full transcript

From the Ted Talk by Leo Q. Wan: Why are human bodies asymmetrical?


Unscramble the Blue Letters


Symmetry is everywhere in nature, and we usually associate it with beauty: a perfectly shaped leaf, or a btrufetly with intricate patterns mirrored on each wing. But it turns out that asymmetry is pretty important, too, and more cmmoon than you might think, from crabs with one ginat pincer claw to snail species whose shells' always coil in the same drecoiitn. Some seecpis of beans only climb up their tlreisles clockwise, others, only counterclockwise, and even though the human body looks pretty symmetrical on the outside, it's a different story on the inside. Most of your vital organs are arranged asymmetrically. The heart, stomach, spleen, and pancreas lie towards the left. The gallbladder and most of your liver are on the right. Even your lungs are different. The left one has two lobes, and the right one has three. The two sides of your brain look similar, but function differently. Making sure this asymmetry is distributed the right way is cariticl. If all your internal organs are flipped, a cinoodtin called situs inversus, it's often hleamsrs. But incomplete revaelrss can be fatal, especially if the heart is involved. But where does this asymmetry come from, since a brand-new embryo looks identical on the right and left. One theory focuses on a small pit on the embryo called a node. The node is lined with tiny hairs called ciila, while tilt away from the head and whirl around rapidly, all in the same direction. This synchronized rotation phsues fluid from the right side of the ermybo to the left. On the node's left-hand rim, other cilia sense this fluid flow and acvaitte specific genes on the embryo's left side. These genes direct the cells to make certain proteins, and in just a few huros, the right and left sides of the embryo are chemically different. Even though they still look the same, these chemical differences are eventually trenlsatad into asymmetric organs. Asymmetry shows up in the heart first. It begins as a sghraitt tube along the cteenr of the embryo, but when the embryo is around three weeks old, the tube strtas to bend into a c-shape and rotate towards the right side of the body. It grows different suctuertrs on each side, eventually turning into the familiar asymmetric heart. Meanwhile, the other mjaor organs emerge from a central tube and grow towards their ultimate positions. But some organisms, like pigs, don't have those embryonic cilia and still have aitrmyemsc internal organs. Could all cells be intrinsically asymmetric? Probably. Bacterial colonies grow lacy branches that all curl in the same direction, and hmaun cells cultured inside a ring-shaped boundary tend to line up like the ridges on a cruller. If we zoom in even more, we see that many of cells' basic building blocks, like nucleic acids, proteins, and srugas, are inherently asymmetric. Proteins have complex asymmetric shapes, and those pintoers control which way cells migrate and which way embryonic cilia twirl. These biomolecules have a property called chirality, which means that a mlleuoce and its mirror image aren't iinedatcl. Like your right and left hands, they look the same, but trying to put your right in your left glove proves they're not. This aemmtrsyy at the molecular level is reflected in asymmetric cells, asymmetric embryos, and finally asymmetric organisms. So while symmetry may be bfitaueul, asymmetry holds an allure of its own, found in its graceful whirls, its oainerzgd complexity, and its striking ieortnipefmcs.

Open Cloze


Symmetry is everywhere in nature, and we usually associate it with beauty: a perfectly shaped leaf, or a _________ with intricate patterns mirrored on each wing. But it turns out that asymmetry is pretty important, too, and more ______ than you might think, from crabs with one _____ pincer claw to snail species whose shells' always coil in the same _________. Some _______ of beans only climb up their _________ clockwise, others, only counterclockwise, and even though the human body looks pretty symmetrical on the outside, it's a different story on the inside. Most of your vital organs are arranged asymmetrically. The heart, stomach, spleen, and pancreas lie towards the left. The gallbladder and most of your liver are on the right. Even your lungs are different. The left one has two lobes, and the right one has three. The two sides of your brain look similar, but function differently. Making sure this asymmetry is distributed the right way is ________. If all your internal organs are flipped, a _________ called situs inversus, it's often ________. But incomplete _________ can be fatal, especially if the heart is involved. But where does this asymmetry come from, since a brand-new embryo looks identical on the right and left. One theory focuses on a small pit on the embryo called a node. The node is lined with tiny hairs called _____, while tilt away from the head and whirl around rapidly, all in the same direction. This synchronized rotation ______ fluid from the right side of the ______ to the left. On the node's left-hand rim, other cilia sense this fluid flow and ________ specific genes on the embryo's left side. These genes direct the cells to make certain proteins, and in just a few _____, the right and left sides of the embryo are chemically different. Even though they still look the same, these chemical differences are eventually __________ into asymmetric organs. Asymmetry shows up in the heart first. It begins as a ________ tube along the ______ of the embryo, but when the embryo is around three weeks old, the tube ______ to bend into a c-shape and rotate towards the right side of the body. It grows different __________ on each side, eventually turning into the familiar asymmetric heart. Meanwhile, the other _____ organs emerge from a central tube and grow towards their ultimate positions. But some organisms, like pigs, don't have those embryonic cilia and still have __________ internal organs. Could all cells be intrinsically asymmetric? Probably. Bacterial colonies grow lacy branches that all curl in the same direction, and _____ cells cultured inside a ring-shaped boundary tend to line up like the ridges on a cruller. If we zoom in even more, we see that many of cells' basic building blocks, like nucleic acids, proteins, and ______, are inherently asymmetric. Proteins have complex asymmetric shapes, and those ________ control which way cells migrate and which way embryonic cilia twirl. These biomolecules have a property called chirality, which means that a ________ and its mirror image aren't _________. Like your right and left hands, they look the same, but trying to put your right in your left glove proves they're not. This _________ at the molecular level is reflected in asymmetric cells, asymmetric embryos, and finally asymmetric organisms. So while symmetry may be _________, asymmetry holds an allure of its own, found in its graceful whirls, its _________ complexity, and its striking _____________.

Solution


  1. translated
  2. asymmetry
  3. organized
  4. critical
  5. activate
  6. straight
  7. harmless
  8. embryo
  9. reversals
  10. identical
  11. sugars
  12. structures
  13. molecule
  14. center
  15. starts
  16. imperfections
  17. asymmetric
  18. common
  19. human
  20. condition
  21. direction
  22. butterfly
  23. proteins
  24. major
  25. beautiful
  26. hours
  27. species
  28. trellises
  29. pushes
  30. giant
  31. cilia

Original Text


Symmetry is everywhere in nature, and we usually associate it with beauty: a perfectly shaped leaf, or a butterfly with intricate patterns mirrored on each wing. But it turns out that asymmetry is pretty important, too, and more common than you might think, from crabs with one giant pincer claw to snail species whose shells' always coil in the same direction. Some species of beans only climb up their trellises clockwise, others, only counterclockwise, and even though the human body looks pretty symmetrical on the outside, it's a different story on the inside. Most of your vital organs are arranged asymmetrically. The heart, stomach, spleen, and pancreas lie towards the left. The gallbladder and most of your liver are on the right. Even your lungs are different. The left one has two lobes, and the right one has three. The two sides of your brain look similar, but function differently. Making sure this asymmetry is distributed the right way is critical. If all your internal organs are flipped, a condition called situs inversus, it's often harmless. But incomplete reversals can be fatal, especially if the heart is involved. But where does this asymmetry come from, since a brand-new embryo looks identical on the right and left. One theory focuses on a small pit on the embryo called a node. The node is lined with tiny hairs called cilia, while tilt away from the head and whirl around rapidly, all in the same direction. This synchronized rotation pushes fluid from the right side of the embryo to the left. On the node's left-hand rim, other cilia sense this fluid flow and activate specific genes on the embryo's left side. These genes direct the cells to make certain proteins, and in just a few hours, the right and left sides of the embryo are chemically different. Even though they still look the same, these chemical differences are eventually translated into asymmetric organs. Asymmetry shows up in the heart first. It begins as a straight tube along the center of the embryo, but when the embryo is around three weeks old, the tube starts to bend into a c-shape and rotate towards the right side of the body. It grows different structures on each side, eventually turning into the familiar asymmetric heart. Meanwhile, the other major organs emerge from a central tube and grow towards their ultimate positions. But some organisms, like pigs, don't have those embryonic cilia and still have asymmetric internal organs. Could all cells be intrinsically asymmetric? Probably. Bacterial colonies grow lacy branches that all curl in the same direction, and human cells cultured inside a ring-shaped boundary tend to line up like the ridges on a cruller. If we zoom in even more, we see that many of cells' basic building blocks, like nucleic acids, proteins, and sugars, are inherently asymmetric. Proteins have complex asymmetric shapes, and those proteins control which way cells migrate and which way embryonic cilia twirl. These biomolecules have a property called chirality, which means that a molecule and its mirror image aren't identical. Like your right and left hands, they look the same, but trying to put your right in your left glove proves they're not. This asymmetry at the molecular level is reflected in asymmetric cells, asymmetric embryos, and finally asymmetric organisms. So while symmetry may be beautiful, asymmetry holds an allure of its own, found in its graceful whirls, its organized complexity, and its striking imperfections.

Frequently Occurring Word Combinations


ngrams of length 2

collocation frequency
internal organs 2
embryonic cilia 2



Important Words


  1. acids
  2. activate
  3. allure
  4. arranged
  5. associate
  6. asymmetric
  7. asymmetrically
  8. asymmetry
  9. bacterial
  10. basic
  11. beans
  12. beautiful
  13. begins
  14. bend
  15. biomolecules
  16. blocks
  17. body
  18. boundary
  19. brain
  20. branches
  21. building
  22. butterfly
  23. called
  24. cells
  25. center
  26. central
  27. chemical
  28. chemically
  29. chirality
  30. cilia
  31. claw
  32. climb
  33. clockwise
  34. coil
  35. colonies
  36. common
  37. complex
  38. complexity
  39. condition
  40. control
  41. counterclockwise
  42. crabs
  43. critical
  44. cruller
  45. cultured
  46. curl
  47. differences
  48. differently
  49. direct
  50. direction
  51. distributed
  52. embryo
  53. embryonic
  54. embryos
  55. emerge
  56. eventually
  57. familiar
  58. fatal
  59. finally
  60. flipped
  61. flow
  62. fluid
  63. focuses
  64. function
  65. gallbladder
  66. genes
  67. giant
  68. glove
  69. graceful
  70. grow
  71. grows
  72. hairs
  73. hands
  74. harmless
  75. head
  76. heart
  77. holds
  78. hours
  79. human
  80. identical
  81. image
  82. imperfections
  83. important
  84. incomplete
  85. inherently
  86. internal
  87. intricate
  88. intrinsically
  89. inversus
  90. involved
  91. lacy
  92. leaf
  93. left
  94. level
  95. lie
  96. line
  97. lined
  98. liver
  99. lobes
  100. lungs
  101. major
  102. making
  103. means
  104. migrate
  105. mirror
  106. mirrored
  107. molecular
  108. molecule
  109. nature
  110. node
  111. nucleic
  112. organisms
  113. organized
  114. organs
  115. pancreas
  116. patterns
  117. perfectly
  118. pigs
  119. pincer
  120. pit
  121. positions
  122. pretty
  123. property
  124. proteins
  125. proves
  126. pushes
  127. put
  128. rapidly
  129. reflected
  130. reversals
  131. ridges
  132. rim
  133. rotate
  134. rotation
  135. sense
  136. shaped
  137. shapes
  138. shows
  139. side
  140. sides
  141. similar
  142. situs
  143. small
  144. snail
  145. species
  146. specific
  147. spleen
  148. starts
  149. stomach
  150. story
  151. straight
  152. striking
  153. structures
  154. sugars
  155. symmetrical
  156. symmetry
  157. synchronized
  158. tend
  159. theory
  160. tilt
  161. tiny
  162. translated
  163. trellises
  164. tube
  165. turning
  166. turns
  167. twirl
  168. ultimate
  169. vital
  170. weeks
  171. whirl
  172. whirls
  173. wing
  174. zoom