Important Questions Biology Class 12 2025-26 PDF with Solution

Biology in Class 12 explores the logic of life and the systems that sustain it. From genetics to evolution, every concept here helps explain how living organisms survive and adapt. This blog compiles 20 updated important questions with concise yet complete answers based on the latest CBSE 2025–26 syllabus, plus 10 extra questions for your own practice.

Here's how this blog can help you:

1. Read one chapter each day and summarize it in your own words.
2. Practice writing 3-mark answers in 5–6 lines and 5-mark answers in 10 to 12 lines
3. Revise from the “FAQs,” “Why is this important,” and “Tips” sections before your exam.

CBSE Most Important Questions For Class 12 Biology

In the table given below, we have provided the links to downloadable PDFs of chapter-wise important questions for class 12 Biology and that too for different categories of marks.

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Important Question Answers of Class 12 Biology

Q1. Why is reproduction essential for organisms?

Ans. Reproduction ensures the continuity of species by producing new individuals. It prevents extinction and maintains population size. It also allows transfer of genetic information from one generation to the next. Through reproduction, variations are introduced, which help organisms adapt over time.

‍Q2. What is double fertilisation in angiosperms? Explain its significance.

Ans. Double fertilisation means two fusion events occur inside the embryo sac. One male gamete fuses with the egg to form a diploid zygote. The other male gamete fuses with the two polar nuclei to form triploid endosperm. This ensures that endosperm develops only when fertilisation occurs, preventing wastage of resources.

Q3. Describe the menstrual cycle in humans.

‍Ans.  The cycle is around 28 days and divided into phases:
Menstrual phase: Shedding of uterine lining.
Follicular phase: FSH stimulates follicle growth; estrogen rises.
Ovulatory phase: LH surge causes ovulation.
Luteal phase: Corpus luteum forms and secretes progesterone.
If fertilisation does not occur, progesterone drops and bleeding starts again.

Q4. What are the advantages of using contraceptives?

Ans. Contraceptives help prevent unwanted pregnancies, reduce maternal health risks, help control population growth, and provide couples the freedom to plan families. Barrier methods also reduce transmission of sexually transmitted diseases.

Q5. State Mendel’s law of independent assortment with an example.

Ans. This law states that the inheritance of one trait is independent of another. Mendel proved this using dihybrid crosses on peas (seed color and seed shape). The 9:3:3:1 phenotypic ratio showed that each character was inherited separately.

Q6. Explain the process of DNA replication in detail.

Ans. Replication is semi-conservative. Helicase unwinds the DNA helix. Single-strand binding proteins stabilize open strands. DNA polymerase adds nucleotides only in 5' to 3' direction. The leading strand is continuous; the lagging strand forms Okazaki fragments. Ligase joins these fragments. The result is two identical DNA molecules.

Q7. What is the central dogma of molecular biology?

Ans. The central dogma states that genetic information flows from DNA to RNA to proteins. DNA transcribes mRNA, which is translated into a polypeptide chain. This explains how genes control traits.

Q8. Explain natural selection with an example.

Ans. Natural selection means organisms with advantageous traits survive and reproduce more. Example: Industrial melanism in peppered moths. Dark-coloured moths survived in polluted areas due to better camouflage, leading to an increase in their population.

Q9. What are vaccines and how do they work?

‍Ans. Vaccines contain weakened or inactivated pathogens. They stimulate the immune system to form memory cells without causing the disease. When exposed to the real pathogen, the body responds quickly and prevents infection.

Q10. What is artificial selection?

Ans. Artificial selection is the manual selection of desirable traits by humans. Farmers choose plants or animals with preferred characteristics to breed. It is widely used in crop improvement and livestock breeding.

Q10. What is artificial selection?

Ans. In primary treatment, large particles are removed. In secondary treatment, aerobic microbes digest organic matter in aeration tanks. This reduces biological oxygen demand (BOD). Sludge from microbes is used to produce biogas anaerobically.

Q12. What is recombinant DNA technology?

Ans. It involves cutting DNA with restriction enzymes, inserting it into a vector like plasmid, and transferring it into a host cell. This allows production of desired proteins like insulin, and development of genetically modified organisms.

Q13. What are genetically modified crops (GM crops)?

Ans. GM crops have altered genetic material to express beneficial traits like pest resistance or improved yield. Example: Bt cotton produces a bacterial toxin that kills bollworms. GM crops reduce pesticide use and increase productivity.

Q14. Explain the term population interaction with examples.

Ans. It refers to relationships between species:
Mutualism (both benefit): Lichen.
Parasitism (one benefit, one harmed): Plasmodium in humans.
Predation: Tiger and deer.
Commensalism: Barnacles on whales.

Q15. What is ecological succession?

Ans. Succession is the gradual and predictable change in species composition over time. It begins with pioneer species and ends in a stable climax community. Example: Lichens colonising bare rock leading to soil formation.

Q16. What are hotspots of biodiversity?

Ans. Hotspots are areas rich in endemic species but intensely threatened by human activities. They have high species richness and high levels of habitat loss. Example: Western Ghats.

‍Q17. What is biomagnification?

Ans. Biomagnification is the increase in concentration of harmful chemicals in the food chain. Example: DDT becomes more concentrated as it moves from plankton to fish to birds, leading to reproductive failure in top predators.

Q18. What is gene therapy?

Ans. Gene therapy involves replacing or correcting faulty genes. In ex vivo therapy, cells are removed, modified with a normal gene, and reintroduced. It is used for diseases like genetic immunodeficiency disorders.

Q19. Describe the life cycle of Plasmodium (malaria parasite).

Ans. Plasmodium enters humans through a mosquito bite, reaches the liver, multiplies, then infects red blood cells. RBCs burst, releasing toxins causing fever. Gametocytes taken up by mosquitoes continue to cycle in the mosquito gut.

Q20. What are assisted reproductive technologies (ART)?

Ans. ART includes techniques helping infertile couples. IVF involves fertilisation outside the body. ZIFT transfers zygote into the fallopian tube. ICSI injects sperm directly into the egg. These methods improve chances of pregnancy.

EXTRA QUESTIONS FOR PRACTICE

Q1. Explain vegetative propagation with two examples.

Q2. What is apomixis and how does it differ from parthenocarpy?

Q3. Write the function of oxytocin during childbirth.

Q4. Define pollination and explain its types.

Q5. What are homologous and analogous organs?

Q6. Explain how antibiotics act against bacteria.

Q7. Define cloning and state one ethical issue related to it.

Q8. What are transgenic animals and give one example.

Q9. Describe the role of lymph in the immune system.

Q10. Explain the structure of an antibody.

Why You Should Definitely Practise These Class 12 Biology Important Questions

Before you jump into solving them, here’s what makes these Class 12 Biology important questions such a smart study move:

• You’ll start spotting the most commonly repeated CBSE question patterns - a total exam hack!
• They help you clear up tricky concepts and get better at those long answers (and diagrams too).
• Your answers start sounding more structured, logical, and exam-ready.
• You’ll revise all the important definitions, processes, and examples without even realizing it.
• Solving them gives you that “I got this!” confidence for the actual exam.
• You don’t have to reread the entire NCERT again and again - questions do the heavy lifting.
• It helps you remember stuff longer since practice - retention.
• You get used to competency-based and application-style questions that CBSE loves nowadays.
• It shows you which chapters need more attention, so you can plan smarter.
• You’ll also get faster and neater at flowcharts, labelled diagrams, and mechanisms.

Tips to Use These Class 12 Biology Important Questions the Smart Way

Here’s how to actually make the most of these Class 12 Biology important questions (and not just read them once and forget):

• Revise NCERT first - almost every Biology answer is rooted there.
• Write in your own words instead of memorising big paragraphs.
• Add diagrams wherever possible - even if the question doesn’t directly ask for one.
• Time yourself while writing long answers so you don’t run out of time on board.
• Keep a separate notebook just for definitions, diagrams, and cycles -total lifesaver before exams.
• Revisit tough questions after a few days to check if you actually remember them.
• Turn long processes into flowcharts (like DNA replication or immune response) - makes revision faster.
• Underline key terms and steps to make your answers look neat and exam-ready.
• Prioritise high-weightage chapters like Genetics and Human Health first.
• And finally, before exams, revise important questions from every chapter to test your full-syllabus grip.

FAQs

Q1. Which chapters are most important for the CBSE Biology board exam?

Ans. Human Reproduction, Principles of Inheritance and Variation, Biotechnology, and Human Health and Disease are high-weightage chapters.

Q2. Are NCERT books enough for scoring above 90 in Biology?

Ans. Yes. NCERT is sufficient for the board exam. Read every line carefully, including the in-text and summary points.

Q3. How should I write long answers effectively?

Ans. Start with a short definition or introduction, use subheadings, and end with a clear conclusion. Always underline keywords and label diagrams neatly.

Q4. What type of questions are repeated every year?

Ans. Definition-based questions, differences, diagrams, and short concept-based answers like “State the function of” or “Name the process of.”

Q5. How should I divide my revision time?

Ans. Spend 3 days each on Genetics and Biotechnology, 2 days on Reproduction and Evolution, and 2 days for the rest, revising daily.