full transcript

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

Unscramble the Blue Letters

setmrymy is everywhere in nature, and we usually associate it with beauty: a perfectly shaped leaf, or a butterfly with intricate pttarens 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 pniecr claw to snail species whose shells' always coil in the same direction. Some species of baens only climb up their trellises clockwise, others, only counterclockwise, and even though the human body looks prtety symmetrical on the outside, it's a different story on the inside. Most of your vital organs are arrgnaed 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 sdeis of your brain look similar, but function differently. Making sure this asymmetry is distributed the right way is critical. If all your inntearl 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 phsues fluid from the right side of the embryo to the left. On the node's left-hand rim, other cliia snsee 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 elantveluy translated into asymmetric organs. Asymmetry shows up in the heart first. It bnegis as a straight tube along the center of the embryo, but when the ebymro 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 seurtrcuts on each side, eventually turning into the familiar asymmetric heart. Meanwhile, the other major organs eemgre 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 amyimrestc? Probably. Bacterial colonies grow lacy branches that all curl in the same direction, and human clles cutreuld 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 bokcls, like nucleic aidcs, proteins, and sugars, are irenthnley asymmetric. ptorines have complex asymmetric shapes, and those proteins control which way cells migrate and which way embryonic cilia twirl. These biomolecules have a pteprory called chirality, which means that a molecule and its mriror iamge aren't identical. Like your right and left hndas, they look the same, but trying to put your right in your left gvloe proves they're not. This ayermtsmy at the mcloeluar 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 ctopeimlxy, and its strkiing imperfections.

Open Cloze

________ is everywhere in nature, and we usually associate it with beauty: a perfectly shaped leaf, or a butterfly with intricate ________ 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 ______ claw to snail species whose shells' always coil in the same direction. Some species of _____ only climb up their trellises clockwise, others, only counterclockwise, and even though the human body looks ______ symmetrical on the outside, it's a different story on the inside. Most of your vital organs are ________ 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 _____ of your brain look similar, but function differently. Making sure this asymmetry is distributed the right way is critical. If all your ________ 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 ______ fluid from the right side of the embryo to the left. On the node's left-hand rim, other _____ _____ 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 __________ translated into asymmetric organs. Asymmetry shows up in the heart first. It ______ as a straight tube along the center of the embryo, but when the ______ 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 __________ on each side, eventually turning into the familiar asymmetric heart. Meanwhile, the other major organs ______ 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 __________? Probably. Bacterial colonies grow lacy branches that all curl in the same direction, and human _____ ________ 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 ______, like nucleic _____, proteins, and sugars, are __________ asymmetric. ________ have complex asymmetric shapes, and those proteins control which way cells migrate and which way embryonic cilia twirl. These biomolecules have a ________ called chirality, which means that a molecule and its ______ _____ aren't identical. Like your right and left _____, they look the same, but trying to put your right in your left _____ proves they're not. This _________ at the _________ 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 __________, and its ________ imperfections.

Solution

  1. asymmetric
  2. mirror
  3. inherently
  4. striking
  5. molecular
  6. complexity
  7. sides
  8. embryo
  9. image
  10. patterns
  11. cilia
  12. sense
  13. begins
  14. internal
  15. symmetry
  16. eventually
  17. blocks
  18. beans
  19. structures
  20. cells
  21. pincer
  22. acids
  23. asymmetry
  24. property
  25. glove
  26. pushes
  27. proteins
  28. arranged
  29. cultured
  30. hands
  31. emerge
  32. pretty

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