CBSE Sample Papers for Class 12 Biology Paper 4

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

CBSE Sample Papers for Class 12  Biology Paper 4

Board	CBSE
Class	XII
Subject	Biology
Sample Paper Set	Paper 4
Category	CBSE Sample Papers

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 4 of Solved CBSE Sample Paper for Class 12 Biology is given below with free PDF download solutions.

Time: 3 Hours
Maximum Marks: 100

General Instructions:

• There are total 26 questions and five sections in the question paper. All questions are compulsory.
• Section A contains question number 1 to 5, Very Short Answer Type Questions of one mark each.
• Section B contains question number 6 to 10, Short Answer Type Questions of two marks each.
• Section C contains question number 11 to 22, Short Answer Type Questions of three marks each.
• Section D contains question number 23, Value Based Question of four mark.
• Section E contains question number 24 to 26, Long Answer Type Questions of five marks each.
• 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.
• No. of printed pages are three.

SECTION-A

Question 1.
Skin acts as a major type of a physical barrier. Discuss its role.

Question 2.
Justify the process proposed by Mendel   in  which   alleles tend to move into differentgametes.

Question 3.
Define secondary productivity.

Question 4.
Vestigial organs differs from atavistic organs in human beings. Discuss with examples of each.

Question 5.
If a dicotyledonous plant tends to bear flowers but fails to produce fruits and seeds. What might be the cause behind this? Explain.

SECTION-B

Question 6.
Differentiate between ageing and senescence.

Question 7.
State the cause behind the discontinuous synthesis of DNA on one parental strand of DNA. Also explain what happens to these short stretches of DNA been synthesized.

Question 8.
On a visit of a Botanical garden, Vidhu got to know about the storage of pollen grains of flowers. What do you think about this? How pollens are stored in a bank according to you? Discuss.

Question 9.
What are the disadvantages of ecological pyramids?
OR
Why the pyramid of energy is always upright?

Question 10.
Biotcchnologists often believe that line of treatment of genetic disease is often different when compared to the infectious disease. Discuss.

SECTION-C

Question 11.
Explain the function of
(1) Restriction endonucleases
(2) DNA polymerase
(3) DNA ligase

Question 12.
Study the given pedigree chart and answer the questions that follow.
(1) Is trait recessive or dominant?
(2) Is the trait sex-linked or autosomal?
(3) Give the genotypes of the parents shown in generation I and their third child shown in generation II and the first grand child shown in further generation.

Question 13.
Describe how the changing levels of FSH, LH and progesterone during menstrual cycle induce changes in the ovary and the uterus in human female.

Question 14.
Explain the adapting features of plants and animals, growing in an inadequate water condition.

Question 15.
What are the benefits of transgenic animals?

Question 16.
Describes the terms
(1) Tetrasomic
(2) Monosomic
(3) Nullisomic

Question 17.
Can a disease be detected before its symptoms appear? Explain the principle involved.
OR
Explain the function of bone marrow and thymus in providing immunity

Question 18.
Does fitness of a population help in evolution?

Question 19.
Biologist believes that Amniocentesis is an advantageous technique as it can easily detect the genetic disorder in a developing foetus. Describe its procedure and also state if it is useful then why is it banned?

Question 20.
Green revolution has increased the food supply but yet it was not enough to feed the growing human population. In a country like India, where majority of farmers are poor, what could be the other option and how the food quality and quantity can be enhanced?

Question 21
Explain the technology of tissue culture briefly.

Question 22.
As a responsible citizen of your nation do you really believe in a natural method of controlling population which states that if a big animal eats a small animal, population will be maintained. Is it really true? Put forth opinion about this phenomenon (both advantages and disadvantages) and the fact behind it.

SECTION-D

Question 23.
Some parents wrote a complaint letter to the local municipality to remove all the hoardings in city advertising the use of condoms and matters relating to AIDS prevention. The children of these parents came to know about the matter and raised their voice against removal of those hoardings. The parents were convinced by the awareness level of their children and withdrew the complaint. If parents considered the hoarding to be sight pollution, then, why do you really disagree? Also discuss the methods by which AIDS spreads and the values promoted by the children to protest against their parents.

SECTION-E

Question 24.
When a garden pea plant with green pods was cross-pollinated with another pea plant with yellow pods, 50% of the progeny bore green pods.

1. Work out the cross to illustrate this
2. What do you refer to this type of cross and why it is done?
3. Sex determination in human beings set an example of male heterogamety. Why it is so?

OR
What is adaptation? Describe the adaptation of plant and animal in desert.

Question 25.
(1) Draw a labelled longitudinal view of an albuminous seed.
(2) How are seeds advantageous to flowering plants?
OR
Differentiate between Microsporogenesis and Megasporogenesis. Name the structure formed at the end of the two events.

Question 26.
Enumerate some major effects of air pollution of plants and animals.
OR
Explain any two ways of improper resource utilisation that can cause degradation of natural resources.

Answers

SECTION-A

Answer 1.
Skin is the first line of mucus coating of defence because it prevents the entry of the pathogens into the body.

Answer 2.
Mendel proposed a law of Segregation which acts as the phenomenon in which alleles tends to move into different gametes.

Answer 3.
Secondary productivity is the rate of formation of new organic matter by the consumers.

Answer 4.
Vestigial organs were functional in their ancestors, e.g., vermiform appendix which is non­functional now in human beings. Whereas atavistic organs have the tendency to revert to their ancestral type, e.g., body formed with a tail.

Answer 5.
This shows that plant is dioecious in nature and bears only staminate flowers.

SECTION-B

Answer 6.

Ageing	Senescence
Ageing is progressive	The terminal irreversible stage of ageing is called senescence.
Ageing leads to senescence.	Senescence lead to death

Answer 7.
Discontinuous synthesis of DNA occurs on the lagging strand of the replication fork which indicates that base pairs runs in the opposite direction to the leading strand. The polymerase attaches to the DNA and replicates away from the fork.The short stretches also known as Okazaki fragments are joined by the enzyme called DNA ligase to form a complete single strand of DNA.

Answer 8.
Pollen Grains from flowers are stored in pollen banks for years altogether in a liquid nitrogen at – 196°C, and can be used in different plant breeding programmes whenever needed.

Answer 9.
Disadvantages of ecological pyramids are:

• It does not accommodate a food web and never takes into account the same species belonging to two or more trophic levels.
• Saprophytes are not given any place in ecological pyramids even though, they play an important role in ecosystem.

OR
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 and therefore pyramid of energy is always upright.

Answer 10.
Genetic diseases are actually not treated with any medication i.e. their signs and symptoms can be taken most care of. Hence, they can be only treated by the manipulation of defective gene and replacing it with the correct one. While the infectious diseases are usually caused by pathogens thus, can be easily treated with medication by hampering the growth of the microbes.

SECTION-C

Answer 11.
(1) Restriction Endonuclease cuts DNA at specific site forming DNA fragments.
(2) DNA Polymerase uses DNA template to catalyse the reaction and also catalyses -polymerization of a large number of nucleotides’in a very short time.
(3) DNA Ligase joins discontinuously synthesized DNA fragments

Answer 12.
Thus, all these three enzymes find heavy uses in DNA replication, transcription and translation.

1. Trait is recessive.
2. Trait is autosomal.
3. Genotype of parents in generation: I-female-Hb^a Hb^s, male-Hb^sHb^s
   Genotype of third child in generation: III-Hb^s Hb^s
   Genotype of first grandchild in generation III-Hb^a Hb^a

Answer 13.
The secretion of gonadotropins, i.e LH and FSH stimulates follicular development as well as secretion of estrogens by the growing follicles. The rapid secretion of LH during mid-cycle induces rupture of Graafian follicle and thereby, release of the ovum. The corpus luteum, developed from Graafian follicle, secretes large amounts of progesterone, which is essential for the maintence of endometrium for implantation.

Answer 14.
Desert plants have thick cuticle on leaf surface to avoid water loss during day via transpiration. Stomata are arranged in deep pits to minimize water loss. Special photosynthetic pathway (CAM plants) enables their stomata to remain closed during day time. E.g. Opuntia have no leaves, they are reduced to spines and the photosynthetic function is taken over by flattened stems.
Whereas animals like Kangaroo rat in deserts of North America is capable of meeting all of its water requirements through its internal fat oxidation (in which water is a byproduct). It also has the ability to concentrate its urine for minimal loss of water.

Answer 15.
Benefits of transgenic animals are:
(1) Normal Physiology and Development: They support in the study that how genes are regulated and how they affect normal function of the body. For example, the study of complex factors involved in growth such as insulin.

(2) Study of Disease: How genes contribute to the development of diseases such as cancer, cystic fibrosis, rheumatoid arthritis, Alzheimer etc can be understood in more detail.

(3) Biological Products: Transgenic animals produce useful biological products by the introduction of the portion of DNA (or genes). For example, Human protein (a-1 antitrypsin) used to treat empysema.

Answer 16
(1)  Tetrasomic is an aneuploidy having one chromosome represented four times. It shows more variability than trisomics.
(2) Monosomic is an aneuploidy in which one chromosome is devoid of its homologue. It is generally weaker than the normal form.
(3) Nullisomic is an aneuploidy deficient in a complete pair of homologous chromosomes. It does not survive except amongst polyploids.

Answer 17.
No, a disease cannot be detected before its symptoms. The detection of a disease by conventional diagnostic tests is very difficult and can be possible by the amplification of their nucleic acid by the technique known as Polymerase Chain Reaction (PCR). The principle involved here is that a single DNA molecule can be copied endlessly in a test-tube, using primers, DNA polymerase enzyme and free nucleotides under appropriate conditions.
OR
Functions of Bone marrow and thymus in providing immunity are:

1. All the blood cells including lymphocytes are produced in the main primary lymphoid organ.
2. Immature lymphocytes differentiates into antigen sensitive lymphocyte.
3. Provides micro environments for the development and maturation of T-lymphocytes.
4. After maturation, lymphocytes migrates to the secondary lymphoid organs like spleen, lymph nodes, MALT, etc.

Answer 18.
Yes, according to Darwin, fitness ultimately refers to reproductive fitness. Those who fit best in an environment, can reproduce well and survive. Hence is selected by the nature. He called this natural selection and simplified it as a mechanism of evolution.

Answer 19.
Amniocentesis is a technique by which genetic disorder in a developing foetus can be detected. This is based on the chromosomal pattern in the amniotic fluid surrounding the developing embryo.

Amniotic fluid contains cells and molecules shed by the foetus. The chromosomes of foetal cells can also be used to find out the sex of the foetus and certain abnormalities. Thus, if an abnormality is found, the mother can get the foetus aborted. Yes, the technique is banned now inspite of its usefulness as the people had started misusing it to carry out female foeticides. And this ban is extremely necessary to maintain or balance the ratio of males and females in our society.

Answer 20.
The other option to enhance the quality of food that could increase the food supply by genetic modification of organisms and by using genetically modified plants are:

1. Made crops more tolerant to abiotic stresses (cold, drought, salt and heat).
2. Reduced reliance on chemical pesticides (pest-resistant crops).
3. Helped to reduce post-harvest losses.
4. Increased efficiency of mineral usage by plants (this prevents early exhaustion of fertility of soil).
5. Enhanced nutritional value of food, e.g., vitamin-A enriched rice.

Answer 21.
Tissue culture is an advanced technique by which whole plant can be regenerated from explants (any small plant part) under sterile condition in a special nutrient media. The nutrient media must provide a carbon source (such as sucrose), in organic salts, vitamins, amino acids and growth regulators such as auxins, cytokinins etc. The capacity to generate a whole plant from any explant is called Totipotency. The plants thus, generated are genetically similar to the original plant through which they are grown, so they are called somaclones.

Answer 22.
The phenomenon of eating lower animals by the bigger one is called predation. The predator helps to keep the population of the prey under a control and also help in maintaining the diversity of species in a community by reducing the intensity of competition among prey species.

But, inspite of all this, it also has an ill-effect on the population of one type of species as if bigger animals will eat lower animals continuously, the population of bigger animals may rise to the population of the lower ones which is again not satisfactory for the community. Thus, a balance should be maintained.

SECTION-D

Answer 23.
Since the awareness among people has not reached to that extent, the forceful and constant reminding is always required. Our country is over-populated and number of AIDS cases are increasing rapidly.
AIDS spreads by unprotected sexual contact, use of contaminated needles and syringes. Children are educated, initiative takers and conscious about their society.

SECTION-E

Answer 24.
(1) To test that 50% progeny is green ‘test cross’ can be done.

The unknown plant is heterozygous.
(2) This type of cross is called test cross because this is done between the organism of unknown dominant genotype with recessive parent in order to evaluate whether the dominant trait is homozygous or heterozygous.
(3) Sex determination in human beings is an example of male heterogamety because males produce two different types of gametes i.e., X and Y.

OR

Adaptation is the quality of the organism (morphological, physiological, behavioural) that enables the organism to survive and reproduce in its habitat. It adapts organisms to live in different types of habitats.

Adaptation of desert plant are as follows:

1. Desert plants have cuticle to minimise transpiration.
2. In some desert plant, leaves modify into spines to minimise loss of water.
3. They have long roots and adaptations to reduce transpiration, e.g., Acacia.

Adaptation of desert animal are as follows:

1. Desert animals concentrate their urine for minimum loss of water, e.g., Kangaroo rat.
2. Desert animals absorb heat from the sun when the body temperature drop below the comfort zone.
3. They live in burrows during hot season and have little water requirement.

Answer 25.
(1) Longitudinal View of an Albuminous Seed

(2) Seeds are advantageous to flowering plants in following ways.

• These are the final product of sexual reproduction.
• Since, reproductive process such as pollination and fertilization are independent of water, seed formation is more dependable.
• Seeds have better adaptive strategies for dispersal to new habitat.
• Hard seed coat provides protection to young embryo.
• Basis for agriculture.

OR

Microsporogenesis	Megasporogenesis
It is the formation of microspores of pollen grains from diploid microspore mother cell.	It is the formation of haploid megaspores from diploid mother cell.
It occurs inside microsporangium or pollen sac of an anther.	It occurs inside the megasporangium or ovule.
There are numerous microspores mother cells	There is generally a single megaspore mother cell.
All the products of microsporogenesis are functional	Only one megaspore is functional, while other gets degenerated.
The products of microsporogenesis give rise to male gametophyte.	The functional product of megasporogenesis gives rise to female gametophyte or embryo sac.

Structures formed at the end of the two events

1. Microsporogenesis – Microspores (pollen grain)
2. Megasporogenesis- Megaspores (embryo sac).

Answer 26.
Effects of air pollutants on plants are:   

• Causes fruit damage, leaf damage, chlorosis and necrosis, mottled spots on leaves,
• Slow the growth yield of crops and cause premature death of plants.
• Weakens plants and increases the infestation by pests.
• Acid rain damages the aerial parts and also acidifies the soils. It leads to the production of free radicals and decrease in photosynthesis and productivity.

Effects on Animals and Humans are:

1. About 40% of human deaths occur due to air pollution,
2. Increased susceptibility to diseases.
3. Causes cancer and genetic mutations.
4. Causes respiratory ailments and asthma, hay fever and allergic diseases.
5. Causes cardiovascular diseases and damage to CNS.
6. Immediate effects like nausea, headache, irritation to the eyes and nose.

OR

Two ways of improper resource utilisation which cause degradation of natural resources are:

(1) Soil Erosion and Desertification
Improper human activities can remove top soil, resulting in arid patches of land. Natural resources get degraded not only by pollutants, but also by improper practices of their ;utilization and maintenance. Soil erosion is caused by human activities like over­, cultivation, nrestricted grazing, deforestration and poor irrigation. All these practices lead to the removal of top soil. Desertification is also a major problem these days, that occurs mainly due to urbanization.

(2) Water-Logging and Soil Salinity

Irrigation without proper drainage of water leads to water-logging in the soil. It draws ‘ salt to the surface of the soil. Deposited salt starts collecting at the roots of the plants and affect the plant growth and productivity. It is extremely damaging to the agriculture. Water-logging and soil salinity are some of the problems that have come in the wake of the Green Revolution.

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