Exam boards in England are to put more simple questions in science papers from next year, it has emerged.
Numbers taking science have fallen during the past two decades
They deny examiners are being told to make GCSEs easier and say the bar is being raised and students will need to show wider knowledge and skills.
A document seen by The Times says that from June, some papers should consist of 70% "low demand" questions, instead of the current level of 55%.
It was prepared by the exam boards' body, Joint Council for Qualifications.
There is concern that fewer students are taking science GCSEs, although there was a small upturn this year.
Since 1984, the number of people studying A-level physics has slumped by 57% and the take-up of chemistry has dropped by 28%.
Under the guidelines - first distributed to exam boards in 2005 - exams should contain more questions in a simple format, such as asking students to tick a multiple-choice box.
The guidelines amount to a non-binding agreement between the exam boards.
The suggestion to increase the proportion of "low demand" questions from 55% to 70% relates to the combined science GCSEs.
Some students take what are known as single or double sciences - where the various science subjects are studied individually in greater detail.
In this latter case, the new guidelines suggest raising the proportion of easier questions from 45% to 50%.
Raising the bar
Jim Sinclair, JCQ director, told the Times the proposed changes were a way of stopping children being "turned off" by science.
He says the changes amount to a raising, not a lowering of the bar.
In a statement on Wednesday, he said: "Examiners have not been told to make GCSE science examination questions easier.
"The JCQ made recommendations in 2005 for the better use of the full mark range on examination papers and the widening of the ranges of marks for the lower grades in foundation tier GCSE science.
"Therefore, the examination will require candidates to demonstrate wider knowledge and understanding to achieve their grades.
"It is not a lowering of the bar, rather a raising of the bar since candidates have to engage with and positively respond to more questions than previously."
The JCQ added that there would still be a requirement for students to do "a significant proportion of extended writing" in the GCSE science assessment.
The Department for Children, Schools and Families (DCSF) insisted there were no plans to alter the way the subject was examined.
"We have recently revised these examinations and we have no plans to look at them again," a spokeswoman said.
Exam boards have to have their exam papers approved by the exams watchdog, the Qualifications and Curriculum Authority (QCA).
A spokesperson said: "The regulators' code of practice, which governs how GCSE qualifications are run, requires awarding bodies to have the prime objectives of maintaining grade standards over time and across different syllabuses.
"The detailed content structure of question papers is a matter for awarding bodies but QCA requires that the standard of work required to achieve a grade C is the same across different tiers and the same as in previous years."
The chief executive of the Association for Science Education, Derek Bell, said there was a need for balance in exam questions.
"It's the biggest tension we have got in science education and in education more generally.
"If you are trying to open access to demonstrate what all students can do, then you have to look at the system of doing it, but on the other hand you have to make sure the higher achievers also reach their potential."