HBSE 12th Biology Solved Sample Paper 2023
Q1.(i) Which of the following is not a Cu releasing IUD?
(A) Cu 7
(B) Multiload 375
(C) LNG-20
(D) All of these
(ii) Phenylketonuria is an example of :
(A) Pleiotropy
(B) Polygenic inheritance
(C) Aneuploidy
(D) Autosomal dominant disorder
(iii) DNA fingerprinting is based on :
(A) Genetic mapping
(B) DNA polymorphism
(C) EST
(D) Bioinformatics
(iv) Which of the following has a brain size of 1400 cc?
(A) Homo sapiens
(B) Australopithecines
(C) Neanderthal man
(D) Homo erectus
(v) Which of the following is obtained from coca plant?
(A) Smack
(B) Crack
(C) Charas
(D) Morphine
(vi) Which of the following is not an essential feature of a cloning vector?
(A) ori site
(B) Selectable marker
(C) Cloning site
(D) Recombinant protein
(vii) Name the hormone produced by interstitial cells.
Testosterone Hormone
(viii) Who gave Chromosomal Theory of inheritance?
Theodor Boveri and Walter Sutton are the two scientists who were credited with developing the Chromosomal Theory of inheritance.
(ix) Write two stop codons.
UAG, UAA and UGA are the standard stop codons.
(x) What is source and use of streptokinase?
The source of streptokinase is Bacteria Streptococcus. It is modified by genetic engineering and is used as a clot buster for removing clots from the blood vessels of patients who have suffered from myocardial infraction.
(xi) What is mycorrhiza?
Mutualistic associations between fungi and plant roots are called mycorrhizae.
(xii) How many polypeptides are in mature human insulin?
Human insulin is made of two polypeptides the, A-chain and B-chain, joined together by disulphide bonds.
(xiii) Give an example of behavioural adaptation.
Migration is main example of behavioral adaptations.
(xiv) What are pioneer species in xerarch succession?
Lichens are usually the pioneer species in xerarch succession.
(xv) What is endemism?
Endemism refers to the presence of a species only in a particular region and not anywhere else.
Q2. Write briefly about self-incompatibility.
Self-incompatibility (SI) is defined as the inability to produce zygotes after self-pollination in a fertile hermaphrodite plant, which has stamens and pistils in the same flower.
Q3. Write a short note on GIFT.
GIFT stands for Gamete Intra-Fallopian Transfer. In GIFT, the ovum collected from the donor or the woman herself is mixed with sperms and is transferred to the fallopian tube of the recipient or ownself. It is used in the cases where a female is unable to produce an ovum but can provide a proper environment for fertilisation or in case of sperm dysfunction.
Q4. What are the measures one has to take to prevent from contacting STDs?
Sexually transmitted diseases (STDs) get transferred from one individual to the other through sexual contact. The use of contraceptives, such as condoms, etc. during intercourse, can prevent the transfer of these diseases.
Q5. How sex determination occurs in birds?
The sex chromosomes in birds are designated Z and W, and the male is the homomorphic sex (ZZ) and the female heteromorphic (ZW). In most avian species the Z chromosome is a large chromosome, usually the fourth or fifth largest, and it contains almost all the known sex-linked genes.
Q6. List the factors affecting Hardy-Weinberg equilibrium.
The Hardy-Weinberg equilibrium is influenced by any factor that disturbs the alleles in a population. Mutations, recombinations during sexual reproduction, genetic drift, gene migration or gene flow, and natural selection are the major factors that influence genetic equilibrium and cause variety in the population.
Q7. Explain commensalism with an example.
This is the interaction in which one species benefits and the other is neither harmed nor benefited. e.g. An orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale benefit while neither the mango tree nor the whale derives any apparent benefit.
Q8. Differentiate between food chain and food web.
A food chain is a basic network that shows the linear flow of nutrients and energy from one trophic level to another. A food web is a multitude of interconnected food chains at many trophic levels. Furthermore, a food web accurately represents all the various food chains that exist in an ecosystem.
Q9. Write a note on biological products obtained from transgenic animals.
A number of biological products such as medicines and nutritional supplements are obtained from transgenic animals. Research for the manufacture of medicines to treat diseases such as phenylketonuria (PKU) and hereditary emphysema is going on. Transgenic animals are specially designed to study the role of genes in the development of certain diseases.
Q10. Draw a well labelled diagram of mature embryo sac.
Q11. Explain law of dominance.
Mendel’s law of dominance states that : “When parents with pure, contrasting traits are crossed together, only one form of trait appears in the next generation. The hybrid offsprings will exhibit only the dominant trait in the phenotype.”
Q12. Explain natural selection giving example of moths.
On this dark background, the pale moths were no longer well-camouflaged and were easily caught by birds so black colour moth survives and becomes common. This is an example of natural selection. As the environment selects the black colour moth so their number increases and nature favours their survival.
Q13. Write a note on treatment of cancer.
Commonly, three types of treatment are available for cancer :
(i) Surgery : Surgically removing localized cancerous mass (Effective for benign tumours)
(ii) Radiation therapy : In this therapy, radiation is used to kill the cancer cells.
(iii) Chemotherapy : Chemotherapeutic drugs are used to kill cancer cells.
Q14. Give details of causative agents, symptoms and mode of infection of pneumonia.
Pneumonia is the infection of the lungs caused by bacteria, viruses and fungi. It can be diagnosed through physical examinations, blood tests and tests for sputum. It ranges from mild to fatal. Pneumonia can be characterised by fever, chills, shortness of breath and chest pain. It can be treated with certain antibiotics.
Q15. Write note on secondary treatment in sewage treatment plant.
Secondary treatment removes the dissolved organic matter by the use of biological agents and hence, known as biological treatment. This is achieved by microbes which can consume and degrade the organic matter converting it to carbon dioxide, water, and energy for their own growth and reproduction. This helps to reduce the BOD of the sewage water.
Q16. Write a note on Bt-cotton.
Bt-cotton plant is a transgenic plant which produces an insecticide to bollworm. Bt-cotton is produced by inserting cry gene from bacteria Bacillus thuringiensis to the plant genome by the help of transgenic technology. The genetically modified DNA in recipient plant produces toxin in sap. When the insect attacks on the plant and suck the sap from the plant, these toxin binds with the gut wall of the insect. These proteins create pores in the gut. This results in damage to the cells and blocks the gut which leads to the death of the insect.
Q17. Explain three major causes of biodiversity loss.
The major causes of biodiversity losses are :
(i) Habitat loss and fragmentation
(ii) Over Population
(iii) Pollution
(iv) Over-exploitation of natural resources
Q18. Explain in detail about menstrual cycle.
It is the reproductive cycle of female primates (such as humans). The menstrual cycle is the sequence of events that begins with one menstruation and ends with the next. Menstruation occurs every 28/29 days in human females.
The menstrual cycle is divided into four phases :
(i) Menstrual phase : Day 1, uterus lining which is prepared for implantation starts to shed which lasts 3 to 5 days.
(ii) Follicular phase : In this phase, the primary follicle starts developing into a mature Graffian follicle. The endometrium also starts proliferating. The uterus starts preparation for another pregnancy.
(iii) Ovulatory phase : Mid-cycle phase, this is the phase in which ovulation takes place i.e., day 13-17. The end of the follicular phase along with the ovulation period defines the fertilisation period.
(iv) Luteal phase : It is the post-ovulation phase, where the fate of the corpus luteum is decided. If fertilisation occurs, pregnancy starts. If fertilisation doesn’t occur, it marks the onset of another cycle.
Hormones that regulate the menstrual cycle are : Follicle-stimulating hormone (FSH), Luteinizing hormone (LH), Estrogen and Progesterone.
OR
Differentiate between oogenesis and spermatogenesis.
Spermatogenesis :
(i) The production of sperms from spermatogonia is known as spermatogenesis.
(ii) Occurs in testes.
(iii) All stages are completed in testes.
(iv) It is a continuous process.
(v) Produces motile gametes.
(vi) Equal cytokinesis occurs during the spermatogenesis producing four sperms.
Oogenesis :
(i) The production of eggs from oogonia is known as oogenesis.
(ii) Occurs inside the ovary.
(iii) The major part of oogenesis occurs inside the ovary. The last few stages occur in the oviduct.
(iv) It is a discontinuous process. The early stages take place in the foetus and the rest in later stages of life.
(v) Produces non-motile gametes.
(vi) Unequal cytokinesis occurs during oogenesis ultimately producing one large ovum and tiny polar bodies.
Q19. Explain in detail about double helix model of DNA.
The double helix is a structure that is made up of two right-handed polynucleotide chains. The polynucleotide chains are coiled on the same axis and run alongside each other forming a double helix. Both the polynucleotide chains are complementary to each other. So, if the sequence of bases in one strand is known then the sequence of bases in other strands can be predicted.
The salient features of double-helix DNA :
– Both strands are antiparallel to each other means if one strand was oriented in 3’ to 5’ direction then the other was oriented 5’ to 3’ direction.
– Both strands are held together by hydrogen bonds between base pairs.
– Adenine forms two hydrogen bonds with Thymine from the opposite strand and vice versa. Similarly, Guanine forms three hydrogen bonds with Cytosine.
– Both the chains are coiled in a right-handed manner.
– The pitch of the double helix DNA is 3.4nm.
– Each turn contains approximately 10 base pairs.
– The DNA bases are stacked with a regular spacing of 3.4 Å.
– Approximately 25 Hydrogen bonds are present in each complete turn in that provide the stability to the double-helical structure as strong as a covalent bond.
OR
Describe Lac-operon.
Lac operon is an operon or a group of genes with a single promoter that encode genes for the transport and metabolism of lactose in E.coli and other bacteria.
– Lac operon contains genes involved in metabolism.
– The genes are expressed only when lactose is present and glucose is absent.
– The operon is turned on and off in response to the glucose and lactose levels: catabolite activator protein and lac repressor.
– The lac repressor blocks the transcription of the operon. In the presence of lactose, it stops acting as a repressor.
– Catabolite activator protein activates the transcription of the operon, only when glucose levels are low.
Q20. Explain PCR.
Polymerase chain reaction is commonly known as PCR. It is used to produce multiple copies of a gene or DNA of interest. The steps of polymerase chain reaction are denaturation, primer annealing and extension of primers.
Each cycle of polymerase chain reaction has three steps :
(i) Denaturation : The first step in PCR is denaturation. Denaturation is required to separate the double-stranded DNA sample. It is done at 94-98 ℃ for 20-30 seconds. It breaks the hydrogen bonds present between base pairs. Denaturation leads to the formation of single strands of DNA.
(ii) Annealing : The second step is the annealing of the primer. Here the reaction temperature is lowered to allow the complementary base pairing between the primer and the complementary part of the single strands of the DNA template. A proper temperature needs to be maintained in order to allow highly specific and proper primer hybridisation. Then DNA polymerase binds to the template-primer hybrid and starts the DNA synthesis.
(iii) Extension : A thermostable DNA polymerase is used for this purpose. Taq polymerase is commonly used for this purpose. It is done at a temperature of 75-80 ℃ (72℃). The DNA polymerase adds nucleotides in the 5’-3’ direction and synthesises the complementary strand of the DNA template.