Important Questions for CBSE Class 12 Biology (Chapter-Wise)
Important Questions for CBSE Class 12 Biology are exactly what most Class 12 students search for a few weeks before the board exams, and for good reason. Biology has a huge syllabus, and without the right direction, revision can feel endless. This page gives you a simple, chapter-wise list of Class 12 Biology important questions, along with key concepts, diagram-based points, and formulas presented in easy tables so you can revise on your phone between classes.
CBSE Class 12 Biology is scoring if you focus on high-weightage chapters like Reproduction, Genetics and Evolution, Biotechnology, and Ecology. These units together carry the largest share of marks in the CBSE board exam, and most previous year questions repeat concepts from the same set of topics every year. Whether you are looking for important 1-mark, 3-mark, and 5-mark questions, or a quick formula sheet before your exam, this guide from MyClass24 is built to save your revision time.
Find the Chapter-wise PDF of Important Questions for CBSE Class 12 Biology
Why Important Questions Matter for Class 12 Biology
Biology is a theory-heavy subject, and it is easy to feel overwhelmed if you try to read every line of the NCERT textbook again and again. Practising important questions helps you identify patterns in how CBSE frames questions, understand which diagrams are asked repeatedly, and build the habit of writing to-the-point answers within the word limit. Most students who score above 90 in Biology follow one simple rule: they master the important questions of every chapter before attempting a full-length paper.
Solving these questions regularly also improves your speed for the exam, where time management genuinely matters given the length of the paper. It further helps you understand which topics deserve labelled diagrams, which need flowcharts, and which are best answered with short, definition-style responses.
Chapter-Wise Important Questions for Class 12 Biology
Below is a chapter-wise breakdown of the most frequently asked and conceptually important questions from the CBSE Class 12 Biology syllabus. Go through each unit carefully, since these questions reflect the pattern followed in recent board papers and sample question papers released by CBSE. Before Solving the Important Questions one must solve NCERT solutions with the help of NCERT solutions for Class 12.
Unit 1: Reproduction
Describe the process of double fertilisation in flowering plants with a labelled diagram.
Differentiate between micropropagation and somatic embryogenesis with suitable examples.
Explain spermatogenesis and highlight the role of hormones in the process.
What are the various methods of contraception? Explain any two natural methods.
Describe the structure of a typical human sperm and mention the function of each part.
Unit 2: Genetics and Evolution
State and explain Mendel's law of independent assortment with a dihybrid cross.
Explain the chromosomal theory of inheritance and describe Morgan's experiments on linkage.
What is Hardy-Weinberg equilibrium? List the factors that disturb genetic equilibrium in a population.
Describe the mechanism of sex determination in humans with a suitable flowchart.
Explain the process of DNA replication, highlighting the role of key enzymes.
Differentiate between homologous and analogous organs with examples supporting evolution.
Unit 3: Biology and Human Welfare
Explain the causative agent, mode of transmission, and prevention of any one bacterial and one viral disease.
What is the difference between innate immunity and acquired immunity?
Describe the process of antibiotic production using microbes, taking penicillin as an example.
Explain how bio-fertilisers and biopesticides help in sustainable agriculture.
Unit 4: Biotechnology and Its Applications
Describe the steps involved in the construction of recombinant DNA.
Explain the role of restriction endonucleases and vectors in genetic engineering.
What is PCR? Explain its significance in biotechnology with a simple diagram.
Describe how Bt cotton is developed and how it helps in pest resistance.
Explain gene therapy with the example of ADA deficiency.
Unit 5: Ecology and Environment
Explain the concept of ecological pyramids with suitable examples of pyramid of number and biomass.
Describe the process of primary and secondary ecological succession.
What are the causes and effects of ozone layer depletion?
Explain the concept of biodiversity hotspots and their significance in conservation.
Describe any two in-situ and two ex-situ methods of biodiversity conservation.
Unit-Wise Weightage of Class 12 Biology (Board Exam Pattern)
Knowing the mark distribution helps you plan your revision time wisely. Use the table below to prioritise chapters that carry higher weightage in the CBSE Class 12 Biology board exam.
Unit | Approximate Weightage |
Reproduction | 16 marks |
Genetics and Evolution | 18 marks |
Biology and Human Welfare | 14 marks |
Biotechnology and Its Applications | 10 marks |
Ecology and Environment | 12 marks |
Important Concepts and Ratios in Genetics (Quick Revision Table)
Concept | Key Formula / Ratio | Where It Is Used |
Monohybrid cross | Phenotypic ratio 3:1 | Mendel's law of dominance |
Dihybrid cross | Phenotypic ratio 9:3:3:1 | Law of independent assortment |
Test cross | Ratio 1:1 | To find genotype of unknown parent |
Hardy-Weinberg principle | p² + 2pq + q² = 1 | Studying genetic equilibrium in populations |
Linkage and recombination | Recombination frequency = (recombinants / total offspring) × 100 | Gene mapping on chromosomes |
Key Enzymes and Tools Used in Biotechnology
Tool / Enzyme | Function |
Restriction endonuclease | Cuts DNA at specific recognition sequences |
DNA ligase | Joins DNA fragments together |
Taq polymerase | Heat-stable enzyme used to amplify DNA in PCR |
Vectors (plasmids, bacteriophages) | Carry foreign DNA into a host cell |
Gel electrophoresis | Separates DNA fragments based on size |
Ecological Pyramids at a Glance
Type of Pyramid | Shape in Most Ecosystems | Example |
Pyramid of number | Usually upright, can be inverted | Tree ecosystem (inverted), grassland (upright) |
Pyramid of biomass | Usually upright, inverted in aquatic ecosystems | Pond ecosystem (inverted) |
Pyramid of energy | Always upright | Applicable to all ecosystems |
Tips to Answer Long-Answer Biology Questions Effectively
Knowing the right questions is only half the preparation. How you present the answer in the exam decides your final score. Keep these simple tips in mind while writing your Biology paper:
Always start with a one-line definition before explaining the concept in detail.
Use labelled diagrams wherever possible; CBSE awards separate marks for correct labelling.
For 5-mark questions, structure your answer with sub-headings or numbered points instead of one long paragraph.
Revise NCERT line-by-line for terminology, since CBSE often frames questions directly from textbook definitions.
Practice writing answers within the prescribed word limit to manage time during the actual exam.
Attempt at least one previous year's question paper every week during the last two months before the exam.
Common Mistakes Students Make While Answering Biology Questions
Skipping diagrams even when the question does not explicitly ask for one, which leads to loss of easy marks.
Mixing up similar-sounding terms such as pollination and fertilisation, or homologous and analogous organs.
Writing overly long answers for 1-mark or 2-mark questions, which wastes valuable exam time.
Not revising the exceptions to Mendel's laws, such as incomplete dominance and co-dominance, which are frequently tested.