﻿PHOTOSYNTHESIS 
  

  

  By 
  E. 
  C. 
  C. 
  Baly, 
  C. 
  B. 
  E., 
  F. 
  R. 
  S. 
  

  

  Professor 
  of 
  Inorganic 
  Chemistry, 
  University 
  of 
  Liverpool 
  

  

  There 
  is 
  no 
  process 
  within 
  the 
  confines 
  of 
  chemistry 
  which 
  is 
  of 
  

   greater 
  interest 
  and 
  importance 
  than 
  that 
  by 
  means 
  of 
  which 
  the 
  

   living 
  plant 
  prepares 
  the 
  food 
  on 
  which 
  its 
  life 
  and 
  growth 
  depend. 
  

   This 
  food 
  consists 
  of 
  starch 
  and 
  sugars, 
  together 
  grouped 
  under 
  the 
  

   general 
  name 
  of 
  carbohydrates, 
  and 
  of 
  certain 
  nitrogen-containing 
  

   compounds 
  known 
  as 
  proteins. 
  The 
  material 
  from 
  which 
  the 
  plant 
  

   starts 
  is 
  carbonic 
  acid, 
  or 
  a 
  solution 
  of 
  carbon 
  dioxide, 
  which 
  it 
  

   obtains 
  from 
  the 
  air, 
  in 
  water 
  which 
  it 
  obtains 
  through 
  its 
  roots 
  

   from 
  the 
  soil. 
  From 
  this 
  substance 
  alone 
  the 
  plant 
  is 
  able 
  to 
  prepare 
  

   its 
  supply 
  of 
  carbohydrates, 
  and 
  it 
  is 
  true 
  to 
  say 
  that 
  this 
  chemical 
  

   process 
  is 
  the 
  fundamental 
  basis 
  of 
  the 
  whole 
  of 
  terrestrial 
  life. 
  

   This 
  may 
  truly 
  be 
  asserted 
  because 
  the 
  production 
  of 
  the 
  proteins 
  

   is 
  very 
  closely 
  associated 
  with 
  it 
  and 
  the 
  initial 
  stage 
  is 
  common 
  to 
  

   the 
  two. 
  

  

  The 
  formation 
  of 
  carbohydrates 
  from 
  carbonic 
  acid 
  when 
  ex- 
  

   pressed 
  by 
  a 
  chemical 
  equation 
  looks 
  simple 
  enough. 
  There 
  is 
  no 
  

   doubt 
  that 
  the 
  first 
  product 
  of 
  the 
  process 
  that 
  can 
  be 
  recognized 
  in 
  

   the 
  plant 
  is 
  a 
  simple 
  sugar, 
  and 
  thus 
  the 
  equation 
  can 
  be 
  written 
  

  

  6H2C03 
  = 
  C6Hi206 
  + 
  602 
  

  

  where 
  the 
  simple 
  carbohydrate 
  is 
  either 
  glucose 
  or 
  fructose. 
  These 
  

   simple 
  sugars 
  undergo 
  condensation 
  immediately 
  they 
  are 
  formed 
  to 
  

   give 
  cane 
  sugar 
  or 
  one 
  of 
  the 
  starches, 
  and 
  these 
  changes 
  can 
  readily 
  

   be 
  written 
  as 
  simple 
  chemical 
  equations. 
  

  

  The 
  mechanism 
  by 
  means 
  of 
  which 
  the 
  plant 
  achieves 
  the 
  syn- 
  

   thesis 
  of 
  these 
  complex 
  compounds 
  from 
  carbonic 
  acid 
  has 
  long 
  been 
  

   a 
  mystery 
  to 
  chemists 
  and 
  to 
  botanists. 
  It 
  is 
  known 
  that 
  the 
  agency 
  

   used 
  by 
  the 
  plant 
  to 
  effect 
  its 
  purpose 
  is 
  sunlight, 
  and 
  thus 
  the 
  term 
  

   photosynthesis 
  has 
  been 
  applied 
  to 
  the 
  operation. 
  It 
  is 
  also 
  known 
  

   that 
  the 
  plant 
  makes 
  use 
  of 
  certain 
  pigments, 
  such 
  as 
  chlorophyll, 
  

  

  1 
  Presented 
  at 
  the 
  weekly 
  evening 
  meeting 
  of 
  the 
  Royal 
  Institution 
  of 
  Great 
  Britain, 
  Feb. 
  3, 
  1928. 
  Re- 
  

   printed 
  by 
  permission 
  of 
  the 
  Royal 
  Institution. 
  

  

  