By Kim Catcheside
BBC News education correspondent
Children in poor areas of England have fewer opportunities to take sciences as separate GCSEs than those in rich areas, research suggests.
Independent schools are more likely to do single sciences
Figures obtained by the Tories suggest state pupils in the richest areas are three times more likely to take physics than those in the poorest.
The Russell Group of top universities says pupils' subject choices could limit their university chances.
The Tories say children in the poorest areas are being held back.
Shadow children's secretary Michael Gove said: "These figures underline yet again the growing divide between less well-off children and the rest.
"Some of the best degrees and best paid jobs require separate sciences, but for children living in the poorest areas of the country these opportunities are being closed before they even leave school."
The party obtained the figures from the government.
They say children at state schools in the ten least deprived education authorities in England are three times more likely to take physics at GCSE than those in the ten poorest LEAs.
% children taking physics GCSE
Buckinghamshire - 17%
Wokingham - 15%
Kingston Upon Thames - 14%
Manchester - 3%
Hackney - 2%
Nottingham - 2%
Islington - 0%
The analysis of the statistics by the Conservatives also reveals that less than a third of all state schools allow pupils to study the three separate sciences at GCSE.
The overwhelming majority only offer combined science which is worth two or three GCSEs.
In contrast, two thirds of private schools offer separate sciences and pupils at independent schools are almost four times more likely to take all three sciences at GCSE.
The director general of the Russell Group of leading universities, Dr Wendy Piatt, worries that differences in science education could be preventing state school pupils from winning places at the top universities.
She said it was important that pupils were given the opportunity to take key subjects like physics and chemistry.
"We are concerned that pupils from some schools are increasingly taking a combination of subjects which puts them at a disadvantage in competing for a university course and which limits their future options," she said.
The Russell Group pointed to other statistics from the government which said pupils who took combined sciences were significantly less likely to go on to take A-level sciences.
And pupils who took separate science GCSEs were 76% more likely to get an A or B grade in A-level chemistry compared to those who took double science.
The director of the Campaign for Science and Engineering Nick Dusic condemned the differences as "indefensible".
Daniel Sandford Smith, from the Institute of Physics, said pupils studying combined science were often missing out on the best of physics.
"The teaching of physics in schools by specialist physics teachers is the best way of ensuring that students at GCSE get a good early taste of physics, hopefully inspiring them to take physics at A-level and maybe further," he said.
Schools Minister Andrew Adonis said the number of pupils taking individual physics, chemistry, and biology GCSE was rising.
The government was investing £140m over the next three years to enhance recruitment and retention of physics and chemistry specialists and to help boost the number of young people studying science subjects.
"By September 2008, all pupils achieving at least level 6 at Key Stage 3 will be entitled to study triple science GCSE," he said.
Science clubs were being piloted and 18,000 people with industry experience in science and engineering were working with teachers in schools to engage and enthuse young scientists.