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

================================================================