Teenagers at a school visited by The TES said that they were struggling with the work required for the Science for the 21st Century course, being piloted in 82 schools.
The course, which will be offered nationwide from next year, will be a major talking point at this year's Association for Science Education conference.
Most pupils take a double GCSE in science. The new "hybrid" qualification replaces this with a compulsory core worth one GCSE, which covers issues such as genetic engineering and space exploration.
Pupils are then free to take academic ("general") modules or vocational ("applied") modules to make up a double science GCSE.
The course aims to use science stories in the news to stimulate pupils'
It encourages youngsters to think for themselves, rather than simply regurgitating facts, placing particular emphasis on the questioning of scientific data.
When The TES visited Springwell comprehensive, just outside Chesterfield, Derbyshire, to gauge the opinions of top-set Year 10 pupils who had completed a term of the new core course, the verdict was near-unanimous.
The course was interesting, but exhausting, they said. "It's much more challenging than what we've done before," said Francesca Goodall, 14. "At key stage 3 the teacher did all the work for you, we used to just copy off the board. Now we have to do all the work ourselves."
Several pupils said they had more homework for science than any other subject. Laura Marshall, 14, said pupils were regularly given nine worksheets to complete during a lesson. Any not completed had to be done as homework. "Most people were taking home something like seven sheets," she said.
The course introduces topical issues such as gene therapy and air pollution to pupils through different media, including a radio presentation.
One pupil said: "Some of it was boring. We had one on evolution which was just an old man talking for ages. But genes and ethics was good."
Several youngsters were unhappy that experimental work was not included in the core, meaning that they had no laboratory sessions for a term.
Critics say the course could lead more youngsters to reject physics, chemistry and biology A-levels, but Springwell pupils on the whole seemed engaged by it.
Professor John Holman, of York University, co-director of the pilot, said the response overall had been positive, but that some schools were concerned about overloading pupils with work.
He added: "This is not dumbing down. It's about teaching youngsters not just to memorise lots of facts, but to be able to read a study about vaccination or genetically modified foods in a critical way.