Important Topics of Biology for IISER Entrance Exam 2025; Check Topics and Subject Weightage
Indian Institutes of Science Education and Research Entrance Exam 2026 ( IISER Entrance Exam )
Registration - 5 Mar '26 - 13 Apr '26
IISER Exam 2025 Biology sections comprise 15 questions, and exam officials test students' domain knowledge and analytical understanding of the Class 11 and 12 Biology syllabus. Check out this Shiksha article to know the IISER exam 2025 important topics of biology to ace the exam with an extra score.
Biology Important Topics For IISER Entrance Exam
The Indian Institutes of Science Education and Research (IISER) offer one of the most prestigious science education programs in India. The IAT is conducted annually for admission into the BS-MS dual degree programs. Among the four subjects tested—Physics, Chemistry, Mathematics, and Biology—many students find Biology either their strongest or weakest link. Regarding the high competition level of the examination, a strategic IISER Biology Preparation must be done by the test takers.
- IISER Entrance Exam Overview and Biology Weightage
- Most Important Topics in Biology for IAT 2025
- IAT 2025: Biology Topic-Wise Weightage
- IISER Entrance Exam 2025: Preparation Strategy for Biology
- Last-Minute Tips for Biology in IAT 2025
- How to Attempt the Biology Section in the exam
IISER Entrance Exam Overview and Biology Weightage
The IISER Entrance Exam consists of 60 multiple-choice questions, 15 from every subject. The paper is distributed equally among the four core subjects:
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Biology – 15 Questions
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Physics – 15 Questions
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Chemistry – 15 Questions
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Mathematics – 15 Questions
Each question carries 3 marks, and 1 mark is deducted for incorrect answers. Hence, a good performance in Biology can significantly boost your overall score.
Also Read: IISER Biology Syllabus 2025 (OUT): Check Class 11 and Class 12 NCERT Biology Syllabus Here
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Most Important Topics in Biology for IAT 2025
Cell Structure and Function:
The portal for document upload and freezing of IISER preferences for IISER 2026 Admissions is expected to begin in the month of July 2026, tentatively. After accepting the offer and paying the seat acceptance fee, the candidate can exercise two options:
- Candidate can FREEZE the seat (they will not participate in further rounds of counselling),
- Candidate can FLOAT (they will participate in further rounds of counselling to get their higher preferences). The FLOAT option is activated by default for those who pay the seat acceptance fee. A student who has chosen to FLOAT will again be considered for seat allocation in the next round. If they are eligible to secure a seat in an IISER that is higher in their preference list than the currently accepted one, they will be offered that seat.
Key Topics:
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Cell theory
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Prokaryotic vs eukaryotic cells
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Cell organelles: structure and function
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Biomolecules
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Cell division: Mitosis and Meiosis
Why it's important: This chapter is heavily conceptual and frequently tested. Questions often revolve around organelle functions and phases of cell division.
Tip: Focus on diagrams and differences (e.g., between prokaryotic and eukaryotic cells, or mitosis vs meiosis).
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Genetics and Evolution:
Key Topics:
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Mendel’s laws of inheritance
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Dihybrid and monohybrid crosses
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Sex determination
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DNA structure, replication, and transcription
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Genetic disorders
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Evolutionary theories
Why it's important: This is a high-yield topic. IAT frequently includes tricky questions involving Punnett squares or pedigree charts.
Tip: Practice lots of genetics problems. Understanding inheritance patterns and calculations is essential.
Human Physiology:
Main Points:
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Digestive system
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Respiratory system
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Circulatory system
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Excretory system
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Nervous and muscular system
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Endocrine glands
Why it's important: At least 2–3 questions are expected from this section. Diagrams and function-based questions are common.
Tip: Use flowcharts and summary tables to remember hormone actions and feedback mechanisms.
Plant Physiology:
Main Topics:
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Photosynthesis
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Respiration in plants
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Transport in plants
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Plant hormones
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Growth and development
Why it's important: This area is rich in conceptual understanding and processes. Numerical and factual questions based on diagrams and reactions are common.
Tip: Focus on light and dark reactions, and functions of plant hormones (like auxins, gibberellins, etc.).
Ecology and Environment:
Important Topics:
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Ecosystems
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Biodiversity and conservation
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Environmental issues
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Organisms and populations
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Biogeochemical cycles
Why it's important: This is often considered easier and scoring. Questions are usually direct and based on facts.
Tip: Focus on understanding the food chains, ecological pyramids, and biogeochemical cycles.
Reproduction:
Main Topics:
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Reproduction in organisms
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Sexual reproduction in flowering plants
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Human reproductive system
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Reproductive health
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Gametogenesis and fertilisation
Why it's important: Diagrams, hormonal control, and stages of development are frequently asked.
Tip: Understand the menstrual cycle, gametogenesis, and male/female reproductive structures clearly.
Biotechnology and Its Applications:
Key Topics:
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Principles of biotechnology
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Genetic engineering (rDNA technology)
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Applications in health and agriculture
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Genetically Modified Organisms (GMOs)
Why it's important: This is a modern and application-based topic. It can have 1–2 questions in IAT.
Tip: Focus on the steps in gene cloning, the use of restriction enzymes, and practical applications like Bt cotton.
Also Read:
| IISER Physics Syllabus | IISER Mathematics Syllabus |
| IISER Biology Syllabus | IISER Chemistry Syllabus |
IAT 2025: Biology Topic-Wise Weightage
Based on analysis of past papers and trends:
| Topic | Approximate Weightage |
|---|---|
| Cell Structure & Function | 2–3 Questions |
| Genetics and Evolution | 2–3 Questions |
| Human Physiology | 2–3 Questions |
| Plant Physiology | 1–2 Questions |
| Ecology and Environment | 1–2 Questions |
| Reproduction | 1–2 Questions |
| Biotechnology | 1 Question |
| Diversity & Classification | 1 Question |
IISER Entrance Exam 2025: Preparation Strategy for Biology
1. Follow NCERT Thoroughly
Most IAT Biology questions are directly or indirectly based on the NCERT. Do not skip:
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Line-by-line reading
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Diagrams and tables
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NCERT summary boxes
2. Practice with PYQs
Solving IISER previous year question papers (PYQs) helps you know the type of questions and difficulty level.
3. Make Topic-Wise Notes
Summarise each chapter with:
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Key terms
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Diagrams
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Important points
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Mnemonics for classification or steps
4. Revise Regularly
Biology involves a lot of memorisation. Use spaced repetition techniques and flashcards for regular revision.
5. Practice papers
Simulate the exam environment with full-length IAT practice papers. Analyse your performance in the Biology section to identify weak areas.
6. Recommended Resources
Books:
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NCERT Class 11 & 12 Biology – Primary resource
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Trueman’s Elementary Biology Vol I & II – For deeper understanding
- MTG Objective NCERT at Your Fingertips (Biology) – For practice questions
Also Read: IISER Entrance Exam 2025 Books: Check Best Books for Exam Preparation
Last-Minute Tips for Biology in IAT 2025
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Quickly revise key concepts and flowcharts
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Focus on high-yield topics like Genetics, Cell Biology, and Human Physiology
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Solve 2–3 mock papers weekly in the last month
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Stay updated with any syllabus changes from the official IISER site
How to Attempt the Biology Section in the exam
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Start with direct questions like Ecology or Reproduction to gain confidence
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Mark doubtful questions for review and come back later
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Avoid guesswork—each incorrect answer reduces your net score
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Use elimination to improve your odds on tricky MCQs
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Student Forum
Anything you would want to ask experts?Answered a week ago
You can check the IISER exam pattern and syllabus on the website, iiseradmission.in. Knowing the paper pattern and syllabus for IISER, you can plan your preparation.
V
Contributor-Level 9
Answered a week ago
220+ marks are a good score in IISER. Students must have a proper strategy to score high. They can plan their preparation according to the IISER exam syllabus. Practising previous year question paper and mock test will help in scoring good marks.
V
Contributor-Level 9
Answered 2 weeks ago
There is no fixed number of entering preference for the IISER Entrance Exam counselling process. There are seven IISER institutes offering 11 programmes. Candidates have to select at least one IISER. Higher the number of preferences, better will be their chance of seat allotment.
N
Beginner-Level 5
Answered 2 weeks ago
Once the IISER Entrance Exam counselling seat allotment result is declared, candidates have the following options.
- FREEZE: By selecting this option, candidates confirm the acceptance of the offer, and that they will not participate in the next rounds of IISER Entrance Exam counselling.
- FLOAT: Selecti
V
Beginner-Level 5
Answered 2 weeks ago
Seat Acceptance Fee or SAF is the fee to be paid to accept the allotted seat at a particular round of IISER counselling process. Unless the SAF is paid, candidates will not be considered for admission.
L
Beginner-Level 5
Answered 2 weeks ago
During the IISER Entrance Exam counselling process, seats are allotted based on the following factors.
- Seats available across IISER institutes in the current round of counselling
- IAT Rank obtained by candidates
- IISER preference given by the candidate
- Candidate category.
Candidates are advised to fill as
A
Beginner-Level 5
Answered 2 weeks ago
IISER does not conduct the counselling or admission process for IISc Bangalore and IIT Madras through the IAT scores. These institutes conduct their own counselling or admission process. IISER counselling process is conducted only for seven IISER institutes located across India.
P
Beginner-Level 5
Answered 2 weeks ago
The IISER Entrance Exam counselling process is conducted in online mode. Candidates have to register on the exam website and fill in their institute in course choices in order of preference. Based on that, the seat allotment will be released. They can either 'Freeze' the seat and take admission, or
M
Beginner-Level 5
Answered 2 weeks ago
The IISER entrance exam scores are accepted by 11 IISER institutes across India. Apart from that, IISc Bangalore and IIT Madras also consider the scores for admission to BS courses offered by them.
P
Beginner-Level 5
Answered 3 weeks ago
Passed 10+2 from a recognised board in 2024, 2025, or 2026 with minimum 60% marks in aggregate (55% for SC /ST /PwD students) are eligible to apply for IISER exam 2026. Candidates must have taken any three subject among Physics, Chemistry, Mathematics, and Biology in class 12.
V
Contributor-Level 9
Once IISER result is declared, a seat allotment list is declared containing roll numbers of candidates who are allocated seats in BS-MS programmes. Candidates can check the first round allotment list on the official website of the exam tentatively by the second week of July 2026. All candidates whose roll numbers appear in the first round allotment list need to log in to their application portal to download the offer letters.