Murali

These Sample papers are part of CBSE Sample Papers for Class 12 Biology. Here we have given CBSE Sample Papers for Class 12 Biology Paper 3.

CBSE Sample Papers for Class 12 Biology Paper 3

Students who are going to appear for CBSE Class 12 Examinations are advised to practice the CBSE sample papers given here which is designed as per the latest Syllabus and marking scheme as prescribed by the CBSE is given here. Paper 3 of Solved CBSE Sample Paper for Class 12 Biology is given below with free PDF download solutions.

Time Allowed: 3 hours
Maximum Marks: 80

General Instructions:

1. There are total 26 questions and five sections in the question paper. All questions are compulsory.
2. Section A contains question number 1 to 5, Very Short Answer Type Questions of one mark each.
3. Section B contains question number 6 to 10, Short Answer Type Questions of two marks each.
4. Section C contains question number 11 to 22, Short Answer Type Questions of three marks each.
5. Section D contains question number 23, Value Based Question of four mark.
6. Section E contains question number 24 to 26, Long Answer Type Questions of five marks each.
7. There is no overall choice in the question paper, however, an internal choice is provided in one question of two marks, one question of three marks and all three questions of five marks. An examiner is to attempt any one of the question out of the two given in the question paper with the same question number.
8. No. of printed pages are three.

SECTION-A

Question 1.
Identify the types of immunization in case of injection of ready made antibodies for a tetanus case.

Question 2.
What are Homologous organs?

Question 3.
What is the sequence of nitrogen bases of the coding strand of DNA in a transcription unit?

Question 4.
Explain the term emasculation.

Question 5.
What is Adaptive radiation?

SECTION-B

Question 6.
How do sweet potato and potato differ in terms of evolution?

Question 7.
Identify the diagram and label the parts.

Question 8.
What are the barriers that comprise innate immunity?

Question 9.
What are the parts of the fallopian tube?

Question 10.
What is out-crossing?

OR

What is succession?

SECTION-C

Question  11.
What is the principle of Genetic equilibrium?

Question  12.
Draw a labelled diagram of a human sperm

Question  13.
List the salient features of DNA double helix model.

OR

Explain the parts of an ovule with a diagram

Question  14.
Explain convergent evolution with examples

Question  15.
What do you mean by withdrawal syndrome? Write the side effects of the use of anabolic steroids in males.

Question  16.
Explain some methods of Molecular Diagnosis.

Question  17.
Explain with examples, how do the plant-animal interactions involve co-evolution.

Question  18.
Cancer is one of the most dreaded diseases of human beings and is a major cause of death all over the globe. Explain the
(1) Causes of cancer
(2) Techniques of detection and diagnosis
(3) Treatment and cure

Question  19.
The rate of decomposition of detritus is affected by the abiotic factors like availability of oxygen, pH of the soil substratum, temperature etc. Discuss.

Question  20.
What are the different methods of breeding?

Question  21.
When is insulin fully functional?

Question  22.
You have identified a useful gene in a bacteria. Make a flow chart of the steps that you would follow to transfer this gene to a plant.

SECTION-D

Question  23.
A young couple quarrelled with the hospital authority on suspicion that their child had been exchanged after birth. The couple based their argument on the fact that their child is O blood group whereas they are A and B blood groups respectively. The doctor smiled and explained.
(a) What values of the doctor is reflected here?
(b) How can the child be O blood group as explained by the doctor?
(c) Which test method can be considered authentic to identify the biological parents of the child?
(d) Name the other blood group(s) which the child could have inherited.

SECTION-E

Question  24.
(a) What may be the probable reasons for greater biodiversity of tropics?
(b) Explain the importance of species diversity in reference to the “rivet popper hypothesis”.

OR

Give the journey of sperm formation with diagram. What are the hormones involved

Question  25.
In a medium where E.coli was growing, lactose was added, which induced the lac operon. Then why does the lac operon shut down after some time after the addition of lactose in the medium. Explain.

OR

Answer the following:
(a) Represent schematically the independent assortment of chromosomes.
(b) What are the requisites for a molecule to be a genetic material?

Question 26.
How do you represent the food and energy relationships between organisms?

OR

What are biogeochemical cycles? Explain the carbon cycle.

Answers

SECTION-A

Answer 1.
Passive immunization.

Answer 2.
The same structure developed along different directions due to adaptations to different needs. This is divergent evolution and these structures are homologous. Homology indicates common ancestry.

Answer 3.
5′ – AUGAAUG – 3′

Answer 4.
If the female parent bears bisexual flowers, removal of anthers from the flower bud before the anther dehisces using a pair of forceps is necessary. This step is referred to as emasculation.

Answer 5.
This process of evolution of different species in a given geographical area starting from a point and literally radiating to other areas of geography (habitats) is called adaptive radiation.

SECTION-B

Answer 6.
Sweet potato is a root modification and potato is a stem modification. Different structures evolving for same function are considered analogous structures and are examples of convergent evolution.

Answer 7.
Structure of microsporangium showing wall layers

Answer 8.
Innate immunity consists of four types of barriers. These are:

1. Physical barriers
2. Physiological barriers
3. Cellular barriers
4. Cytokine barriers

Answer 9.
Infundibulum with fimbriae, Ampulla, Isthmus that joins with the uterus.

Answer 10.
The practice of mating of animals within the same breed, but having no common ancestors on either side of their pedigree up to 4-6 generations. The offspring of such a mating is known as an out-cross.

OR

The gradual and fairly predictable change in the species composition of a given area is called Ecological succession. Example: hydrarch and xerarch succession.

SECTION-C

Answer 11.
Hardy-Weinberg principle states that allele frequencies in a population are stable and is constant from,generation to generation. The gene pool (total genes and their alleles in a population) remains constant. This is called genetic equilibrium. Sum total of all the allelic frequencies is 1. Individual frequencies, for example, can be named/), q, etc. In a diploide P and q represent the frequency of allele A and allele a. The frequency of AA individuals in a population is simply p₂ The probability that an allele A with a frequency of p appear on both the chromosomes of a diploid individual is simply the product of the probabilities, i.e.,p₂ Similarly of aa is q₂, of  Aa 2pq. Hence, p₂ + 2pq + q₂ = 1. This is a binomial expansion of (p + qf. When frequency measured differs from expected values, the difference (direction) indicates the extent of evolutionary change. Disturbance in genetic equilibrium, or Hardy-Weinberg equilibrium, i.e., change of frequency of alleles in a population would then be interpreted as resulting in evolution.

Answer 12.

Answer 13.
The salient features of the Double-helix structure of DNA are as follows:

1. It is made of two polynucleotide chains, where the backbone is constituted by sugarphosphate, and the bases project inside.
2. The two chains have anti-parallel polarity. It means, if one chain has the polarity 5′ – >3′, the other has 3′ – >5′.
3. The bases in two strands are paired through hydrogen bond (H-bonds) forming base pairs. Adenine forms two hydrogen bonds with Thymine from opposite strand and vice-versa. Similarly, Guanine is bonded with Cytosine with three H-bonds. As a result, always a purine comes opposite to a pyrimidine. This generates approximately uniform distance between the two strands of the helix.
4. The two chains are coiled in a right-handed fashion. The pitch of the helix is 3.4 nm (a nanometre is one billionth of a metre, that is 10-9 m) and there are roughly 10 bp in each turn. Consequently, the distance between a bp in a helix is approximately equal to 0.34 nm.
5. The plane of one base pair stacks over the other in double helix. This, in addition to H-bonds, confers stability of the helical structure.

OR

The ovule is a small structure attached to the placenta by means of a stalk called funicle. The body of the ovule fuses with funicle in the region called hilum. Each ovule has one or two protective envelopes called integuments. Integuments encircle the ovule except at the tip where a small opening called the micropyle is organised. Opposite the micropylar end, is the chalaza, representing the basal part of the ovule. Enclosed within the integuments is a mass of cells called the nucellus. Cells of the nucellus have abundant reserve food materials. Located in the nucellus is the embryo sac or female gametophyte.

Answer 14.
Convergent evolution: Evolution of different structures for the same function and hence having similarity. The similar habitat that has resulted in selection of similar adaptive features in different groups of organisms but toward the same function. Examples are the eye of the octopus and of mammals, the flippers of Penguins and Dolphins. Sweet potato (root modification) and potato (stem modification). Similarities in proteins and genes performing a given function among diverse organisms give clues to common ancestry.

Answer 15.
The tendency of the body to manifest a characteristic and unpleasant withdrawal syndrome if regular dose of drugs/alcohol is abruptly discontinued. This is characterised by anxiety, shakiness, nausea and sweating, which may be relieved when use is resumed again. In some cases, withdrawal symptoms can be severe.

The side effects of the use of anabolic steroids in males are: Reduction of the size of testicles, decreased sperm production, potential for kidney and liver dysfunction, breast enlargement, premature baldness, enlargement of the prostate gland, and premature closure of the growth centres of the long bones which result in stunted growth, acne, increased aggressiveness, mood swing, depression.

Answer 16.
Some methods of Molecular Diagnosis are:

(1) Recombinant DNA Technology: It includes isolating the antibiotic resistance gene by cutting out a piece of DNA from a plasmid which was responsible for conferring antibiotic resistance.

(2) Polymerase Chain Reaction (PCR): In this a single stranded DNA or RNA is tagged with a radioactive molecule which is allowed to hybridise to its complementary DNA in a clone of cells followed by using autoradiography.

(3) ELISA: It is based on the principle of antigen-antibody interaction. Infection by pathogen can be detected by the presence of antigens (proteins, glycoroteins, etc.) or by detecting the antibodies synthesised against the pathogen

Answer 17.
Plant-animal interactions often involve co-evolution of the mutualists. For example, the evolutions of the flower and its pollinator species are tightly linked with one another.
In many species of fig trees, there is a tight one-to-one relationship with the pollinator species of wasp. It means that a given fig species can be pollinated only by its ‘partner’ wasp species and no other species. The female wasp uses the fruit’not only as on oviposition (egg-laying) site but uses the developing seeds within the fruit for nourishing its larvae. The wasp pollinates  the fig inflorescence while searching for suitable egg-laying sites. In return for the favour of pollination, the fig offers the wasp some of its developing seeds, as food for the developing wasp larvae.

Another example, is of the Mediterranean orchid Ophrys which employs ‘sexual deceit’ to get pollination done by a species of bee. One petal of its flower bears an uncanny resemblance to the female of the bee in size, colour and markings. The male bee is attracted to what it perceives as a female, ‘pseducopulates’ with the flower, and during that process is dusted with pollen from the flower. When this same bee ‘pseudocopulates’ with another flower, it transfers pollen to it and thus, pollinates the flower. If the female bee’s colour patterns change even slightly for any reason during evolution, pollination success will be reduced unless the orchid flower co-evolves to maintain the resemblance of its petal to the female bee

Answer 18.
(1) Causes of Cancer:

• Ionizing radiations like X-rays and gamma rays and non-ionizing radiations like UV.
• The chemical carcinogens present in tobacco smoke have been identified as a major cause of lung cancer.
• Oncogenic viruses have genes called viral oncogenes.

(2) Techniques of detection and diagnosis

• Biopsy and histopathological studies of tissues and blood.
• Bone marrow tests for increased cell counts in the case of leukemias.
• Use of antibodies against cancer-specific antigens.
• Techniques of molecular biology is used for detection of genes in individuals with inherited susceptibility to certain cancers.
• Radiography, CT and MRI for cancer of internal organs.

(3) Treatment and Cure:

• Surgery
• Radiation therapy: In radiotherapy, tumor cells are irradiated lethally, taking proper care of the normal tissues surrounding the tumor mass.
• Immunotherapy
• Chemotherapeutic drugs are used to kill cancerous cells. Some of these are specific for particular tumors.
• Use of a-interferons, which activate immune system to destroy tumor.

Answer 19.
Decomposition is largely an oxygen-requiring process. The rate of decomposition is controlled by chemical composition of detritus and climatic factors. In a particular climatic condition, decomposition rate is slower if detritus is rich in lignin and chitin, and quicker, if detritus is rich in nitrogen and water-soluble substances like sugars. Temperature and soil moisture are the most important climatic factors that regulate decomposition through their effects on the activities of soil microbes. Warm and moist environment favour decomposition whereas low temperature inhibits decomposition resulting in build up of organic materials.

Answer 20.
The different methods of breeding are:

1. Inbreeding
2. Out-breeding
3. Out-crossing
4. Cross-breeding and
5. Interspecific hybridisation

Answer 21.
Insulin is synthesised as a pro-hormone which like a pro-enzyme also needs to be processed before it becomes a fully mature and functional hormone and contains an extra stretch called the C peptide. This C peptide is not present in the mature insulin and is removed during maturation into insulin

Answer 22.

SECTION-D

Answer 23.
(a) The doctor was assertive, patient and pragmatic.
(b) A child can be of blood group O if the parents are heterozygotes, i.e., Ai x Bi. If the child receives i from both the parents, it becomes, ii, and expresses O blood group.
(c) DNA finger printing
(d) A or B or AB.

SECTION-E

Answer 24.
(a) Reasons for the greater biodiversity of tropics.

1. Speciation is generally a function of time, unlike temperate regions subjected to frequent glaciations in the past, latitudes have remained relatively undisturbed for millions of years and thus, had a long evolutionary time for species diversification.
2. Tropical environments, unlike temperate ones, are less seasonal, relatively more constant and predictable. Such constant environments promote niche specialisation and lead to a greater species diversity.
3. There is more solar energy available in the tropics, which contributes to higher productivity; this in turn might contribute indirectly to greater diversity.

(b) The rivet popper hypothesis was used by Paul Ehrlich. It states that in an airplane (ecosystem) all parts are joined together using thousands of rivets (species). If every passenger travelling in it starts popping a rivet to take home (causing a species to become extinct), it may not affect flight safety (proper functioning of the ecosystem) initially, but as more and more rivets are removed, the plane becomes dangcrousl y- weak over a period of time. Furthermore, which rivet is removed may also be critical. Loss of rivets on the wings (key species that drive major ecosystem functions) is obviously a more serious threat to flight safety than loss of a few rivets on the seats or windows inside the plane.
OR

In testis, the immature male germ cells (spermatogonia) produce sperms by spermatogenesis that begins at puberty.
The spermatgonia (sing, spermatogonium) present on the inside wall of seminiferous tubules multiply by mitotic division and increase in numbers. Each spermatogonium is diploid and contains 46 chromosomes. Some of the spermatogonia called primary spermatocytes periodically undergo meiosis.

A primary spermatocyte completes the first meiotic division (reduction division) leading to formation of two equal, haploid cells called secondary spermatocytes, which have only 23 chromosomes each. The secondary spermatocytes undergo the second meiotic division to produce four equal, haploid spermatids. The spermatids are transformed into spermatozoa (sperms) by the process called spermiogenesis. After spermiogenesis, sperm heads become embedded in the Sertoli cells, and are finally released from the seminiferous tubules by the process called spermiation.

The hormones involved are:

• Gonadotropin Releasing Hormone (GnRH)
• Luteinising Hormone (LH)
• Follicle Stimulating Hormone (FSH

Answer 25.
The lac operon consists of one regulatory gene (the i gene) and three structural genes (z, y, and a).
The (i gene) codes for the repressor of the lac operon. The z gene codes for beta-galactosidase (β-gal), which is primarily responsible for the hydrolysis of the disaccharide, lactose into its monomeric units, galactose and glucose. The y gene codes for permease, which increases permeability of the cell to
β-galactosides. The a gene encodes a transacetylase. Hence, all the three gene products in lac operon are required for metabolism of lactose.

Lactose is the substrate for the enzyme beta-galactosidase and it regulates switching on and off of the operon. Hence, it is termed as inducer. In the absence of a preferred carbon source such as  glucose, if lactose is provided in the growth medium of the bacteria, the lactose is transported into the cells through the action of permease. The lactose then induces the operon in the following manner. The repressor of the operon is synthesised (all-the-time – constitutively) from the i gene.

The repressor protein binds to the operator region of the operon and prevents RNA polymerase from transcribing the operon. In the presence of an inducer, such as lactose or allolactose, the repressor is inactivated by interaction with the inducer. This allows RNA polymerase access to the promoter and transcription proceeds. Essentially, regulation of lac operon can also be visualised as regulation of enzyme synthesis by its substrate. Glucose or galactose cannot act as inducers for lac operon. Thus, regulation of lac operon by repressor is referred to as negative regulation.

(b) The requisites for a molecule to be a genetic material are:

• It should be able to generate its replica (Replication).
• It should chemically and structurally be stable.
• It should provide the scope for slow changes (mutation) that are required for evolution.
• It should be able to express itself in the form of ‘Mendelian Characters’.

Answer 26.
The food or energy relationship is expressed in terms of number, biomass or energy. The base of each pyramid represent the producer or the first trophic level while the apex represents tertiary or top level consumer. The three ecological pyramids that are usually studied are:
(a) pyramid of number;
(b) pyramid of biomass and
(c) pyramid of energy
Calculations of any energy content, biomass, or numbers must include all organisms at that trophic level. No generalisations can be true with a few individuals at any trophic level into account. Also a given organism may occupy more than one trophic level simultaneously. One must remember that the trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.

In most ecosystems, all the pyramids, of number, of energy and biomass are upright, i.e., producers are more in number and biomass than the herbivores, and herbivores are more in number and biomass than the carnivores. Also energy at a lower trophic level is always more than at a higher level. .

The pyramid of biomass in sea is also generally inverted because the biomass of fishes far exceeds that of phytoplankton. Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. Each bar in the energy pyramid indicates the amount of energy present at each trophic level in a given time or annually per unit area. There are certain limitations of ecological pyramids such as it does not take into account the same species belonging to two or more trophic levels. It assumes a simple food chain, something that almost never exists in nature; it does not accommodate a food web. Moreover, saprophytes are not given any place in ecological pyramids even though they play a vital role in ecosystem.


The movement of nutrient elements through the various components of an ecosystem is called nutrient cycling or biogeochemical cycles.
Nutrient cycles are of two types:
(a) gaseous and
(b) sedimentary.
Carbon cycling occurs through atmosphere, ocean and through living and dead organisms. A considerable amount of carbon returns to the atmosphere as CO₂ through respiratory activities of the producers and consumers. Decomposers also contribute substantially to CO₂ pool by their processing of waste materials and dead organic matter of land or oceans. Some amount of the fixed carbon is lost to sediments and removed from circulation. Burning of wood, forest fire and combustion of organic matter, fossil fuel, volcanic activity are additional sources for releasing CO₂ in the atmosphere.

We hope the CBSE Sample Papers for Class 12 Biology Paper 3 help you. If you have any query regarding CBSE Sample Papers for Class 12 Biology Paper 3, drop a comment below and we will get back to you at the earliest.

CBSE Sample Papers for Class 12 Physics Paper 4 are part of CBSE Sample Papers for Class 12 Physics. Here we have given CBSE Sample Papers for Class 12 Physics Paper 4.

CBSE Sample Papers for Class 12 Physics Paper 4

Time Allowed : 3 Hours

Max. Marks : 70

General Instructions 

• All questions are compulsory. There are 26 questions in all.
• This question paper has five sections: Section A, Section B, Section C, Section D and Section E.
• Section A contains five questions of 1 mark each. Section B contains five questions of 2 marks each. Section C contains twelve questions of 3 marks each. Section D contains one value based question of 4 marks and Section E contains three questions of 5 marks each.
• There is no overall choice. However, an internal choice has been provided in 1 question of 2 marks, 1 question of 3 marks and all the 3 questions of 5 marks weightage. You have to attempt only 1 of the choices in such questions.
• You may use the following values of physical constants wherever necessary :

Questions
SECTION : A

Question 1.
Show graphically, the variation of the de-Broglie wavelength (λ) with the potential (V) through which an electron is accelerated from rest.

Question 2.
A resistance R is connected across a cell of emf e and internal resistance r. A potentiometer now measures the potential difference between the terminals of the cell as V. Write the expression for V in terms of ε, V and R.

Question 3.
A plane electromagnetic wave travels in vacuum along Z-direction. What can you say about the direction of electric and magnetic field vector?

Question 4.
A point charge is placed at point O as shown in the figure. Is the potential difference V_A-V_B positive, negative or zero, if Q is
(i) positive
(ii) negative?

Question 5.
The permeability of magnetic material is 0.9983. Name the type of magnetic materials it represents.

SECTION : B

Question 6.
Two uniformly large parallel thin plates having charge densities +σ and -σ are kept in the X- Z plane at a distance ‘d’ apart. Sketch an equipotential surface due to electric field between the plates. If a particle of mass m and charge ‘-q’ remains stationary between the plates, what is the magnitude and direction of this field?

OR

Question 7.
Two convex lenses of same focal length but of aperture A₁ and A₂ (A₂ < A₁), are used as the objective lenses in two astronomical telescopes having identical eyepieces. What is the ratio of their resolving power? Which telescope will you prefer and why? Give reason.

Question 8.
A magnetic needle free to rotate in a vertical plane parallel to the magnetic meridian has its north tip down at 60° with the horizontal. The horizontal component of the earth’s magnetic field at the place is known to be 0.4 G. Determine the magnitude of the earth’s magnetic field at the place.

Question 9.
Figure shows two identical capacitors, C₁ and C₂, each of 1μF capacitance connected to a battery of 6 V. Initially switch ‘S’ is closed. After sometime ‘S’ is left open and dielectric slabs of dielectric constant K = 3 are inserted to fill completely the space between the plates of the two capacitors.

How will the
(i) charge and
(ii) potential difference between the plates of the capacitors be affected after the slabs are inserted?

Question 10.
Draw the output waveform at X, using the given inputs A and B for the logic circuit shown below. Also, identify the logic operation performed by this circuit.

Question 11.
Draw the transfer characteristic curve of a base biased transistor in CE configuration. Explain clearly how the active region of the V₀ versus V_i– curve in a transistor is used as an amplifier.

Question 12.
(i) Define modulation index.
(ii) Why is the amplitude of modulating signal kept less than the amplitude of carrier wave?

Question 13.
A current is induced in coil C₁due to the motion of current carrying coil C₂.
(a) Write any two ways by which a large deflection can be obtained in the galvanometer G.
(b) Suggest an alternative device to demonstrate the induced current in place of a galvanometer.

Question 14.
Define the terms
(i) drift velocity,
(ii) relaxation time. A conductor of length L is connected to a dc source of emf ε. If this conductor is replaced by another conductor of same material and same area of cross-section but of length 3L, how will the drift velocity change?

Question 15.
Name the semiconductor device that can be used to regulate an unregulated dc power supply. With the help of I-V characteristics of this device, explain its working principle.

Question 16.
Draw a schematic diagram showing the
(i) ground wave
(ii) sky wave and
(iii) space wave propagation modes for em waves.
Write the frequency range for each of the following :
(i) Standard AM broadcast
(ii) Television
(iii) Satellite communication

Question 17.
How are infrared waves produced? Why are these referred to as ‘heat wave’? Write their one important use.

Question 18.
Using Gauss’s law obtain the expression for the electric field due to a uniformly charged thin spherical shell of radius R at a point outside the shell. Draw a graph showing the variation of electric field with r, for r > R and r < R.

Question 19.
An electron and a photon each have a wave lenght of 1.00 nm.
Find
(a) their momenta,
(b) the energy of the photon and
(c) the kinetic energy of electron

Question 20.
Describe Young’s double slit experiment to produce interference pattern due to a monochromatic source of light. Deduce the expression for the fringe width.

OR

Use Huygens principle to verify the laws of refraction.

Question 21.
(a) Describe briefly, with the help of suitable diagram, how the transverse nature of light can be demonstrated by the phenomenon of polarization.
(b) When unpolarized light passes from air to a transparent medium, under what condition does the refracted light get polarized?

Question 22.
The energy levels of a hypothetical atom are shown. Which of the shown transitions will result in the emission of a photon of wavelength 275 nm? Which of these transitions correspond to emission of radiation of

(i) maximum and
(ii) minimum wavelength?

SECTION : D

Question 23.
In the circuit shown, R₁ = 4 Ω, R₂ = R₃ = 15 Ω, R₄ = 30Ω and E= 10 V. Calculate the equivalent resistance of the circuit and the current in each resistor.

SECTION : E

Question 24.
(i)  With the help of a labelled diagram, describe briefly the underlying principle and working of a step up transformer.
(ii) Write any two sources of energy loss in a transformer.
(iii) A step up transformer converts a low input voltage into a high output voltage. Does it violate law of conservation of energy? Explain.

OR

Derive an expression for the impedance of a series LCR circuit connected to an AC supply of variable frequency. Plot a graph showing variation of current with the frequency of the applied voltage. Explain briefly how the phenomenon of resonance in the circuit can be used in the tuning mechanism of a radio or a TV set.

Question 25.
State Biot-Savart law, giving the mathematical expression for it. Use this law to derive the expression for the magnetic field due to a circular coil carrying current at a point along its axis. How does a circular loop carrying current behave as a magnet?

OR

With the help of a labelled diagram, state the underlying principle of a cyclotron. Explain clearly how it works to accelerate the charged particles. Show that cyclotron frequency is independent of energy of the particle. Is there an upper limit on the energy acquired by the particle? Give reason.

Question 26.
(a) Draw a ray diagram to show refraction of a ray of monochromatic light passing through a glass prism.Deduce thee xpression for the refractive index of glass in terms of angle of prism and angle of minimum deviation.
(b) Explain briefly how the phenomenon of total internal reflection is used in fibre optics.

OR

(a) Obtain Lens Maker formula using the expression

Here the ray of light propagation from a rarer medium of refractive index (n₁) to a denser medium of refractive index (n₂) is incident on the convex side of spherical refracting surface of radius of curvature R.
(b) Draw a ray diagram to show the image formation by a concave mirror when the object is kept between its focus and the pole. Using this diagram, derive the magnification formula for the image found.

 Answers :
SECTION : A

Answer 1.

Answer 2.

Answer 3.
In electromagnetic wave, the electric field vector E and magnetic field vector B show their variations perpendicular to the direction of propagation of wave as well as perpendicular to each other. As the electromagnetic wave is travelling along Z-direction, hence E and B show their variation in XY-plane.

Answer 4.
If Q is positively charged, V_A-V_B = positive. If Q is negatively charged, V_A-V_B = negative.

Answer 5.
Paramagnetic material (0 < μ < 1).

SECTION : B

Answer 6.
Downward force due to gravity is balanced by upward force due to electric field.


When this dipole is placed in an electric field along + X-axis, it will experiences a torque.

According to Right Hand Thumb Rule, torque will be into the plane of the paper.

Answer 7.

∴  The telescope with objective of aperture A₁ should be preferred for viewing as this would :

1. give a better resolution.
2. have a higher light gathering power of telescope.

Answer 8.
Given,

Answer 9.
When S is closed: Potential difference across C₁  = Potential difference across C₂ = 6V
V₁ = V₂ = 6V
∴ q₁ = q₂ = 1μF x 6V = 6μC
When S is open and dielectric slab (K = 3) are put in between plates of capacitors,
C₁ = 3 x 1μF = 3μF
C₁ = 3 x 1μF = 3μF
When S is open, potential difference across C₁ , V₁= 6V
∴ q₁ = 3μF x 6V = 18μC
Potential difference across C₂

Answer 10.

The logic operation performed by this circuit is OR.

SECTION : C

Answer 11.

In the active region, a (small) increase of V_i results in a (large, almost linear) increase in I_c. This results in an increase in the voltage drop across R.

Answer 12.
(i) Modulation index is defined as the ratio of amplitude of modulating signal to amplitude of carrier wave. It is given by

A_m = amplitude of modulation wave
A_c = amplitude of carrier wave
(ii) The amplitude of modulating signal is kept less than the amplitude of carrier wave to avoid noise.

Answer 13.
(a) Any two ways to obtain large deflection in G :

• Moving C₂ faster towards C₁.
• Insertion of soft iron core in C₁
  

(b) Alternative device that can be used in place of galvanometer is LED.

Answer 14.
(i) Drift velocity :
The average velocity with which the free electrons drift towards positive terminal under the influence of an external field is called drift velocity.
(ii) Relaxation time :
Average time interval between two successive collisions of an electron with the ions/ atoms of the conductor.
The drift velocity will be inversely proportional to L, i.e.,

Answer 15.
A Zener diode is a specially designed diode which is operated in reverse breakdown region continuously with any damage. When Zener diode is operated in the reverse break down region, the voltage across it remains practically constant (V_z) for a large change in reverse current. Therefore, for any increase/ decrease of the input voltage there is a increase/ decrease of the voltage drop across series resistance without any change in the voltage across Zener diode,

Answer 16.
(i) Standard AM Broadcast : 540-1600 kHz
(ii) Television : 54-72 MHz VHF (very high frequencies); 76-88 MHz TV; 174-216 MHz UHF (ultra high frequencies); 420-890 MHz TV
(iii) Satellite communication : 5.925-6.425 GHz uplink and 3.7-4.2 GHz downlink.

Answer 17.
Infrared rays are produced by hot bodies and molecules. Infrared waves are called heat waves as they cause heating effect. Infrared waves are used to maintain earth’s warmth, in physiotherapy, remote switches etc.

Answer 18.
Electric field at point P at a distance r out side the spherical shell.

According to gauss law,

image

Answer 19.
λ_e =λ_photon = 1.00 nm= 10^-9 m
(a) For electron or photon, momentum

Answer 20.

S is a narrow slit (of width about 1 mm) illuminated by a monochromatic source of light. At a suitable distance (=10 mm) from S, two slits S₁ and S₂ are placed parallel to S. When a screen is placed at a large distance (about 2m) from the slits S₁ and S₂, alternate dark and bright bands appear on the screen. These are the interference bands or fringes. The band disappear when either slit is covered.
Explanation :
According to Huygens principle, the monochromatic source of light illuminating the slit S tends out spherical wavefront. The two waves of same amplitude and same frequency superimpose on each other, dark fringes appear on the screen when the crest of one wave falls on the trough of other and they neutralize the effect of each other. Bright fringes appear on the screen when the crest of one wave coincides with the crest of other and they reinforce each other.

Expression for the fringe width :
Let d = distance between slits S₁ and S₂
D = distance of screen from two slits and
x – distance between the central maxima
‘O’ and observation point P.
Light waves spread out from S and fall on both S₁ and S₂. The spherical waves emanating from S₁ and S₂ will produce interference fringes on the screen MN.


Now, the intensity at point P is maximum or minimum accordingly as the path difference is an integral multiple of wavelength or an odd integral multiple of half wavelength.

OR

Wavefront :
The continuous locus of all the particles of a medium, which are vibrating in the same phase is called wavefront.
Laws of refraction :
Let PP’ represent the surface separating medium 1 and medium 2 as shown in fig.

Which is Snell’s Law of refraction of light (second law)
First Law, incident wavefront, refracted wave front, normals all lie in the same plane.

Answer 21.

(a) When a polaroid P₁ is rotated in the path of an unpolarised light, there is no change in transmitted intensity. The light transmitted through Polaroid P₁ is made to pass through Polaroid P₂. On rotating polaroid P₂, in path of light transmitted from P₁ we notice a change in intensity of transmitted light. This shows the light transmitted from P₁ is polarized. Since light can be polarized, it has transverse nature.
(b) Whenever unpolarised light is incident from air to a transparent medium at an angle of incidence equal to polarizing angle, the reflected light gets fully polarized.

Answer 22.
If a photon of wavelength λ = 275nm is to be emited , they energy of photon is given by

hence transition B would result in the emission of a photon of wavelenght 275nm.
(i) Transition A corresponds to max wavelenght due to least energy change transition.
(ii) Transition D corresponds to min wavelenght due to least energy change transition.

SECTION : D

Answer 23.
R₂  R₃  R₄  are in parallel combination

SECTION : E

Answer 24.
(i) Step-Up Transformer :

Principle :
It works on the principle of mutual induction. When alternating current is passed through a coil an induced emf is set up in the neighbouring coil.
Working :
When an alternating voltage is applied to the primary, the resulting current produces an alternating magnetic flux which links the secondary and induces an emf in it. We consider an ideal transformer in which the primary has negligible resistance and all the flux in the core links with both primary and secondary windings. Let (Φ) be the flux in each turn in the core at any time t due to current in the primary when a voltage V_p is applied to it.
Then the induced emf or voltage E_ç, in the secondary with N_s, turns is

The alternating flux also induces an emf, called back emf in the primary given by

But E_p = V_p (since resistance of primary is small) and E_s. = V_s (since secondary current is small)

(i) Sources of energy loss in transformer are : Heat loss due to resistance of windings, loss due to eddy currents.
(ii) A step up transformer steps up the voltage while it steps down the current. So the input and output power remain same (provided there is no loss). Hence there is no violation of the principle of energy conservation.

OR

The effective resistance offered by a series LCR circuit to the flow of current is called its impedance. It is denoted by Z. Suppose an inductance L, capacitance C and resistance R are connected in series to a source of alternating emf, V = V₀ sin ωt
Let I be the instantaneous value of current in series circuit. Then voltages across the three components are

• V_L = X_L It is ahead of current I in phase by 90°
• V_c = X_C It lags behind the current I in phase by 90°
• V_R = RI. It is in phase with current I.

These voltages are shown in the phasor diagram given below :

As V_L and V_c are in opposite direction, their resultant is OD = V_L – V_c, in the positive y-direction.

Here, V/ I is the effective resistance of the series LCR circuit and is called its impedance (Z).

The given graph showing variation of current with the frequency of the applied voltage. The radio and TV receiver sets are the practical applications of series resonant circuits. Signals of several different frequencies are available in air. By turning the tuning knob of the radio set, we vary the frequency of the LC circuit till it matches the frequency of the desired signal.

A series resonant circuit allows maximum current through it. So, it is called acceptor circuit. A series resonance circuit is that circuit in which inductance L, capacitance C and resistance R are connected in series. The impedance of this circuit has a minimum value and the current through the circuit is maximum.

Answer 25.
Biot-Savart Law states that the magnitude of magnetic Y field dB due to current element is directly proportional to the current I,


Explanation :
A circular current loop produces magnetic field and its magnetic moment is the product of current and its area.
M = IA

OR

Principle :
Acharged particle can be accelerated to high energy by making it cross the same electric field again and again using a perpendicular magnetic field.

Working :
High frequency oscillator maintains moderate alternating potential difference between the dees. This potential difference establishes an electric field that reverse its direction periodically. Suppose a positive ion of moderate mass produced at the centre of the dees, finds D₂ at negative potential.It gets accelerated towards it. A uniform magnetic field, normal to the plane of the dees, makes it move in a circular track. Particle traces a semicircular track and returns back to the region between the dees. The moment it arrives in the region electric field reverses its direction and accelerate the charge towards D₁ This way charge keeps on getting accelerated until it is removed out of the dees. Centripetal force, needed by the charged particle to move in circular track, is provided by the magnetic field.

Thus, frequency of revolution is independent of the energy of the particle. Yes, there is an upper limit on the energy acquired by the charged particle. The charged particle gains maximum speed when it moves in a path of radius equal to the radius of the dees.

Answer 26.
(a)


Each optical fibre consists of a core and cladding, refractive index of the material of the core is higher than that of cladding. When a signal, in the form of light, is directed into the optical fibre, at an angle greater than the critical angle, it undergoes repeated total internal reflections along the length of the fibre and comes out of it at the other end with almost negligible loss of intensity.

OR

(a)

The point, where image of an object, located at infinity is formed, is called the focus F, of the lens and the distance f gives its focal length.

We hope the CBSE Sample Papers for Class 12 Physics Paper 4 help you. If you have any query regarding CBSE Sample Papers for Class 12 Physics Paper 4, drop a comment below and we will get back to you at the earliest.

These Sample papers are part of CBSE Sample Papers for Class 12 Biology. Here we have given CBSE Sample Papers for Class 12 Biology Paper 2.

CBSE Sample Papers for Class 12 Biology Paper 2

Students who are going to appear for CBSE Class 12 Examinations are advised to practice the CBSE sample papers given here which is designed as per the latest Syllabus and marking scheme as prescribed by the CBSE is given here. Paper 2 of Solved CBSE Sample Paper for Class 12 Biology is given below with free PDF download solutions.

Time Allowed: 3 hours
Maximum Marks: 80

General Instructions:

1. There are total 26 questions and five sections in the question paper. All questions are compulsory.
2. Section A contains question number 1 to 5, Very Short Answer Type Questions of one mark each.
3. Section B contains question number 6 to 10, Short Answer Type Questions of two marks each.
4. Section C contains question number 11 to 22, Short Answer Type Questions of three marks each.
5. Section D contains question number 23, Value Based Question of four mark.
6. Section E contains question number 24 to 26, Long Answer Type Questions of five marks each.
7. There is no overall choice in the question paper, however, an internal choice is provided in one question of two marks, one question of three marks and all three questions of five marks. An examiner is to attempt any one of the question out of the two given in the question paper with the same question number.
8. No. of printed pages are three.

SECTION-A

Question 1.
Observe the pedigree chart and answer the following questions:
(a) Identity whether the trait is sex linked or autosomal.
(b) Give an example of a disease in human beings which shows such a pattern of inheritance.

Question 2.
Identify the reason for the selection of DNA polymerase from Thermus aquaticus for Polymerase Chain Reaction

Question 3.
Govt, of India has raised the marriageable age of females to 18 yrs and of males 21 yrs. Suggest any two measures adopted by the government for the purpose.

Question 4.
Thymus of a new born child was degenerating right from birth due to genetic disorder. Predict its two impacts on the health of the child.

Question 5.
Give an example of a chromosomal disorder caused due to non-disjunction of autosomes

SECTION-B

Question 7.
A single pea plant in your kitchen garden produces pods with seeds, but the individual papaya plant does not. Explain.

Question 8.
Suggest four important steps to produce a disease resistant plant through conventional plant breeding technology.

Question 9.
Name a genus of baculovirus. Why are they considered good biocontrol agents?

Question 10.
Explain the relationship between CFCs or Ozone in the stratosphere.

OR

Why are sacred groves highly protected?

SECTION-C

Question 11.
Why is breast feeding recommended during the initial period of an infant’s growth? Give reasons.

Question 12.
Give an example of an autosomal recessive trait in humans. Explain its pattern of inheritance with the help of a cross.

Question 13.
Describe the experiment that helped Louis Pasteur to dismiss the theory of spontaneous generation of life

Question 14.
Plant breeding technique has helped sugar industry in North India. Explain how.

Question 15.
Suggest and describe a technique to obtain multiple copies of a gene of interest in vitro.

Question 16.
What is GMO? List any five possible advantages of a GMO to a farmer.

Question 17.
During a school trip to ‘Rohtang Pass’, one of your classmate suddenly developed “altitude sickness”. But, she recovered after sometime.
(a) Mention one symptom to diagnose the sickness.
(b) What caused the sickness?
(c) How could she recover by herself after sometime?

Question 18.
How has RNAi technique help to prevent the infestation of roots into tobacco plants by nematode Meloidegyne incognitia?

Question 19.
“In a food chain, a trophic level represents a functional level, not a specie.” Explain. 3

OR

(a) Name any two places where it is essential to install electrostatic precipitators. Why is it required to do so?
(b) Mention one limitation of the electrostatic precipitator

Question 20.
Prior to a sports event, blood and urine sample of sports person are collected for drug tests.3
(a) Why is there a need to conduct such tests?
(b) Name the drugs the authorities usually look for.
(c) Write the generic names of two plants from which these drugs are obtained.

Question 21.
Describe the experiment that helped to demonstrate the semi conservative mode of DNA replication.

Question 22.
Given below is a list of six micro-organisms. State their usefulness to humans:
(a) Nucleopolyhedrovirus
(b) Saccharomycs cerebisiae
(c) Monascus purpureus
(d) Trichoderma polysporum
(e) Penicillium notatum
(f) Propionibacterium sharmanii

SECTION-D

Question 23.
Reproductive and Child Flealthcare (RCH) programme are currently in operation. One of the majof tasks of these programmes is to create awareness amongst people about the wide range of reproduction related aspects. As this is important and essential for building a reproductively healthy society.
(a) “Providing sex education in schools is one of the ways to meet this goal.” Give four points in support of your opinion regarding this statement.
(b) List any two ‘indicators’ that indicate a reproductively healthy society.

SECTION-E

Question 24.
(a) Explain the post-pollination events leading to seed production in angiosperms.
(b) List the different types of pollination depending upon the source of pollen grains.

OR

(c) Briefly explain the events of fertilisation and implantation in an adult human female.
(d) Comment on placenta as an endocrine gland.

Question 25.
(a) How are the following formed and involved in DNA packing in a nucleus of a cell? 5

• Histone octomer
• Nucleosome
• Chromatin

(b) Differentiate between Euchromatin and Heterochromatin.

OR

Explain the role of lactose as an inducer in a lac operon

Question 26.
(a) Why should we conserve biodiversity? How can we do it?
(b) Explain the importance of biodiversity hot spots and sacred groves.

OR

(a) Represent diagrammatically three kinds of age-pyramids for human populations.
(b) How does an age pyramid for human population at given point of time help the policy makers in planning for future

Answers

SECTION-A

Answer 1.

(a) Sex-linked.

(b) Haemophilia/Colourblindness.

Answer 2.
Identify the reason for the selection of DNA polymerase from Thermus aquaticus for Polymerase Chain Reaction.

Answer 3.
Incentives given to couples with small families/media publicity – posters of happy couples with two children (slogan-Hum Do Humare Do)/Motivate to promote smaller families by using contraceptive methods. (Any two)

Answer 4.
Thymus provides micro-environment for the development and maturation of T-lymphocytes; its degeneration will weaken the immune system so the child will be prone to frequent infections.

Answer 5.
Down’s Syndrome.
SECTION-B

Answer 6.
Pea: Flowers of pea plants are bisexual, monoecious / self pollinated (to produce pods with viable seeds.

Papaya: Dioecious plant/unisexual plant bearing male and female flowers on separate plants, unable to produce viable seeds as there is no cross pollination/it could be a male plant which is unable to produce fruit and seeds.

Answer 7.
Stop codon: does not code for any amino acid/terminates the synthesis of polypeptide chain. Unambiguous codon: one codon codes for one amino acid only
Degenerate codon: some amino acids are coded by more than one codon
Universal codon: genetic code is same for all organisms (bacteria to humans)

Answer 8.
Steps for producing disease resistant plants:

1. Screening of germplasm (for resistance sources)
2. Hybridization of selected parents !
3. Selection and evaluation of hybrids
4. Testing and release of new varieties

Answer 9.
Nucleopolyhedrovirus.
Species specific, narrow spectrum insecticidal application, no negative impact on non target organisms.

Answer 10.
UV rays act on CFC’s, release Cl atoms, which act on ozone to release O₂, resulting in ozone layer depletion/causing ozone hole.

 OR

Sacred groves are highly protected because of religious and cultural traditions, refuge for large number of rare and threatened plants/ecologically unique and biodiversity rich regions.

SECTION-C

Answer 11.
Colostrum, rich in nutrients, rich in antibodies/rich in IgA/provide passive immunity/provides :immunity to new born/helps to develop resistance in new born/readily available for new born? hygienic/develops a bond between mother and child.

Answer 12.
Sickle cell anaemia/Phenylketonuria/Thalassemia/O Blood group /Non-rolling of tongue / fused or attached ear lobes / inability to taste PTC (phenyl thiocarbamide).

Similar cross can be considered for any other trait mentioned above.

Answer 13.

Two pre sterilised flasks with killed yeast, one sealed, other open to air, differential growth of life in two flasks/life was found only in open flask. The given diagram can be considered in lieu of above explanation.
Life comes from pre-existing life (it came from air entering the flask)/proved the theory of biogenesis.

Answer 14.
Two species (Saccharum barberi and Saccharum officinarum) were crossed to get sugarcane varieties with high yield/thick stem/high sugar content/ability to-grow in North India.

Answer 15.
PCR/Polymerase Chain Reaction.
Separation/ denaturation of two strands of two dsDNA, using two sets of primers / small chemically synthesised oligonucleotides complementary to regions of DNAand (thermostable) DNA polymerase/Taq polymerase, extension of the primers, by enzyme using nucleotides replicates the DNA and if the process of replication is repeated many times, multiple copies of DNA are produced.
The following diagram can be considered in lieu of the explanation.

Answer 16.
1. Plants/bacteria/ fungi/ animals whose genes have been altered by manipulation.
2. Tolerance to abiotic stresses/like cold/drought/salt/heat, reduced reliance on chemical pesticides/pest resistant crops, reduce post harvest losses, increased efficiency of mineral usage by plants, enhanced nutritional value, to create tailor made plant.

Answer 17.
(a) Nausea/fatigue/heart palpitation
(b) Low atmospheric pressure at high altitude, body deprived of O₂.
(c) Increase in RBC, decreases binding capacity of haemoglobin, increased breathing rate, get acclimatised.

Answer 18.
Using Agrobacterium vectors, nematode specific genes introduced into host plant, produced sense antisense RNA in host cells, ds RNA – initiated RNAi, silenced specific mRNA of nematode, parasite could not survive in transgenic host.

Answer 19.
Position of a species in any trophic level is determined by the function performed by that mode of nutrition of species in a particular food chain. A given species may occupy more than one trophic level in the same ecosystem (in different food chains) at the given time. If the function of the mode of nutrition of species changes its position shall change in the trophic levels, same species can be at primary consumer level in one food chain and at secondary consumer level in another food chain in the same ecosystem at the given time.

OR

(a) Thermal power plants/smelters/ other particulate matter releasing industries.
To remove particulate matter (Any two)
(b) Very small particulate matter/less than 2.5 micrometres are not removed/velocity of air between plates must be low enough to allow the dust to fall/cannot work without electricity.

Answer 20.
(a) To detect drug abuse/use of banned drugs/use of cannabinoids/anabolic steroids/narcotic analgesic/diuretics/hormones/drugs used to accelerate performance / increase muscle strength/bulk/promote aggressiveness/to ensure fair game.
(b) Cannabinoids/cocaine/coca alkaloid / coke /crack/ hashish /charas/ganj a /hemp plant extract.
(c) Cannabis/Atropa/Erythroxylum/Datura. (Any two)

Answer 21.
Matthew Meselson and Franklin Stahl grew E.coil in ¹⁵NH₄C1 for many generations to get ¹⁵N incorporated into DNA. Then the cells are transferred into ¹⁴NH₄C1. The extracted DNA are centrifuged in CsCl and measured to get their densities, DNA extracted from the culture after one generation (20 minutes), showed intermediate hybrid density, DNA extracted after two generations (40 minutes) showed light DNA and hybrid DNA.

A correctly labelled diagrammatic representation in lieu of the above explanation of experiment to be considered.

Answer 22.
(a) As bio control agents / species specific / narrow spectrum insecticidal application / no negative impacts on plants / mammals / birds / fish / non target insects / Integrated Pest Management.
(b) Used in bread making/brewing industry/ethanol/CO, production
(c) Cholesterol lowering agent/competitively inhibiting the enzyme responsible for synthesis of cholestrol
(d) Produces cyclosporin-A/immuno suppressive agent
(e) Produces antibiotic penicillin
(f) Produces large holes in swiss cheese/products large amount of CO₂ in swiss cheese.

SECTION-D

Answer 23.
(a)

• Provide right information to the young so as to discourage children from believing in myths and
• misconception about sex related aspects.
• Proper information about reproductive organs
• Proper information about adolescence and related changes
• Safe hygienic practices
• STDs/AIDS
• Available birth control options
• Care of pregnant mothers
• Post natal care
• Importance of breast feeding
• Equal opportunities for male and female child
• Awareness of problems due to uncontrolled population growth
• Sex abuse
• Sex related crimes (Any four)

(b) Better awareness about sex related matters/increase in number of assisted deliveries/better post natal care/decrease in IMR (Infant Mortality Rate)/decrease MMR(Matemal Mortality Rate)/increase in number of couples with small families/better detection and cure of STDs/ overall increased medical facilities for sex related problems/total well being in all aspects of reproduction/physical-behavioural-social /physically and functionally normal reproductive organs/normal emotional and behavioural interaction among all sex related aspects. (Any two)

SECTION-E

Answer 24.
(a) Pollen pistil interaction, germination of pollen tube that carries two male gametes, double
fertilization / syngamy and triple fusion, development of endosperm, development of embryo, maturation of ovule into seed.
(b) Autogamy/self pollination/Geitonogamy Xenogamy/cross pollination

OR

(a) Fertilization:

• Sperm comes in contact and enters the secondary oocyte
• Activates / induces secondary oocyte to complete meiosis II leads to formation of ovum/ootid
• The haploid nucleus of sperm and that of ovum fused to form a diploid zygote completing the process of fertilization

Implantation:

• Trophoblast layer of blastocyst attaches to the endometrium (of the uterus)
• The uterine cells divide rapidly and cover the blastocyst,
• The blastocyst becomes embedded in the endometrium and the implantation is

Answer 25.
(a)
1. Eight molecules of (positively charged basic proteins called) histones are organised to form histone octamer.
2. Negatively charged DNA wrapped around positively charged histone octamer to give rise to nucleosome
3. Nucleosome constitute the repeating unit of a structure called chromatin

(b)

OR

Lactose/inducer binds with repressor protein, inactivates it, frees operator gene, RNA polymerase freely move over structural genes/RNA polymerase access to the promoter, transcribing to, lac mRNA, which on translation, produce transacetylase, permease, β-galactosidase.
The following diagram to be considered in lieu of above explanation.

Answer 26.
(a)
(1) Narrowly utilitarian-related examples like derive economic benefits from nature food (cereals, pulses, fruits)/firewood/fibre/construction materials/industrial products (tannins, lubricants, dyes, resi’ns, perfumes) / product of medicinal importance/drugs.

• Broadly utilitarian — 20% of total 0₂ from Amazon forests / pollination / aesthetic pleasures.
• Ethical — millions of species (plants, animals, microbes) share this planet/we need to realise that every species has an intrinsic value (even if it may not have any economic value to us)/we have a moral duty to care for their well being and pass on our biological legacy to future generations.

(2)

• In situ conservation / biosphere reserves/ national parks / sanctuaries / sacred groves.
• Ex situ conservation/zoological parks /botanical gardens/wild life safari parks/cryopreservation/seed banks/tissue culture (eggs in vitro).

(b) Hot spots – regions with high level of species richness, high degree of endemism Sacred groves – tracts of forest containing tree/wildlife were venerated, and given total protection/to protect last refuges for a large number of rare and threatened plants.

OR

(b) Planning of health/ education/transport/ infrastructure/finance/food/employment can depend on the age-pyramid analysis of a population. (Any two explanations)

We hope the CBSE Sample Papers for Class 12 Biology Paper 2 help you. If you have any query regarding CBSE Sample Papers for Class 12 Biology Paper 2, drop a comment below and we will get back to you at the earliest.

These Sample papers are part of CBSE Sample Papers for Class 12 Biology. Here we have given CBSE Sample Papers for Class 12 Biology Paper 1.

CBSE Sample Papers for Class 12 Biology Paper 1

Students who are going to appear for CBSE Class 12 Examinations are advised to practice the CBSE sample papers given here which is designed as per the latest Syllabus and marking scheme as prescribed by the CBSE is given here. Paper 1 of Solved CBSE Sample Paper for Class 12 Biology is given below with free PDF download solutions.

Time Allowed: 3 hours
Maximum Marks: 80

General Instructions:

1. There are total 26 questions and five sections in the question paper. All questions are compulsory.
2. Section A contains question number 1 to 5, Very Short Answer Type Questions of one mark each.
3. Section B contains question number 6 to 10, Short Answer Type Questions of two marks each.
4. Section C contains question number 11 to 22, Short Answer Type Questions of three marks each.
5. Section D contains question number 23, Value Based Question of four mark.
6. Section E contains question number 24 to 26, Long Answer Type Questions of five marks each.
7. There is no overall choice in the question paper, however, an internal choice is provided in one question of two marks, one question of three marks and all three questions of five marks. An examiner is to attempt any one of the question out of the two given in the question paper with the same question number.
8. No. of printed pages are three.

SECTION-A

Question 1.
Recently chikungunya cases were reported from various parts of the country. Name the vector responsible for it.

Question 2.
Why cashew is referred to as false fruit?

Question 3.
Name two animals that have become extinct due to over-exploitation.

Question 4.
What forms the backbone of a polynucleotide strand of a nucleic acid?

Question 5.
How is the presence of cyanobacteria in the paddy fields beneficial to rice crop?

SECTION-B

Question 6.
Why should a bisexual flower be emasculated and then bagged prior to artificial pollination in hybridisation programmes?

Question 7.
How does CuT act as an effective contraceptive for human females?

Question 8.
How and why is the bacterium, Thermus aquaticus, useful in rDNA technology?

Question 9.
Differentiate between predation and competition.

Question 10
Highlight any four advantages of genetically modified or transgenic animals.

SECTION-C

Question 11.
Draw a diagram of a mature embryo of grass and label six parts in it.

OR

Describe the structure of a microsporangium of an angiosperm along with its diagram.

Question 12.
Who proposed chromosome theory of inheritance? Point structure of Microsporangium
out any two similarities between the behaviour of genes and that of chromosomes.   

Question 13.
A person is suffering from Amoebiasis. Mention the pathogen that causes it and one organ of the body that gets affected. Give three symptoms and one mode of its transmission.

Question 14.
How do organisms manage with the stressful conditions prevailing in their habitat for short duration? Explain with the help of one example each.

Question 15.
Mention three uses of PCR in molecular diagnostics.   

Question 16.
Explain the three ways in which natural selection operates on different traits in nature.

Question 17.
Explain the antibiotics resistance observed in bacteria in light of Darwinian selection theory.

Question 18.
What is the cause of adenosine deaminase deficiency in a person? What is the importance of this enzyme? Why is it that even after infusion of genetically engineered lymphocytes into the patient suffering from ADA deficiency, the cure is not permanent?

Question 19.
(a) What is the objective of Water Act?
(b) Mention any four problems caused due to deforestation.

Question 20.
Draw well labelled diagram of a magnified view of seminiferous tubule.    

Question 21.
(a) List two essential roles of ribosomes during translation.
(b) Who discovered nuclei acid? What was it called then?

Question 22.
Fill in the spaces a, b and c in the table showing certain events and their sites in human
(male / female) reproductive system

SECTION-D

Question 23.
In many villages, people do not go for vaccination/immunization because of some fear or religious beliefs; they feel they are healthy and they do not have the disease.

1. How can we explain to them that vaccination will help to prevent the diseases?
2. How can this idea be made to reach them?

SECTION-E

Question 24.
(a) What are

1. introns, and
2. exons?

(b) Represent schematically the steps in transcription in Eukaryotes.

OR

(a) Expand BAC and YAC.
(b) What is a promoter in a transcription unit?
(c) Differentiate between template strand and coding strand.

Question 25.
(a) What is meant by contact inhibition?
(b) Why is using tobacco in any form injurious to health? Explain.
(c) Why do sports persons often fall a victim to cocaine addiction?

OR

How are morphological and biochemical/’physiological characteristics of plants associated with resistance to certain pests? Explain with the examples

Question 26.
(a) Why pollen grains are known as living fossils?
(b) Study the population growth curves in the graph given below and answer the questions which follow:

• Identify the growth curves ‘a’ and ‘b’
• Which one of them is considered a more realistic one and why?
• If \(\cfrac { dN }{ dt } =rN\left( \cfrac { K-N }{ K } \right) \) is the equation of one of the
  growth curves, what does K stands for?
• What is symbolized by N?

OR

(a) Name any two human activities that influence carbon cycle.
(b) Describe the particular type of agriculture which is also responsible for deforestation.

Answers

SECTION-A

Answer 1.
Vector responsible for chikungunya is Aedes aegyptii.

Answer 2.
Cashew is referred to as false fruit because the thalamus also contributes to the fruit formation.

Answer 3.
Two animals that have become extinct due to over-exploitation are:

1. Dodo bird
2. Caspian Bali (species of Tiger)
3. Quagya (Any two)

Answer 4.
Phosphodiester linkage forms the backbone of a polynucleotide strand of a nucleic acid.

Answer 5.
The presence of cyanobacteria in the paddy fields is beneficial to rice crop because these bacteria have the property of nitrogen fixation due to the presence of heterocysts (nitrogen fixing cells).

SECTION-B

Answer 6.
A bisexual flower is emasculated to prevent self pollination and then bagged to further prevent its stigma from contamination by unwanted pollen. This is all done to get the desired result in the artificial hybridisation.

Answer 7.
CuT acts as an effective contraceptive for human females due to the following reasons:

1. It releases Cu ions which suppresses sperm motility.
2. Cu ions also reduces the fertilising capacity of the sperms.

Answer 8.
In PCR reaction, in the process of repeated DNA replication, the segment of DNA is amplified to approximately 1 billion time which is achieved by a thermostable DNA polymerase isolated from bacterium Thermus aquaticus.

The bacterium Thermus aquaticus (Taq) is useful in rDNA technology because it contains thermostable enzyme – DNA polymer as (Taq-DNA polymerase) which can withstand high temperature.

Answer 9.

Answer 10.
(1) Biological Products: Transgenic animals produces useful biological products only by the introduction of the portion of DNA or genes, which codes for a particular product like human protein (α-1-antitrypsin) is produced to treat emphysema.The first transgenic cow, Rosie produced human protein-enriched milk (2.4 gms per litre).

(2) Vaccine Safety: Transgenic mice are being used in testing the safety of vaccines before they are used on human beings.

(3) Chemical Safety Testing: It is also called as toxicity/safety testing. Transgenic animals are developed with genes exposed to toxic substance and are used to study their effects.

(4) Growing of Spare Parts: Spare parts (e.g., heart, pancreas) of pig for human use can be grown through the formation of transgenic animals

SECTION-C

Answer 11.

OR

1. In a transverse section, a typical microsporangium appears circular in outline.
2. It is generally surrounded by four wall layers—the epidermis, endothecium, middle layers, and the tapetum.
3. The outer three wall layers perform the function of protection and help in dehiscence of anther to release the pollen.
4. The innermost wall layer is the Tapetum. It nourishes the developing pollen grains. Cells of the tapetum possess dense cytoplasm and generally have more than one nucleus.

Answer 12.
Chromosomal theory of inheritance was proposed by Sutton and Boveri.

Answer 13.
Pathogen – Entamoeba histolytica
Organ affected – Large intestine
Symptoms:

1. Constipation
2. Abdominal pain
3. Cramps, stools are covered with mucous and blood clots.

Mode of Transmission: Houseflies act as mechanical carriers which transmit the parasite from the faces of infected person to the food and drinking water.

Answer 14.
Some organisms possess phenotypic adaptations which help them to respond quickly to an unfavourable situation.
For example, at high altitudes due to the low atmospheric pressure the human body does not get sufficient oxygen which causes altitude or mountain sickness characterised by nausea, vomiting and heart palpitation. The body compensates this low oxygen availability by increasing red blood cells, which decreases the binding-capacity of haemoglobin thereby increasing breathing rate.

Answer 15.
1. PCR (Polymerase Chain Reaction) is used to detect the presence of gene sequences of the infectious agents.
2. It is used to detect specific microbes from the samples of soil, sediments and water.
3. It is also used to detect HIV in AIDS patient.

Answer 16.
The three types of natural selection are as follows:
(1) Stabilizing Selection: The stabilizing influence of natural selection -in an environment changes little in space and time. It is also called maintenance evolution.

(2) Directional or Progressive Selection: Directional selection produces a regular change within a population in one direction in respect to certain characteristics.

(3) Disruptive Selection: In this original population splits into two groups which later evolved into two different species.

Answer 17.
In the original population of bacteria, there were some bacteria which possessed antibiotic resistant genes. When antibiotic was not used, these bacteria had no advantage with the use of antibiotics, these bacteria survived, reproduced and spread throughout the population.

Answer 18.
1. ADA is caused by the deletion of the gene responsible for the enzyme adenosine deaminase.
2. The enzyme adenosine deaminase plays crucial role in the functioning of the immune system.
3. The infusion of genetically engineered lymphocytes into the patient suffering from ADA deficiency is not a permanent cure because these cells are not immortal.

Answer 19.
(a) India has passed the Water Act in 1974. The objective of Water Act is the prevention and control of water pollution.
(b) Four problems caused due to deforestation are:       

1. Deforestation has enhanced CO₂ level which has contributed to the greenhouse effect or global warming.
2. It has caused soil erosion.
3. It has disturbed the hydrological cycle or water cycle.
4. It has lead to the loss of diversity.

Answer 20.

Answer 21.
(a) Two essential roles of ribosomes during translation are:

1. The larger subunit of ribosome has a groove for pushing out the newly formed polypeptide and protects the same from cellular enzymes.
2. The smaller unit of ribosome has a point for recognising mRNA and binding area for initiation factors.

(b) Nucleic acids were first identified by Friedrich Meischer. It was named as nucleic acids because it was isolated from the nuclei of cells.

Answer 22.
a → Ovary
b → Testis
c → Ampullary Isthmic Junction(fallopian tube)

Answer 23.
1. We can explain the villagers that vaccination is not given to cure any disease at the given time. Now they may be healthy, but when an epidemic of a disease occurs, or when they happen to encounter an infectious disease, the body does not have enough of antibodies to fight against. By vaccination, the body produces antibodies and also memory cells that can produce antibodies during an encounter with the same pathogen.

2. Advertisement propaganda can be made:

• By giving examples of cases where death has occurred due to failure of vaccination.
• Advertisement in newspapers about vaccination and its benefits.

SECTION-E

Answer 24.
(a) Coding segments in DNA are known as Exons whereas non-coding segments are known as introns.

(a) BAC → Bacterial Artificial Chromosome
YAC → Yeast Artificial Chromosome
(b) Promoter initiates the process of transcription.
(c)

Answer 25.
(a) Contact inhibition is a property by virtue of which normal cells by contact with other cells inhibit their uncontrolled growth.
(b) Harmful effects of Tobacco:

1. Tobacco contains nicotine which stimulates the adrenal gland to release adrenaline and noradrenaline into blood circulation, both of which raise blood pressure and increase , heart rate.
2. It is associated with increased incidence of cancers of lung, throat, urinary bladder, bronchitis, emphysema, gastric ulcer and coronary heart disease.
3. Tobacco chewing is associated with increase risk of cancer of the orai cavity.

(c) Sports person often take cocaine to increase their energy level for the game because it has a potent stimulating action to provide them instant energy. With regular intake they fall victim to cocaine addiction as it acts on their nervous system producing a sense of euphoria and interferes with the transport of the nano-transmitter dopamine.

OR

Morphological and biochemical characteristics of plants associated with resistance to certain pests has been seen in many host crop plants such as:

• Hairy leaves in cotton are resistant to Jassids and cereals leaf beetle in wheat.
• In wheat solid stems lead to non-preference by the stem sawfly.
• In cotton, smooth leaved and nectar-less varieties do not attract bollworms.
• In maize, high aspartic acid, low nitrogen and sugar content leads to resistance to maize stem borers.
• Thoms in Acacia, Cactus are the most common morphological means of defence in plants

Answer 26.
(a) The outer hard layer of pollen grain called the exine is made up of sporopollenin. It can withstand the worst condition of fossilization such as high temperatures and action of strong acids and alkali.

No enzyme is so far known that can degrade sporopollenin. Pollen grains are well preserved as fossils because of the presence of sporopollenin.

(b)
1. a → exponential curve
2. b→ logistic curve
3. Since resources for growth for most animal populations are finite and will become limiting sooner or later, therefore the logistic growth model/curve is considered to be a more realistic one.
4. K — carrying capacity
5. N — Population density at time “t”

OR

(a)
1. Combustion of fossil fuels
2. Deforestation

(b) Slash and Burn cultivation or Jhum cultivation or Jhuming is a type of agriculture which is responsible for deforesation. It is technically known as shifting cultivation. In India about five lakh hectares of land is cleared every year through hopping, burning the remainder, mixing the ash with soil & sowing the cleared land with crop seeds.

We hope the CBSE Sample Papers for Class 12 Biology Paper 1 help you. If you have any query regarding CBSE Sample Papers for Class 12 Biology Paper 1, drop a comment below and we will get back to you at the earliest.

CBSE Sample Papers for Class 12 Physics Paper 3 are part of CBSE Sample Papers for Class 12 Physics. Here we have given CBSE Sample Papers for Class 12 Physics Paper 3.

CBSE Sample Papers for Class 12 Physics Paper 3

Time Allowed : 3 Hours

Max. Marks : 70

General Instructions 

• All questions are compulsory. There are 26 questions in all.
• This question paper has five sections: Section A, Section B, Section C, Section D and Section E.
• Section A contains five questions of 1 mark each. Section B contains five questions of 2 marks each. Section C contains twelve questions of 3 marks each. Section D contains one value based question of 4 marks and Section E contains three questions of 5 marks each.
• There is no overall choice. However, an internal choice has been provided in 1 question of 2 marks, 1 question of 3 marks and all the 3 questions of 5 marks weightage. You have to attempt only 1 of the choices in such questions.
• You may use the following values of physical constants wherever necessary :

Questions :
SECTION : A

Question 1.
In which orientation, a dipole placed in a uniform electric field is in
(i) stable,
(ii) unstable equilibrium?

Question 2.
Which part of electromagnetic spectrum has largest penetrating power?

Question 3.
A plot of magnetic flux (Φ) versus current (I) is shown in the figure  for two inductors A and B. Which of the two has larger value of self inductance.

Question 4.
Figure shows three point charges, + 2q, -q and +3q. Two charges + 2q and -q are enclosed within a surface ‘S’. What is the electric flux due to this configuration through the surface ‘S’?

Question 5.
A glass lens of refractive index 1.45 disappears  when immersed in a liquid. What is the value of refractive index of the liquid.

SECTION : B

Question 6.
What is the ratio of radii of the orbits corresponding to first excited state and ground state in a hydrogen atom?

Question 7.
A wire of resistance 8R,is bent in the form of a circle. What is the effective resistance between the ends of a diameter AB?

Question 8.
State the conditions for the phenomenon of total internal reflection to occur.

Question 9.
Explain the function of a repeater in a communication system.

Question 10.
(i) Write two characteristics of a material used for making permanent magnets.
(ii) Why is core of an electromagnet made of ferromagnetic materials?

OR

Draw magnetic field lines when a
(i) diamagnetic,
(ii) paramagnetic substance is placed in an external magnetic field. Which magnetic property distinguishes this behaviour of the field lines due to the two substances?

SECTION : C

Question 11.
Draw a circuit diagram of an illuminated photodiode in reverse bias. How is photodiode used to measure light intensity?

Question 12.
An electric lamp having coil of negligible inductance connected in series with a capacitor and an AC source is glowing with certain brightness. How does the brightness of the lamp change on reducing the
(i) capacitance, and
(ii) the frequency? Justify your answer.

Question 13.
Arrange the following electromagnetic radiations in ascending order of their frequencies :

1. Microwave
2. Radio wave
3. X-rays
4. Gamma rays

Write two uses of any one of these.

Question 14.
The radii of curvature of the faces of a double convex lens are 10 cm and 15 cm. If focal length of the lens is 12 cm, find the refractive index of the material of the lens.

Question 15.
An electron is accelerated through a potential difference of 100 volts. What is the de-Broglie wavelength associated with it? To which part of the electromagnetic spectrum does this value of wavelength correspond?

Question 16.
A heavy nucleus X of mass number 240 and binding energy per nucleon 7.6 MeV is split into two fragments Y and Z of mass numbers 110 and 130. The binding energy of nucleons in Y and Z is 8.5 MeV per nucleon. Calculate the energy Q released per fission in MeV.

Question 17.

1. The bluish colour predominates in clear sky.
2. Violet colour is seen at the bottom of the spectrum when white light is dispersed by a prism. State reasons to explain these observations.

Question 18.
Plot a graph showing the variation of stopping potential with the frequency of incident radiation for two different photosensitive materials having work functions W₁ and W₂ (W₁ > W₂).
On what factors does the
(i) slope and
(ii) intercept of the lines depend?

Question 19.
A parallel plate capacitor is charged by a battery. After sometime the battery is disconnected and a dielectric slab with its thickness equal to the plate separation is inserted between the plates. How will
(i) the capacitance of the capacitor,
(ii) potential difference between the plates and
(iii) the energy stored in the capacitor be affected?
Justify your answer in each case.

Question 20.
Write the principle of working of a potentiometer. Describe briefly, with the help of a circuit diagram, how a potentiometer is used to determine the internal resistance of a given cell.

Question 21.

Write the expression for the magnetic moment ( m ) due to a planar square loop of side l carrying a steady current I in a vector form. In the given figure this loop is placed in a horizontal plane near a long straight conductor carrying a steady current I₁ at a distancel as shown.
Given reasons to explain that the loop will experience a net force but no torque. Write the expression for this force acting on the loop.

Question 22.
(a) Depict the equipotential surfaces for a system of two identical positive point charges placed at a distance d apart.
(b)

SECTION : E

Question 23.
For the last four months, the English teacher of Komal had erratic body movement, lack of coordination etc in her daily activities. Occasionally she had headache also. Komal suggested to get a MRI and other complete medical check up. After that she was diagnosed a brain tumour.

1. What values are displayed by Komal?
2. How can radioisotopes help a doctor to diagnose brain tumour?

Question 24.
Describe briefly, with the help of a labelled diagram, the basic elements of an A.C. generator. State its underlying principle. Show diagrammatically how an alternating emf is generated by a loop of wire rotating in a magnetic field. Write the expression for the instantaneous value of the emf induced in the rotating loop

OR

A series LCR circuit is connected to an ac source having voltage V = V_m sin cot. Derive the expression for the instantaneous current T and its phase relationship to the applied voltage. Obtain the condition for resonance to occur. Define ‘power factor’. Sate the conditions under which it is
(i) maximum and
(ii) minimum.

Question 25.
State Huygens principle. Show, with the help of a suitable diagram, how this principle is used to obtain the diffraction pattern by a single slit. Draw a plot of intensity distribution and explain clearly why the secondary maxima become weaker with increasing order (n) of the secondary maxima.

OR

Draw a ray diagram to show the working of a compound microscope. Deduce an expression for the total magnification when the final image is formed at the near point. In a compound microscope, an object is placed at a distance of 1.5 cm from the objective of focal length 1.25 cm. If the eye-piece has a focal length of 5 cm and the final image is formed at the near point, estimate the magnifying power of the microscope.

Question 26.
(a) Explain the formation of depletion layer and potential barrier in a p-n junction output.
(b) In the figure given below the input waveform is converted into the output waveform by a device ‘X’. Name the device and draw its circuit diagram.

(c) Identify the logic gate represented by the circuit as shown and write its truth table.

OR

(a) Draw the circuit diagram of a common emitter transistor as an amplifier, define current gain and voltage gain of it.
(b) Distinguish between a conductor, a semiconductor and an insulator on the basis of energy band diagrams.