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TN State Board 12th Biology Model Question Paper 2 English Medium

General Instructions:

  1. The question paper comprises of four parts. Questions for Botany and Zoology are asked separately.
  2. You are to attempt all the parts. An internal choice of questions is provided wherever applicable.
  3. All questions of Part I, II, III and IV are to be attempted separately.
  4. Question numbers 1 to 8 in Part I are Multiple Choice Questions of one mark each. These are to be answered by choosing the most suitable answer from the given four alternatives and writing the option code and the corresponding answer.
  5. Question numbers 9 to 14 in Part II are two-marks questions. These are to be answered in about one or two sentences.
  6. Question numbers 15 to 19 in Part III are three-marks questions. These are to be answered in about three to five short sentences.
  7. Question numbers 20 and 21 in Part IV are five-marks questions. These are to be answered in detail. Draw diagrams wherever necessary.

Time: 2.30 Hours
Maximum Marks: 70

Bio-Botany [Maximum Marks: 35]

Part – I

Choose the correct answer. [8 × 1 = 8]

Question 1.
In majority of plants, pollen is liberated at _______.
(a) 1 celled stage
(b) 2 celled stage
(c) 3 celled stage
(d) 4 celled stage
Answer:
(b) 2 celled stage

Question 2.
Which one of the following is an example for polygenic inheritance?
(a) Flower color in Mirabilis jalapa
(b) Pod shape in garden pea
(c) Production of male honey bee
(d) Skin color in humans
Answer:
(d) Skin color in humans

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 3.
Assertion (A): Complete linkage is noticed in male species of Drosophila.
Reason (R): Completely linked genes show some crossing over.
(a) A is true, R is false
(b) Both A and R are false
(c) A is true, R is not correct explanation of A
(d) R explains A
Answer:
(a) A is true, R is false

Question 4.
Virus free germ plants are developed from _______.
(a) Organ culture
(b) Meristem culture
(c) Protoplast culture
(d) Cell suspension culture
Answer:
(b) Meristem culture

Question 5.
The unit of measuring ozone thickness is ______.
(a) Joule
(b) Kilos
(c) Dobson
(d) Watt
Answer:
(c) Dobson

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 6.
If 1200 Joules of solar energy is trapped by producers, how much of joules of energy does the organism in the third tropic level will receive?
(a) 120 joules
(b) 12 joules
(c) 1.2 joules
(d) 0.12 joules
Answer:
(c) 1.2 joules

Question 7.
Dwarfing gene of wheat is ______.
(a) Pal 1
(b) Atomita 1
(c) Norin 10
(d) Pelita 2
Answer:
(c) Norin 10

Question 8.
Which one of the following match is correct.
(a) Palmyra – Native of Brazil
(b) Saccharum – Abundant in Kanyakumari
(c) Steveocide – Natural sweetner
(d) Palmyra sap – fermented to give ethanol
Answer:
(c) Steveocide – Natural sweetner

Part – II

Answer any four of the following questions. [4 × 2 = 8]

Question 9.
Write the origin and area of cultivation of green gram and red gram.
Answer:

Origin

Cultivation

Green gram. Maharashtra (India). Madhya Pradesh, Karnataka and Tamil Nadu.
Red gram. South India. Maharashtra, Andhra Pradesh, Madhya Pradesh, Karnataka and Gujarat.

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 10.
State the law of independent assortment.
Answer:
When two pairs of traits are combined in a hybrid, segregation of one pair of characters is independent to the other pair of characters. Genes that are located in different chromosomes assort independently during meiosis.

Question 11.
Expand (i) PEG (ii) PHB
Answer:
(i) PEG – Poly Ethylene Glycol
(ii) PHB – Poly Hydroxy Butyrate

Question 12.
Based on the materials used, how will you classify the culture technology. Explain.
Answer:
Based on explants used culture technology are of following types:
Organ culture – Embryos, anthers, root and shoot part are used.
Meristem culture – Meristematic tissues are used.
Protoplast culture – Protoplasts are used.
Cell culture – Single cells or aggregate of cells from callus are used.

Question 13.
Give four examples of plants cultivated in commercial agroforestry.
Answer:
Casuarina, Eucalyptus, Teak, Malaivembu

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 14.
How does an orchid ophrys ensures its pollination by bees?
Ahnswer:
The plant, Ophrys an orchid, the flower looks like a female insect to attract the male insect to get pollinated by the male insect and it is otherwise called ‘floral mimicry’.

Part – III

Answer any three questions in which question number 19 is compulsory. [3 × 3 = 9]

Question 15.
List out the objectives of plant breeding.
Answer:

  • To increase yield, vigour and fertility of the crop.
  • To increase tolerance to environmental condition, salinity, temperature and drought.
  • To prevent the premature falling of buds and fruits, etc.
  • To improve synchronous maturity.
  • To develop resistance to pathogens and pests.
  • To develop photosensitive and thermos-sensitive varieties.

Question 16.
Spindle shaped pyramid of number is noticed in forest ecosystem. Give Reasons.
Answer:
In a forest ecosystem the pyramid of number is spindle in shape, it is because the base (T1) of the pyramid occupies large sized trees (Producer) which are lesser in number. Herbivores (T2) (Fruit eating birds, elephant and deer) occupying second trophic level, are more in number than the producers. In final trophic level (T4), tertiary consumers (lion) are lesser in number than the secondary consumer (T3) (fox and snake).

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 17.
Distinguish between mound layering and air layering.
Answer:

Mound Layering

Air Layering

In mound layering, lower flexible branch with leaves is bent to ground and a part of the stem is buried in the soil and the tip of branch is exposed above the soil. After the roots emerge from the buried stem, a cut is made in parent plant so that the buried plant grows into a new plant. In air layering, the stem is girdled at nodal part and hormones are applied and covered with moist soil using polythene sheet. Roots emerge in these branches after 2-4 months. Such branches are removed from parent plant and grown separately.

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 18.
Explain the sex determination mechanism in Carica papaya.
Answer:
Tamil Nadu 12th Biology Model Question Paper 2 English Medium img 1
Carica papaya, 2n = 36 (Papaya) has 17 pairs of autosomes and one pair of sex chromosomes. Male papaya plants have XY and female plants have XX. Unlike human sex chromosomes, papaya sex chromosomes look like autosomes and it is evolved from autosome. The sex chromosomes are functionally distinct because the Y chromosome carries the genes for male organ development and X bears the female organ developmental genes. In papaya sex determination is controlled by three alleles. They are m, M1 and M2 of a single gene.
Tamil Nadu 12th Biology Model Question Paper 2 English Medium img 2

Question 19.
Write the protocol for artificial seed preparation.
Answer:
Tamil Nadu 12th Biology Model Question Paper 2 English Medium img 3
Later these seeds are grown in vitro medium and converted into piantiets. These piantiets require a hardening period (either green house or hardening chamber) and then shifted to normal environment condition.

Part – IV

Answer all the questions. [2 × 5 = 10]

Question 20.
(a) Bring out the inheritance of chloroplast gene with on example.
Answer:
Chloroplast Inheritance:
It is found in 4 O’ Clock plant (Mirabilis jalapa). In this, there are two types of variegated leaves namely dark green leaved plants and pale green leaved plants. When the pollen of dark green leaved plant (male) is transferred to the stigma of pale green leaved plant (female) and pollen of pale green leaved plant is transferred to the stigma of dark green leaved plant, the F, generation of both the crosses must be identical as per Mendelian inheritance.
Chloroplast inheritance.

But in the reciprocal cross the F1 plant differs from each other. In each cross, the F1 plant reveals the character of the plant which is used as female plant.

This inheritance is not through nuclear gene. It is due to the chloroplast gene found in the ovum of the female plant which contributes the cytoplasm during fertilization since the male gamete contribute only the nucleus but not cytoplasm.

[OR]

(b) Explain in detail about various types of direct gene transfer method.
Answer:
Tamil Nadu 12th Biology Model Question Paper 2 English Medium img 4
(1) Chemical mediated gene transfer:
Certain chemicals like polyethylene glycol (PEG) and dextran sulphate induce DNA uptake into plant protoplasts.

(2) Microinjection: The DNA is directly injected into the nucleus using Electroporation Methods of Gene Transfer fine tipped glass needle or micro pipette to transform plant cells. The protoplasts are immobilised on a solid support (agarose on a microscopic slide) or held with a holding pipette under suction.

(3) Electroporation Methods of Gene Transfer: A pulse of high voltage is applied to protoplasts, cells or tissues which makes transient pores in the plasma membrane through which uptake of foreign DNA occurs.

(4) Liposome mediated method of Gene Transfer: Liposomes the artificial phospholipid vesicles are useful in gene transfer. The gene or DNA is transferred from liposome into vacuole of plant cells. It is carried out by encapsulated DNA into the vacuole. This technique is advantageous because the liposome protects the introduced DNA from being damaged by the acidic pH and protease enzymes present in the vacuole. Liposome and tonoplast of vacuole fusion resulted in gene transfer. This process is called lipofection.

(5) Biolistics: The foreign DNA is coated onto the surface of minute gold or tungsten particles (1-3 mm) and bombarded onto the target tissue or cells using a particle gun (also called as gene gun/micro projectile gun/shotgun). Then the bombarded cells or tissues are cultured on selected medium to regenerate plants from the transformed cells.

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 21.
(a) Explain the steps involved in protoplast culture.
Answer:
Protoplasts are cells without a cell wall, but bounded by a cell membrane or plasma membrane. Using protoplasts, it is possible to regenerate whole plants from single cells and also develop somatic hybrids. The steps involved in protoplast culture are:

(1) Isolation of protoplast: Small bits of plant tissue like leaf tissue are used for isolation of protoplast. The leaf tissue is immersed in 0.5% Macrozyme and 2% Onozuka cellulase enzymes dissolved in 13% sorbitol or mannitol at pH 5.4. It is then incubated over-night at 25°C. After a gentle teasing of cells, protoplasts are obtained, and these are then transferred to 20% sucrose solution to retain their viability. They are then centrifuged to get pure protoplasts as different from debris of cell walls.

(2) Fusion of protoplast: It is done through the use of a suitable fusogen. This is normally PEG (Polyethylene Glycol). The isolated protoplast are incubated in 25 to 30% concentration of PEG with Ca++ ions and the protoplast shows agglutination (the formation of clumps of cells) and fusion.

(3) Culture of protoplast: MS liquid medium is used with some modification in droplet, plating or micro-drop array techniques. Protoplast viability is tested with fluorescein diacetate before the culture. The cultures are incubated in continuous light 1000-2000 lux at 25 °C. The cell wall formation occurs within 24-48 hours and the first division of new cells occurs between 2-7 days of culture.

(4) Selection of somatic hybrid cells: The fusion product of protoplasts without nucleus of different cells is called a hybrid. Following this nuclear fusion happen. This process is called somatic hybridization.

[OR]

(b) Write a note on Henna.
Answer:
Botanical name: Lawsonia inermis.
Family: Lythraceae.
Origin and Area of cultivation: It is indigenous to North Africa and South-west Asia. It is grown mostly throughout India, especially in Gujarat, Madhya Pradesh and Rajasthan.

Uses:
An orange dye ‘Henna’ is obtained from the leaves and young shoots of Lawsonia inermis. The principal colouring matter of leaves ‘lacosone’ is harmless and causes no irritation to the skin. This dye has long been used to dye skin, hair and finger nails. It is used for colouring leather, for the tails of horses and in hair-dyes.

Bio-Zoology [Maximum Marks: 35]

Part – I

Choose the correct answer. [8 × 1 = 8]

Question 1.
Animals giving birth to young ones are ______.
(a) Oviparous
(b) Ovoviviparous
(c) Viviparous
(d) Both a and b
Answer:
(c) Viviparous

Question 2.
Messelson and Stahl’s experiment proved ________.
(a) Transduction
(b) Transformation
(c) DNA is the genetic material
(d) Semi-conservative nature of DNA reflication.
Answer:
(d) Semi-conservative nature of DNA reflication.

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 3.
Match column I with column II
Tamil Nadu 12th Biology Model Question Paper 2 English Medium img 5
(a) A – (iv), B – (ii), C – (i), D – (iii)
(b) A – (iv), B – (i), C – (iii), D – (ii)
(c) A – (i), B – (iv), C – (ii), D – (iii)
(d) A – (iv), B – (i), C – (ii), D – (iii)
Answer:
(d) A – (iv), B – (i), C – (ii), D – (iii)

Question 4.
Choose the correctly matched pair.
(a) Amphetamines – Stimulant
(b) LSD – Narcotic
(c) Heroin – Psychotropic
(d) Benzodiazepine – Pain killer
Answer:
(a) Amphetamines – Stimulant

Question 5.
The first clinical gene therapy was done for the treatment of ________.
(a) AIDS
(b) Cancer
(c) Cystic fibrosis
(d) SCID
Answer:
(d) SCID

Question 6.
Some organisms are able to maintain homeostasis by physical means ________.
(a) Conform
(b) Regulate
(c) Migrate
(d) Suspend
Answer:
(b) Regulate

Question 7.
Select the correct linear equation describing the species area relationship?
(a) log C = log S + Z log A
(b) Z log A = log S + log C
(c) log S = log C + Z log A
(d) log C = log S ± Z log C
Answer:
(b) Z log A = log S + log C

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 8.
Oil strains in laundry can be removed using _______.
(a) Peptidane
(b) Protease
(c) Amylase
(d) Lipase
Answer:
(d) Lipase

Part – II

Answer any four of the following questions. [4 × 2 = 8]

Question 9.
The unicellular organisms which reproduce by binary fission are considered immortal. Justify.
Answer:
In unicellular organisms during binary fission, the entire cell (organism) divides completely to form two daughter cells which later on develop into adult and the process goes on repeatedly during each division leading to immortality of cell (organism). Hence unicellular organisms like amoeba are ‘biologically immortal’.

Question 10.
What is colostrum? Write its significance.
Answer:
The mammary glands secrete a yellowish fluid called colostrum during the initial few days after parturition. It has less lactose than milk and almost no fat, but it contains more proteins, vitamin A and minerals. Colostrum is also rich in IgA antibodies. This helps to protect the infant’s digestive tract against bacterial infection.

Question 11.
Define haplodiploidy.
Answer:
In haplodiploidy, the sex of the offspring is determined by the number of sets of chromosomes it receives. Fertilized eggs develop into females (Queen or Worker) and unfertilized eggs develop into males (drones) by parthenogenesis. It means that the males have half the number of chromosomes (haploid) and the females have double the number (diploid).

Question 12.
Mention the main objections to Darwinism.
Answer:
Some objections raised against Darwinism were –

  • Darwin failed to explain the mechanism of variation.
  • Darwinism explains the survival of the fittest but not the arrival of the fittest.
  • He focused on small fluctuating variations that are mostly non-heritable.
  • He did not distinguish between somatic and germinal variations.
  • He could not explain the occurrence of vestigial organs, over specialization of some organs like large tusks in extinct mammoths and over sized antlers in the extinct Irish deer, etc.

Question 13.
Differentiate between cell mediated Immunity and Antibody Mediated Immunity.
Answer:

Cell Mediated Immunity (CMI)

Antibody Mediated Immunity (AMI)

1. In CMI, pathogens are destroyed by cells without producing antibodies. 1. In AMI, pathogens are destroyed by antibodies.
2. It is carried out by T cells, Macrophages, NK cells 2. It is carried out by B cells, T helper cells, APC cells.

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 14.
What are attenuated recombinant vaccines?
Answer:
Attenuated recombinant vaccines includes genetically modified pathogenic organisms (bacteria or viruses) that are made nonpathogenic and are used as vaccines. Such vaccines are referred to as attenuated recombinant vaccines.

Part – III

Answer any three questions in which question number 19 is compulsory. [3 × 3 = 9]

Question 15.
Alien species invasion is a threat to endemic species – substantiate this statement.
Answer:
Exotic species are organisms often introduced unintentionally or deliberately for commercial purpose, as biological control agents and other uses. They often become invasive and drive away the local species and is considered as the second major cause for extinction of species. Tilapia fish (Jilabi kendai) (Oreochromis mosambicus) introduced from east coast of South Africa in 1952 for its high productivity into Kerala’s inland waters, became invasive, due to which the native species such as Puntius dubius and Labeo kontius face local extinction.

Amazon sailfin catfish is responsible for destroying the fish population in the wetlands of Kolkata. The introduction of the Nile Perch, a predatory fish into Lake Victoria in East Africa led to the extinction of an ecologically unique assemblage of more than 200 nature species of cichlid fish in the lake.

Question 16.
In what way Peyang conserved the forests?
Answer:
The ‘Forest man of India’, Jadav Payeng who created 1,360 acres of dense and defiant forest was born in Arunasapori (a river island on the Brahmaputra). He had just completed his Class X exams in 1979 when he started to sow the seeds and shoots on the eroded island covered with sand and silt. Thirty-six years later he had converted the once unproductive land into a forest.

Payeng’s forest is now home to five Royal Bengal tigers, over a hundred deer, wild boar, vultures, and several species of birds. For his remarkable initiative, the Jawaharlal Nehru University invited Payeng in 2012 on Earth Day and honoured him with the title of the ‘ Forest Man of India ’.

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 17.
Amniocentesis, the foetal sex determination test, is banned in our country. Is it necessary comment?
Answer:
Amniocentesis is a prenatal technique used to detect any chromosomal abnormalities in the foetus and it is being often misused to determine the sex of the foetus. Once the sex of the foetus is known, there may be a chance of female foeticide. Hence, a statutory ban on amniocentesis is imposed.

Question 18.
Write the objectives of Human Genome project.
Answer:
The main goals of Human Genome Project are as follows:

  • Identify all the genes (approximately 30000) in human DNA.
  • Determine the sequence of the three billion chemical base pairs that makeup the human DNA
  • To store this information in databases.
  • Improve tools for data analysis.
  • Transfer related technologies to other sectors, such as industries.
  • Address the ethical, legal and social issues (ELSI) that may arise from the project.

Question 19.
Explain the role of cry-genes in genetically modified crops.
Answer:
Bacillus thuringiensis is a soil dwelling bacterium which is commonly used as a biopesticide and contains a toxin called cry toxin. Scientists have introduced this toxin producing genes into cotton and have raised genetically engineered insect resistant cotton plants.

During sporulation Bacillus thuringiensis produces crystal proteins called Delta-endotoxin which is encoded by cry genes. Delta-endotoxins have specific activities against the insects of the orders Lepidoptera, Diptera, Coleoptera and Hymenoptera. When the insects ingest the toxin crystals their alkaline digestive tract denatures the insoluble crystals making them soluble. The cry toxin then gets inserted into the gut cell membrance and paralyzes the digestive tract. The insect then stops eating and starves to death.

Part – IV

Answer all the questions. [2 × 5 = 10]

Question 20.
(a) Describe the structure of human spermatozoa with a labelled diagram.
Answer:
Tamil Nadu 12th Biology Model Question Paper 2 English Medium img 6
The human sperm is a microscopic, flagellated and motile gamete. The whole body of the sperm is enveloped by plasma membrane and is composed of a head, neck and a tail. The head comprises of two parts namely acrosome and nucleus. Acrosome is a small cap like pointed structure present at the tip of the nucleus and is formed mainly from the Golgi body of the spermatid.

It contains hyaluronidase, a proteolytic enzyme, popularly known as sperm lysin which helps to penetrate the ovum during fertilization. The nucleus is flat and oval. The neck is very short and is present between the head and the middle piece. It contains the proximal centriole towards the nucleus which plays a role in the first division of the zygote and the distal centriole gives rise to the axial filament of the sperm. The middle piece possesses mitochondria spirally twisted around the axial filament called mitochondrial spiral or nebenkem.

It produces energy in the form of ATP molecules for the movement of sperms. The tail is the longest part of the sperm and is slender and tapering. It is formed of a central axial filament or axoneme and an outer protoplasmic sheath. The lashing movements of the tail push the sperm forward.

[OR]

(b) Explain the Mechanism of ‘lac’ – operon of the E-coli.
Answer:
The Lac (Lactose) operon: The metabolism of lactose in E.coli requires three enzymes-permease, P-galactosidase (β-gal) and transacetylase. The enzyme permease is needed for entry of lactose into the cell, P-galactosidase brings about hydrolysis of lactose to glucose and galactose, while transacetylase transfers acetyl group from acetyl Co A to β-galactosidase.

The lac operon consists of one regulator gene (‘i’ gene refers to inhibitor) promoter sites (p), and operator site (o). Besides these, it has three structural genes namely lac z, y and lac a. The lac ‘z’ gene codes for β-galactosidase, lac ‘y’ gene codes for permease and ‘a’ gene codes for transacetylase. Jacob and Monod proposed the classical model of Lac operon to explain gene expression and regulation in E.coli.

In lac operon, a polycistronic structural gene is regulated by a common promoter and regulatory gene. When the cell is using its normal energy source as glucose, the ‘i’ gene transcribes a repressor mRNA and after its translation, a repressor protein is produced. It binds to the operator region of the operon and prevents translation, as a result, β-galactosidase is not produced. In the absence of preferred carbon source such as glucose, if lactose is available as an energy source for the bacteria then lactose enters the cell as a result of permease enzyme. Lactose acts as an inducer and interacts with the repressor to inactivate it.

The repressor protein binds to the operator of the operon and prevents RNA polymerase from transcribing the operon. In the presence of inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase to bind to the promotor site and transcribe the operon to produce lac mRNA which enables formation.
Tamil Nadu 12th Biology Model Question Paper 2 English Medium img 7

Tamil Nadu 12th Biology Model Question Paper 2 English Medium

Question 21.
(a) Explain stabilizing, directional and disruptive selection with examples.
Answer:
(1) Stabilising selection (centipetal selection): This type of selection operates in a stable environment. The organisms with average phenotypes survive whereas the extreme individuals from both the ends are eliminated. There is no speciation but the phenotypic stability is maintained within the population over generation. For example, measurements of sparrows that survived the storm clustered around the mean, and the sparrows that failed to survive the storm clustered around the extremes of the variation showing stabilizing selection.

(2) Directional Selection: The environment which undergoes gradual change is subjected to directional selection. This type of selection removes the individuals from one end towards the other end of phenotypic distribution. For example, size differences between male and female sparrows. Both male and female look alike externally but differ in body weight. Females show directional selection in relation to body weight.

(3) Disruptive selection: (centrifugal selection) When homogenous environment changes into heterogenous environment this type of selection is operational. The organisms of both the extreme phenotypes are selected, whereas individuals with average phenotype are eliminated. This results in splitting of the population into sub population/species.

This is a rare form of selection but leads to formation of two or more different species. It is also called adaptive radiation. (e.g:) Darwin’s finches beak size in relation to seed size inhabiting Galapagos islands. Group selection and sexual selection are other types of selection. The two major group selections are Altrusim and Kin selection.
Tamil Nadu 12th Biology Model Question Paper 2 English Medium img 8
Operation of natural selection on different traits (a) Stablishing (b) Directional and (c) Disruptive

[OR]

(b) Tabulate the various types of innate immunity and their action mechanism.
Answer:
Tamil Nadu 12th Biology Model Question Paper 2 English Medium img 9

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