Biology marking scheme cbse, High school final essays of Biology

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MS-Biology/044/57-5-2 1 26-05-44N
Marking Scheme
Strictly Confidential
(For Internal and Restricted use only)
Senior Secondary School Examination, 2026 (XIIth)
SUBJECT NAME : Biology (Q.P. CODE 044/57-5-2)
General Instructions: -
1
The CBSE has decided to introduce On Screen Marking (OSM) for the evaluation of
Class XII answer Book with the 2026 Examination.
2
You are aware that evaluation is the most important process in the actual and correct
assessment of the candidates. A small mistake in evaluation may lead to serious
problems which may affect the future of the candidates, education system and
teaching profession. To avoid mistakes, it is requested that before starting evaluation,
you must read and understand the spot evaluation guidelines carefully.
3
“Evaluation policy is a confidential policy as it is related to the confidentiality
of the examinations conducted, evaluation done and several other aspects. Its
leakage to public in any manner could lead to derailment of the examination
system and affect the life and future of millions of candidates. Sharing this
policy/document to anyone, publishing in any magazine and printing in
Newspaper/Website, etc. may invite action under various rules of the Board
and IPC.”
4
Evaluation is to be done as per instructions provided in the Marking Scheme. It should
not be done according to one’s own interpretation or any other consideration. Marking
Scheme should be strictly adhered to and religiously followed. However, while
evaluating, answers which are based on latest information or knowledge and/or
are innovative, they may be assessed for their correctness otherwise and due
marks be awarded to them. In Class-XII, while evaluating two competency-
based questions, please try to understand given answer and even if reply is not
from marking scheme but correct competency is enumerated by the candidate,
due marks should be awarded.
5
The Marking scheme carries only suggested value points for the answers.
These are in the nature of Guidelines only and do not constitute the complete answer.
The students can have their own expression and if the expression is correct, the due
marks should be awarded accordingly.
6
The Head-Examiner must go through the first five answer books evaluated by each
evaluator on the first day, to ensure that evaluation has been carried out as per the
instructions given in the Marking Scheme. If there is any variation, the same should
be zero after deliberation and discussion. The remaining answer books meant for
evaluation shall be given only after ensuring that there is no significant variation in
the marking of individual evaluators.
7
Evaluators will mark ( √ ) wherever answer is correct. For wrong answer CROSS ‘X’
be marked. Evaluators will not put right () while evaluating which gives an
impression that answer is correct and no marks are awarded. This is most common
mistake which evaluators are committing.
8
If a question has parts, please award marks on the right-hand side for each part in
the OSM Portal. Marks awarded for different parts of the question will be totaled up
by the OSM System.
9
If a question does not have any parts, marks must be awarded in the left-hand margin
in the OSM Portal. This may also be followed strictly.
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Marking Scheme Strictly Confidential (For Internal and Restricted use only) Senior Secondary School Examination, 2026 (XIIth) SUBJECT NAME : Biology (Q.P. CODE 044/57-5-2) General Instructions: - 1 The CBSE has decided to introduce On Screen Marking (OSM) for the evaluation of Class XII answer Book with the 2026 Examination. 2 You are aware that evaluation is the most important process in the actual and correct assessment of the candidates. A small mistake in evaluation may lead to serious problems which may affect the future of the candidates, education system and teaching profession. To avoid mistakes, it is requested that before starting evaluation, you must read and understand the spot evaluation guidelines carefully. 3 “Evaluation policy is a confidential policy as it is related to the confidentiality of the examinations conducted, evaluation done and several other aspects. Its leakage to public in any manner could lead to derailment of the examination system and affect the life and future of millions of candidates. Sharing this policy/document to anyone, publishing in any magazine and printing in Newspaper/Website, etc. may invite action under various rules of the Board and IPC.” 4 Evaluation is to be done as per instructions provided in the Marking Scheme. It should not be done according to one’s own interpretation or any other consideration. Marking Scheme should be strictly adhered to and religiously followed. However, while evaluating, answers which are based on latest information or knowledge and/or are innovative, they may be assessed for their correctness otherwise and due marks be awarded to them. In Class-XII, while evaluating two competency- based questions, please try to understand given answer and even if reply is not from marking scheme but correct competency is enumerated by the candidate, due marks should be awarded. 5 The Marking scheme carries only suggested value points for the answers. These are in the nature of Guidelines only and do not constitute the complete answer. The students can have their own expression and if the expression is correct, the due marks should be awarded accordingly. 6 The Head-Examiner must go through the first five answer books evaluated by each evaluator on the first day, to ensure that evaluation has been carried out as per the instructions given in the Marking Scheme. If there is any variation, the same should be zero after deliberation and discussion. The remaining answer books meant for evaluation shall be given only after ensuring that there is no significant variation in the marking of individual evaluators. 7 Evaluators will mark ( √ ) wherever answer is correct. For wrong answer CROSS ‘X’ be marked. Evaluators will not put right (✓) while evaluating which gives an impression that answer is correct and no marks are awarded. This is most common mistake which evaluators are committing. 8 If a question has parts, please award marks on the right-hand side for each part in the OSM Portal. Marks awarded for different parts of the question will be totaled up by the OSM System. 9 If a question does not have any parts, marks must be awarded in the left-hand margin in the OSM Portal. This may also be followed strictly.

10 No marks to be deducted for the cumulative effect of an error. It should be penalized only once.

11 A full scale of marks 0 ̶ 70 has to be used. Please do not hesitate to award full marks

if the answer deserves it. 12 Every examiner has to necessarily do evaluation work for full working hours i.e., 8 hours every day and evaluate 20 answer books per day in main subjects and 25 answer books per day in other subjects (Details are given in Spot Guidelines).This is in view of the reduced syllabus and number of questions in question paper. 13 Ensure that you do not make the following common types of errors committed by the Examiner in the past :- ● Answers marked as correct, but marks not awarded. (Ensure that the right tick mark is correctly and clearly indicated. It should merely be a line. Same is with the X for incorrect answer.) ● Half or a part of answer marked correct and the rest as wrong, but no marks awarded. 14 While evaluating the answer books if the answer is found to be totally incorrect, it should be marked as cross (X) and awarded zero (0) Marks. 15 The^ Examiners^ should^ acquaint^ themselves^ with^ the^ guidelines^ given^ in^ the “Guidelines for Spot Evaluation” before starting the actual evaluation. 16 The candidates are entitled to obtain photocopy of the Answer Book on request on payment of the prescribed processing fee. All Examiners/Additional Head Examiners/Head Examiners are once again reminded that they must ensure that evaluation is carried out strictly as per value points for each answer as given in the Marking Scheme. 17 If a candidate attempts both alternatives/options in a question where only one option/ alternative is required to be attempted, the Evaluator shall award marks in both the options. The system will take the higher of two scores and disregard the other response. 18 In a question having two options/alternatives, if a candidate has attempted only one, then the evaluator shall mark “NA” (Not attempted) against the option that has not been attempted by the candidate.

(i) Gets attached to the endometrium/Implantation/placenta formation. (ii) It forms ectoderm mesoderm and endoderm/forms germ layers / form embryo.

  1. (a) (i) Award marks if attempted. (ii) It provides nourishment to the embryo.

OR

(b) Production of hybrid seed is very costly, no segregation of characters in the hybrid progeny in apomictic seeds, farmers need not to buy hybrid seeds every year, use of apomictic seeds would be cost effective, any other correct reason (any two correct reasons)

19. (a) The meristem is removed from a diseased plant, and grown in-vitro/ by tissue

culture method plant produced is virus free.

OR

(b)  Treat the bacterial cell with a specific concentration of a divalent cation such as Ca ++.  Incubating bacteria (host) with recombinant DNA on ice.

 Place them at 42^0 C/ give heat shock at 42^0 C

 Put them back on ice this enables the bacteria to take up the recombinant DNA. ½ x 4

  1. Grazing food chain^ Detritus food chain  Starts from producers. ^ Starts from

Detritus/decomposers/dead

organic matter.  It is the major conduit for energy flow in aquatic ecosystem  It is the major conduit for energy flow in terrestrial ecosystem  Less fraction of energy flow (because food chain is large)  Larger fraction of energy flow (because food chain is smaller) (any other relevant difference, any two) 1 x 2 2

OR

(b)  It does not take into account the same species belonging to two or more trophic levels.  It assumes a simple food chain, something that almost never exists in nature  It does not accommodate a food web.  saprophytes are not given any place in ecological pyramids even though they play a vital role in the ecosystem. (Any two) 1 x 2

  1. The exceptions are found is - (a)

(i) mitochondrial codons. (ii) some protozoans.

  • Some codes are said to be degenerate because some amino acids are coded by more than one codon.

SECTION-C

  1. (a) (b) Leydig cells secrete testosterone/ androgens (which is necessary for spermatogenesis)

½ X 4

    • Polygenic inheritance – In this one character is controlled by three or more genes and each gene contributes to phenotype so it is the additive (cumulative) effect of all the genes that is expressed.
  • e.g. Human skin colour is controlled by three genes, where dominant genes (ABC) are responsible for dark skin colour and recessive ones (abc) is responsible for light skin colour. AABBCC X aabbcc Dark skin light skin Gamete F1 – Intermediate skin colour (or any other relevant example)

AaBbCc ABC abc ½

Abingdon tortoise in Galapagos islands became extinct within a decade after the goats were introduced into the island probably due to the greater browsing efficiency of the goat or the feeding efficiency of one species (tortoise) is

reduced by the interfering presence of the other species (goat)/any other correct

example.

SECTION-D

29. (a) Plasmids and bacteriophages have the ability to replicate / They multiply within

the bacterial cells independently of the chromosomal DNA / an alien piece of

DNA can be ligated to them / They can be multiplied equal to their specific copy

numbers. (b)(i) (I) ori (II) Pvu II OR (b) (ii) G : ampR^ /ampicillin-resistance gene, H : tetR/^ tetracycline-resistance gene. (c) Pst I , Pvu I, BamH I, Sal I

½ X 4

  1. (a) Because RNA polymerase carries out polymerisation in 5'  3' direction only. (b) (i) Since hnRNA contains both exons or coding sequence and introns or non coding seqeunce undergo splicing to remove the introns or non-coding sequence

/ for the removal of introns.

OR

(b) (ii).

- Capping / addition of mGppp (Methyl Guanosine Triphosphate) at 5' of hnRNA.

- Tailing / Adenylate residue (200-300) are added at the 3' end in a template

strand as poly A tail. (c)  If a segment of DNA produces two polypeptides the genetic information

machinery becomes complicated / two different polypeptides will be formed

and one of which may not be useful for the cell. The two complementary RNA molecules produced simultaneously will form a double- stranded RNA that will not be translated into polypeptides.

SECTION-E

  1. (a)  In Pea plants:

Phenotypic ratio:- violet : white = 3 : 1 (½) Conclusion: This is the case of dominance (½)  In Antirrhinum plant Phenotypic ratio:- Red : Pink : white = 1 : 2 : 1 (½) Conclusion: This is a case of incomplete dominance (½) OR (b) (i) ½x

½x

 It lasts for longer period  It lasts for shorter period  Memory cells are formed  Memory cells are not formed (any three correct difference) OR (b) (i) (I) Wuchereria bancrofti , and Wuchereria malayi

(II) Chronic inflammation of the organs/ swelling in lower limbs / gross deformities

in genital organs.

  1. (^) (a)  Fertilisation

Fertilisation occurs in the ampulla/ampullary-isthmic junction of the fallopian

tube, when sperm comes in contact with the ovum, it induces changes in the zona pellucida of the ovum that block the entry of additional sperms and thus ensures only one sperm, the secretions of the acrosome help the sperm to enter the cytoplasm of the ovum by dissolving the zona pellucida and plasma membrane , after the entry of sperm into the cytoplasm of ovum induces completion of meiosis II (of secondary oocyte), fusion occurs between the nucleus of ootid (ovum) and that of sperm to form a diploid zygote  Implantation:  The trophoblast layer gets attached to the endometrium.  The uterine cells divide rapidly and cover the blastocyst as a result the blastocyst becomes embedded in the endometrium of uterus ½ x 6 1x OR (b) (i)Hormones in sequence of their secretion in a pregnant woman. FSH; LH; hCG; Relaxin. (ii)  FSH: Source: Anterior Pituitary. Function: Stimulates follicular development  LH: Source: Anterior Pituitary. Function: It causes rupture of Graafian follicle and release of ovum into

fallopian tube/Ovulation

 hCG: Source: Placenta. Function: It supports foetal growth, metabolic changes in mother and maintenance of pregnancy.  Relaxin:

Mast cells, cause allergy Transmitted by the bite of female mosquito vector. (ii) (I) Virus infected cells, Protect the non-infected cells of our body from viral infections (III) (II)

Source: Ovary. Function: It facilitates parturition.