CBSE Class 12 Biology 2017 board exam was held on 5 April 2017. Here, you will get CBSE Marking Scheme which was used for the evaluation of CBSE Class 12 Biology 2017 board exam answer booklets.
This Marking Scheme is provided with key points. During the evaluation of board exam answer booklets, the answers with all key points (as given in marking scheme) were awarded maximum marks.
CBSE Class 12 Biology Marking Scheme also contains key answers (or values point) with mark wise break up. This gives a better idea about the division of marks inside a question. With this Marking Scheme, one can easily understand about the requirement of a perfect answer.
Students can download CBSE Class 12 Biology Marking Scheme (All India): 2017 in PDF format from the download link given at the end of this article. CBSE Class 12 Biology 2017 board exam question paper (All India) is also available for reference.
Some content from the Marking Scheme:
Question 1. Name the type of cross that would help to find the genotype of a pea plant bearing violet flowers.
Test cross = 1 [1 Mark]
Question 2. State two postulates of Oparin and Haldane with reference to origin of life.
(i) First form of life could have come from pre-existing non-living organic molecules / RNA & Protein = ½
(ii) Formation of life was preceded by chemical evolution / formation of diverse organic molecules from inorganic constituents = ½ [1 Mark]
Question 3: A herd of cattle is showing reduced fertility and productivity. Provide one reason and one suggestion to overcome this problem.
Reason: Inbreeding depression / continuous inbreeding = ½
Suggestion: Should be mated with unrelated superior cattle of the same breed / out - breeding / out - crossing = ½ [1 Mark]
Question 4: What are Cry genes ? In which organism are they present ?
The genes which code for Bt toxin / Cry proteins / toxic proteins , Bacillus thuringiensis = ½ + ½
Question 5. An electrostatic precipitator in a thermal power plant is not able to generate high voltage of several thousands. Write the ecological implication because of it.
Air Pollution //
particulate matter/dust particles released in the air. [1 Mark]
Section - B
Question number 6-10 are of two marks each
Question 6: A pollen grain in angiosperm at the time of dehiscence from an anther could be 2-celled or 3-celled. Explain. How are the cells placed within the pollen grain when shed at a 2-celled stage?
• In 2-celled stage the mature pollen grain contains a generative and vegetative cell, whereas in 3- celled stage one vegetative cell and two male gametes are present = ½ + ½
• The generative cell floats in the cytoplasm of vegetative cell =1 [2 Marks]
Question 7: Differentiate between the genetic codes given below:
(a) Unambiguous and Universal
(b) Degenerate and Initiator
One codon codes for only one amino acid = ½
More than one codon coding for the same amino acid. = ½.
Genetic code / codons are(nearly) same for all organisms / from bacteria to human = ½
Start codon / AUG = ½
Question 8. Mention one application for each of the following :
(a) Passive: immunization
(a) Provide preformed antibodies / anti-toxins for quick response in case of infection by deadly
microbes(tetanus) or snake bite = ½
(b) Reduces symptoms of allergy = ½
(c) Provides passive immunity / antibodies / Ig A to new born = ½
(d) Protection of non-infected cells from further viral infection = ½
Question 9. Name the microbes that help production of the following products commercially:
(b) Citric acid
(d) Butyric acid
(a) Monascus purpureus
(b) Aspergillus niger
(c) Penicillium notatum
(d) Clostridium butylicum = ½ × 4
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