PUC EXAM 2 KEY ANSWERS

PART - A

Select the correct alternative from the choices given below. (15x1=15)
1) Statement I: Apomixis is the production of seeds from unfertilized ovule.
Statement II: Embryo produced from apomictic seeds are not generally identical to parental plants.
(a) Statement I is true and statement II is false
(b) Statement I is false and statement II is true
(c) Both Statement I and statement II are true
(d) Both Statement I and statement II are false

2.The figure shows a section of human ovary. Select the option which gives correct identification of either 'A' or 'B'
with function or characteristics.

a) A- Tertiary follicle - Forms Graffian follicle

(b) B-Corpus luteum - Secretes progesterone
(c) B- Corpus luteum - Secretes estrogen
(d) A - Primary Oocyte - It is prophase I of mitotic division

3.Which of the following hormone is produced only during pregnancy?

(a) L.H. (b) hCG. (c) Estrogen. (d) F.S.H

4) Oral contraceptive mainly contains

(a) Estrogen and L.H.
(b) Progesterone and Estrogen
(c) Progesterone and L.H
(d) Progesterone, Estrogen and L.H

5) In a plant, red fruit (R) is dominant over yellow fruit (r). Tallness (T) is dominant ove dwarfness (t). If plant RRTt
genotype crossed with plant that is rrtt,

(a) 25% will be tall with red fruit

(b) 75% will be tall with red fruit
(c) 50% will be tall with red fruit
(d) All the offspring will be tall with red fruit
6) A couple has three daughters. What is the possibility of them having a son next time?

(a) 0%
(b) 25%
(c) 50%
(d) 100%

7) Which of the following characters was not chosen by Mendel?

(a) pod shape

(b) pod colour
(c) position of flower
(d) position of pod

8) RNA polymerase I transcribes

(a) mRNA
(b) tRNA
(c) rRNA
(d) hnRNA

9) Single step large mutation leading to speciation is called

(a) Natural selection

(b) Branching descent
(c) Founder effect
(d) Saltation

10) Haemozoin is a

(a) Precursor of Haemoglobin

(b) Toxin released from streptococcus-infected cell
(c) Toxin released from plasmodium-infected cell
(d) Toxin released from Haemophilus-infected cell

11) Secondary treatment is mainly

(a) Physical process
(b) Mechanical process
(c) Biological process
(d) Chemical process

12) Main Purpose of stirred tank bioreactor is

(a) Purification of the product

(b) Providing anaerobic condition for the culture
(c) Addition of proper mixing preservative
(d) Availability of oxygen throughout the process
13) The capacity to generate a whole plant from any cells or explant is called as

(a) Pluripotent
(b) Micropropagation
(c) Somatic hybrids
(d) Totipotency

14) Identify the decomposer among the following in pond ecosystem.

A. BacteriaB. Fungi
C. Flagellates
D. Phytoplankton
(a) A only
(b) A & B only
(c) A & D only
(d) A, B & C only

15) The most species-rich taxonomic group among invertebrates.

(a) Birds
(b) Insects
(c) Mammals
(d) Fishes

II. Fill in the blanks by choosing the appropriate word/words from those given below: (5x1=5)

(Chemical, Mycorhizae, L.H, Endemic, sacred, Recombinant protein)

16) Ovulation is induced by hormone L.H

17) Inorganic chemicals are formed by organic molecules which leads to first form of life, this support Chemical
evolution.

18) The symbiotic association fungi with roots of higher plants Mycorhizae

19) If any protein encoding gene is expressed in a heterologous host, it is called as Recombinant protein

20) The species confined to a particular region and not found elsewhere is called as Endemic

PART - B

III. Answer any five of the following questions in 3-5 sentences each, wherever applicable: (5 x 2 = 10)

21) Why apple is called a false fruit? Which part of the flower forms this fruit?

The fruit develops from the ovary and floral parts.

Thalamus part of the flower forms this fruit.

22) List any two preventive methods of Sexually Transmitted Infections (STIs)
i. Avoid sex with unknown partners/multiple partners.
ii. Always use condoms during coitus.
iii. In case of doubt, go to a qualified doctor for early detection and get complete treatment.

23) Differentiate between exons and introns.

Exons- coding sequences
Introns - Non Coding sequences

24) Comment the similarities and dissimilarities between thorns of Bougainvillea and tendrils of cucurbita
with respect to evolution
Homology in plants: E.g. Thorns of Bougainvillea and tendrils of Cucurbita.
- The origin of homologous organs is due to Divergent evolution. It is the evolution by which related species become
less similar to survive and adapt in different environmental condition.
- Homology indicates common ancestry.

25) When ELISA test was conducted on an immune-suppressed person, he tested positive for pathogens.
a) Which disease the patient is suffering from?(1)
AIDS
b) Name the causative entity (1)
HIV

26) How primary treatment is carried out in STP?

It is the physical removal of particles. It includes
a. Removal of floating debris by sequential filtration.
b. Removal of the grit (soil & pebbles) by sedimentation.
The settled solids form the primary sludge and the supernatant form the primary effluent.

27) Mention the 'Evil quartet' which causes biodiversity losses.

Habitat loss and fragmentation
Over-exploitation
Alien species invasions
Co-extinction
PART - C

IV. Answer any five of the following questions in about 40-80 words each wherever applicable(5 x 3 = 15)

28) Draw a neat labeled diagram of embryosac.

29) What is placenta? List the functions of placenta.
The chorionic villi & uterine tissue are interdigitated to form placenta. It is a structural and functional unit b/w
embryo (foetus) and maternal body.
• Acts as barrier between the foetus and mother.
• Supply O2, nutrients etc. from mother to foetus.
Remove CO2 and excretory wastes from foetus.
• Acts as an endocrine gland. It secretes Human chorionic gonadotropin (hCG), human placental lactogen (hPL),
oestrogens, progesterone & relaxin.

30) Categorise the following into different kinds of IUD such as non-medicated Copper releasing and Hormone
releasing ones.
Copper releasing IUDs: CuT, Cu7, Multiload 375.
Hormone releasing IUDs: Progestasert, LNG-20.

31) Darwin's finches of Galapagos island represent the best example for adaptive radiation. Substantiate.
Adaptive radiation (evolution by adaptation) is the evolution of different species in a geographical area starting from
a point

32) Write the scientific name of microorganism involved in the production of

(a) Penicillin: Penicillium notatum
(b) Cyclosporin A : Trichoderma polysporum
(c) Streptokinase: Streptococcus

33) Mention the carcinogens with one example each.

Physical agents: E.g. Ionizing radiations like X-rays and gamma rays and non-ionizing radiations like UV.
▪ Chemical agents: Tobacco smoke
▪ Biological agents: E.g. oncogenic viruses, c-onc (cellular oncogenes or proto oncogenes) etc. When C-onc in
normal cells is activated, the cells become oncogenic.

34) Diagrammatically represent pyramid of energy in a grassland ecosystem.

PART - D

V. Answer any four of the following questions in about 200-250 words each wherever applicable:(4 × 5 = 20)

35) Flowering plants have developed many devices to discourage self-pollination and encourage cross-
pollination. Justify.

a. Avoiding synchronization: Here, the pollen is released before the stigma becomes receptive or stigma becomes
receptive before the release of pollen. It prevents autogamy.
b. Arrangement of anther & stigma at different positions:This also prevents autogamy.
c. Self-incompatibility: It is a genetic mechanism to prevent self-pollen (from the same flower or other flowers of
the same plant) from fertilization by inhibiting pollen germination or pollen tube growth in the pistil.
d. Production of unisexual flowers: If male & female flowers are present on the same plant (i.e., monoecious, e.g.
castor & maize), it prevents autogamy but not geitonogamy. In dioecious plants (e.g. papaya), male and female
flowers are present on different plants (dioecy).This prevents both autogamy and geitonogamy.

36) Mention the five differences between spermatogenesis and oogenesis.

37) The F₂ progeny of monohybrid cross showed phenotypic ratio 1:2:1 unlike that of Mendel's, monohybrid
F₂ ratio with the help of suitable example. Work out cross and explain how it is possible?

Flower colour in snapdragon (dog flower or Antirrhinum sp.) and Mirabilis jalapa (4’O clock plant).Here, cross
between homozygous red & white produces pink flowered plant. Thus phenotypic & genotypic ratios are same.
Phenotypic ratio= 1 Red: 2 Pink: 1 White
Genotypic ratio= 1 (RR): 2 (Rr): 1(rr)
This means that R was not completely dominant over r.
38) Write a note on prevention & control measures of drug/alcohol abuse.

(i) Avoid undue peer pressure - Every child has his/her own choice and personality, which should be respected and
nurtured. A child should not be pushed unduly to perform beyond his/her threshold limits; be it studies, sports or
other activities.
(ii) Education and counselling - Educating and counselling him/her to face problems and stresses, and to accept
disappointments and failures as a part of life. It would also be worthwhile to channelize the child’s energy into
healthy pursuits like sports, reading, music, yoga and other extracurricular activities.
(iii) Seeking help from parents and peers - Help from parents and peers should be sought immediately so that they
can guide appropriately. Help may even be sought from close and trusted friends. Besides getting proper advise to
sort out their problems, this would help young to vent their feelings of anxiety and guilt.
(iv) Looking for danger signs - Alert parents and teachers need to look for and identify the danger signs discussed
above. Even friends,if they find someone using drugs or alcohol, should not hesitate to bring this to the notice of
parents or teacher in the best interests of the person concerned. Appropriate measures would then be required to
diagnose the malady and the underlying causes. This would help in initiating proper remedial steps or treatment.
(v) Seeking professional and medical help - A lot of help is available in the form of highly qualified psychologists,
psychiatrists, and de-addiction and rehabilitation programmes to help individuals who have unfortunately got in the
quagmire of drug/alcohol abuse. With such help, the affected individual with sufficient efforts and will power, can
get rid of the problem completely and lead a perfectly normal and healthy life.

39) Explain how gene therapy is used to correct adenosine deaminase deficiency disorder.
This disorder is caused due to the deletion of the gene for adenosine deaminase (an enzyme crucial for the immune
system to function).
- This can be cured by bone marrow transplantation or by enzyme replacement therapy (injection of ADA). But
these are not completely curative.
- In gene therapy, lymphocytes from the patient’s blood are grown in a culture. Then, a functional ADA cDNA (using
a retroviral vector) is introduced into lymphocytes. Then, they are returned to the patient. This should be periodically
repeated as these cells are not immortal.
- If the ADA gene (from marrow cells) is introduced into cells at early embryonic stages, it could be a permanent
cure.

40) What is mutualism? Mention four examples.

Mutualism: Both species are benefitted (+)
Lichen: It is a mutualistic relationship between a fungus & photosynthesizing algae or cyanobacteria.
• Mycorrhizae: Associations between fungi & the roots of higher plants. The fungi help the plant in the absorption
of essential nutrients from the soil while the plant provides the fungi with carbohydrates.
• Mutualism b/w plant & animal through pollination and seed dispersion:
Examples:
1. Fig trees & wasps. The fig species is pollinated only by its ‘partner’ wasp species. Female wasp pollinates
the fig inflorescence while searching for suitable egg-laying sites in fruits. The fig offers the wasp some
developing seeds, as food for the wasp larvae.
2. Orchids show diversity of floral patterns. They can attract the right pollinator insect (bees & bumblebees)
to ensure pollination. Not all orchids offer rewards.
3. ‘Sexual deceit’ of Ophrys (Mediterranean orchid). One petal of its flower resembles female bee in size, colour
& markings. So male bee ‘pseudocopulates’ with the flower and is dusted with pollen. When this bee
‘pseudocopulates’ with another flower, it transfers pollen to it.
If the female bee’s colour patterns change slightly during evolution, pollination success will be reduced
unless the orchid flower co-evolves to maintain the resemblance of its petal to the female bee.

41) Explain how elongated DNA of eukaryotic organism fitted into small-sized nucleus.
In eukaryotes, there is a set of positively charged, basic proteins called histones.
▪ Histones are rich in positively charged basic amino acid residues lysines and arginines.
▪ 8 histones form histone octamer.
▪ Negatively charged DNA is wrapped around histone octamer to give nucleosome.
▪ A typical nucleosome contains 200 bp.
Therefore, total number of nucleosomes in human = 6.6x109bp/200 = 3.3x107
▪ Nucleosomes constitute the repeating unit to form chromatin. Chromatin is the thread-like stained bodies
▪ Nucleosomes in chromatin = ‘beads-on-string’.
▪ Chromatin is packaged → chromatin fibres → coiled and condensed at metaphase stage → chromosomes.
▪ Higher level packaging of chromatin requires non-histone chromosomal (NHC) proteins.

VI. Answer any one of the following questions in 200-250 words each.(1 x 5 = 5)

42) Given below is a representation of amino acid composition of relevant translated portion of beta chain of
hemoglobin related to shape of human red blood cells.

(a) Is this representation indicates a normal or genetically affected person? Give reason in support to your answer. (2)
Genetically affected gene
The defect is caused by the substitution of Glutamic acid (Glu) by Valine (Val) at the sixth position of the β-globin
chain of the haemoglobin (Hb).
(b) Mention the phenotypic difference in a normal and affected person with respect to this gene.(2)
The mutant Hb molecule undergoes polymerization under low oxygen tension causing the change in shape of the
RBC from biconcave disc to elongated sickle like structure.
(c) Who are likely to suffer more from the defect related to this gene among the males, the females or both equally.
Why? (1)
Both male and females are affected because This is an autosome linked recessive disease.
• It can be transmitted from parents to the offspring when both the partners are carrier (heterozygous) for the gene.

43) In context to lac-operon, when Jacob and Monad cultured E.coli cells in the presence of lactose medium,
E.coli cells metabolized lactose by synthesizing enzymes. Explain how lac-operon switch OFF and switch ON.
Switch OFF

If there is no lactose (inducer), lac operon remains switched off. The regulator gene synthesizes mRNA to produce
repressor protein. This protein binds to the operator gene and blocks RNA polymerase movement. So the structural
genes are not expressed.
Switch ON.

- If lactose or allolactose is provided in the growth medium, it is transported into E. coli cells by the action of
permease.Lactose (inducer) binds with repressor protein. So repressor protein cannot bind to operator gene. The
operator gene becomes free and induces the RNA polymerase to bind with promoter gene. Then transcription starts.
- Regulation of lac operon by repressor is called negative regulation.

44) Describe the characteristics that of plasmid should possess to be as cloning vector in genetic engineering.

a. Origin of replication (ori)

- This is a sequence where replication starts.
- A piece of DNA linked to ori can replicate within the host cells. This also controls the copy number of linked DNA.
So, for getting many copies of the target DNA, it should be cloned in a vector whose origin support high copy number.

b.Selectable marker (marker gene)

- It is a gene that helps to select the transformants and eliminate the non-transformants.
- Transformation is a procedure through which a piece of DNA is introduced in a host bacterium. Such bacterium is
called transformant. If transformation does not take place, it is non-transformant.
- Selectable markers of E. coli include the genes encoding resistance to antibiotics like ampicillin, chloramphenicol,
tetracycline, kanamycin etc. Normal E. coli cells have no resistance against these antibiotics.

c. Cloning sites
- To link the alien DNA, the vector needs a single or very few recognition sites for restriction enzymes.
- More than one recognition sites generate several fragments. It complicates the gene cloning.
- Ligation of alien DNA is carried out at a restriction site present in one of the two antibiotic resistance genes.
E.g. ligation of foreign DNA at Bam H I site of tetracycline resistance gene in vector pBR322. As a result,
recombinant plasmid is formed. If ligation does not occur, it is called non-recombinant plasmid.
- The recombinant plasmids lose tetracycline resistance due to insertion of foreign DNA.
- When the plasmids are introduced into E. coli cells, 3 types of cells are obtained:
o Non-transformants: They have no plasmid. So they are not resistant to either tetracycline or ampicillin.
o Transformants with non-recombinant plasmid:They are resistant to both tetracycline & ampicillin.
o Transformants with recombinant plasmid: They are resistant only to ampicillin.
- Recombinant plasmids can be selected out from non-recombinant ones by plating transformants on ampicillin
medium. Then the transformants are transferred on tetracycline medium.
- The recombinants grow in ampicillin medium but not on tetracycline medium. But, non-recombinants grow on the
medium containing both the antibiotics.
- Thus, one antibiotic resistance gene helps to select the transformants. The inactivated antibiotic resistance gene
helps to select recombinants.
- Selection of recombinants due to inactivation of antibiotics requires simultaneous plating on 2 plates having different
antibiotics. Therefore, alternative selectable markers have developed to differentiate recombinants from non
recombinants based on their ability to produce colour in the presence of a chromogenic substrate.
- In this, a recombinant DNA is inserted within the coding sequence of an enzyme, -galactosidase. So, the gene for
synthesis of this enzyme is inactivated. It is called insertional inactivation. Such colonies do not produce
any colour. These are identified as recombinant colonies.
- If the plasmid in bacteria have no an insert, it gives blue coloured colonies in presence of chromogenic substrate.
d.Vectors for cloning genes in plants & animals Genetic tools of some pathogens can be transformed into
useful vectors for delivering genes to plants & animals. E.g.
• Agrobacterium tumefaciens (a pathogen of many dicot plants) can deliver a piece of DNA (T-DNA) to transform
normal plant cells into a tumor. These tumor cells produce the chemicals required by the pathogen.
The tumor inducing (Ti) plasmid of A. tumefaciens is modified into a cloning vector which is not pathogenic but
can use mechanisms to deliver genes of interest into plants.
• Retroviruses in animals can transform normal cells into cancerous cells. So, they are used to deliver desirable
genes into animal cells.

KARTHIK S

BIOLOGY LECTURER SHIVAMOGGA

8951521713