GCSEs and A-levels in geography and science are easier than they were 10 years ago, the exams watchdog warns.
Ofqual says standards have slipped, with pupils often facing more multiple-choice or short-structured questions, with less scientific content.
It reviewed biology and chemistry GCSEs and A-levels between 2003 and 2008, A-level geography between 2001 and 2010.
The Department for Education said it was committed to "restoring confidence" in the examinations system.
The watchdog said GCSE biology was easier in 2008 than in 2003 as there were more short papers with multiple-choice and short-answer questions.
This made it harder to discriminate between candidates and meant more able candidates had less opportunity to show their knowledge and abilities.
The A-level biology review criticised the Welsh exam board, WJEC, for having a high percentage of short-structured questions, which reduced the amount of information pupils had to read and take in. This made the papers "less demanding", although overall they were deemed to be sufficiently so for the level of qualification.
The CCEA exam board was over-generous in its marking of some questions and had less demanding course work, Ofqual said.
The A-level chemistry review found the exams had become easier between 2003 and 2008, as the questions were structured differently.
"In 2008 there were more short-answer questions, involving simple recall, and fewer questions that required students to formulate multiple-step responses."
The A-level geography review found that the removal of coursework from the qualification in 2010 - which was usually a 4,000-word investigation - had made it "less demanding".
It also revealed that between 2001 and 2010, there had been a shift towards "human geography", away from physical geography and fewer subjects were covered.
The review added that in general, the geographical content of A-level geography had "softened" in 2010, and that harder topics, such as ecology or atmospheric systems, had been removed from exams or made optional.
Ofqual said: "GCSEs will be revised following the National Curriculum Review in England and A-levels will also be revised in the near future.
"We will use the findings from these reviews to inform the development of regulations for those new qualifications."
A spokesman for WJEC said: "Like all the awarding organisations, we work closely with the regulators in England and Wales in order to maintain standards year on year.
"We were pleased that Ofqual were satisfied with the overall level of challenge presented in WJEC's assessments, and we look forward to examining the reports in detail to inform future work in developing new specifications."
A DfE spokesman said: "Ofqual's reports show evidence of a gradual decline in standards and that the exams system as a whole falls short of commanding the level of confidence we need.
"In particular these reports show that in recent years not enough has been demanded of students, and that they are not being asked to demonstrate real depth and breadth of knowledge.
"It is good that Ofqual has already taken action to strengthen the science GCSEs, and we are committed to restoring confidence in all GCSEs and A-levels as rigorous and valued qualifications which match the best in the world."