A petition demanding the pass mark on the 2019 papers are lowered has reached over 6,400 signatures.
But the Scottish Qualifications Authority (SQA) said exams, which pupils sat on Tuesday, were "valid tests of the subject".
Enraged pupils and parents took to Twitter following the biology exam to complain about the difficulty level of this year's paper.
One parent said: "Who do you talk to regarding biology exams that were not proper examinations, my daughter sat a paper that had nothing to do with biology."
Another wrote: "As a nurse who has higher biology and a degree... the biology test given to my daughter was a joke and was a math exam and nothing at all to do with biology."
The petition set up online calls for the SQA to "change the grade boundaries of the 2019 higher biology and higher human papers. They were nothing like ANY past paper and 90% of papers were made up of maths."
The SQA have defended the complexity of the exams.A spokesperson said: "The 2019 Higher Biology and Human Biology question papers, and the National 5 Biology question paper, were all valid tests of the subject, using content from across the course, giving candidates a fair opportunity to display and apply their knowledge and understanding of the course.
"The papers are designed to sample across the full breadth of the course, and ensure candidates have the opportunity to demonstrate their knowledge, skills and understanding."
"External experts review papers to ensure the standards are consistent with previous papers and course expectations.""More than 21,000 candidates sat National 5 Biology, while over 14,000 sat Higher Human Biology, and Higher Biology combined, and while we are aware of some discussion on social media, we would suggest this is of a relatively low volume."
In 2015 the exam body lowered the pass score for Higher maths to just 33.8% after determining the paper for that year was too hard.