Ikigai Daily
Menu
WonderPlant evolution fact

Maize, sugarcane and sorghum grow well in heat and strong sun partly because they use C4 photosynthesis, a way of concentrating carbon dioxide inside the leaf. This method has evolved independently more than 60 times in different groups of plants.

C4 photosynthesis

EvolutionClimateFoodBiologyScience

The story behind the card

Most plants use C3 photosynthesis, which relies on an enzyme called RuBisCO to capture carbon dioxide. In heat and drought, plants close the pores in their leaves to save water, carbon dioxide inside runs low, and RuBisCO grabs oxygen instead, wasting energy in a process called photorespiration. C4 plants first trap carbon dioxide in their outer leaf cells as a compound with four carbon atoms, which gives the pathway its name, then carry it to inner cells where RuBisCO works and release it there, so the enzyme is surrounded by carbon dioxide. With more than 60 separate origins, it is one of the most often repeated adaptations in plant evolution. Scientists are now trying to engineer the trait into rice.

Türkçe oku
Mısır, şeker kamışı ve sorgum sıcakta ve güçlü güneş altında iyi yetişir; bunun bir nedeni, karbondioksiti yaprağın içinde yoğunlaştıran C4 fotosentezini kullanmalarıdır. Bu yöntem, farklı bitki gruplarında birbirinden bağımsız olarak 60'tan fazla kez ortaya çıktı.

Bitkilerin çoğu C3 fotosentezi yapar ve karbondioksiti RuBisCO adlı bir enzimle yakalar. Sıcak ve kurak havada bitki su kaybetmemek için yapraklarındaki gözenekleri kapatır, yaprağın içinde karbondioksit azalır ve RuBisCO bu kez oksijene bağlanır. Fotosolunum denen bu süreç enerjiyi boşa harcar. C4 bitkileri ise karbondioksiti önce yaprağın dış hücrelerinde dört karbon atomlu bir bileşik olarak tutar; yol adını da buradan alır. Ardından bu bileşiği RuBisCO'nun çalıştığı iç hücrelere taşıyıp karbondioksiti orada serbest bırakır; böylece enzimin çevresi karbondioksitle dolar. 60'tan fazla ayrı kökeniyle bu, bitki evriminde en sık tekrarlanan uyumlardan biridir. Bilim insanları bugün bu özelliği pirince kazandırmaya çalışıyor.

Sources and further reading

Background reading: C4 carbon fixation
Get the mobile appAbout our cards

Related cards

These cards share a subject or reading mode with the card above.

WonderEvolution

In industrial Britain, the dark form of the peppered moth, first recorded in Manchester in 1848, became common where soot blackened the trees and hid it from birds. When the air was cleaned up in the twentieth century, the pale form returned.

The peppered moth became a textbook example of natural selection. By the 1890s nearly all peppered moths around Manchester were dark. In the 1950s Bernard Kettlewell's field experiments suggested that birds ate more of the moths that stood out against the bark, though critics later questioned his methods. After clean-air laws such as the UK's Clean Air Act of 1956 cut soot, the dark form became rare again. The geneticist Michael Majerus answered the critics with a six-year experiment in Cambridge involving 4,864 moths; published after his death, in 2012, it confirmed that birds took more of the conspicuous moths. In 2016 scientists traced the dark colour to a piece of mobile DNA inserted into a gene called cortex around 1819.

Peppered moth evolutionRead card
WonderEvolution

Most adults in the world make little lactase, the enzyme that digests milk sugar, after childhood. In several peoples with a long history of dairy farming, genetic changes that keep the enzyme working for life spread through natural selection, a trait called lactase persistence.

In Europe the most common variant sits in a stretch of DNA that switches the lactase gene (LCT) on and off; a widely cited estimate puts its first spread at roughly 7,500 years ago. Different mutations with the same effect arose independently among cattle herders in East Africa and pastoralists in the Middle East, so evolution reached one solution several times. Scientists call this gene-culture coevolution: a cultural habit, keeping animals for milk, changed which genes helped people survive. The story is more complicated than it first looked. A 2022 study in Nature found that Europeans used milk for thousands of years while the variant stayed rare, and suggested it spread fastest in famines and epidemics, when milk could make people without it seriously ill.

Lactase persistenceRead card
WonderBiology

Cultivated sweet potatoes carry DNA that passed into them naturally, long ago, from a soil bacterium called Agrobacterium, and some of those bacterial genes are still active. No laboratory was involved: the crop is a naturally genetically modified plant.

Agrobacterium is known for inserting part of its own DNA into plants, making them produce nutrients for it; since the 1980s, genetic engineers have used the same trick to add genes to crops. In 2015 a team led by Tina Kyndt and Godelieve Gheysen of Ghent University, working with the International Potato Center, reported bacterial DNA in the sweet potato genome. One insertion, containing four bacterial genes, was present in all 291 cultivated varieties they tested but not in the plant's close wild relatives. That pattern suggests early farmers may have unknowingly favoured plants carrying it, perhaps for a trait it affected, although which trait, if any, is still unknown. The case is often mentioned in debates about genetically modified food.

Sweet potatoRead card
WonderMigration

Pronghorn from Grand Teton National Park travel up to about 240 km (150 miles) between their summer range and their winter range in Wyoming's Upper Green River Basin. Roads, fences and new building now cut across this ancient route.

Pronghorn look like antelopes but are the last surviving members of a family found only in North America. They can reach about 88 km/h, a speed beaten on land only by the cheetah, yet they rarely jump: faced with a fence, they look for a gap to crawl under, so tight wire fencing can block a route completely. At Trappers Point, a narrow bottleneck on the route, archaeologists found remains of pronghorn hunts about 6,000 years old. In 2008 the US Forest Service designated the Path of the Pronghorn, the first federally protected wildlife migration corridor in the United States. In 2012, overpasses and underpasses built on US Highway 191 near Pinedale gave the herds a safe way across the road.

Path of the PronghornRead card
WonderEvolution

Convergent evolution happens when unrelated organisms independently evolve similar traits, such as streamlined bodies in sharks, dolphins and extinct ichthyosaurs.

Sharks are fish, dolphins are mammals and ichthyosaurs were marine reptiles, yet all three evolved a similar streamlined, fin-driven body built for fast swimming. The same pattern shows up elsewhere: camera-like eyes, with a lens that focuses light onto a retina, evolved independently in both vertebrates and octopuses, and the extinct Australian thylacine looked strikingly like a wolf despite being a marsupial with no close relation to dogs. Convergent evolution does not mean life is aiming for a fixed set of designs. Natural selection simply favours whatever body plan works best under a given set of physical pressures, so unrelated lineages can arrive at strikingly similar answers.

Convergent evolutionRead card
Next card in the archiveFazlur Rahman Khan, a Bangladeshi-American structural engineer, made very tall buildings cheaper to build with his 'tube' systems, in which a tower's outer walls work together to resist the wind. They shaped Chicago's John Hancock Center and the Sears Tower, now Willis Tower.Read next →