Most Important 3 Marks Questions for Biology Class 12th CBSE Board Exam 2018

Most Important 3 Marks Questions for Biology Class 12th CBSE Board Exam 2018

Most Important 3 Marks Questions for Biology Class 12th CBSE Board Exam 2018

Most Important 3 Marks Questions for Biology Class 12th CBSE Board Exam 2018 are given below:


Draw a labeled diagram of the microscopic structure of a human sperm.


Expand MOET. Explain the procedure of this technology in cattle improvement.


(a) One of the codons on mRNA is AUG. Draw the structure of tRNA adapter molecule for this codon.

(b) Name the RNA polymerase that transcribes tRNA in eukaryotes.

(c) What is unique about the amino acid this tRNA binds with?


One of the codons on mRNA is AUG. Draw the structure of tRNA adapter molecule for this codon. Explain the uniqueness of this tRNA.


Given below is a part of the template strand of a structural gene:


(a) Write its transcribed mRNA strand with its polarity.

(b) Explain the mechanism involved in the initiation of transcription of this strand.


How and why is the bacterium Thermus aquaticus employed in recombinant DNA technology? Explain.


(a) Name the different gases contained in the flask used as an experimental setup by S.L. Miller.

(b) On the basis of the composition of gases in this experiment, what was the condition in the flask?

(c) Write the conclusion drawn from this experiment.


(a) What are “molecular scissors”? Give one example.

(b) Explain their role in recombinant DNA technology.


(i) How and at what stage does Plasmodium enter into a human body?

(ii) With the help of a flow-chart, only show the stages of asexual reproduction in the life cycle of the parasite in the infected human.

(iii) Why does the victim show symptoms of high fever?


It has been recorded that the temperature of the earth’s atmosphere has increased by 0.6°C.

(a) What has caused this increase?

(b) Explain its consequences.


Explain the pattern of inheritance of haemophilia in humans. Why is the possibility of a human female becoming a haemophilic extremely rare? Explain.


Explain the process of charging of tRNA. Why is it essential in translation?


How do organisms manage with stressful conditions existing in their habitat for short duration? Explain with the help of one example each.


A non-haemophilic couple was informed by their doctor that there is a possibility of a haemophilic child be born to them. Explain the basis on which the doctor conveyed this information. Give the genotypes and the phenotypes of all the possible children who could be born to them.


Name the type of immunity that is present at the time of birth in humans. Explain any two ways by which it is accomplished.


Define totipotency of a cell. List the requirements if the objective is to produce somaclones of a tomato plant on the commercial scale.


Give the scientific name of the parasite that causes malignant malaria in humans. At what stage does this parasite enter the human body? Trace its life cycle in the human body.


Draw a labeled schematic sketch of replication fork of DNA. Explain the role of the enzymes involved in DNA replication.


Explain the causes of global warming. Why is it a warning to mankind?


Particulate and gaseous pollutants along with harmless gases are released from the thermal power plants.

(i) Name any two harmless gases released.

(ii) Name the most widely used device for removing particulate pollutants from the air. Explain how the device is used.


(a) Draw a schematic representation of the structure of a transcription unit and show the following in it:

(i) A direction in which the transcription occurs

(ii) A polarity of the two strands involved

(iii) Template strand

(iv) Terminator gene

(b) Mention the function of promoter gene in transcription.


(a) In human genome which one of the chromosomes has the most genes and which one has the fewest?

(b) Scientists have identified about 1.4 million single nucleotide polymorphs in the human genome. How is the information of their existence going to help the scientists?


Draw and label the enlarged view of microsporangium of an Angiosperm. State the function of its innermost wall layer.


Diagrammatically represent the experimental set up that proved Oparin – Haldane hypothesis.


True-breeding pea plants showing contrasting character for flower position were cross-bred.

(a) Mention the position of flowers in F1 generation.

(b) Work out the cross up to the F2 generation.

(c) Compute the relative fraction of various genotypes in the F2 generation?


Your classmate complains of a headache and cough. The doctor confirms that he is suffering from Pneumonia and not the common cold, on the basis of certain symptoms. List these symptoms. Mention any two precautions to be followed to prevent the spread of this disease.


Cow dung and water are mixed and this slurry is fed into the biogas plant for digestion by microbes. The person performing the process shares that there is no need to provide inoculum for it, why? What is the role of microbes at the source? Under which condition will they be most active and effective?


A person is born with a hereditary disease with a weakened immune system due to deficiency of an enzyme. Suggest a technique for the complete cure for this disease, identify the deficient enzyme and explain the technique used for cure.


Draw the diagram of microsporangium of an Angiosperm and label any four parts State the function of its innermost wall layer.


Give reason : –

(a) A liverwort plant is unable to complete its life cycle in a dry environment.

(b) A number of male gametes produced are much more than the female gametes produced.

(c) Organisms exhibiting external fertilization show great synchrony between the sexes and release a large number of gametes into surrounding medium.

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