Peter Peacock, the minister, said the gradual nature of the improvements at different levels reflected a rise in standards, and not any "dumbing down."
Standard grade 1-6 awards have barely changed over five years, from 96.3 per cent in 2001 to 97.3 per cent. The Higher pass rate of 71.2 per cent compares with 71.9 per cent in 2001.
Mr Colella said: "The pass rate is always objectively determined, depending on the difficulty of exam questions from year to year and the differences in the cohort of pupils."
Principal examiners for every subject will now be writing their reports and will take these factors into account. They will be looking at comparisons with previous exam diets and suggesting amendments to next year's papers where necessary.
The 2005 results show an acceleration in the trend of fewer entries for Standard grade, down 22,684 on last year, and a rise in the number of candidates for Intermediate levels, which went up by 12,223.
Mr Colella said these figures probably reflected the fact that more students were taking fewer subjects and that schools are using the increasing flexibility open to them. The increase in numbers sitting Intermediate exams is partly accounted for by a greater uptake by special schools, Mr Colella said.