曼拓教育微信平台最新推出的“名师带你背单词”，摘录了由曼拓学员反馈的PTE考试真题中的高频词汇，以及来自各类与PTE常考学科相关的文章中的高分词汇。经由曼拓名师的归纳、总结，帮助同学们提高背单词的效率，让大家背地精准，背地方便。

这些精选的单词不仅仅适用于PTE考试，更能提高英语阅读、写作能力。如果每天都能记5-10个新单词，就再也不用担心看不懂的澳洲新闻，用不上高端的写作替换词啦！

今天曼拓君整理了这一周的词汇，帮助大家复习、回顾，加深印象。

 

曼拓君

acidic          coral          stunted          biomass          dwindle          urchin          exotic          clam          hydrothermal          eukaryotic          skywards          biosphere          unimaginably          intricate          membranes          endoplasmic reticulum          mitochondria          prokaryote          sac          morphed          engulfed          extruded          bleb          afresh          compelling          interim          naiveté          dogma          archaea          extracellular          protrusion          yeast          snatched          molecule          dynamics          diffusion          sulphuric          prevail          enchanting

本周的单词、词组同学们都还有印象吗？如果忘记了，赶紧跟着曼拓君再复习一下。

 

曼拓君

接下去为大家放出PTE Retell Lecture真题原文以及PTE精选练习文章

 

曼拓君

Warmer, more acidic oceans are bad news for tropical coral reefs: the coral becomes stunted and bleached. But climate change's oceanic effects could go, literally, much deeper than that—killing off creatures that live four miles down, in permanent darkness. So says a study in the journal Global Change Biology. [Daniel O. B. Jones et al., Global reductions in seafloor biomass in response to climate change.

Researchers modeled nutrient flow in the oceans under several greenhouse gas emissions scenarios. And they found that, by the year 2100, nutrients at the ocean's surface may dwindle, leaving fewer leftovers to float down to organisms below. The result could be a massive die-off of life on the seafloor, like sea cucumbers, starfish, urchins and worms. Under a severe emissions scenario, the loss of marine life globally would equal the biomass of the entire human race.

One bright spot in the deep darkness: the exotic tube worms and giant clams that thrive at hydrothermal vents don't need surface nutrients to survive. But plenty of other species do, the researchers say—and we don't even know much of what's down there. This study makes one thing clear: when it comes to climate change and the oceans, we're already in deep.

It's one of the most critical events in the development of life on Earth. But we may have been thinking about it all wrong.

Our planet world be vastly different had eukaryotic cells never evolved

Take a walk in the woods and what do you see? Trees reaching skywards with birds in their branches and, at their roots, mushrooms pushing through the leaf litter. These, and all the organisms you can see with the naked eye, have one fundamental similarity. Like us, they are constructed from the same kind of cell. Under the microscope, the differences between plants, animals and fungi fall away to reveal a common internal structure.

The biosphere would be unimaginably different had this “eukaryotic” cell never evolved, making its origin one of the most critical events in the development of life on Earth. Almost everybody agrees that the complex eukaryotic cell evolved from a simple ancestor. The question is how.

Inside the eukaryotic cell is an intricate meshwork of membranes called the endoplasmic reticulum (ER), interspersed with other structures such as the energy-generating mitochondria. At the core is the nucleus, a large compartment with a double membrane, within which lies the cell’s genetic material. Take away this type of cellular organisation and the only thing left on the planet would be simple cells known as prokaryotes – bacteria, for example – which under a microscope appear as little more than tiny gel-filled sacs.

Biologists have always assumed that the eukaryotic cell evolved when a prokaryote folded parts of its outer membrane inwards, pinching off portions to generate internal compartments (see diagram). Some membranes, it is imagined, wrapped around the DNA to make the membrane of the nucleus, while others morphed into the ER. And at some time during this process, free-living bacteria are thought to have been engulfed by the rest of the cell in a process akin to swallowing, called phagocytosis. These bacteria went on to become mitochondria. While lots of variants of this model have been developed over the years, all make the implicit assumption that eukaryotes evolved from the outside in – by pulling pieces of external membrane and mitochondria into the cell.

We think this is the wrong way round. In a recent paper, we propose instead thateukaryotic cells evolved from the inside out – that a prokaryote extruded blebs of outer membranethrough its cell wall, and these fused to form the peripheral parts of theeukaryotic cell that contain the ER and mitochondria (BMC Biology, vol 12, p 76). Like the famous optical illusion in which onecan see either two faces or a candlestick, when theeukaryotic cell is viewed afreshfrom this perspective, many things look different. Now the outer membrane ofthe eukaryotic cell is an evolutionary novelty,while the nuclear envelope corresponds to the boundary of the original prokaryotic ancestor – the opposite of what is assumed by traditionalhypotheses.

Although our inside-out modelwas published last year, the idea was born some 30 years ago when David wasstudying botany at the University of Oxford. Looking at an image of a largeeukaryotic cell next to a much smaller prokaryotic cell, David wondered why itwas always assumed that the boundaries of the two types of cell wereequivalent, when it was easy enough to imagine that the prokaryote cellcorresponded to the nucleus of the eukaryote. His essay on the topic, writtenin 1984, described this basic idea. While it got a respectable mark, it did notseem very compelling at the time.For a start, no prokaryote was then known to extrude membrane outwards. Davidsat on the idea, always thinking that somebody else would come forward with theconcept, and his research turned in other directions.

Thirty years later, when Davidstarted to think again about the origin and early evolution of life, he wassurprised to see that, in the interim,nobody had suggested that complex cells arose in this way. Perhaps it requiredthe naiveté of an undergraduate toquestion dogma? So David dusted off hisinside-out model and wrote up a short piece to explain how it might work andwhy it ought to be considered as an alternative explanation for the origin ofeukaryotes. And it was much more compelling now it is known that theprokaryotes most closely related to eukaryotes, the archaea, often produce extracellular protrusions. As well as friends and colleagues, David sent the essay to hiscousin, Buzz.

“We think complex cells evolved from the inside out, not theoutside in”

As a cell biologist working with yeast, flies and human cells, Buzz had long grown accustomed to staring at the elaborate internal structure ofeukaryotes but had never heard a convincing explanation for the origin of this dazzling complexity. Maybe the inside-out model could shed light on this, andon other puzzling features of modern eukaryotes too.

We started exchanging drawingsmade in snatched moments, on napkinsand loose sheets of paper, on buses, planes and trains. Looking at thesesketches, answers to some unexplained aspects of eukaryotic cell biology seemedto jump off the page: for instance, the model explained why the ER is directly linked to the bounding membrane of the nucleus, and why they both containchemicals similar to archaeal cell wall components.

Echoes of the past

The success of this way ofthinking got us wondering whether modern cells retain any echoes of their pastin the way they work. By thinking about the way cells grew and divided as theyevolved into modern eukaryotes, we were able to make some startling predictions for various aspects of cell biology that are currently poorly understood. Forinstance, the inside-out model suggests a role for the ER in determining thepattern of diffusion of molecules within cells, and predicts functions for several unstudied proteins in archaea.

To test these predictions, Buzzand his students have begun examining the dynamics of diffusion within eukaryoticcells. They will also look at proteins that are shared by eukaryotes andarchaea to test their functions and locations within archaeal cells, somethingthat will require overcoming the technical challenge of imaging these cells in sulphuric acidsolution at 76 °C, theirpreferred growth conditions. Meanwhile, David is using computational analysisof various genes to test competing ideas about how the ancestors ofmitochondria made a living.

Regardlessof whether the inside-out view prevails,testing these ideas will provide a better understanding of how eukaryotes cameto be. This may help to explain why eukaryotes evolved just once on Earth and, in so doing,will shape our expectations as to whether other planets might, in addition tomicroscopic prokaryote-like cells, harbour large and complex organisms such asthose that make life on Earth so enchanting.

报名方式

1、联系电话：0424 858 001

2、曼拓教育官方微信平台：mentoreducation

3、添加曼拓教育课程咨询：mentorsyd      或扫码添加

4、直接前来曼拓教育：Suite 401, 630 George Street, Sydney, 2000

5、点击底部“阅读原文”直接报名