Important 3 Marks Questions for CBSE Class 12 Biology Board Exam 2020-21

Class 12 CBSE students are provided with some of the important 3 marks biology questions here. These questions are extremely important to analyze the current preparation and get exposed to a variety of question types. The questions of CBSE Class 12 Biology exam are in accordance with the latest CBSE curriculum and cover most of the syllabus topics.

Important Pointers for 3 Marks Questions:

  1. Generally, 9 questions are asked in 3 marks questions with any 1 question having a choice.
  2. In 3 marks questions, students need to answer relevant points with labeled diagrams (preferably).
  3. Proper explanation and relevant details with diagrams should be included as step-wise marking is present.

CBSE class 12 students are also suggested to visit important questions for Class 12 biology to get various sample questions from different biology chapters.

Important 3 marks Biology Questions For Class 12 Board Exam

Question 1:

What does Hardy-Weinberg Principle of equilibrium indicate? List any two factors that could alter the equilibrium. What would such an alteration lead to?

Question 2:

What is ‘predation’? Explain with the help of suitable examples why is it required in a community with rich biodiversity.

Question 3:

Name and describe the technique that helps in separating the DNA fragments formed by the use of restriction endonuclease.

Question 4:

List out the salient features of chromosome theory.

Question 5:

Describe the inter-relationship between productivity, gross primary productivity and net productivity.

Question 6:

(a) Write the desirable characters a farmer looks for in his sugarcane crop.

(b) How did plant breeding techniques help north Indian farmers to develop cane with desired characters?

Question 7:

High yielding cattle is a good solution for food enhancement. How does the MOET technology help to increase the herd size?

Question 8:

Secondary treatment of the sewage is also called Biological treatment. Justify this statement and explain the process.

Question 9:

Name a human disease, its causal organism, symptoms (any three) and vector, spread by intake of water and food contaminated by human faecal matter.

Question 10:

What are Palindromes? Explain with an example?

Question 11:

State the function of a reservoir in a nutrient cycle. Explain the simplified model of the carbon cycle in nature.

Question 12:

How do snails, seeds, bears, zooplanktons, fungi and bacteria adapt to conditions unfavourable for their survival?

Question 13:

Name and describe ‘the technique that helps in separating the DNA fragments formed by the use of restriction endonuclease.

Question 14:

Describe any three potential applications of genetically modified plants.

Question 15:

Enumerate any six essentials of good, effective dairy farm management practices

Question 16:

Describe the roles of heat, primers and the bacterium Thermus aquaticus in the process of PCR.

Question 17:

Explain the events in a normal woman during her menstrual cycle on the following days:

(a) Pituitary hormone levels from 8 to 12 days.

(b) Uterine events from 13 to 15 days.

(c) Ovarian events from 16 to 23 days.

Question 18:

How does the study of fossils support evolution? Explain.

Question 19:

(a)What is Recombinant DNA Technology?

(b)Describe the application and the processes of Recombinant DNA Technology?

Question 20:

(a) Explain the significance of ‘palindromic nucleotide sequence’ in the formation of recombinant DNA.

(b) Write the use of restriction endonuclease in the above process.

Question 21:

(a) ‘‘Organisms may be conformers or regulators.’’ Explain this statement and provide one example of each.

(b) Why are there more conformers than regulators in the animal world?

Question 22:

Why is pedigree analysis done in the study of human genetics? State the conclusions that can be
drawn from it.

Question 23:

Make a list of any three outbreeding devices that flowering plants have developed and explain how they help to encourage cross-pollination.

Question 24:

Define the following terms:

  1. Lactation.
  2. Oogenesis.
  3. Parturition.
  4. Implantation.
  5. Spermatogenesis.

Question 25:

What are methanogens? How do they help to generate bio gas?

Question 26:

With the help of a flow chart, show the phenomenon of biomagnification of DDT in an aquatic food chain.

Question 27:

Why angiosperm anthers are called dithecous? Describe the structure of its microsporangium.

Question 28:

State the medicinal value and the bio active molecules produced by Streptococcus, Monascus
and Trichoderma.

Question 29:

Explain the structure of an ecosystem in detail with the flowchart.

Question 30:

(a) Can a plant flowering in Mumbai be pollinated by pollen grains of the same species growing in New Delhi? Provide explanations for your answer.

(b) Draw the diagram of a pistil where pollination has successfully occurred. Label the parts involved in reaching the male gametes to its desired destination.

Question 31:

Mention any two human diseases caused by roundworms. Name their causative agents and their mode of transmission into the human body.

Question 32:

What is disturbance in Hardy-Weinberg genetic equilibrium indicative of? Explain how it is caused.

Question 33:

(a) Differentiate between exons and introns.

(b) What is a plasmid? Why is it selected as a vector?

Question 34:

Explain the process of pollination in Vallisneria. How is it different in water-lily, which is also an aquatic plant?

Question 35:

During a monohybrid cross involving a tall pea plant with a dwarf pea plant, the offspring populations were tall and dwarf in equal ratio. Work out a cross to show how it is possible.

Question 36:

Explain the significance of satellite DNA in DNA fingerprinting technique.

Question 37:

Describe the inter-relationship between productivity, gross primary productivity and net productivity.

Question 38:

Drinking water problem in our urban areas is caused mainly because we fail to protect our water bodies. Explain how accelerated eutrophication chokes our water bodies to death.

Question 39:

Describe any three potential applications of genetically modified plants.

Question 40:

What is ecological succession? Where and why would the rate of succession be faster in a newly created pond or a forest destroyed by a forest fire?

These were a few important 3 marks questions from biology for the CBSE class 12 board exam. There is a high chance that similar questions might be included in the exam. These questions are from a wide range of biology topics and are all from the syllabus chapters. Along with these, students can also check CBSE question papers for class 12 biology and get more sample questions for practice.

Keep visiting BYJU’S to get more such important questions and preparation tips for the class 12 board exams.


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