Oswal Practice Papers CBSE Class 12 Biology Solutions (Practice Paper - 9)

Section-A

1. (c) (ii) and (iv)

Explanation :

The technically correct terms for the floral whorls are (from outermost to innermost) calyx, corolla, androecium and gynoecium. They are made up of sepals, petals, stamens and carpels respectively.

2. (a) 2: Liver; 4: RBC

Explanation :

Plasmodium enters the human body as sporozoites (infectious form) through the bite of infected female Anopheles mosquito. The parasites initially multiply within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture. The rupture of RBCs is associated with release of a toxic substance, haemozoin, which is responsible for the chill and high fever recurring every three to four days.

	A	B	C	D
(d)	Promoter	Template strand	Coding strand	Terminator

Explanation :

The segment of DNA that takes part in transcription is called transcription unit. It has three components. Promoter is located upstream of structural gene. It is called 5′ end of coding strand which is 3′ end of template strand. Terminator region is present downstream of structural gene at the 3′ end of coding strand which is actually 5′ end of the template strand.

4. (a) Convergent evolution

Explanation :

Convergent evolution is defined as the process whereby distantly related organisms independently evolve similar traits to adapt to similar necessities. Pigeon, bat and mosquito all use their wings for flying but their origin or structure is different.

5. (b) Mixed with an inoculum containing Streptococcus faecalis.

Explanation :

Yogurt is fermented milk. The milk is heated to 80-90°C for half an hour and then it is cooled to 40-43°C and mixed with an inoculum containing Streptococcus. Preparation of Yogurt takes approximately 4-5 hours. The original flavour of Yogurt is of acetaldehyde.

6. (a) pathogens

Explanation :

A wide range of organisms including bacteria, viruses, fungi, protozoans, helminths, etc., cause diseases in plants and animals. Such disease causing organisms are called pathogens. While vectors are the carriers of pathogens which may be insects or worms.

7. (b) deer rabbit frog rat

Explanation :

Deers are prey to lions. Rabbits are prey to foxes. Snakes eat frogs. Hawks prey to rats. So, option (a) is correct.

8. (a) Stiffness of neck

Explanation :

Stiffness of neck is the first symptom of tetanus. Then there is difficulty in swallowing and chewing. Subsequently, spasms of muscles of the jaw and face take place. There is severe pain. It is often a fatal disease.

9. (a) D = N/S

Explanation :

The formula for finding the population density is D = N/S or population density = a number of organisms/ area.

10. (a) Competition

Explanation :

In competition interaction, the fitness of one organism overpowers the presence and fitness of another. In these organisms of same or different species, living in the same or different community fight for the same resources.

11. (c) 4 3 2 1

Explanation :

Following is the list of bacteria and their commercially important products.

	Column I (Bacterium)		Column II (Product)
A.	Aspergilus niger	4.	Citric acid
B.	Acetobacter aceti	3.	Acetic acid
C.	Clostridium butylicum	2.	Butyric acid
D.	Lactobacillus	1.	Lactic acid

12. (a) Only I and II are true
13. (b) Both A and R are true and R is not the correct explanation of A.

Explanation :

The accessory glands of the male reproductive system are the seminal vesicles, prostate gland, and the bulbourethral glands. Bulbourethral glands also known as Cowper glands, provide mucus that lubricates the urethra and counteracts the acidity of any urine leftover in the urethra. Thus, both assertion and reason are true but reason is not the correct explanationof the assertion.

14. (b) Both A and R are true but R is not the correct explanation of A.

Explanation :

ABO blood group system is an example of multiple alleles. Also, the presence of A and B alleles give rise to the AB blood group and is codominant. There are 3 alleles for the gene that determines blood type. Thus both assertion and reason are true but reason is not the correct explanation of the assertion.

15. (b) Both A and R are true and R is not the correct explanation of A.

Explanation :

Sacred groves especially in Meghalaya (Khasi and Jaintia Hills), Aravalli Hills of Rajasthan, Western Ghats of Karnataka and Maharashtra and Sarguja, Chanda and Bastar of MP are last refugees of many rare and threatened plants, medicinal plants and animal species. They are biodiversity rich regions.

16. (c) A is true but R is false.

Explanation :

Malignant malaria caused by Plasmodium falciparum is the most serious one and can even be fatal. The parasites initially multiply within the liver cells and then attack the red blood cells (RBCs) resulting in their rupture. The rupture of RBCs is associated with the chill and high fever recurring every three to four days. Thus, assertion is true but reason is false.

Section-B

17. (a) Double fertilization is a complex process where out of two sperm cells, one fuses with the egg cell and the other fuses with two polar nuclei which result in a diploid (2n) zygote and a triploid (3n) primary endosperm nucleus (PEN) respectively.
(b) The end products of double fertilization are:
(i) Diploid Zygote
(ii) Primary Endosperm Nucleus

18. Pedigree analysis is done for the study of human genetics because:
(a) Controlled crosses are not possible in case of human beings.
(b) Analysis of traits in several generations of a family.
So, as to trace the pattern of inheritance the pedigree analysis is used to identify whether the trait is sex linked or not and dominant or recessive.

19. Contact inhibition refers to the phenomenon by which, the contact with other cells inhibits the uncontrolled growth of the cancerous cells. Metastasis is when the tumour cells reach the distant organs site through the blood. The group of gene is oncogenes. When activated under certain conditions there is oncogenic transformation of cells. The techniques to detect cancers are Biopsy, Radiography, CT and MRI through which the presence of cancer can be detected. The alpha interferon activates the immune system and destroys the tumours, so it is given to the cancer patients as the part of the treatment.

20.

Drug	Name of drug	Source
Drug 1	Morphine	Papaver samniferum
Drug 2	Amphetamines	Ephedra plants
Drug 3	Nicotine	Tabacoo leaves
Drug 4	Heroin	Acetylation of morphine
Drug 5	Cannabinoids	Cannabis sativa

21. (a) Decline in available food resources. As the population size decreases between 2 and 3 time there must be decline in available food which results in decline in size of population between 2 and 3 time.

(b) It is one of the growth models that explain the pattern of growth within the population. The model states that, if a population has a constant birth rate through time, and is never limited by availability of food and disease outbreak, then the population tends to grow exponentially. Through an exponential growth the birth rate alone determines the rate of growth as fast or slow.

Section-C

22. (a) The hard outer layer called exine is made up of sporopollenin which is one of the most resistant organic material. It can withstand high temperature, strong acids and alkalis. It cannot be degraded by any of the known enzymes. Hence, it acts as a shield and protects the pollen grain from getting damaged.

(b) Exine does not form a continuous layer around the pollen grain. Exine of the pollen grain has prominent aperture called germ pore where sporopollenin is absent. Germ pores serve as an outlet for the formation of pollen tube.

(c) Pollen grains at a large can be stored for years in liquid nitrogen (– 196ºC). So, after this treatment they are stored in pollen banks. Such conserved pollen grains can be used in plant breeding programs.

23. (a) Leydig cell are situated outside seminiferous tubules in the interstitial space. They synthesise or secrete male hormones.

(a) Leydig cell are situated outside seminiferous tubules in the interstitial space. They synthesise or secrete male hormones.

(b) Sertoli cells are lined inside the seminiferous tubules. They play a role in providing the nutrition to the sperms.

(c) Primary spermatocytes are found in the testes in a structure known as the seminiferous tubules. They are diploid (2n) cells containing 46 chromosomes. After meiosis, two secondary spermatocytes are formed.

24. (a) The above diagram shows the action of restriction endonuclease and thus forms a recombinant DNA after completion of entire process.

(b) Eco stands for Escherichia coli, R stands for the name of the strain and Roman I indicates the order in which the enzymes were isolated from the strains of the bacteria.

(c) They are the resultant of hydrogen bonding that act as the site for attachment for the separated DNA fragments and facilitate the action of enzyme called DNA ligase.

25. (a) The two exceptions are presence of mitochondrial codons and it is absent in some protozoans. Since, some amino acids are coded by more than one codon therefore they are said to be degenerate.

(b) (i) Stop Codon: They do not code for any amino acids and terminate the synthesis of polypeptide chain.
(ii) Unambiguous Codon: One codon codes for only one amino acid.
(iii) Degenerate Codon: Some amino acids are coded by more than one codon.
(iv) Universal Codon: It is same for all organisms (either bacteria or human).

26. t-RNA has clover leaf shape or the shape of an inverted L. It has an anticodon loop with bases which are complementary to a specific codon. It has an amino acid acceptor end. As it reads the code on one hand and binds with the specific amino acid on the other hand, it is referred to as an adapter molecule. The hn-RNA in a eukaryotic cell is subjected to a process called splicing where the introns are removed and the exons are joined in a defined order.

(a) DNA replication is semi-conservative because each helix that is created, contains one strand from the helix from which it was copied. The replication of one helix results in two daughter helices each of which contains one of the original parental helical strands.
During S-Phase (Synthesis phase), DNA replicates in cell cycle.

(b) Mechanism of DNA replication: The interwined DNA strands start separating from a particular point called origin of replication (single in prokaryotes and many in eukaryotes). This unwinding is catalyzed by enzyme called Helicases. Enzymes called Topoisomerases break and reseal one of the strands of DNA so that the unwound strands will not wind back. When the double stranded DNA is unwounded upto Replication Fork, enzyme DNA dependent DNA polymerase catalyses the joining of Deoxyribonucleotide (A, G, C and T) in the 5′–3’ direction. The enzyme forms one new strand in a continuous stretch (leading strand) in the 5’–3’ direction on one of the template strands. On the other template strand, the enzyme forms short stretches (discontinuous) strand of DNA also in the 5’–3’. The discontinuous fragments are later joined by DNA-ligase. The two strands are held together by hydrogen bonds between nucleotides.

27. (a) This technique was developed by an American company. Eli Lilly an American company, prepared two DNA sequences corresponding to A and B chains of human insulin and introduced them in plasmids of two different E.coli to produce insulin chains separately and joined them later to get an
active Insulin.

(b) No, this statement is false. The two chains A peptide and B peptide are joined by disulfide bond and C peptide is prohormone which is continuously removed for formation of active insulin.

28. (a) During production of insulin by rDNA technique, the major challenge was to get the assembled insulin into mature form.

(b) Presence of C-peptide makes the insulin inactive.

Section-D

29. (a) The process proceeds from initiation to elongation and from elongation to termination.

(b) It is the end process of transcription. When the polymerases reach the region of termination, the nascent RNA falls off along with RNA polymerase. This stage is a termination stage.

(c) The initiation factor (σ) is responsible for initiation whereas, termination factor (ρ) is responsible for termination of the transcription.

(c) The process of transcription and translation occurs in the same compartment. Also, the process of translation begins much earlier before mRNA fully gets transcribed. Hence due to their occurrence, they can be coupled in the bacteria.

30. (a) Each antibody molecule consists of two shorter chains called light chains and two longer chains called heavy chains. So to represent the number of chains it is designated as H₂L₂.

(b) It is the response given by the antibodies that are found in blood, such responses are called Humoral Immune Response.

IgA: The Immunoglobulin A is a neutralizing antibody that acts as the first line of defence against mucosal pathogens. It gets attached to the epithelial surfaces and prevents the invasion of pathogens. It comprises about 10 to 15 % of the total antibodies present in the body.
IgM: It functions in production of B-cells. It is the first antibody to appear in response to the exposure of an antigen. It appears in the early course of infection and can reappear from time to time as per the growth of infection. It is also responsible for reactions of blood transfusion in ABO blood system.
IgE: This specific antibody is found in lungs, skin and mucous membrane that travels to the cell and releases the chemicals causing allergic reactions.
IgG: This immunoglobulin is responsible for deciding the Rh-factor of the blood. They function in protecting the body from viral and bacterial infections. It comprises about 70 to 80 % of the total antibodies present in the body.

(c) Antibodies, also known as immunoglobulins are a type of protein molecule produced by B-lymphocytes in response to pathogens. Each antibody consists of four polypeptides—two heavy chains (H) and two light chains (L) joined to form a “Y” shaped molecule.

Section-E

31. True fruits—Mango and Grape.
False fruit—Apple and Pear (Thalamus present),
Mulberry (Fused Perianth),
Jackfruit and Pineapple (Development of the fruit from an entire inflorescence).

Blastomeres
Morula
Blastocyst
Umbilical cord
Neuroendocrine mechanism.

32. (a) (a) The individual numbered as 1 of generation II will have blood group as ‘B’. The genotype of which will be IB i.

(b) The individual numbered 2 of III generation can have blood group as ‘A’ or ‘O’ with the genotypes IA i, and ii respectively whereas the individual numbered as 3 of the III generation can have the blood group as AB, A or O with the genotype as IA IB, IA i, ii respectively. The blood group is determined by the presence or absence of one or both the glycoprotein that is group A, B and AB. While the group O has neither of them.

(a) It is Hardy Weinberg’s principle.
(b) If p represents the frequency of allele ‘A’, q represents the frequency of allele ‘a’, then frequency of AA = p², aa = q² and Aa = 2pq. Total genes and their alleles in a population or gene pool remains constant (called as genetic equilibrium). The sum total of all allelic frequencies is:
p + q = 1
(p + q)² = 1 or p² + q² + 2pq =1.

(c) In a population of diploid organisms,
If frequency of allele A = p
and frequency of allele a = q, then the expected genotype frequency under random mating
are:
AA = p² (for AA homozygotes)
Aa = q² (for aa homozygotes)
Aa = 2pq (for Aa heterozygotes)
In the absence of selection, mutation, genetic drift or other forces, p and q are constant through generations.
Therefore, p² + 2pq + q²= 1

33. (i) Ecological pyramids are graphical representation of the relationship among the organisms at different trophic levels.
Pyramid of Energy:
(a) Shows transfer of energy from one trophic level to another.
(b) Always upright.
Pyramid of Biomass:
(a) Shows transfer of amount of food from one trophic level to another.
(b) Mostly upright but can be inverted also.
Pyramid of Numbers:
(a) It shows the number of organisms at each trophic level.
(b) Mostly upright. It can be inverted.
(ii) (a) It does not accomodate the food web.
(b) It does not take into account the same species and saprophytes are not given any place.

(a) Ecosystem maintains a balance in the environment. It provides fresh air to breathe and sequesters carbon to regulate the climate. It cycles the nutrients through various biogeochemical cycles so that we have access to clean drinking water without any costly methods. It provides food and shelter to a number of living organisms. It also provides raw materials for different industrial and domestic purposes.

(b) The 10% energy flow law suggested by Lindemann, is followed in the ecosystem. As per this law, only 10% of the energy that is available at every trophic level is transferred to the next trophic level. The remaining is lost in the form of heat(during respiration). As we approach the higher levels,
energy keeps declining that is available to entities. Hence the topmost carnivore attains the least amount of energy in a food chain.

(c) An aquarium is an artificial ecosystem made by man. An ecosystem is said to be complete if it possesses all the biological and physical components vital for the survival of fishes. Hence it is a complete ecosystem.