusing per unit area of membrane per unit time. Note that this is already scaled for the area of the membrane.
D is the diffusion coefficient, which will differ from gas to gas, and from membrane to membrane, according to the size of the gas molecule in question, and the nature of the membrane itself (particularly its viscosity, temperature and hydrophobicity).
φ is the concentration of the gas.
x is the position across the thickness of the membrane.
dφ/dx is therefore the concentration gradient across the membrane. If the two compartments are individually well-mixed, then this is simplifies to the difference in concentration of the gas between the inside and outside compartments divided by the thickness of the membrane.
The negative sign indicates that the diffusion is always in the direction that - over time - will destroy the concentration gradient, i.e. the gas moves from high concentration to low concentration until eventually the inside and outside compartments reach equilibrium.

tag: ul

text: Fig. 1. Fick's Law for gas-exchange surface

text: Gases must first dissolve in a liquid in order to diffuse across a membrane, so all biological gas exchange systems require a moist environment.[3] In general, the higher the concentration gradient across the gas-exchanging surface, the faster the rate of diffusion across it. Conversely, the thinner the gas-exchanging surface (for the same concentration difference), the faster the gases will diffuse across it.[4]

text: In the equation above, J is the flux expressed per unit area, so increasing the area will make no difference to its value. However, an increase in the available surface area, will increase the amount of gas that can diffuse in a given time.[4] This is because the amount of gas diffusing per unit time (dq/dt) is the product of J and the area of the gas-exchanging surface, A:

text: Single-celled organisms such as bacteria and amoebae do not have specialised gas exchange surfaces, because they can take advantage of the high surface area they have relative to their volume. The amount of gas an organism produces (or requires) in a given time will be in rough proportion to the volume of its cytoplasm. The volume of a unicellular organism is very small, therefore it produces (and requires) a relatively small amount of gas in a given time. In comparison to this small volume, the surface area of its cell membrane is very large, and adequate for its gas-exchange needs without further modification. However, as an organism increases in size, its surface area and volume do not scale in the same way. Consider an imaginary organism that is a cube of side-length, L. Its volume increases with the cube (L3) of its length, but its external surface area increases only with the square (L2) of its length. This means the external surface rapidly becomes inadequate for the rapidly increasing gas-exchange needs of a larger volume of cytoplasm. Additionally, the thickness of the surface that gases must cross (dx in Fick's Law) can also be larger in larger organisms: in the case of a single-celled organism, a typical cell membrane is only 10 nm thick;[5] but in larger organisms such as roundworms (Nematoda) the equivalent exchange surface - the cuticle - is substantially thicker at 0.5 µm.[6]

text: Interaction with circulatory systems[edit]

text: In multicellular organisms therefore, specialised respiratory organs such as gills or lungs are often used to provide the additional surface area for the required rate of gas exchange with the external environment. However the distances between the gas exchanger and the deeper tissues are often too great for diffusion to meet gaseous requirements of these tissues. The gas exchangers are therefore frequently coupled to gas-distributing circulatory systems, which transport the gases evenly to all the body tissues regardless of their distance from the gas exchanger.[7]

text: Some multicellular organisms such as flatworms (Platyhelminthes) are relatively large but very thin, allowing their outer body surface to act as a gas exchange surface without the need for a specialised gas exchange organ. Flatworms therefore lack gills or lungs, and also lack a circulatory system. Other multicellular organisms such as sponges (Porifera) have an inherently high surface area, because they are very porous and/or branched. Sponges do not require a circulatory system or specialised gas exchange organs, because their feeding strategy involves one-way pumping of water through their porous bodies using flagellated collar cells. Each cell of the sponge's body is therefore exposed to a constant flow of fresh oxygenated water. They can therefore rely on diffusion across their cell membranes to carry out the gas exchange needed for respiration.[8]

text: In organisms that have circulatory systems associated with their specialized gas-exchange surfaces, a great variety of systems are used for the interaction between the two.

text: In a countercurrent flow system, air (or, more usually, the water containing dissolved air) is drawn in the opposite direction to the flow of blood in the gas exchanger. A countercurrent system such as this maintains a steep concentration gradient along the length of the gas-exchange surface (see lower diagram in Fig. 2). This is the situation seen in the gills of fish and many other aquatic creatures.[9] The gas-containing environmental water is drawn unidirectionally across the gas-exchange surface, with the blood-flow in the gill capillaries beneath flowing in the opposite direction.[9][10][11] Although this theoretically allows almost complete transfer of a respiratory gas from one side of the exchanger to the other, in fish less than 80% of the oxygen in the water flowing over the gills is generally transferred to the blood.[9]

text:
Alternative arrangements are cross current systems found in birds.[12][13] and dead-end air-filled sac systems found in the lungs of mammals.[14][15] In a cocurrent flow system, the blood and gas (or the fluid containing the gas) move in the same direction through the gas exchanger. This means the magnitude of the gradient is variable along the length of the gas-exchange surface, and the exchange will eventually stop when an equilibrium has been reached (see upper diagram in Fig. 2).[9]
Cocurrent flow gas exchange systems are not known to be used in nature.

text: Mammals[edit]

text: The gas exchanger in mammals is internalized to form lungs, as it is in most of the larger land animals.[citation needed] Gas exchange occurs in microscopic dead-end  air-filled sacs called alveoli, where a very thin membrane (called the blood-air barrier) separates the blood in the alveolar capillaries (in the walls of the alveoli) from the alveolar air in the sacs.

text: Exchange membrane[edit]

text: The membrane across which gas exchange takes place in the alveoli (i.e. the blood-air barrier) is extremely thin (in humans, on average, 2.2 μm thick).[14] It consists of the alveolar epithelial cells, their basement membranes and the endothelial cells of the pulmonary capillaries (Fig. 4).[14][16] The large surface area of the membrane comes from the folding of the membrane into about 300 million alveoli, with diameters of approximately 75-300 µm each. This provides an extremely large surface area (approximately 145 m2) across which gas exchange can occur.[14]

text: Alveolar air[edit]

text: Air is brought to the alveoli in small doses (called the tidal volume), by breathing in (inhalation) and out (exhalation) through the respiratory airways, a set of relatively narrow and moderately long tubes which start at the nose or mouth and end in the alveoli of the lungs in the chest. Air moves in and out through the same set of tubes, in which the flow is in one direction during inhalation, and in the opposite direction during exhalation.

text: During each inhalation, at rest, approximately 500 ml of fresh air flows in through the nose. Its is warmed and moistened as it flows through the nose and pharynx. By the time it reaches the trachea the inhaled air's temperature is 37 °C and it is saturated with water vapor. On arrival in the alveoli it is diluted and thoroughly mixed with the approximately  2.5–3.0 liters of air that remained in the alveoli after the last exhalation. This relatively large volume of air that is semi-permanently present in the alveoli throughout the breathing cycle is known as the functional residual capacity (FRC).[15]

text: At the beginning of inhalation the airways are filled with unchanged alveolar air, left over from the last exhalation. This is the dead space volume, which is usually about 150 ml.[17] It is the first air to re-enter the alveoli during inhalation. Only after the dead space air has returned to the alveoli does the remainder of the tidal volume (500 ml - 150 ml = 350 ml) enter the alveoli.[15] The entry of such a small volume of fresh air with each inhalation, ensures that the composition of the FRC hardly changes during the breathing cycle (Fig. 5).[15] The alveolar partial pressure of oxygen remains very close to 13–14 kPa (100 mmHg), and the partial pressure of carbon dioxide varies minimally around 5.3 kPa (40 mmHg) throughout the breathing cycle (of inhalation and exhalation).[15] The corresponding partial pressures of oxygen and carbon dioxide in the ambient (dry) air at sea level are 21 kPa (160 mmHg) and 0.04 kPa (0.3 mmHg) respectively.[15]

text: This alveolar air, which constitutes the FRC, completely surrounds the blood in the alveolar capillaries (Fig. 6). Gas exchange in mammals occurs between this alveolar air (which differs significantly from fresh air) and the blood in the alveolar capillaries. The gases on either side of the gas exchange membrane equilibrate by simple diffusion. This ensures that the partial pressures of oxygen and carbon dioxide in the blood leaving the alveolar capillaries, and ultimately circulates throughout the body, are the same as those in the FRC.[15]

text: The marked difference between the composition of the alveolar air and that of the ambient air can be maintained because the functional residual capacity is contained in dead-end sacs connected to the outside air by long, narrow, tubes (the airways: nose, pharynx, larynx, trachea, bronchi and their branches and sub-branches down to the bronchioles). This anatomy, and the fact that the lungs are not emptied and re-inflated with each breath, provides mammals with a "portable atmosphere", whose composition differs significantly from the present-day ambient air.[18]

text: The composition of the air in the FRC is carefully monitored, by measuring the partial pressures of oxygen and carbon dioxide in the arterial blood. If either gas pressure deviates from normal, reflexes are elicited that change the rate and depth of breathing in such a way that normality is restored within seconds or minutes.[15]

text: Pulmonary circulation[edit]

text:
All the blood returning from the body tissues to the right side of the heart flows through the alveolar capillaries before being pumped around the body again. On its passage through the lungs the blood comes into close contact with the alveolar air, separated from it by a very thin diffusion membrane which is only, on average, about 2 μm thick.[14] The gas pressures in the blood will therefore rapidly equilibrate with those in the alveoli, ensuring that the arterial blood that circulates to all the tissues throughout the body has an oxygen tension of 13−14 kPa (100 mmHg), and a carbon dioxide tension of 5.3 kPa (40 mmHg). These arterial partial pressures of oxygen and carbon dioxide are homeostatically controlled. A rise in the arterial

P

C
O

2

{\displaystyle P_{{\mathrm {CO} }_{2}}}

, and, to a lesser extent, a fall in the arterial

P

O

2

{\displaystyle P_{{\mathrm {O} }_{2}}}

, will reflexly cause deeper and faster breathing till the blood gas tensions return to normal. The converse happens when the carbon dioxide tension falls, or, again to a lesser extent, the oxygen tension rises: the rate and depth of breathing are reduced till blood gas normality is restored.

text:
Since the blood arriving in the alveolar capillaries has a

P

O

2

{\displaystyle P_{{\mathrm {O} }_{2}}}

 of, on average, 6 kPa (45 mmHg), while the pressure in the alveolar air is 13 kPa (100 mmHg), there will be a net diffusion of oxygen into the capillary blood, changing the composition of the 3 liters of alveolar air slightly. Similarly, since the blood arriving in the alveolar capillaries has a

P

C
O

2

{\displaystyle P_{{\mathrm {CO} }_{2}}}

 of also about 6 kPa (45 mmHg), whereas that of the alveolar air is 5.3 kPa (40 mmHg), there is a net movement of carbon dioxide out of the capillaries into the alveoli. The changes brought about by these net flows of individual gases into and out of the functional residual capacity necessitate the replacement of about 15% of the alveolar air with ambient air every  5 seconds or so. This is very tightly controlled by the continuous monitoring of the arterial blood gas tensions (which accurately reflect partial pressures  of the respiratory gases in the alveolar air) by the aortic bodies, the carotid bodies, and the blood gas and pH sensor on the anterior surface of the medulla oblongata in the brain. There are also oxygen and carbon dioxide sensors in the lungs, but they primarily determine the diameters of the bronchioles and pulmonary capillaries, and are therefore responsible for directing the flow of air and blood to different parts of the lungs.

text:
It is only as a result of accurately maintaining the composition of the 3 liters alveolar air that with each breath some carbon dioxide is discharged into the atmosphere and some oxygen is taken up from the outside air. If more carbon dioxide than usual has been lost by a short period of hyperventilation, respiration will be slowed down or halted until the alveolar

P

C
O

2

{\displaystyle P_{{\mathrm {CO} }_{2}}}

 has returned to 5.3 kPa (40 mmHg). It is therefore strictly speaking untrue that the primary function of the respiratory system is to rid the body of carbon dioxide “waste”. In fact the total concentration of carbon dioxide in arterial blood  is about 26 mM (or 58 ml per 100 ml),[19] compared to the concentration of oxygen in saturated arterial blood of about 9 mM (or 20 ml per 100 ml blood).[15] This large concentration of carbon dioxide plays a pivotal role in the determination and maintenance of the pH of the extracellular fluids. The carbon dioxide that is breathed out with each breath could probably be more correctly be seen as a byproduct of the body’s extracellular fluid carbon dioxide and  pH homeostats

text: If these homeostats are compromised, then a respiratory acidosis, or a respiratory alkalosis will occur. In the long run these can be compensated by renal adjustments to the H+ and HCO3− concentrations in the plasma; but since this takes time, the hyperventilation syndrome can, for instance, occur when agitation or anxiety cause a person to breathe fast and deeply[20] thus blowing off too much CO2 from the blood into the outside air, precipitating a set of distressing symptoms which result from an excessively high pH of the extracellular fluids.[21]

text: Oxygen has a very low solubility in water, and is therefore carried in the blood loosely combined with hemoglobin. The oxygen is held on the hemoglobin by four ferrous iron-containing heme groups per hemoglobin molecule. When all the heme groups carry one O2 molecule each the blood is said to be “saturated” with oxygen, and no further increase in the partial pressure of oxygen will meaningfully increase the oxygen concentration of the blood. Most of the carbon dioxide in the blood is carried as HCO3− ions in the plasma. However the conversion of dissolved CO2 into HCO3− (through the addition of water) is too slow for the rate at which the blood circulates through the tissues on the one hand, and alveolar capillaries on the other. The reaction is therefore catalyzed by carbonic anhydrase, an enzyme inside the red blood cells.[22] The reaction can go in either direction depending on the prevailing partial pressure of carbon dioxide. A small amount of carbon dioxide is carried on the protein portion of the hemoglobin molecules as carbamino groups. The total concentration of carbon dioxide (in the form of bicarbonate ions, dissolved CO2, and carbamino groups) in arterial blood (i.e. after it has equilibrated with the alveolar air) is about 26 mM (or 58 ml/100 ml),[19] compared to the concentration of oxygen in saturated arterial blood of about 9 mM (or 20 ml/100 ml blood).[15]

text: Other vertebrates[edit]

text: Fish[edit]

text: The dissolved oxygen content in fresh water is approximately 8–10 milliliters per liter compared to that of air which is 210 milliliters per liter.[23] Water is 800 times more dense than air[24] and 100 times more viscous.[23] Therefore, oxygen has a diffusion rate in air 10,000 times greater than in water.[23] The use of sac-like lungs to remove oxygen from water would therefore not be efficient enough to sustain life.[23] Rather than using lungs, gaseous exchange takes place across the surface of highly vascularized gills. Gills are specialised organs containing filaments, which further divide into lamellae. The lamellae contain capillaries that provide a large surface area and short diffusion distances, as their walls are extremely thin.[25] Gill rakers are found within the exchange system in order to filter out food, and keep the gills clean.

text: Gills use a countercurrent flow system that increases the efficiency of oxygen-uptake (and waste gas loss).[9][10][11] Oxygenated 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 countercurrent maintains steep concentration gradients along the entire length of each capillary (see the diagram in the "Interaction with circulatory systems" section above). Oxygen is able to continually diffuse down its gradient into the blood, and the carbon dioxide down its gradient into the water.[10] The deoxygenated water will eventually pass out through the operculum (gill cover). Although countercurrent exchange systems theoretically allow an almost complete transfer of a respiratory gas from one side of the exchanger to the other, in fish less than 80% of the oxygen in the water flowing over the gills is generally transferred to the blood.[9]

text: Amphibians[edit]

text: Amphibians have three main organs involved in gas exchange: the lungs, the skin, and the gills, which can be used singly or in a variety of different combinations. The relative importance of these structures differs according to the age, the environment and species of the amphibian. The skin of amphibians and their larvae is highly vascularised, leading to relatively efficient gas exchange when the skin is moist. The larvae of amphibians, such as the pre-metamorphosis tadpole stage of frogs, also have external gills. The gills are absorbed into the body during metamorphosis, after which the lungs will then take over. The lungs are usually simpler than in the other land vertebrates, with few internal septa and larger alveoli; however, toads, which spend more time on land, have a larger alveolar surface with more developed lungs. To increase the rate of gas exchange by diffusion, amphibians maintain the concentration gradient across the respiratory surface using a process called buccal pumping.[26] The lower floor of the mouth is moved in a "pumping" manner, which can be observed by the naked eye.

text: Reptiles[edit]

text: All reptiles breathe using lungs. In squamates (the lizards and snakes) ventilation is driven by the axial musculature, but this musculature is also used during movement, so some squamates rely on buccal pumping to maintain gas exchange efficiency.[27]

text: Due to the rigidity of turtle and tortoise shells, significant expansion and contraction of the chest is difficult. Turtles and tortoises depend on muscle layers attached to their shells, which wrap around their lungs to fill and empty them.[28] Some aquatic turtles can also pump water into a highly vascularised mouth or cloaca to achieve gas-exchange.[29][30]

text: Crocodiles have a structure similar to the mammalian diaphragm - the diaphragmaticus - but this muscle helps create a unidirectional flow of air through the lungs rather than a tidal flow: this is more similar to the air-flow seen in birds than that seen in mammals.[31] During inhalation, the diaphragmaticus pulls the liver back, inflating the lungs into the space this creates.[32][33] Air flows into the lungs from the bronchus during inhalation, but during exhalation, air flows out of the lungs into the bronchus by a different route: this one-way movement of gas is achieved by aerodynamic valves in the airways.[34][35]

text: Birds[edit]

text: Birds have lungs but no diaphragm. They rely mostly on air sacs for ventilation. These air sacs do not play a direct role in gas exchange, but help to move air unidirectionally across the gas exchange surfaces in the lungs. During inhalation, fresh air is taken from the trachea down into the posterior air sacs and into the parabronchi which lead from the posterior air sacs into the lung. The air that enters the lungs joins the  air which is already in the lungs, and is drawn forward across the gas exchanger into anterior air sacs. During exhalation, the posterior air sacs force air into the same parabronchi of the lungs, flowing in the same direction as during inhalation, allowing continuous gas exchange irrespective of the breathing cycle. Air exiting the lungs during exhalation joins the air being expelled from the anterior air sacs (both consisting of "spent air" that has passed through the gas exchanger) entering the trachea to be  exhaled  (Fig. 10).[13] Selective bronchoconstriction at the various bronchial branch points ensures that the air does not ebb and flow through the bronchi during inhalation and exhalation, as it does in mammals, but follows the paths described above.

text:
The unidirectional airflow through the parabronchi exchanges respiratory gases with a crosscurrent blood flow (Fig. 9).[12][13] The partial pressure of O2 (

P

O

2

{\displaystyle P_{{\mathrm {O} }_{2}}}

) in the parabronchioles declines along their length as O2 diffuses into the blood. The capillaries leaving the exchanger near the entrance of airflow take up more O2 than capillaries leaving near the exit end of the parabronchi.  When the contents of all capillaries mix, the final

P

O

2

{\displaystyle P_{{\mathrm {O} }_{2}}}

 of the mixed pulmonary venous blood is higher than that of the exhaled air, but lower than that of the inhaled air.[12][13]

text: Plants[edit]

text: Gas exchange in plants is dominated by the roles of carbon dioxide, oxygen and water vapor. CO2 is the only carbon source for autotrophic growth by photosynthesis, and when a plant is actively photosynthesising in the light, it will be taking up carbon dioxide, and losing water vapor and oxygen. At night, plants respire, and gas exchange partly reverses: water vapor is still lost (but to a smaller extent), but oxygen is now taken up and carbon dioxide released.[36]

text: Plant gas exchange occurs mostly through the leaves. Gases diffuse into and out of the intercellular spaces within the leaf through pores called stomata, which are typically found on the lower surface of the leaf. Gases enter into the photosynthetic tissue of the leaf through dissolution onto the moist surface of the palisade and spongy mesophyll cells. The spongy mesophyll cells are loosely packed, allowing for an increased surface area, and subsequently an increased rate of gas-exchange. Uptake of carbon dioxide necessarily results in some loss of water vapor,[37] because both molecules enter and leave by the same stomata, so plants experience a gas exchange dilemma: gaining enough CO2 without losing too much water. Therefore, water loss from other parts of the leaf is minimised by the waxy cuticle on the leaf's epidermis. The size of a stoma is regulated by the opening and closing of its two guard cells: the turgidity of these cells determines the state of the stomatal opening, and this itself is regulated by water stress. Plants showing crassulacean acid metabolism are drought-tolerant xerophytes and perform almost all their gas-exchange at night, because it is only during the night that these plants open their stomata. By opening the stomata only at night, the water vapor loss associated with carbon dioxide uptake is minimised. However, this comes at the cost of slow growth: the plant has to store the carbon dioxide in the form of malic acid for use during the day, and it cannot store unlimited amounts.[38]

text: Gas exchange measurements are important tools in plant science: this typically involves sealing the plant (or part of a plant) in a chamber and measuring changes in the concentration of carbon dioxide with an infrared gas analyzer. If the environmental conditions (humidity, CO2 concentration, light and temperature) are fully controlled, the measurements of CO2 uptake and water release reveal important information about the CO2 assimilation and transpiration rates. The intercellular CO2 concentration reveals important information about the photosynthetic condition of the plants.[39][40] Simpler methods can be used in specific circumstances: hydrogencarbonate indicator can be used to monitor the consumption of CO2 in a solution containing a single plant leaf at different levels of light intensity,[41] and oxygen generation by the pondweed Elodea can be measured by simply collecting the gas in a submerged test-tube containing a small piece of the plant.

text: Invertebrates[edit]

text: The mechanism of gas exchange in invertebrates depends their size, feeding strategy, and habitat (aquatic or terrestrial).

text: The sponges (Porifera) are sessile creatures, meaning they are unable to move on their own and normally remain attached to their substrate. They obtain nutrients through the flow of water across their cells, and they exchange gases by simple diffusion across their cell membranes. Pores called ostia draw water into the sponge and the water is subsequently circulated through the sponge by cells called choanocytes which have hair-like structures that move the water through the sponge.[42]

text: The cnidarians include corals, sea anemones, jellyfish and hydras. These animals are always found in aquatic environments, ranging from fresh water to salt water. They do not have any dedicated respiratory organs; instead, every cell in their body can absorb oxygen from the surrounding water, and release waste gases to it. One key disadvantage of this feature is that cnidarians can die in environments where water is stagnant, as they deplete the water of its oxygen supply.[43] Corals often form symbiosis with other organisms, particularly photosynthetic dinoflagellates. In this symbiosis, the coral provides shelter and the other organism provides nutrients to the coral, including oxygen.

text: The roundworms (Nematoda), flatworms (Platyhelminthes), and many other small invertebrate animals living in aquatic or otherwise wet habitats do not have a dedicated gas-exchange surface or circulatory system. They instead rely on diffusion of CO2 and O2 directly across their cuticle.[44][45] The cuticle is the semi-permeable outermost layer of their bodies.

text: Other aquatic invertebrates such as most molluscs (Mollusca) and larger crustaceans (Crustacea) such as lobsters, have gills analogous to those of fish, which operate in a similar way.

text: Unlike the invertebrates groups mentioned so far, insects are usually terrestrial, and exchange gases across a moist surface in direct contact with the atmosphere, rather than in contact with surrounding water. The insect's exoskeleton is impermeable to gases, including water vapor, so they have a more specialised gas exchange system, requiring gases to be directly transported to the tissues via a complex network of tubes. This respiratory system is separated from their circulatory system. Gases enter and leave the body through openings called spiracles, located laterally along the thorax and abdomen. Similar to plants, insects are able to control the opening and closing of these spiracles, but instead of relying on turgor pressure, they rely on muscle contractions.[46] These contractions result in an insect's abdomen being pumped in and out. The spiracles are connected to tubes called tracheae, which branch repeatedly and ramify into the insect's body. These branches terminate in specialised tracheole cells which provides a thin, moist surface for efficient gas exchange, directly with cells.[47]

text: The other main group of terrestrial arthropod, the arachnids (spiders, scorpion, mites, and their relatives) typically perform gas exchange with a book lung.[48]

text: Summary of main gas exchange systems[edit]

text:
Surface area
Diffusion distance
Maintaining concentration gradient
Respiratory organs

Human
Total alveoli[49] = 70–100 m2
Alveolus and capillary (two cells)
Constant blood flow in capillaries; breathing
Lungs

Fish
Many lamellae and filaments per gill
Usually one cell
Countercurrent flow
Gills

Insects
Specialised tracheole cell
One cell
Buccal pumping
Spiracles

Sponges
Ostia pores
One cell
Water movement
None

Flatworms
Flat body shape
Usually one cell
Countercurrent flow
None

Cnidarians
Oral arms
Usually one cell
Water movement
None

Reptiles
Many lamellae and filaments per gill
Alveolus and capillary (two cells)
Countercurrent flow
Lungs

Amphibians
Many lamellae and filaments per gill
Alveolus and capillary (two cells) or one cell
Countercurrent flow
Lungs, skin and gills

Plants
High density of stomata; air spaces within leaf
One cell
Constant air flow
Stomata

tag: table


document_title: Rape in English law

question_text: what is the prison sentence for statutory rape in uk

text: Rape in English law

text: "Intentionally", s.1(1)(a)[edit]

text: See Intention (criminal law)

text: Penetration, s.1(1)(a) & (b)[edit]

text: See section 79(2).

text: Meaning of expressions relating to parts of the body[edit]

text: See sections 79(3) and (9)

text: Consent, s.1(1)(b) & (c) & (2)[edit]

text: This expression is defined by section 74. The evidential and conclusive presumptions created by sections 75 and 76 apply to this offence (s.1(3)). They must be read with section 77.

text: "Rape by deception" (or "by fraud")[edit]

text: The term "rape by deception" covers cases where sexual activity was procured by deceit, and the question of when deceit is substantial enough to mitigate consent. In English law, the basis for such claims is "very narrow", as ruled by the Court of Appeal in R v Linekar [1995] 3 All ER 69 73. Past cases where deceit has negated consent and rape has been ruled, include R v Assange and R(F) v DPP (the sexual act was performed in a way that broke a condition agreed previously), and R - v - McNally (deceit as to gender).[4] The Sexual Offences Act 1956 contained a ground of "procuring intercourse by false pretences" but this was abolished in the 2003 Act.[citation needed]

text: A paper on website The Student Lawyer examined the basis for fraud as grounds for negating consent. It concluded that the issues which might arise if this was a legal basis to negate consent, could be far wider than might be first appreciated. Examples given by the author included sex in the following circumstances:[5] "Andrew is secretly having an affair but denies this to his wife... Barney exaggerates his financial success and pretends to like the same music and films as his date in order to impress her... Charlie dyes his hair and pretends to be in his mid-30s on a dating website when he is really in his 50s... Derek is unhappy in his marriage and is considering whether to leave his wife; he does not mention his misgivings..." In these examples, the sexual partner in each case would not have consented had all matters likely to be relevant to their decision been fully disclosed, and a reasonable person might be expected to realise this.

text: A high profile and unusual case where this issue arose, was the 2011 UK undercover policing relationships scandal in which police officers obtained sex by deceiving as to their identity, as part of their duties. Crown Prosecutors declined to prosecute on the basis that legally, the actions would not constitute rape as consent to the act itself was informed and the grounds for rape by deceit as to identity was extremely limited.[4][6]

text: Capacity[edit]

text: A man or woman assisting another man to commit a rape can be prosecuted for the crime as an accessory.[7]

text: Mode of trial[edit]

text: Rape is an indictable-only offence.[8]

text: Sentence[edit]

text: A person guilty of rape is liable on conviction to imprisonment for life or for any shorter term.[9]

text: For further information, see the Crown Prosecution Service sentencing manual.

text: Relevant cases[edit]

text:
R v Billam (1986) 8 Cr App R (S) 48
R v Millberry [2002] EWCA Crim 2891, [2003] Crim LR 207, [2003] 2 Cr App R (S) 31, [2003] 2 All ER 939, [2003] 2 Cr App R (S) 31, [2003] 1 WLR 546, [2003] 1 Cr App R 25.
R v Corran and others [2005] 2 Cr App R (S) 73, [2005] 2 Cr App R (S)73, [2005] EWCA Crim 192
R v Abokar Ahmed Ismail [2005] 2 Cr App R (S) 88
A-Gs Reference No. 86 of 2005 (Christopher James S.) 2 Cr App R(S)

text: In R v Millberry, the Court of Appeal held that "there are, broadly, three dimensions to consider in assessing the gravity of an individual offence of rape. The first is the degree of harm to the victim; the second is the level of culpability of the offender; and the third is the level of risk posed by the offender to society." Subsequently, the court held in Attorney General's Reference (Nos. 91, 119, 120 of 2002) that these three dimensions can be applied to sentencing for other categories of sexual offences.

text: Rape of a child under 13[edit]

text: This is a statutory offence created by section 5 of the Sexual Offences Act 2003.

text:
“
(1) A person commits an offence if—

(a) he intentionally penetrates the vagina, anus or mouth of another person with his penis, and

(b) the other person is under 13.

”

text: Any consent of the complainant is of no relevance if he or she is under the age of thirteen.

text: Civil liability[edit]

text: Loss of service[edit]

text: No person is liable in tort under the law of England and Wales-

text:
to a parent (or person standing in place of a parent) on the ground only of his having deprived the parent (or other person) of the services of his or her child by raping that child;[10] or
on the ground only of having deprived another of the services of his female servant by raping her.[11]

text: History[edit]

text: Rape was an offence under the common law of England and was classified as a felony.

text: The common law defined rape as "the carnal knowledge of a woman forcibly and against her will."[12] The common law defined carnal knowledge as the penetration of the female sex organ by the male sex organ (it covered all other acts under the crime of sodomy). The crime of rape was unique in the respect that it focused on the victim's state of mind and actions in addition to that of the defendant. The victim was required to prove a continued state of physical resistance, and consent was conclusively presumed when a man had intercourse with his wife. "One of the most oft-quoted passages in our jurisprudence" on the subject of rape is by Lord Chief Justice Sir Matthew Hale from the 17th century, "rape...is an accusation easily to be made and hard to be proved, and harder to be defended by the party accused, tho never so innocent."[12] Lord Hale is also the origin of the remark, "In a rape case it is the victim, not the defendant, who is on trial." However, as noted by Sir William Blackstone in his Commentaries on the Laws of England, by 1769 the common law had recognized that even a prostitute could suffer rape if she had not consented to the act.[13]

text: Section 16 of the Offences against the Person Act 1828 read as follows:

text: And be it enacted, That every Person convicted of the Crime of Rape shall suffer Death as a Felon

text: Here, "death as a felon" means death by hanging and confiscation of the land and good, which were pronounced against felons, as opposed to the quartering which befell traitors. "Thus it was assumed that the definition of rape was so well understood and established by the common law of England that a statutory definition was unnecessary."[14] The death penalty for rape was abolished by section 3 of the Substitution of Punishments for Death Act 1841 which substituted transportation for life. Transportation was abolished by the Penal Servitude Act 1857, which substituted penal servitude for life. These sections were replaced by section 48 of the Offences against the Person Act 1861. Penal Servitude was abolished by the Criminal Justice Act 1948, which substituted imprisonment for life. These sections were replaced by sections 1(1) and 37(3) of, and paragraph 1(a) of the Second Schedule to the Sexual Offences Act 1956.

text: In January 1982, the Government accepted an amendment to the Criminal Justice Bill the effect of which, if enacted, would be to compel judges to sentence men convicted of rape to imprisonment. This followed a case earlier that month in which John Allen, 33, businessman and convicted of raping a 17-year-old hitchhiker, had been fined £2,000 by Judge Bernard Richard, who alleged the victim's "contributory negligence"[15][16]

text: The final paragraph of section 4 of the Criminal Law Amendment Act 1885 provided that it was rape for a man to have carnal knowledge of a married woman by impersonating her husband. This provision was replaced by section 1(2) of the Sexual Offences Act 1956.

text: Rape ceased to be a felony on 1 January 1968 as a result of the abolition of the distinction between felony and misdemeanour by the Criminal Law Act 1967.

text: The definition of rape at common law was discussed in DPP v. Morgan [1976] AC 182, [1975] 2 WLR 913, [1975] 2 All ER 347, 61 Cr App R 136, [1975] Crim LR 717, HL.

text: A statutory definition of "rape" was provided by section 1 of the Sexual Offences (Amendment) Act 1976. This was intended to give effect to the Report of the Advisory Group on the Law of Rape (Cmnd 6352) and to the opinions expressed by the House of Lords in DPP v. Morgan.[17]

text: It read:

text: (1)For the purposes of section 1 of the Sexual Offences Act 1956 (which relates to rape) a man commits rape if—

text: and references to rape in other enactments (including the following provisions of this Act) shall be construed accordingly.

text: In R v R[18][19] it was held that the word "unlawful" in that section did not exclude "marital rape" (see Marital rape#England and Wales).

text: Section 1 of the Sexual Offences Act 1956 was substituted on the 3 November 1994 by section 142 of the Criminal Justice and Public Order Act 1994, providing a new and broader definition:

text:
“
(1) It is an offence for a man to rape a woman or another man.
(2) A man commits rape if -

(a) he has sexual intercourse with a person (whether vaginal or anal) who at the time of the intercourse does not consent to it; and
(b) at the time he knows that the person does not consent to the intercourse or is reckless as to whether that person consents to it.

(3) A man also commits rape if he induces a married woman to have sexual intercourse with him by impersonating her husband.
(4) Subsection (2) applies for the purposes of any enactment.

”

text: The effect of this was to make what is termed male rape amount to the offence rape instead of (where it took place in private and both parties were over 18 - s.12(1A) as substituted) or in addition to (in all other cases) the offence of buggery. The first person to be convicted under the wider definition (for attempted rape) was Andrew Richards on 9 June 1995.[20] The word "unlawful" did not appear in this section because of R v R.

text: That section was replaced on 1 May 2004 by section 1 of the Sexual Offences Act 2003, providing a still broader definition. References to vaginal or anal sexual intercourse were replaced by references to penile penetration of the vagina, anus or mouth. It also altered the requirements of the defence of mistaken belief in consent so that one's belief must be now both genuine and reasonable. Presumptions against that belief being reasonably held also now apply when violence is used or feared, the complainant is unconscious, unlawfully detained, drugged, or is by reason of disability unable to communicate a lack of consent. The change in this belief test from the old subjective test (what the defendant thought, reasonably or unreasonably) to an objective test was the subject of some debate (see [4] and [5]), as it permits a man to be convicted of rape if he thought a person was consenting, were the circumstances thought by a jury to be unreasonable.

text: Capacity

text: At common law a boy under the age of fourteen years could not commit rape as a principal offender[21] as he was irrebutably presumed to be incapable of sexual intercourse. This rule was abolished by section 1 of the Sexual Offences Act 1993. A boy under the age of fourteen years could commit rape as an accomplice.[22]

text: It was never decided whether a boy under fourteen could be convicted of attempting to commit rape as a principal, rather than an accomplice, if he attempted to have sexual intercourse or actually succeeded in doing so. The reported dicta did not agree on this point.[23]

text: A woman could not commit rape as a principal offender, by the nature of the offence, but she could commit rape as an accomplice.[24]

text: Attempt[edit]

text: Section 37(3) of, and paragraph 1(b) of the Second Schedule to, the Sexual Offences Act 1956 provided that a person guilty of an attempt to commit rape was liable to imprisonment for a term not exceeding seven years. Attempted rape became a statutory offence under section 1(1) of the Criminal Attempts Act 1981. But the maximum penalty was not affected by this.[25] The maximum penalty for attempted rape was increased to imprisonment for life by sections 3(1) and (2) of the Sexual Offences Act 1985.

text: In the Sexual Offences (Amendment) Act 1976, the expression "a rape offence" included:[26]

text:
attempted rape
aiding, abetting, counselling and procuring attempted rape

text: Compensation[edit]

text: Special provision was made in relation to rape by sections 109(3)(a) and 111(6) of the Criminal Justice Act 1988.


document_title: Florida Territory

question_text: when did florida become a territory of the united states

text: Florida Territory

text: Background[edit]

text: Florida was first discovered in 1513 by Juan Ponce de León who claimed the land as a possession of Spain. St. Augustine, the oldest continually inhabited European settlement in the continental U.S., was founded on the northeast coast of Florida in 1565. Florida continued to remain a Spanish possession until the end of the Seven Years' War when Spain ceded it to the Kingdom of Great Britain in exchange for the release of Havana. In 1783, after the American Revolution, Great Britain ceded Florida back to Spain.[2]:xvii

text: The second term of Spanish rule was influenced by the nearby United States. There were border disputes along the boundary with the state of Georgia and issues of American use of the Mississippi. These disputes were supposedly solved in 1795 by the Treaty of San Lorenzo which, among other things, solidified the boundary of Florida and Georgia along the 31st parallel. However, as Thomas Jefferson had once predicted, the U.S. could not keep its hands off Florida.[2]:xviii–xix

text: American involvement pre-1821[edit]

text: In 1812, United States forces and Georgia "patriots" under General George Mathews invaded Florida to protect American interests.[3]:39 (See Seminole Wars.)

text: Runaway slaves had been sheltered for many years by the Florida natives, called Seminoles by Americans. They lived in a semi-feudal system; the Seminoles gave the now "free" blacks protection, while the former slaves shared crops with the natives. Although the escaped slaves were still considered inferior by the Seminoles, the two groups lived in harmony. The slaveholders in Georgia and the rest of the South became furious over this state of affairs as slaves continued to escape to Florida.[3]:18–22

text: The 1812 liberation of East Florida, or "Patriot War," was perceived by many as ill-advised. President Madison withdrew his support and the Spanish authorities were promised a speedy exit of the American troops.[3]:39

text: In 1818, after years of additional conflicts involving natives, fugitive slaves, and settlers, General Andrew Jackson wrote to President James Monroe, who had been inaugurated in March 1817, informing him that he was invading Florida. Jackson's force departed from Tennessee and marched down to the Florida panhandle. Spanish officers surrendered coastal fortifications at Fort San Marcos (also known as Fort St. Marks) in Florida Oriental; and about six weeks later, Fort Barrancas and Pensacola in Florida Occidental.[3]:50–54

text: Adams–Onís Treaty[edit]

text: The Adams–Onís Treaty, also known as the Transcontinental Treaty, was signed on February 22, 1819, by John Quincy Adams and Luis de Onís y González-Vara, but did not take effect until after it was ratified by Spain on October 24, 1820, and by the United States on February 19, 1821. The U.S. received Florida under Article 2 and inherited Spanish claims to the Oregon Territory under Article 3, while ceding all its claims on Texas to Spain under Article 3[2]:xi (with the independence of Mexico in 1821, Spanish Texas became Mexican territory), and pledged to indemnify up to $5,000,000 in claims by American citizens against Spain under Article 11.[note 1] Under Article 15, Spanish goods received exclusive most favorable nation tariff privileges in the ports at Pensacola and St. Augustine for twelve years.

text: In Dorr v. USA (195 U.S. 138, 141–142 (1904)) Justice Marshall is quoted more extensively as follows:

text: The 6th article of the treaty of cession contains the following provision:

text: 'The inhabitants of the territories which His Catholic Majesty cedes the United States by this treaty shall be incorporated in the Union of the United States as soon as may be consistent with the principles of the Federal Constitution, and admitted to the enjoyment of the privileges, rights, and immunities of the citizens of the United States.' [8 Stat. at L. 256.]

text: [195 U.S. 138, 142] 'This treaty is the law of the land, and admits the inhabitants of Florida to the enjoyment of the privileges, rights, and immunities of the citizens of the United States. It is unnecessary to inquire whether this is not their condition, independent of stipulation. They do not, however, participate in political power; they do not share in the government till Florida shall become a state. In the meantime Florida continues to be a territory of the United States, governed by virtue of that clause in the Constitution which empowers Congress 'to make all needful rules and regulations respecting the territory or other property belonging to the United States."

text: Territorial Florida and the Seminole Wars[edit]

text: President James Monroe was authorized on March 3, 1821, to take possession of East Florida and West Florida for the United States and provide for initial governance.[5] Andrew Jackson served as the federal military commissioner with the powers of governor of the newly-acquired territory, from March 10 through December of 1821. On March 30, 1822, the United States merged East Florida and part of what formerly constituted West Florida into the Florida Territory.[6] William Pope Duval became the first official governor of the Florida Territory and soon afterward the capital was established at Tallahassee, but only after removing a Seminole tribe from the land.[3]:63–74

text: The central conflict of Territorial Florida was the Seminole inhabitants. The federal government and most white settlers desired all Florida Indians to migrate to the West. On May 28, 1830, Congress passed the Indian Removal Act requiring all Native Americans to move west of the Mississippi River.[3]:87 The Act itself did not mean much to Florida, but it laid the framework for the Treaty of Payne's Landing, which was signed by a council of Seminole chiefs on May 9, 1832. This treaty stated that all Seminole inhabitants of Florida should be relocated by 1835, giving them three years. It was at this meeting that the famous Osceola first voiced his decision to fight.[3]:89–95

text: Beginning in late 1835, Osceola and the Seminole allies began a guerrilla war against the U.S. forces.[3]:105–110 Numerous generals fought and failed, succumbing to the heat and disease as well as lack of knowledge of the land. It was not until General Thomas Jesup captured many of the key Seminole chiefs, including Osceola who died in captivity of illness, that the battles began to die down.[3]:137–160 The Seminoles were eventually forced to migrate. Florida joined the Union as the 27th state on March 3, 1845.[7] By this time, almost all of the Seminoles were gone, except for a small group living in the Everglades.