Tamil Nadu 12th Biology Model Question Paper 1 English Medium

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TN State Board 12th Biology Model Question Paper 1 English Medium

General Instructions:

1. 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.
Choose the correct statement from the following
(a) Gametes are involved in asexual reproduction
(b) Bacteria reproduce asexually by budding
(c) Conidia formation is a method of sexual reproduction
(d) Yeast reproduce by budding
Answer:
(c) Conidia formation is a method of sexual reproduction

Question 2.
The dominant epistasis ratio is _______.
(a) 9 : 3 : 3 : 1
(b) 12 : 3 : 1
(c) 9 : 3 : 4
(d) 9 : 6 : 1
Answer:
(b) 12 : 3 : 1

Question 3.
The process of recombinant DNA technology has the following steps
i. Amplification of the gene.
ii. Insertion of recombinant DNA into the host cells.
iii. Cutting of DNA at specific location using restriction enzyme.
iv. Isolation of genetic material (DNA).
Pick out the correct sequence of steps for recombinant DNA technology.
(a) ii, iii, iv, and i
(b) iv, ii, iii, and i
(c) i, ii, iii, and iv
(d) iv, iii, i, and ii
Answer:
(d) iv, iii, i, and ii

Question 4.
A widely used fusogen in protoplast culture is _______.
(a) Polymethyl glycol
(b) Polyethylene glycol
(c) Polyethylene chloride
(d) Polyvinyl chloride
Answer:
(b) Polyethylene glycol

Question 5.
A specific place in an ecosystem, where an organism lives and performs its functions is _______.
(a) habitat
(b) niche
(c) landscape
(d) biome
Answer:
(b) niche

Question 6.
Assertion (A): Ozone acts as a natural sun block.
Reason (R): UV rays reaching the earth are deviated from earth.
(a) A is correct R is incorrect
(b) A is incorrect R is correct
(c) R explains A
(d) Both A and R are incorrect
Answer:
(c) R explains A

Question 7.
Jaya and Ratna are the semi dwarf varieties of _______.
(a) wheat
(b) rice
(c) cowpea
(d) mustard
Answer:
(b) rice

Question 8.
Find out the correctly matched pair:
(a) Rubber – Shorea robusta
(b) Dye – Lawsonia inermis
(c) Timber – Cyperus papyrus
(d) Pulp – Hevea brasiliensis
Answer:
(b) Dye – Lawsonia inermis

Part – II

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

Question 9.
“Tissue culture is the best method for propagating rare and endangered plant species”- Discuss.
Answer:
Micropropagation of plants invitro through tissue culturing is a modem and alternative tool to conserve and safeguard rare plant species. Since the basic principle behind PTC is totipotency. With the help of a single explant it is possible to generate a huge population of plantlets within a short span of time. Conservation through micropropagation offers the possibility to rescue endangered and endemic species.

Question 10.
Extra-nuclear inheritance is called as cytoplasmic inheritance. Why?
Answer:
Extra nuclear inheritance is due to genes located on the cytoplasmic organelles such as chloroplast and mitochondrion hence it is called cytoplasmic inheritance.

Question 11.
Differentiate Aneuploidy from Euploidy.
Answer:
Aneuploidy:
Ploidy involving individual chromosomes within a diploid set.
E.g: Trisomy.

Euploidy:
Ploidy involving entire sets of chromosomes.
E.g: Polyploidy.

Question 12.
How do you use the biotechnology in modern practice?
Answer:
In modem practice, biotechnology is used in the development of herbicide resistance plants, improved crop varieties, producing pharma products like insulin, developing vaccines, diagnosing genetic diseases and designing drugs etc.

Question 13.
Classify plant tissue culture based on the explants used.
Answer:

1. Organ culture
2. Meristem culture
3. Protoplast culture
4. Cell culture

Question 14.
What are ecological equivalents? Give one example.
Answer:
Taxonomically different species occupying similar habitats (Niches) in different geographical regions are called Ecological equivalents.
E.g: Certain species of epiphytic orchids of Western Ghats of India differ from the epiphytic orchids of South America. But they are epiphytes.

Part – III

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

Question 15.
Write a note on Replica plating technique of colony selection.
Answer:

• Replica plating technique is a method in which the pattern of colonies growing on a culture plate is copied.
• A sterile filter plate is pressed against the culture plate and then lifted.
• Then the filter plate is pressed against a second sterile culture plate
• This results in the new plate being infected with cell in the same relative positions as the colonies in the original plate.
• The medium used in the second plate will differ from that used in the first.
• The method may include an antibiotic or without a growth factor. Thus, transformed cells can be selected.

Question 16.
List the characteristics of ecological succession.
Answer:

• It is a systematic process which causes changes in specific structure of plant community.
• It is resultant of changes of abiotic and biotic factors.
• It transforms unstable community into a stable community.
• Gradual progression in species diversity, total biomass, niche specialisation, and humus content of soil takes place.
• It progresses from simple food chain to complex food web.
• It modifies the lower and simple life form to the higher life forms.
• It creates inter-dependence of plants and animals.

Question 17.
How Eichhornia crassiper spoils the Indian ecosystem?
Answer:
Eichhornia crassipes is an invasive weed native to South America. It was introduced as aquatic ornamental plant, which grows faster throughout the year. Its widespread growth is a major cause of biodiversity loss worldwide. It affects the growth of phytoplanktons and finally changing the aquatic ecosystem.

It also decreases the oxygen content of the water bodies which leads to eutrophication. It poses a threat to human health because it creates a breeding habitat for disease causing mosquitoes (particularly Anopheles) and snails with its free floating dense roots and semi submerged leaves. It also blocks sunlight entering deep and the water ways hampering agriculture, fisheries, recreation and hydro power.

Question 18.
Write a short note on foxtail millet.
Answer:
Foxtail Millet:
Botanical name: Setaria italica.
This is one of the oldest millet used traditionally in India. Which is domesticated first in China about 6000 years. Rich in protein, carbohydrate, vitamin B and C, Potassium and Calcium.
Uses: It supports in strengthening of heart and improves eye sight. Thinai porridge is given to lactating mother.

Question 19.
Define the following terms.
(a) Emasculation
(b) Bagging
(c) Biofortification
Answer:
(a) Emasculation: Removal of anthers of a flower before anthesis to prevent self pollination.
(b) Bagging: Covering the stigma of the flower with a back to protect it against any undesirable pollen grains.
(c) Biofortification: Breeding crops with higher levels of vitamins and minerals or higher protein and healthier fats.

Part – IV

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

Question 20.
(a) Enumerate the advantages of Artificial seeds.
Answer:
Artificial seeds have many advantages over the true seeds as follows:

• Millions of artificial seeds can be produced at any time at low cost.
• They provide an easy method to produce genetically engineered plants with desirable traits.
• It is easy to test the genotype of plants.
• They can potentially stored for long time under cryo preservation method.
• Artificial seeds produce identical plants.
• The period of dormancy of artificial seeds is greatly reduced, hence growth is faster with a shortened life cycle.

[OR]

(b) Write in detail about Autogenic succession and Allogenic succession.
Answer:
Autogenic succession:
Autogenic succession occurs as a result of biotic factors. The vegetation reacts with its environment and modifies its own environment causing its own replacement by new communities. This is known as autogenic succession.

Example: In forest ecosystem, the larger trees produce broader leaves providing shade to the forest floor area. It affects the shrubs and herbs which require more light (heliophytes) but supports the shade tolerant species (sciophytes) to grow well.

Allogenic succession:
Allogenic succession occurs as a result of abiotic factors. The replacement of existing community is caused by other external factors (soil erosion and leaching, etc.,) and not by existing organisms.
Example: In a forest ecosystem soil erosion and leaching alter the nutrient value of the soil leading to the change of vegetation in that area.

Question 21.
(a) Explain Dihybrid cross in pea plant.
Answer:
The crossing of two plants differing in two pairs of contrasting traits is called dihybrid cross. In dihybrid cross, two characters (colour and shape) are considered at a time. Mendel considered the seed shape (round and wrinkled) and cotyledon colour (yellow & green) as the two characters. In seed shape round (R) is dominant over wrinkled (r); in cotyledon colour yellow (Y) is dominant over green (y).

Hence the pure breeding round yellow parent is represented by the genotype RRYY and the pure breeding green wrinkled parent is represented by the genotype rryy. During gamete formation the paired genes of a character assort out independently of the other pair. During the F₁ x F₂ fertilization each zygote with an equal probability receives one of the four combinations from each parent. The resultant gametes thus will be genetically different and they are of the following four types:

1. Yellow round (YR) – 9/16
2. Yellow wrinkled (Yr) – 3/16
3. Green round (yR) – 3/16
4. Green wrinkled (yr) -1/16

These four types of gametes of F₁ dihybrids unite randomly in the process of fertilization and produce sixteen types of individuals in F₂ in the ratio of 9 : 3 : 3 : 1 as shown in the figure. Mendel’s 9 : 3 : 3 : 1 dihybrid ratio is an ideal ratio based on the probability including segregation, independent assortment and random fertilization.

In sexually reproducing organism / plants from the garden peas to human beings, Mendel’s findings laid the foundation for understanding inheritance and revolutionized the field of biology. The dihybrid cross and its result led Mendel to propose a second set of generalisations that we called Mendel’s Law of independent assortment.

(b) What are the objectives of Afforestation programme?
Answer:
Afforestation Objectives:

• To increase forest cover, planting more trees, increases CO₂ production and air quality.
• Rehabilitation of degraded forests to increase carbon fixation and reducing CO₂ from atmosphere.
• Raising bamboo plantations.
• Mixed plantations of minor forest produce and medicinal plants.
• Regeneration of indigenous herbs / shrubs.
• Awareness creation, monitoring and evaluation.
• To increase the level and availability of water table or ground water and also to reduce nitrogen leaching in soil and nitrogen contamination of drinking water, thus making it pure not polluted with nitrogen.
• Nature aided artificial regeneration.

Bio-Zoology [Maximum Marks: 35]

Part – I

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

Question 1.
In which mode of reproduction variations are seen?
(a) Asexual
(b) Parthenogenesis
(c) Sexual
(d) Both a and b
Answer:
(c) Sexual

Question 2.
Father of a child is colour blind and mother is carrier for colour blindness, the probability of the child being colour blind is _______.
(a) 25%
(b) 50%
(c) 100%
(d) 75%
Answer:
(b) 50%

Question 3.
Which of the following was the contribution of Hugo de Vries?
(a) Theory of mutation
(b) Theory of natural Selection
(c) Theory of inheritance of acquired characters
(d) Germ plasm theory
Answer:
(a) Theory of mutation

Question 4.
The most common substrate used in distilleries for the production of ethanol is ________.
(a) Soyameal
(b) Groundgram
(c) Molasses
(d) Corn meal
Answer:
(c) Molasses

Question 5.
Vaccines that use components of a pathogenic organism rather than the whole organism are called _______.
(a) attenuated recombinant vaccines
(b) Sub-unit recombinant vaccines
(c) DNA vaccines Match the
(d) conventional vaccines
Answer:
(b) Sub-unit recombinant vaccines

Question 6.
Match the following.

Contraceptives	Type
A. Multiload 375	(i) Oral intake
B. Saheli	(ii) mechanical
C. Tubectomy	(iii) IUD
D. Vault	(iv) Surgical

(a) A – iii, B – i, C – iv, D – ii
(b) A – iv, B – iii, C – i, D – ii
(c) A – ii, B – iv, C – i, D – iii
(d) A – iii, B – iv, C – ii, D – i
Answer:
(a) A – iii, B – i, C – iv, D – ii

Question 7.
Meselson and Stahl’s experiment proved ________.
(a) Transduction
(b) Transformation
(c) DNA is the genetic material
(d) Semi-conservative of DNA replication
Answer:
(d) Semi-conservative of DNA replication

Question 8.
The sporozoite of the malarial parasite is present in ________.
(a) saliva of infected female Anopheles mosquito
(b) RBC of human suffering from malaria
(c) Spleen of infected humans
(d) Gut of female Anopheles mosquito
Answer:
(a) saliva of infected female Anopheles mosquito

Part – II

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

Question 9.
Expand the acronyms (a) FSH (b) LH (c) hCG (d) hPL
Answer:
FSH – Follicle Stimulating Hormone
LH – Luteinizing Hormone
hCG – human Chorionic Gonadotropin
hPL – human Placental Lactogen

Question 10.
What are STD’s? How are they transmitted?
Answer:
Sexually transmitted diseases (STD) are called as Sexually transmitted infections (STI). Normally STI are transmitted from person to person during intimate sexual contact with an infected partner. Infections like Hepatitis-B and HIV are transmitted sexually as well as by sharing of infusion needles, surgical instruments, etc with infected people, blood transfusion or from infected mother to baby.

Question 11.
Mention the symptoms of Down’s syndrome.
Answer:
Severe mental retardation, defective development of the central nervous system, increased separation between the eyes, flattened nose, ears are malformed, mouth is constantly open and the tongue protrudes.

Question 12.
Name the chemical substance which is called by the name
(a) Kornberg Enzyme
(b) Ochoa’s enzyme
Answer:
DNA polymerase I is also known as Kornberg enzyme.
Polynucleotide phosphorylase is also known as Ochoa’s enzyme.

Question 13.
How does Neanderthal man differ from the modern man in appearance?
Answer:
Neanderthal man differ from the modem human in having semierect posture, flat cranium, sloping forehead, thin large orbits, heavy brow ridges, protruding jaws and no chin.

Question 14.
Distinguish between Epitope and Paratope.
Answer:
Epitope:
Epitope is an antigenic determinant and is the active part of an antigen.

Paratope:
A paratope is the antigen – binding site and is a part of an antibody which recognizes and binds to an antigen.

Part – III

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

Question 15.
A person is infected by HIV. How will you diagnose for AIDS?
Answer:
A simple blood test is available that can determine whether the person has been infected with HIV. The ELISA test (Enzyme Linked Immunosorbent Assay) detects the presence of HIV antibodies. It is a preliminary test. Western blot test is more reliable and a confirmatory test. It detects the viral core proteins. If both tests detect the presence of the antibodies, the person is considered to be HIV positive.

Question 16.
Explain in simple about the production process of industrial alcohol.
Answer:
The process of ethanol production starts by milling a feed stock followed by the addition of dilute or fungal amylase (enzyme) from Aspergillus to break down the starch into fermentable sugars. Yeast is then added to convert the sugars to ethanol which is then distilled off to obtain ethanol which is upto 96 percent in concentration.

Ethanol and biodiesel, represents the first generation of biofuel technology. Ethanol is often used as a fuel, mainly as a biofuel additive for gasoline

Question 17.
How Edible vaccines are synthesized?
Answer:
Edible vaccines are prepared by molecular pharming using the science of genetic engineering. Selected genes are introduced into plants and the transgenic plants are induced to manufacture the encoded protein. Edible vaccines are mucosal targeted vaccines which cause stimulation of both systemic and mucosal immune response. At present edible vaccines are produced for human and animal diseases like measles, cholera, foot and mouth disease and hepatitis.

Question 18.
Describe J-shape and S-shape growth curves.
Answer:
Populations show characteristic growth patterns or forms. These patterns can be plotted and termed as J-shaped growth form and S-shaped growth form (Sigmoid form). Their growth is represented by S shaped growth curve.

J shaped growth form: When a population increases rapidly in an exponential fashion and then stops abruptly due to environmental resistance or due to sudden appearance of a limiting factor, they are said to exhibit J-shaped growth form.

Many insects show explosive increase in number during the rainy season followed by their disappearance at the end of the season. S-Shapea growth form (sigmoid growth) Some populations, as in a population of small mammals, increase slowly at first then more rapidly and gradually slow down as environmental resistance increases whereby equilibrium is reached and maintained. Their growth is represented by S shaped growth curve.

Question 19.
‘Red data book’-What do you know about it?
Answer:
Red Data book or Red list is a catalogue of taxa facing risk of extinction. IUCN – International Union of Conservation of Nature and Natural Resources, which is renamed as WCU – World Conservation Union (Morges Switzerland) maintains the Red Data book. The concept, of Red list was mooted in 1963. The purpose of preparation of Red List are:

• To create awareness on the degree of threat to biodiversity .
• Identification and documentation of species at high risk of extinction
• Provide global index on declining biodiversity
• Preparing conservation priorities and help in conservation of action
• Information on international agreements on conservation of biological diversity Red list has eight categories of species.
  (i) Extinct (ii) Extinct in wild (iii) Critically Endangered (iv) Endangered (v) Vulnerable (vi) Lower risk (vii) Data deficiency (viii) Not evaluated

Part – IV

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

Question 20.
(a) What are Extra embryonic membranes? Mention their location. Explain their structure and functions.
Answer:
The extra embryonic membranes include amnion, yolk sac, allantois and chorion. They protect the embryo from dessication, mechanical shock, absorption of nutrients, gaseous exchange and placental formation.

Embryonic membrane	Function
Amnion	Inner most two layered membrane with amniotic fluid providing buoyancy to embryo from injury, regulates temperature and acts as medium for foetal movement.
Chorion	Outermost layer covering and protecting the embryo.
Allantois	Forms a out pocketing of embryonic tissue at the tail of yolk sac which forms umbilical cord that links embryo to placenta and finally becomes the part of urinary bladder.
Yolk sac	Forms a part of gut and acts a source of earliest blood cells and blood vessels.

[OR]

(b) List out the effects of air pollution.
Answer:

• Affects all organisms as they depend on the atmosphere for respiration.
• Causes irritation in the throat, nose, lungs and eyes. It causes breathing problems and aggravates existing health conditions such as emphysema and asthma.
• Contaminated air reduces the body’s defense mechanism and decreases the body’s capacity to fight other infections in the respiratory system.
• Frequent exposure to polluted air increases the risk of cardiovascular diseases. Breathing air that is filled with fine particulate matter can induce hardening of the arteries, triggering cardiac arrhythmia or even a heart attack.
• People who exercise outdoors can sometimes be susceptible to adverse effects of air . pollution because it involves deeper and faster breathing. Hence it is advisable to walk or jog in the mornings in places with ample tree cover.
• Gas leaks can be lethal or affect the quality of air in the affected area.
• CO in the atmosphere interferes with 02 transport since haemoglobin has greater affinity for carbon monoxide. At low concentration it causes headache and blurred vision. In higher concentration, it can lead to coma and death.

Question 21.
(a) Explain the mode of sex determination in honeybees.
Answer:
Hapiodiploidy in Honeybees:
In hymenopteran insects such as honeybees, ants and wasps, a mechanism of sex determination called hapiodiploidy mechanism of sex determination is common. In this system, 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), hence the name haplodiplody for this system of sex determination.

This mode of sex determination facilitates the evolution of sociality in which only one diploid female becomes a queen and lays the eggs for the colony. All other females which are diploid having developed from fertilized eggs help to raise the queen’s eggs and so contribute to the queen’s reproductive success and indirectly to their own, a phenomenon known as Kin Selection. The queen constructs their social environment by releasing a hormone that suppresses fertility of the workers.

[OR]

(b) How primary immune response differ from secondary immune response?
Answer:
Primary Immune Response:

1. It occurs as a result of primary contact with an antigen.
2. Antibody level reaches peak in 7 to 10 days.
3. Prolonged period is required to establish immunity.
4. There is rapid decline in antibody level.
5. It appears mainly in the lymph nodes and spleen.

Secondary Immune Response:

1. It occurs as a result of second and subsequent contacts with the same antigen.
2. Antibody level reaches peak in 3 to 5 days.
3. It establishes immunity in a short time.
4. Antibody level remains high for longer period.
5. It appears mainly in the bone marrow, followed by the spleen and lymph nodes.