KENDRIYA VIDYALAYA SANGATHAN
ERNAKULAM REGION
HALF YEARLY
MARKING SCHEME
CLASS XII BIOLOGY
TIME:3 hrs MAX MARKS :70
SECTION A
1.
Incomplete dominance/ Dominant allele not completely dominant
over the recessive. ½ +½
1
2.
Coconut are monoecious / Plants have male and female flowers on
the same individual. ½
Date palm are dioecious/ male and female flowers on separate
individuals. ½
1
3.
These are called as Lobed fins evolved into first
Amphibians.
1
4.
Statins , Monascus purpureus ½ + ½
1
5.
‘Saheli’ ,
nonsteroidal/ Once a week pill/few side effects/high
contraceptive value. (any one) ½ +½
1
SECTION-B
6.
Genetic variations are created by mutations in plants resulting
in the creations of a new character. The plants with desirable
character are selected as source in breeding. ½ +½
Example: Induced mutation in mung bean has made it resistant to
yellow mosaic virus and powdery mildew . 1
2
7.
Amoebiasis , Entamoeba histolytica ½ +½
Constipation / abdominal pain and cramps / stools with excess
mucous and blood clots (any 2) 1
Or
Introduction of inactivated or weakened pathogen ; Antibodies
produced neutralize pathogens during actual infection:;and memory T
and B cells produced recognize pathogen quickly on subsequent
exposure. ½ +½
Example: hepatitis B vaccine- production of antigenic
polypeptide of pathogen in yeast. ½ +½
2
8.
Rotifers/ honeybees/lizards/ turkey (any 2) ½ +½
Female gamete undergoes development without fertilization;
parthenogenesis. ½ +½
2
9.
Hugo de Vries, evening primrose.½ +½
Mutation theory: Large differences in character appearing
suddenly-
Saltation/random/directionless.(any 1) ½
Darwin’s theory: Small differences occurring gradually/
directional. (any 1) ½
2
10.
Klinefelters syndrome.XXY ½ +½
Musculine, feminine characters/ gynaecomastia/sterile ½ +½
2
SECTION C
11.
(a) pollen release and stigma receptivity is not
syncronised.
Different positions of stigma and anther
Self incompatibility.
Production of unisexual flowers. ½ x 4
(b) Continued self pollination results in inbreeding depression-
decrease in productivity and fertility. ½ +½
3
12.
(a)p2 +q2 +2pq =1
Hardy Weinberg principle states that the Allelic frequencies in
a population are stable and remain constant from generation to
generation. it is called genetic equilibrium. Sum total of all the
allelic frequencies is one when frequency is measured, differs from
expected values, the difference indicate the extent of evolutionary
change. 1 +1
(b)Genetic drift: When migration of a section of population to
another place occurs, gene frequencies change in the original as
well as in the new population. Sometime the change in allele
frequency in a new sample of population is so different that they
become a different species. This effect is called founders effect.
1
Or
Indicates common ancestory, divergent evolution. / Same
structures developed along different directions due to adaptations
to different needs. 1+1
Homologous structures: same anatomical structure, perform
different functions. 1
3
13.
(a) Inbreeding – mating of more closely related individuals
within the same breed for 4-6 generations. 1
(b) Increases homozygosity-exposes harmful recessive genes that
are eliminated by selection;
Accumulation of superior genes and elimination of less desirable
genes;
Selection at each step, increases productivity of inbred
population. (Any 2) 1+1
3
14.
(a) tRNA,5srRNA,snRNA (any 2) 1
(b) It contains exons and introns , hence non functional.
Processing: Splicing-introns are removed.
Capping: -methyl guanosine triphosphate added at 5’ end
Tailing- Adenylate residues added at 3’end. ½ x 4
3
15.
A )Thalassemia: quantitative: less no. of globin molecules/
Occurs due to mutation or deletion resulting in reduced
synthesis of 1 type of globin chains , results in excess synthesis
of the other.; excess globin chain accumulates in RBC and forms
precipitates, which damages the cell causing cell lysis leading to
anaemia.
Sickle cell anaemia: . Qualitative /
Caused due to gene mutation, substitution of glutamic acid by
valine.Defective haemoglobin under oxygen stress, becomes
sickled.As a result the cells cannot pass through narrow
capillaries, affecting blood supply to different organs 4 x ½
b)alpha:mutation in 1 or more of the 4 genes on HBA1,HBA2 on
chromosome 16
beta: mutation of 1 or both HBB genes on chromosome 11 ½ +½
3
16.
(a) PEN undergoes successive nuclear divisions, gives rise to
free nuclear endosperm known as coconut water. Cell wall formation
occurs and cellular endosperm –white kernel is formed. 1+ 1
(b) castor/ coconut;
pea,/groundnut,/beans ½ +½
3
17.
Extraction of gametes from the parents/donors. ½
Invitro fertilization (simulated conditions in laboratory) ½
transfer of the zygote / early embryo (at 8 blastomere stage ) ,
into the fallopian tube( ZIFT) ;more than 8 blastomeres in uterus
((IUT)- 1+ 1
3
18.
Gene I has 3 alleles IA,IB, i/ each person possess 2 of the
three alleles.
Multiple allelism, co dominance 1+ 1
The plasma membrane of RBC has sugar polymers. The kind of sugar
is controlled by the gene. 1
3
19.
After implantation, finger like projections appear on the
trophoblast called chorionic villi. Villi and uterine tissue
interdigitate with each other and form structural and functional
unit called placenta. 1+1
HCG/HPL/Relaxin. ½ +½
3
20.
(a)Primary: physical process: filtration, sedimentation.solids
that settle are called primary sluge. 1
Activated sludge: biological treatment, aeration tank, growth of
flocs, BOD reduced, settling tank- flocks allowed to settle. 1
(b) anaerobic sludge digester: anaerobic bacteria digest
bacteria and fungi to produce biogas.1
3
21.
Diagram +labelling any 4 = ½ x 4
(b) development of antrum, theca organises to form interna and
outer theca externa.
3
22.
Satellite DNA occurs as highly repeated short DNA segments.
Shows high degree of polymorphism. They do not code for protein.
Forms bulk of genome. They are specific to each individual and vary
in number from person to person but are inherited. 1+1+1
3
SECTION –D
23.
Blood group matching, and tissue matching should be done prior
to the organ transplant , the body is able to identify the
‘non-self’ graft, triggers the cell mediated immune response , this
rejects the graft
5x ½ =2 ½
Views-
Cornea can be transplanted to any one and a blind can see the
world . Heart / lung/ Kidney can be transplanted and a person is
gifted with life , the mind set to volunteer to register for organ
donation – (particularly eye donation) ( any other valid views) 3x
½ =1 ½
4
SECTION -E
24.
(a) AIDS 1/2
(b) HIV, 1/2
Explanation with flow chart: 2+2
Or
(a) Failed to keep pace with demand , failed to provide fast and
efficient system of crop improvement
(b)isolation of explants, grown in sterile condition , nutrient
medium.1+1
(c ) somaclones: identical, grows from 1 cell/ organ 1
Somatic hybrids; fusion of protoplast of 2 different cells.1
5
25.
(a)Menstrual phase occurs when released ovum not fertilised ,
break down of endometrial lining (of the uterus) and its blood
vessel form the liquid that comes out through the vagina , lasts
for 3 to 5 days.Level of ovarian and pituitary hormones fall = ½ x
4
(b) Graafian follicle ruptures to release the ovum (secondary
oocyte) , remaining parts of the Graafian follicle transform into
corpus luteum 1+1
( c) Yes, appropriate precautions between 10 to 17th day of the
menstrual cycle when chances of fertilization are high. ½,½
Or
(a)
Diagram , labeling: 2
(b)zygote gives rise to proembryo, globular, heart shaped and
mature embryo. ½ x 4
(c)coleorhiza, coleoptile. ½,½
5
26.
(a)Polycistronic
Gene i codes for repressor
Structural genes: z –beta galactosidase; y- permease, a-
galactosidase.
Operator; promoter. 2
(b)diagram-2 marks
( c) Inducer, substrate that regulates switching on and off of
operon. 1
Or
Explanation of steps; Infection, blending, centrifugation.
1+1+1
diagram;2 marks.
5
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