CBSE Class 12 Biology Important Questions for Board Exam

CBSE Class 12 Biology Important Questions for Board Exam:- The CBSE Class 12 board exams are coming soon, starting from 15th February 2025. The Biology exam will be held on Tuesday, 25th March 2025, from 10:30 AM to 1:30 PM. With the exam not far away, students must focus on their preparation. To score well, it is important to revise Biology Class 12 important questions thoroughly. Biology is a subject that needs a clear understanding of concepts, accurate definitions, and proper diagrams. 

Practising Biology important question Class 12 papers, including previous year questions, is very helpful at this stage. These questions give an idea of what topics are most likely to appear and help students understand their preparation level. Solving Biology important question papers every day can improve confidence and highlight areas that need more attention. Check out the below article to get some of the CBSE Class 12 Biology Important Questions for Board Exam.

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CBSE Class 12 Biology Important Questions for Board Exam

Question 1. Give one example each of a fungus which reproduces by (Delhi 2014C)

(i) budding

(ii) conidia

Answer: Fungus that reproduces by

(i) budding – Yeast

(ii) conidia – Penicillium

Question 2. Give one example of a plant that reproduces by (Delhi 2014C)

(i) runner

(ii) offset

Answer: Below are is the example of a plant that reproduces by

(i) runner – Oxalis

(ii) offset -Pistia

Question 3. Which of the following statements is true of Hydra? (All India 2013C)

(i) It produces asexual gemmules.

(ii) It produces unicellular buds.

(iii) It produces multicellular buds.

Answer: (iii) Hydra produces multicellular buds.

Question 4. Which one of the following statements is true of ginger? (All India 2013C)

(i) Germinating bud appears from the eye of the stem tuber.

(ii) Germinating bud appears from the node of rhizome.

(iii) Germinating bud appears from the notch of the leaf margin.

Answer: (ii) The germinating bud appears from the node of rhizome in ginger.

Question 5. State the function of filiform apparatus found in mature embryo sac of an angiosperm. (Foreign 2014)

Answer: The special cellular thickenings present in synergids at the micropylar tip called filiform apparatus, found in mature embryo sac of an angiosperm help in guiding the entry of pollen tubes up to the synergids.

Question 6. Give an example of a plant which came into India as a contaminant and is a cause of pollen allergy. (All India 2014)

Answer: Parthenium or Carrot grass is a major contaminant which came to India and caused pollen allergy.

Question 7. A bilobed, dithecous anther has 100 microspore mother cells per microsporangium. How many male gametophytes this anther can produce? (Delhi 2010)

Answer: An anther is a four-sided (tetragonal) structure consisting of four microsporangia.

Each microsporangium has 100 microspore

mother cells, so total number of microspore

mother cells in anther = 4 × 100 = 400

microspore mother cells. Meiosis in each microspore mother cell produces 4 male gametes, so 400 cells will produce = 4 × 400 = 1600 male gametes.

Question 8. An anther with malfunctioning tapetum often fails to produce viable male gametophytes. Give one reason. (Delhi 2010)

Or

Write the function of tapetum in anthers. (Delhi 2012)

Answer: The anther with malfunctioning tapetum cannot provide complete nutrition to the developing microspores or male gametophytes. So, it fails to produce viable male gametophyte.

Question 9. Why are human testes located outside the abdominal cavity? Name the pouch in which they are present. (all India 2014)

Answer: Human testes are located outside the abdominal cavity as it helps in maintaining low temperature (2-2.5%) lower than body temperature) required for spermatogenesis.

Testes are enclosed in a pouch called scrotum.

Question 10. Write the location and functions of following in human testes

(i) Sertoli cells

(ii) Leydig cells (All India 2014)

Or

Name the cells that nourish the germ cells in the testes. Where are these cells located in the testes? (All India 2013C)

Check out: CBSE Class 12 Science Stream Sample Papers

Answer: (i) Location of Sertoli cells Within the lining of seminiferous tubule of testis.

Function of Sertoli cells They provide nutrition to the developing sperms or germ cells.

(ii) Location of Leydig cells In the interstitial spaces between the seminiferous tubules. Function of Leydig cells They synthesise and secrete male hormones, i.e. androgens, testosterone.

Question 11. Write the function of the seminal vesicle. (Delhi 2012)

Answer: Seminal vesicle produces an alkaline secretion containing prostaglandins, proteins and fructose. The high fructose content provides energy to the spermatozoa. These secretions form 60-70% of the fluid found in the semen.

Question 12. List the different parts of human oviduct through which the ovum travels till it meets the sperm for fertilisation. (Delhi 2014C)

Answer: The different parts of human oviduct through which the ovum travels, till it gets fertilised are given below in the sequence

Fimbriae, finger-like projections Collect the ovum from ovary after ovulation.

Infundibulum Ovum from fimbriae is guided into funnel-shaped infundibulum, part of Fallopian tube.

Ampulla A wider part of oviduct that leads ovum into isthmus.

Isthmus It has a narrow lumen which opens into uterus. In the junction of ampulla- isthmus, the ovum gets fertilised.

Question 13. In a dihybrid cross, when would the proportion of parental gene combinations be much higher than non-parental types, as experimentally shown by Morgan and his group? (All India 2012)

Answer: The proportion of parental gene combination is much higher than non-parental types, when the two genes show linkage and are inherited together.

Question 14. Write possible genotypes Mendel got when he crossed F1 tall plant with a dwarf pea plant. (Foreign 2012)

Answer: Tt and tt (in ratio of 1:1) genotypes were obtained on crossing F1 tall plant with a dwarf parent plant. It is a test cross.

Question 15. Garden pea plant produced round, green seed. Another of same species produced wrinkled yellow seeds. Identify dominant traits. (Foreign 2012)

Answer: The dominant trait in pea plant is round and green seeds, while the recessive trait is wrinkled and yellow seeds.

Question 16. Mention two contrasting flower related traits studied by Mendel in pea plant experiments. (All India 2011C)

Answer: The two contrasting flower traits in pea plant are

Question 17. Name the contrasting pod related traits studied by Mendel in his pea plant experiment. (All India 2011C)

Answer: The two contrasting pod related traits in pea plant are

• Inflated/Constricted shape.

• Green/Yellow colour.

Question 18. Mention the type of allele that expresses itself only in homozygous state in an organism. (Foreign 2011)

Answer: Recessive allele expresses itself only in homozygous condition because in the presence of a dominant allele its effect is masked.

Question 19. Pea flowers produce assured seed sets. Give a reason. (All India 2010)

Answer: Pea flowers produce assured seed sets because they have cleistogamous flowers, which undergo natural self-pollination.

Question 20. Explain polygenic inheritance with the help of an example. (All India 2019)

Answer: Refer to text ‘Polygenic Inheritance, on page no. 94 and 95.

Check out: CBSE Class 12 Competency Based Question Bank For Board Exams

Question 21. When does a geneticist need to carry a test cross? (Foreign 2015)

Or

How would you find the genotype of an organism exhibiting a dominant phenotype? (Delhi 2012C)

Answer: A geneticist needs to carry a test cross when he/she wants to determine the genotype of an organism, with a dominant phenotype trait, whether it is homozygous or heterozygous.

Or

Genotype of the dominant phenotype is determined by a test cross. In it, the F1 progeny is crossed to its recessive parent. When F1 progeny (heterozygous) crossed with dwarf plant, the monohybrid test cross ratio is 1 : 1. But, all tall plants are obtained when both homozygous parents are crossed.

Question 22. Why did TH Morgan select Drosophila melanogaster to study sex-linked genes for his lab experiments. (Foreign 2015)

Or

Write the scientific name of the fruitfly. Why did Morgan prefer to work with fruit flies for his experiments? State any three reasons. (All India 2014)

Answer: The scientific name of fruitfly is Drosophila melanogaster.

TH Morgan preferred this organism for his study because of the following reasons

• It has fast and short life cycle.

• It has’only four pairs of chromosomes.

• It reproduces quickly.

Question 23. Give an example of a gene responsible for multiple phenotypic expressions. What are such genes called? State the cause that is responsible for such an effect. (Foreign 2015)

Or

Explain pleiotropy with the help of an example. (Foreign 2014)

Answer: Pleiotropy is the phenomenon in which a single gene exhibits multiple phenotypic expressions. The genes exhibiting pleiotropy are called pleiotrppic genes. Pleiotropism occurs mainly because of mutation in a particular gene, e.g. phenylketonuria which is a disorder caused by mutation in the gene coding for the enzyme phenylalanine hydroxylase. In the absence of this enzyme, phenylalanine is not converted into tyrosine and accumulation of phenylalanine takes place. The affected individual shows hair and skin pigmentation and mental problems.

Question 24. State the two principal outcomes of the experiments conducted by Louis Pasteur on origin of life. (Delhi 2019)

Answer: Louis Pasteur’s experiments demonstrated that life comes only from pre-existing life. He showed that in swan-neck pre-sterilised flasks, life did not evolved from ‘killed yeast’ while in another flask open to air, new living organisms arose from ‘killed yeast.’

Question 25. State two postulates of Oparin and Haldane’s theory with reference to the origin of life. (All India 2017)

Answer: Oparin and Haldane proposed the following postulates with reference to origin of life.  The first form of life came from pre-existing non-living organic molecules. The conditions on earth favouring chemical evolution were high temperature, volcanic storms and reducing atmosphere. Evolution Class 12 Important Questions and Answers Biology Chapter 7

Question 26. Write the hypothetical proposals put forth by Oparin and Haldane. (Foreign 2015)

Answer: Oparin and Haldane proposed the theory of chemical evolution. According to them, life originated from pre-existing non-living organic molecules and the formation of life was preceded by chemical evolution.

Question 27. Why are analogous structures a result of convergent evolution? (All India 2014)

Answer: When two species have structures that are similar in function but differ in origin and anatomy, they are called analogous structures. These structures develop in different species which move from different areas to a common habitat where they adapt themselves accordingly, therefore it is called convergent evolution.

Question 28. Name the type of evolution that has resulted in the development of structures like wings of butterfly and bird. What are such structures called? (Delhi 2014C)

Answer: Convergent evolution has resulted in the development of structures like wings of butterfly and birds. Such structures are called analogous organs.

Question 29. Write the term used for resemblance of varieties of placental mammals to corresponding marsupials in Australia. (Delhi 2013C)

Answer: Adaptive radiation occurring through parallel evolution results in the resemblance of placental mammals to marsupials in Australia.

Question 30. Identify the examples of convergent evolution from the following

(i) Flippers of penguins and dolphins

(ii) Eyes of Octopus and mammals

(iii) Vertebrate brains (Delhi 2013)

Answer: (i) and (ii) are the examples of analogous organs representing convergent evolution.

Vertebrate brains are the example of divergent evolution.

Check out: Class 12th Sample Papers

Question 31. Identify the examples of homologous structures from the following

(i) Vertebrate hearts

(ii) Thorns in Bougainvillea and tendrils of Cucurbita.

(iii) Food storage organs in sweet potato and potato. (Delhi 2013)

Answer: Homologous organs are derived through divergent evolution thus, indicating common ancestry.

Examples of homology are

(i) Vertebrate heart and brain.

(ii) In plants, thorns and tendrils of Bougainvillea and Cucurbita represent homology.

On the other hand, food storage organs, i.e. tubers in sweet potato and potato are analogous organs.

Question 32. State the significance of the study of fossils in evolution. (Delhi 2012)

Answer: Fossils help us to know the morphological details of the organisms that were present in the past and relate them to the organisms of the present for better understanding the process of evolution. We can also trace the time at which the particular organism existed.

Question 33. State the significance of biochemical similarities among diverse organisms in evolution. (Delhi 2012)

Answer: Similarities in biochemicals such as DNA, help in deriving the line of evolution. Organisms with more similar DNA sequences are considered close relatives that might have evolved from the same ancestor.

Question 34. What is the cell that receives a recombinant gene called ? (All India 2019)

Answer: Host cell is the cell that receives a recombinant gene. Biotechnology: Principles and Processes Class 12 Important Questions and Answers Biology Chapter 11

Question 35. Write the specific point in the palindrome and the bond that is cut by Eco Rl. (All Indio 2019)

Answer: Restriction endonuclease Eco RI cuts the DNA at the sequence known as palindromic sequence, i.e. GAATTC. The type of bond broken by Eco RI is phosphodiester bond between the G and A bases of the palindrome. This site is known as restriction site.

Question 36. Why do DNA fragments move towards the anode during gel electrophoresis ? (Delhi 2011c)

Answer: DNA fragments are negatively charged molecules and hence, they move toward the positive charged anode during gel electrophoresis.

Question 37. Suggest a technique to a researcher who needs to separate fragments of DNA. (Delhi 2016)

Or

Mention the use of gel electrophoresis in biotechnology experiments. (Outside Delhi 2016C)

Answer: Gel electrophoresis is used to separate the fragments of DNA that were cut by restriction endonucleases.

Question 38. Name the technique that is used to alter the chemistry of genetic material (DNA, RNA) to obtain desired result. (Delhi 2016C)

Answer: The technique used to alter the chemistry of genetic material to obtain desired result is called genetic engineering.

Question 39. Why is it not possible for an alien DNA to become part of a chromosome anywhere along its length and replicate normally? (All India 2014)

Answer: The alien DNA itself cannot multiply and replicate but requires a specific sequence for initiating its replication called origin of replication in a chromosome ori acts as the starting point of replication as they it aids in binding of DNA polymerase.

Question 40. Mention the type of host cells suitable for the gene guns to introduce an alien DNA. (Delhi 2014)

Answer: Plant host cells are suitable for the gene guns to introduce an alien DNA.

Question 41. Write the two components of first artificial recombinant DNA molecule constructed by Cohen and Boyer. (Foreign 2014)

Answer: The two components of first artificial recombinant DNA molecule constmcted by Cohen and Boyer are Antibiotic resistance gene

Plasmid of Salmonella typhimurium

Question 42. Name the host cells in which microinjection technique is used to introduce an alien DNA. (Foreign 2014)

Answer: The microinjection technique is usually carried out in animal cell to inject alien DNA directly into the nucleus.

Question 43. Name the material used as matrix in gel electrophoresis and mention its role. (All India 2014C)

Answer: The material used as matrix in gel electrophoresis is agarose.

This agarose gel acts as a sieve to separate the DNA fragments according to their size.

CBSE Class 12 Biology Study Tips

Incorporate CBSE Class 12 Biology important questions into your daily revision sessions to strengthen your preparation for the board exam. With the exam approaching on 25th March 2025, it is essential to focus on the main topics, practice diagrams, and solve previous year's papers. Here are some detailed tips to help you:

1. Focus on Important Chapters and Topics:

• Reproduction: This unit includes Reproductive Health, Human Reproduction, and Sexual Reproduction in Flowering Plants. Practice diagrams of the human reproductive system and the structure of a flower.

• Genetics and Evolution: Study Mendel’s experiments, inheritance patterns, DNA replication, and theories of evolution. These are commonly asked in class 12 Biology important questions for the board exam 2025.

• Biotechnology: Focus on Biotechnology: Principles and Processes and Applications of Biotechnology. Learn topics like genetic engineering, recombinant DNA technology, and bioreactors.

• Ecology and Environment: Important areas include Ecosystem, Biodiversity Conservation, Organisms and Populations, and Environmental Issues. Case-based questions and reasoning questions often come from these topics.

2. Practice Diagrams Daily:
   Diagrams are an integral part of Biology. Make sure you can draw and label diagrams like the Human Brain, Human Heart, Nephron, Pollination, and Nitrogen Cycle. Good diagrams with proper labelling can secure full marks in questions.

3. Revise NCERT Thoroughly:
   The NCERT textbook is the base for the board exam. Most class 12 Biology important questions are directly picked from NCERT. Pay attention to tables, examples, summaries, and in-text questions.

4. Solve 12th Biology Important Questions:
   Daily practice of 12th Biology important questions from previous year papers helps you understand the types of questions asked in the exam. It also familiarises you with repeated topics and common patterns.

5. Prepare for Application-Based and Assertion-Reason Questions:
   Application-based questions often appear from chapters like Genetics, Biotechnology, and Ecology. These questions test your understanding, so focus on the concepts and practice sample questions to gain confidence.

6. Time Management and Smart Planning:
   Divide your time wisely. Spend more time on high-weightage topics and Biology important questions Class 12. Make a timetable that includes daily revision of chapters and questions.

7. Use Sample Papers and Mock Tests:
   Sample papers and mock tests are a great way to revise. They often include class 12 Biology important questions for board exam 2025. Solving these will improve your speed, accuracy, and understanding of the paper pattern.

8. Take Notes for Quick Revision:
   Prepare short notes for important definitions, processes, and diagrams. Highlight key terms, as these are often asked in the exam. This will save time during your last-minute revision.

Also Read, CBSE Class 12 Chemistry Important Questions for Board Exam

CBSE Class 12 Question Bank for All Subject

CBSE Class 12 Biology Important Questions FAQs

1. What are the most important topics for CBSE Class 12 Biology?

Ans. Focus on chapters like Reproduction, Genetics and Evolution, Biotechnology, and Ecology. These units carry high weightage in exams and include several class 12 Biology important questions for board exam 2025.

2. How can I prepare for diagrams in Biology?

Ans. Practice drawing and labelling key diagrams like the Human Heart, Brain, Nephron, Flower Structure, and DNA Replication. Refer to NCERT diagrams and ensure accuracy in labelling.

3. Are NCERT books enough for Biology Class 12 preparation?

Ans. Yes, NCERT books are sufficient for preparing Biology important question Class 12. Focus on the exercises, examples, and summaries at the end of each chapter.

4. How important is solving previous year question papers?

Ans. Very important! Solving previous year papers helps identify 12th Biology important questions and familiarises you with the question pattern and marking scheme.

5. What are the most scoring sections in the Biology exam?

Ans. Sections like diagrams, definitions, and direct questions from NCERT are scoring. Focus on chapters like Biotechnology and Genetics for application-based and factual questions.