GCSEs and A-levels in science and geography are easier than they were 10 years ago, the exams regulator has said.
Standards have slipped, with teenagers often facing more multiple choice and short structured questions and papers with less scientific content, according to reports published by Ofqual.
The watchdog conducted reviews of GCSEs and A-levels in biology and chemistry between 2003 and 2008 as well as A-level geography between 2001 and 2010 and A-level critical thinking in 2010.
The findings show that among the GCSEs, changes to the way the exams were structured had "reduced the demand" of the qualifications, while the A-level reviews found that changes to the way papers were assessed had in many cases made them easier.
GCSE biology was easier in 2008 than in 2003 because there were more short papers with multiple choice and short answer questions, Ofqual found. This made it harder to discriminate between students and meant that top students had less chance to show their knowledge and abilities, the review said.
The GCSE science qualifications reviewed are no longer taken by students, while the A-level qualifications examined are still current. Exam boards will have made changes to these in light of Ofqual's findings.
In a statement, Ofqual said that GCSEs are due to be revised after the national curriculum review, which is under way at the moment, while A-levels are also set to be reviewed.
A Department for Education 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."