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Leaf Growth & Tree Height Limited By Physics

Leaf Growth & Tree Height Limited By Physics | Biology | Scoop.it

New research indicates that leaf growth may not be as complicated as it seems. When compared species to species, shorter trees exhibit a greater variety of leaf sizes than taller ones, with the tallest trees all having leaves that measure 10 to 20 centimeters in length.

 

The scientists published their findings in the journal Physical Review Letters⊃1;. The narrow size range may be simply explained in the inner workings of trees. If this is correct, this could also explain why the tallest trees can only attain about 100 meters.

 

The team only considered angiosperms like maples and oaks, not gymnosperms, like pines and redwoods. They reviewed data for 1925 species and found that among angiosperms shorter than 30 meters, leaf length varies enormously, from 3 cm all the way up to 60 cm. The range narrows as the trees become taller.

 

The flow of sap and energy throughout the tree is what explains this. A leaf of an angiosperm produces a sugary sap that flows into a network of cells called the phloem, which transports the sap down to the tree’s trunk and through the roots. While it’s in transit, the tree metabolizes the sugar. The flow is driven by the difference in concentration in the sugars, which generates osmotic pressure.

 

The scientists modeled a tree as a pair of cylindrical tubes. A short, permeable tube, which represented the phloem in the leaf, was attached to a long, impermeable tube, the phloem in the trunk. Sap diffuses into the leave phloem and travels down into the trunk phloem. The longer the permeable leaf tube is, the more the surface area it has, so the more easily sap can enter. In the trunk phloem, the longer the tube is, the more resistance it offers to flow.

 

The scientists then considered how the total flow of sap and energy varies with leaf length. If the leaves are big, the resistance from the trunk limits the flow and making the leaves bigger than a certain maximum length yields no additional flow or benefit. On the other hand, if the leaves are very small, their resistance limits the flow. And if the leaf is shorter than a certain minimum length, the sap would flow through the phloem more slowly than it could diffuse through the entire tree.

 

Trees taller than 100 meters simply could not produce leaves that obey both length limits, setting a limit for tree height. Other scientists think that the uniformity of leaf size amongst the tallest trees could come from the comparable environments and conditions that produce them.

 

One way to test how the flow speed varies with the height of a tree and the length of its leaves would be to directly measure it in different species of tall trees, but that might require taking an MRI machine into a rain forest canopy.


Via Dr. Stefan Gruenwald
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mdashf's curator insight, May 8, 2013 3:11 AM

why some trees are so tall while others are short? well their leaves size will be affected as well deoending on their heights. Its like very tall men will have proportionate to their height smaller fingers. But shorter men and women will grow fingers in many differet ratio to their height. You lose certain privilege if you are tall. 

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Question 1 & 2

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Where do you see the future of biology implement in any area of life you chose eg. gene manipulation in human? 

 

From a biological point of view, do you think global outbreaks of virus could cause a so called zombie apocalypse?

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Science Fiction Realized: Researchers Develop Super Batteries - Organic Connections

Imagine super batteries where a cellphone could to jump-start a dead car battery—and then recharge in the blink of an eye.
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Intelligence in the ocean: Whales give each other tips about new fishing techniques

Intelligence in the ocean: Whales give each other tips about new fishing techniques | Biology | Scoop.it

Whales are one the most fascinating and intelligent creatures we know and we certainly want to protect these biggest fishes, or actually mamals, in the sea. But luckily whales are not helpless against the latest ecological changes. A new study found they work together in adapting to their environments, just like us.

 

For a period of 27 years a team of researchers monitored the fishing habits of a community of American humpback whales. The dimishing of their usual prey in the 1980′s led some of the whales to invent a new hunting technique: first hitting their tail on the water before diving down.

But it weren’t just these few smart ones that benefited from their own innovation. The whales were intelligent enough to also pass it on to the others. In 2007 around 40 percent of the population was using the new fishing skill.

 

Didn’t all these whales just discover the tail-on-the-water-thing themselves? No, say the researchers. Their analysis revealed that the new behavior spreaded roughly along the lines of social networks. Yes, whales have them too, apparently.

 

So culture is not something uniquely human. These marine animals, very distinct from our own primate lineage, also are able to transmit knowledge and keep traditions. It’s actually not so surprising if you know that whales also teach each other their mysterious songs. Maybe many years from now we find out that all this time they have been singing about fishing techniques.


Via Dr. Stefan Gruenwald
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Scientists have crossed two strains of avian flu virus to create one that can be transmitted through the air

Scientists have crossed two strains of avian flu virus to create one that can be transmitted through the air | Biology | Scoop.it

As the world is transfixed by a new H7N9 bird flu virus spreading through China, a study reminds us that a different avian influenza — H5N1 — still poses a pandemic threat.

 

A team of scientists in China has created hybrid viruses by mixing genes from H5N1 and the H1N1 strain behind the 2009 swine flu pandemic, and showed that some of the hybrids can spread through the air between guinea pigs.

 

Flu hybrids can arise naturally when two viral strains infect the same cell and exchange genes. This process, known as reassortment, produced the strains responsible for at least three past flu pandemics, including the one in 2009.

 

There is no evidence that H5N1 and H1N1 have reassorted naturally yet, but they have many opportunities to do so. The viruses overlap both in their geographical range and in the species they infect, and although H5N1 tends mostly to swap genes in its own lineage, the pandemic H1N1 strain seems to be particularly prone to reassortment.

 

“If these mammalian-transmissible H5N1 viruses are generated in nature, a pandemic will be highly likely,” says Hualan Chen, a virologist at the Harbin Veterinary Research Institute of the Chinese Academy of Sciences, who led the study.

 

“It's remarkable work and clearly shows how the continued circulation of H5N1 strains in Asia and Egypt continues to pose a very real threat for human and animal health,” says Jeremy Farrar, director of the Oxford University Clinical Research Unit in Ho Chi Minh City, Vietnam.

 

Chen's results are likely to reignite the controversy that plagued the flu community last year, when two groups found that H5N1 could go airborne if it carried certain mutations in a gene that produced a protein called haemagglutinin (HA). Following heated debate over biosecurity issues raised by the work, the flu community instigated a voluntary year-long moratorium on research that would produce further transmissible strains. Chen’s experiments were all finished before the hiatus came into effect, but more work of this nature can be expected now that the moratorium has been lifted.

 

“I do believe such research is critical to our understanding of influenza,” says Farrar. “But such work, anywhere in the world, needs to be tightly regulated and conducted in the most secure facilities, which are registered and certified to a common international standard.”

 

Virologists have created H5N1 reassortants before. One study found that H5N1 did not produce transmissible hybrids when it reassorts with a flu strain called H3N2. But in 2011, Stacey Schultz-Cherry, a virologist at St. Jude Children's Research Hospital in Memphis, Tennessee, showed that pandemic H1N1 becomes more virulent if it carries the HA gene from H5N1.

 

Chen’s team mixed and matched seven gene segments from H5N1 and H1N1 in every possible combination, to create 127 reassortant viruses, all with H5N1’s HA gene. Some of these hybrids could spread through the air between guinea pigs in adjacent cages, as long as they carried either or both of two genes from H1N1 called PA and NS. Two further genes from H1N1, NA and M, promoted airborne transmission to a lesser extent, and another, the NP gene, did so in combination with PA.


Via Dr. Stefan Gruenwald
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Insight

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I would use Scoop in my future classroom to encourage students to see the depth of biological science in a technological appealing way. They can also discover science in a vast variety of different instances and hopefully find one they enjoy and develop a passion to learn.

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