Download Answer Key First Term Set A

ITL Public School
Half yearly Exam (2016-17)
Date: 19/09/2016
Class: XII
Biology (044)
Time: 3 hrs
M. M: 70
SECTION A
The hilly areas in kerala, Karnatka and Tamil Nadu are transformed into blue
stretches due to mass flowering of a plant. Name the plant.
Ans Strobilanthus kunthiana(neelakuranji)
2
The gene I that controls ABO blood grouping in human beings has three alleles
IA , IBand i.
How many genotypes are likely to be present in human population?
1
Also, how many phenotypes are possibly present?
Ans (a)6 (b) 4
3
In case of infertile couple, the male partner can inseminate normally but the
mobility of sperms is below 40 percent. Judge which kind of ART is suited in this
situation to form an embryo in the laboratory, without involving a donor?
Ans Intra Cytoplasmic sperm Injection(ICSI)
4
Why hnRNA is required to undergo splicing?
Ans
5
hnRNA undergoes splicing in order to remove introns which are non-coding
sequences and exons are joined to form functional mRNA.
“Sweet potatoes tubers and potato tubers are the result of convergent evolution”.
Justify the statement.
Ans Sweet potato tuber is a modified root whereas potato tuber is a modified stem.
These are anatomically different structures but perform the same function of food
storage. Therefore they are the result of convergent evolution.
SECTION B
6
Ans
(a) If one can induce parthenocarpy through application of growth substances,
which fruits would you select to induce parthenocarpy and why?
(b)What is the difference between parthenocarpic fruits and false fruits?
(a) Banana as these fruits are seedless.
(b)Parthenocarpic fruits-fruits develop without fertilization. banana
False fruits-Thalmus also contribute to the fruit. e.g. Apple
7
All reproductive tract infections (RTIs) are STDs, but all STD are not RTIs.
Comment.
OR
Why tender coconut is considered a healthy source of nutrition?
How are pea seeds different from castor seeds with respect to endosperm?
Ans
Among the common STDs –gonorrhea, genital herpes ,chlamydiasis
,hepatitis-B,AIDS etc. hepatitis-B and AIDS are not infections of
reproductive organs though their mode of transmission could be sexual
contacts also. All other diseases are transmitted through sexual contact
and also infections of the reproductive tract.
OR
(a) rich source of minerals and vitamins.
(b)Pea seeds-non-endospermic seeds and Castor seeds- Endospemic seeds
8
Ans
(a)State the function of mast cells in allergy response?
(b)Name ant two techniques that serve the purpose of early diagnosis of some
bacterial/viral human diseases.
(a) Mast cells release chemicals like histamine and serotonin in allergic
response.
(b)ELISA,PCR
9
Ans
Mention the target cells of luteinsing hormone in human males and females.
Explain the effects and changes which the hormone induces in each case.
Males- leydig cells
Females- mature growing follicles
LH in males stimulates the leydig cells (interstial cells) of testes to synthesise
and secrete androgens which in turn stimulate the process of spermatogenesis.
LH in females stimulates ovulation and transformation of graffian follicle into
corpus luteum to secrete progesterone which prepares endometrial lining.
10 Give two reasons why both the strands of DNA are not copied during
transcription
Ans (a) If both the strands of DNA are copied, two different RNAs
(complementary to each other) and hence two different polypeptides
will produce; If a segment of DNA produces two polypeptides, the
genetic information machinery becomes complicated.
(b) The two complementary RNA molecules (produced simultaneously)
would form a double stranded RNA rather than getting translated into
polypeptides.
(c) RNA polymerase carries out polymerisation in 5. 3. direction and
hence the DNA strand with 3. . 5. polarity acts as the template strand.
(Any two)
11
Ans
SECTION C
Explain the cause of Sickle-cell Anaemia and its inheritance.
A substitution of single nitrogen base GAG to GUG at the sixth codon of beta
polypeptide chain of haemoglobin molecule causes change in RBC which results
in sickle cell anaemia.
12
Read the graph given below. Correlate the ovarian events that take place in the
human female according to the levels of the pituitary hormones during the
following days:
i) 6-15 days
fertilized)
ii) 16 -25 days
iii) 26 – 28 days (if the ovum is not
b) specify the sources of hormones mentioned in the graph?
Ans
it is the follicular phase where FSH stimulates ovarian follicles to secrete
estrogens which in turn stimulates the proliferation of endometrium of uterine
wall, which thickens.
ii) Secretion of progesterone maintains endometium which is necessary for
implantationof fertilized ovumor other events of pregnancy.
iii)when fertilization does not takes place, the endometrial lining disintegrates
leading to menstruation and thus marking the new cycle
b) estrogen is secreted by ovarian follicles and progesterone is secreted by
corpus luteum
13
Figures given below are of Darwin’s finches?
Variety of beaks of Darwin's finches.
(a) Mention the specific geographical area where these were found.
(b) Name and explain the phenomenon that has resulted in the evolution of such
diverse species in the region.
(c) How did Darwin visit the particular geographical area?
Ans
(a) Galapagos Island.
(b) Adaptive radiation. Process of evolution of different species in a geographical
area starting from point and literally radiating to other areas of habitats is called
adaptive radiation.
(c) Through sea voyage in a sail ship called H.M.S. Beagle.
14
a) A low level of expression of lac operon occurs at all the times; can you
explain the logic behind these phenomena?
b) “Migration may enhance or blurr the effects of selection” Comment.
Ans
a) in the complete absence of expression of lac operon, permease will not be
synthesized which is essential for transport of lactose from medium into the cells. If
lactose cannot be transported in to the cell, then it cannot act as inducer hence
cannot relive the lac operon from its repressed state.
b) Migration may cause enrichment of the gene pool of such alleles, that are being
selected for or decreases the effect of selection though replishment of alleles that
were selected against by nature.
15
A population has been exhibiting genetic equilibrium
Answer the following with regard to above statement
a)
Explain the above statement.
b)
Name the under lying principle.
c)
List any two factors which would upset the genetic equilibrium of the
population
Or
A thallasemic child needed repeated blood transfusions got infected by HIV.
a)
Use as diagrammatic sketch and arrows to show how the virus increased
in number
b)
Why did the increased number of HIV virus deteriorate the child’s
immunity?
c)
Which diagnostic test showed that the infective virus was HIV?
Ans a) the statement says that allele frequencies in a population are stable and is
constant from generation to generation the gene pool remains constant
b) Hardy – Weinberg principle.
c) Gene migration, genetic drift, mutation, genetic recombination and natural
selection.
Or
a) Repeated attack of HIV decreases the number of helper T-Lymphocytes.
Persons suffer from bouts of fever diarrhoea and weight loss.
b) ELISA TEST (enzyme linked immuno sorbent assay)
16
1. Study the illustration given and answer the question
Question that follows
a) Identify “a”
b) Name and state the function of “c”
c) Identify “d”
d) Explain the role of hormones in the formation and release of “a”
Ans
a) “a” part is ovum
b) “c” part is zona pellucida, it protects ovum and regulates interaction
between ovum and sperms during fertilization
c) “d” part is cells of corona radiate
d) FSH stimulates follicular development. LH ruptures graafian follicle and
releases ovum
17
A woman with O blood group marries a man with AB blood group
(i) Work out all the possible phenotypes and genotypes of the progeny.
(ii) Discuss the kind of dominance in the parents and the progeny in this case.
Ans
i) Blood group AB has alleles as IA, IB and O group has ii which on cross gives the
both blood groups A and B while the genotype of progeny will be IAi and IBi.
(ii) IA and IB are equally dominant (co-dominant). In multiple allelism, the gene I
exists in 3 allelic forms, IA, IB and i.
18
a). Identify the polarity from a to a’ in a given diagram and mention how many
mode amino acids are expected to be added to this polypeptide chain
b) Mention the DNA sequence coding for serine and the anticodon of tRNA for
the same amino acid.
c) Why are some untranslated sequences of bases seen in mRNA coding for a
polypeptide? Where exactly are they present on mRNA?
Ans a) Polarity from a to a’ is 5'
3’ no more amino acids will added to this
polypeptide chain.
b)TCA, anticodon UCA
c)The untranslated sequence of bases are required for efficient translation process
that are present before the start codon at the 5’ end and after the stop at 3’ end.
19
Fill in the blanks in the different column of the table given below :
Disease
Amoebiasis
Typhoid
C
Ans
20
Ans
21
Ans
22
Ans
Casual
organisms
Entamoeba
histolytica
b
Plasmodium
Medium of
transfer
A
Symptoms
Diarrhoea
Contaminatefood High fever
Bite of infected
Chill and
female
high fever
Water, vegetables, fruits etc. contaminated with the eggs of the parasite.
(b) Salmonella typhi
(c) Malaria
Illustrate schematically the process of initiation, elongation and termination
during transcription of a gene in a bacterium.
Diagram
Differentiate between microsporogenesis and megasporogenesis. What type of
cell division occurs during these events? Name the structure formed at the end of
these two events.
Microsporogenesis . Process of formation of microspore from a Pollen
mother cell.
Megsporogenesis . Process of formation of megaspore from megaspore
mother cell.
Meiotic division in both Diagram
Explain Hershey –Chase experiment. Also mention contribution of Meselson
and Stahl in DNA structure.
Hershey and Chase Experiement : In 1952, Hershey and Chase performed
an experiment on bacteriophages (Viruses that infect bacteria) and proved that
DNA is the genetic material.
Bacteriophage Bacteriophage
Radioactive (35S) Radioactive (32P)
labelled protein coat labelled DNA
↓↓
Infection : E.coli E.coli
↓
Blending : Viral coats removed from the bacteria.
↓
Centrifugation : Viral particles separated from the bacterial cell.
↓↓
No radioactive (35S) Radioactive (35P)
detected in bacterial cells detected in baterial
but detected in cells but not in
supernatant supernatant
Conclusion : DNA is the genetic material.
Meselson and Stahl.s Experiment :
❑ Meselson and Stahl performed the experiment in 1958 on E.coli to prove
that DNA replication is semiconservative.
❑ E.coli was grown in 15NH4Cl for many generations.
❑ 15N was incorporated into newly synthesised DNA.
❑ This heavy DNA could be differentiated from normal DNA by centrifugation.
SECTION D
23 A large number of married couples world over are childless. It is shocking to
know that in India the female partner is often blamed for the couple being
childless.
a. Why in your opinion the female partner for such situations in India?
Mention any two values that you as a biology student can promote to check
this social evil.
b. State any two reasons responsible for cause of infertility.
c. Suggest a technique that can help the couple to have child where problem is
with the male partner
Ans
24
a. inequality of sexes, lack of awareness, mutual respect between both partners,
educate them
b. physical abnormality in reproductive system, congenetial, immunological and
psychological problems.
c. ICSI,AI,IUI
SECTION E
Differentiate between the process of transcription in prokaryotes and
eukaryotes.
OR
Stanley Miller performed an experiment by recreating in the lab the probable
conditions of the atmosphere of the primitive earth.
(i) What was the purpose of the experiment?
(ii) In what form was the energy supplied for the chemical reaction to occur?
(iii) What is biogenesis?
(iv) Give a diagrammatic representation of Miller’s experiment.
Ans Transcription in Prokaryotes : In prokaryotes the process of transcription is
completed in three steps:
1. Initiation : RNA polymerase binds with initiation factor (sigma factor) and
then binds to promotor site.
2. Elongation : RNA polymerase separates from sigma factor and adds
nucleoside triphosphate as substrate. RNA is formed during the process
following the rule of coplementarity and remains bound to enzyme RNA
polymerase.
3. Termination : On reaching terminator region RNA polymerase binds with
rho factor (terminator factor). As a result nascent RNA separates.
Transcription in Eukaryotes :
❑ In eukaryotes three types of RNA polymerases found in the nucleus (apart
from RNa polymerases are found in the organelles) are involved in
transcription.
RNA Polymerase I : Transcribes rRNAs.
RNA Polymerase II : Transcribes hnRNA (which is precursor of mRNA).
RNA Polymerase III : Transcribes tRNA, 5 srRNA and snRNA.
❑ The primary transcript has both exon and intron regions.
❑ Introns which are non-coding regions removed by a process called splicing.
Experimental Evidence for Abiogenesis (Miller.s Experiment) :
Stanley Miller in 1953 demonstrated in a laboratory that electric discharges
can produce complex organic compounds from a mixture of methane,
ammonia, water vapours and hydrogen. In his experiment he found that
simple organic compounds including some amino acids are formed. In
similar experiments others observed the formation of sugar, nitrogen bases,
fats and pigments.
Divergent evolution : It shows relationship of structures having same
origin but perform different functions. It is called homology. Examples : (i)
Wings of a bird, forelimbs of horse, flippers of whale. (ii) Thorns of
Bougainvillea and tendrils of cucurbita.
25
A woman has conceived and implantation has occurred in her uterus. Explain
the sequence of changes up to parturition which take place within her body.
OR
“Incompatibility is a natural barrier in the fusion of gametes”. Justify the
statement.
Ans After implantation the chorionic villi and uterine tissue become interdigitated
to form placenta.
• Placenta facilitates supply of O2 & nutrients to the embryo and removes CO2
& excretory materials produced by the embryo.
• Increased production of hormones like estrogens, progesterone, prolactin are
essential for supporting foetal growth, metabolic changes in the mother &
maintenance of pregnancy.
• The inner cell mass differentiates into three distinct germ layers (mesoderm,
ectoderm & endoderm ) which given rise to all tissues (organs) in adults.
• After one month of pregnancy the embryo’s heart is formed.
• By th end of the second month of pregnancy the foetus develops limbs &
digits.
• By the end of 12 weeks (first trimester) most of the major organ systems are
formed.
• By the end of 24 weeks (second trimester) the body is covered with fine hair,
eye-lids separate and eyelashes are formed.
• The signals for parturition originate from the fully developed foetus and the
placenta which induces mild uterine contractions called foetal ejection reflex.
• This triggers release of oxytocin from maternal pituitary along with
stimulatory reflex resulting in stronger contractions leads to parturition. = ½ ×
10 = 5
OR
• Incompatibility is considered as the most widespread & effective device to
prevent inbreeding and outbreeding.
• Pollen pistil interaction is a dynamic process involving pollen recognition
followed by promotion or inhibition of the pollen.
13
• It acts as a natural barrier by the interaction of chemical substances produced
by the style.
• Normally the pollen belonging to right mating type germinate on stigma,
develop pollen tube & bring about fertilization.
• The pollen grains belonging to other mating type are discarded = 1 × 5 = 5
26
(a) Draw the embryo sac of a flowering plant and label (i) central cell (ii)
Chalazal end of the embryo sac (iii) synergids.
(b) Name the cell that develops into the embryo sac and explain how this cell
leads to the formation of Embryo sac. Also mention the role played by the
various cells of the embryo sac.
OR
Show diagrammatically the stages of embryonic development from zygote up
to implantation in humans.
Ans a)Three correct labels
i. The functional megaspore developes into embryo sac
ii. Nucleus undergoes mitotic division and the two cells move to the opposite
poles
}
1×4=4
38
iii. Two successive mitotic division - an eight nucleate embryo sac ½ × 3
iv. Cell wall formation takes place after nuclear divisins ½ × 7
v. Three cells group together at the micropylar end - egg apparatus with an
egg
cell and two synergids
vi. Three cells group together at the chalazal end - antipodal cells
vii. The remaining two nuclei move to the centre - fuse to form secondary
nucleus. 5
Or
. Zygote ——— A ½
Cleavage —— B 2 celled stage ½
C 4 celled stage ½
D Morula with vitelline membrane 1
E Blastocyst with trophoblast and inner cell mass 1
F Implantation f blastocys ½
G In the endometrium within wal ½