GSEB 2020 Biology Question Paper with Answer and Solution

(B) The spleen is known as the 'graveyard of erythrocytes' because it removes old and damaged red blood cells from circulation. Additionally,it acts as a major reservoir or storehouse for erythrocytes,releasing them into the bloodstream when the body requires an increased oxygen-carrying capacity.

(D) The correct answer is $D$.
$Azospirillum$ and $Azotobacter$ are well-known examples of free-living nitrogen-fixing bacteria found in the soil.
$Rhizobium$ is a symbiotic nitrogen-fixing bacterium.
$Nostoc$ and $Anabaena$ are cyanobacteria that can fix nitrogen,but they are often associated with symbiotic relationships (e.g.,in $Azolla$ or $Cycas$ roots) or exist in colonies,whereas $Azospirillum$ and $Azotobacter$ are specifically classified as free-living soil bacteria.

(D) nucleoside is formed by the attachment of a nitrogenous base to a pentose sugar. The bond formed between the nitrogen of the nitrogenous base and the $1'$ carbon of the sugar is known as an $N$-glycosidic bond.
- Disaccharides contain glycosidic bonds (between two sugars).
- Dipeptides contain peptide bonds.
- Triglycerides contain ester bonds.
Therefore,the correct option is $D$.

(A) Acorns contain high concentrations of tannins,which are a type of phenolic compound. However,in the context of toxic secondary metabolites produced by plants to deter herbivores,glycosides (specifically tannins or related compounds) are often cited. Among the given options,$A$ (Glycosides) is the correct classification for the chemical compounds found in acorns that cause toxicity in grazing animals like cattle and sheep.

(C) Statement $A$ is correct because species diversity generally decreases as we move from the equator towards the poles due to variations in climate and solar energy.
Statement $R$ is incorrect because the Amazon rain forest in South America is known for having the greatest biodiversity on Earth,not less.

(B) According to the $NCERT$ textbook diagram representing the global biodiversity of invertebrates,insects constitute the largest group,occupying the largest sector of the pie chart. The 'Other animal groups' (which includes minor phyla) occupy the smallest sector of the pie chart. Therefore,the correct sequence for maximum and minimum taxa is Insects and Other animal groups,respectively. Thus,option $B$ is correct.

(A) The correct answer is $A$. The nematode $Meloidogyne \, incognitia$ infects the roots of tobacco plants and causes a significant reduction in yield. Biotechnology, specifically $RNA$ interference $(RNAi)$, is used to develop pest-resistant tobacco plants by silencing specific genes of this nematode.

(C) The correct answer is $C$. Adenosine deaminase $(ADA)$ deficiency is a severe combined immunodeficiency $(SCID)$ disorder. It is most commonly caused by a deletion in the gene that codes for the enzyme adenosine deaminase. This enzyme is crucial for the proper functioning of the immune system,specifically for the maturation of $T$-lymphocytes. The absence of this enzyme leads to the accumulation of toxic metabolites,which destroy the immune cells.

(C) Rosie was the first transgenic cow produced by scientists.
She was genetically engineered to produce human protein-enriched milk,specifically containing human alpha-lactalbumin.
This milk was nutritionally more balanced for human babies than natural cow milk.

(A) The proteins encoded by the genes $CryIAc$ and $CryIAb$ are used to control cotton bollworms and corn borers,respectively.
These genes are derived from the bacterium $Bacillus$ $thuringiensis$ $(Bt)$.
$CryIAc$ is specifically effective against cotton bollworms,while $CryIAb$ is effective against corn borers.
Therefore,the correct sequence is Cotton bollworm and Corn borer.

(A) In the $pBR322$ cloning vector,the $tet^{R}$ (tetracycline resistance) gene contains restriction sites for $BamH I$ and $Sal I$.
The $amp^{R}$ (ampicillin resistance) gene contains restriction sites for $Pst I$ and $Pvu I$.
Therefore,$BamH I$ is the correct restriction site present in the $tet^{R}$ gene.

(A) In biotechnology,the isolation of $DNA$ from cells requires the breakdown of the cell wall to release the genetic material.
$1$. Bacterial cell walls are composed of peptidoglycan,which is degraded by the enzyme $Lysozyme$.
$2$. Plant cell walls are composed of cellulose,which is degraded by the enzyme $Cellulase$.
$3$. Fungal cell walls are composed of chitin,which is degraded by the enzyme $Chitinase$.
Therefore,the correct sequence for bacterial,plant,and fungal cell wall breakdown is $Lysozyme$,$Cellulase$,and $Chitinase$ respectively.

(B) Retroviruses are a group of viruses that contain $RNA$ as their genetic material. They possess an enzyme called reverse transcriptase,which allows them to convert their $RNA$ into $DNA$ inside the host cell. This viral $DNA$ then integrates into the host genome. Certain retroviruses,known as oncogenic retroviruses,carry viral oncogenes $(v-onc)$ or can activate host proto-oncogenes,which leads to the transformation of normal cells into cancerous cells.

(C) According to the $10\%$ Law of energy transfer in an ecosystem,only about $10\%$ of the energy available at one trophic level is transferred to the next trophic level.
$1$. Primary Producers: $100 \ J$
$2$. Primary Consumers (First trophic level to second): $10\%$ of $100 \ J = 10 \ J$
$3$. Secondary Consumers (Second trophic level to third): $10\%$ of $10 \ J = 1 \ J$
Therefore,the secondary consumer receives $1 \ J$ of energy.

(B) In an ecosystem,the trophic level is determined by the organism's position in the food chain.
$1$. The primary producers (plants) occupy the first trophic level.
$2$. Primary consumers (herbivores) feed on producers and occupy the second trophic level.
$3$. Insects and worms that feed on plants are primary consumers.
$4$. Since the sparrow feeds on these insects and worms,it acts as a carnivore that consumes primary consumers,placing it at the third trophic level,which is defined as a secondary consumer.

(A) The annual net primary productivity of the whole biosphere is estimated to be approximately $170$ billion tons (dry weight) of organic matter. This value represents the total amount of biomass produced by all producers (plants, algae, and bacteria) across the entire planet in a year.

(B) In a marine ecosystem,the biomass pyramid is inverted. This is because the biomass of producers (phytoplankton) is significantly lower than the biomass of the consumers (zooplankton and small fish) that feed on them. Since the producers have a very high turnover rate,they support a larger biomass of consumers at any given time,resulting in an inverted shape.

(A) Tendrils of $Cucurbita$ and thorns of $Bougainvillea$ are classic examples of homologous organs.
Homologous organs are those that share a common anatomical structure and developmental origin but may perform different functions.
This phenomenon,where organisms with a common ancestor evolve different traits to adapt to different environments,is known as divergent evolution.
Therefore,the correct answer is $A$ (Divergent).

(D) The correct answer is $D$. Lobe-finned fish (coelacanths) are considered the ancestors of the first amphibians. These fish had fins with fleshy lobes that allowed them to move on land for short periods,eventually leading to the evolution of tetrapods (amphibians).

(C) The correct answer is $C$.
Natural selection can lead to three different outcomes based on the distribution of traits in a population:
$1$. Stabilising selection: The mean value of the trait is favoured,resulting in a single,narrower peak.
$2$. Directional selection: One extreme phenotype is favoured,shifting the peak in one direction.
$3$. Disruptive selection: Both extreme phenotypes are favoured over the intermediate phenotype,resulting in the formation of two peaks in the distribution graph.
Therefore,the formation of two peaks indicates the effect of disruptive selection.

(A) The similarity in the anatomical structure of the forelimbs of different mammals (like humans,whales,bats,and cheetahs) is an example of homologous organs.
These organs share a common ancestral origin but have evolved to perform different functions due to adaptation to different environments.
This process,where organisms with a common ancestor evolve different traits,is known as $Divergent$ $evolution$.

(D) The correct answer is $D$.
Withdrawal syndrome refers to the set of physical and psychological symptoms that occur when a person who is dependent on a substance (such as drugs or alcohol) suddenly stops or reduces its intake.
Common symptoms include restlessness,shivering,nausea,sweating,anxiety,and tremors.
Turner's syndrome,Down's syndrome,and Klinefelter syndrome are genetic disorders caused by chromosomal abnormalities,not by the cessation of substance use.

(A) Passive immunity (or passive resistance) occurs when ready-made antibodies are directly given to the body to protect against a foreign agent.
$A$. Polio vaccine (oral) contains weakened pathogens that stimulate the body to produce its own antibodies,which is an example of active immunity.
$B$. Vaccine against snake venom (antivenom) contains pre-formed antibodies,which is passive immunity.
$C$. Colostrum contains $IgA$ antibodies transferred from mother to infant,which is natural passive immunity.
$D$. Tetanus antitoxin contains pre-formed antibodies,which is passive immunity.
Therefore,the Polio vaccine is the only option that relates to active immunity rather than passive resistance.

(D) The acetylation of morphine produces $Heroin$ (also known as $Diacetylmorphine$).
$Heroin$ is a white,odorless,bitter crystalline compound.
It is synthesized by the acetylation of morphine,which is extracted from the latex of the poppy plant,$Papaver$ $somniferum$.
Therefore,the correct option is $D$.

(B) Certain viruses known as oncogenic viruses have genes called viral oncogenes that can cause the transformation of normal cells into cancerous cells. Among the given options,$Retroviruses$ are well-known for their ability to transform normal cells into cancerous cells through the action of their viral oncogenes $(v-onc)$.

(A) The correct answer is $IgA$.
Colostrum is the yellowish fluid secreted by the mother during the initial days of lactation.
It contains abundant antibodies,specifically $IgA$,which are essential to provide passive immunity to the newborn infant.

(A) The correct matches are as follows:
$(i)$ Salmonella typhi causes Typhoid fever $(q)$.
(ii) Plasmodium is the parasite responsible for Malaria $(p)$.
(iii) Entamoeba histolytica causes Amoebiasis $(s)$.
(iv) Epidermophyton is a fungus that causes Ringworm $(r)$.
Therefore,the correct matching is (i - q),(ii - p),(iii - s),(iv - r). The correct option is $A$.

(D) Interferons are antiviral proteins secreted by virus-infected cells to protect neighboring healthy cells. They are part of the innate immune system. None of the provided options $(A, B, C, D)$ are known to specifically inhibit the secretion of interferons in a physiological context. Viral infection actually stimulates the production of interferons. Therefore,the question is scientifically flawed as none of the options act as an inhibitor of interferon secretion.

(A) Biological response modifiers are substances that stimulate the body's immune system to fight cancer. $\alpha$-interferons are commonly used as biological response modifiers in cancer treatment because they help activate the immune system to destroy tumor cells.

(A) The correct answer is $A$.
Leydig's cells,also known as interstitial cells,are located in the interstitial spaces outside the seminiferous tubules.
These cells synthesize and secrete testicular hormones called androgens,primarily testosterone,under the influence of Luteinizing Hormone $(LH)$.

(B) Sertoli cells (also known as nurse cells) are specialized cells found within the seminiferous tubules of the testes. Their primary function is to provide structural and metabolic support,as well as nourishment,to the developing germ cells (spermatogonia) during the process of spermatogenesis.

(C) Oxytocin is a peptide hormone produced by the hypothalamus and released by the posterior pituitary gland.
It plays a critical role in the process of parturition (childbirth) by stimulating powerful contractions of the smooth muscles of the uterus.
These contractions help in the expulsion of the fetus from the birth canal.
Therefore,the correct option is $C$.

(A) The correct pair is $Cyclosporin-A$ - an immunosuppressive agent.
$Cyclosporin-A$ is produced by the fungus $Trichoderma$ $polysporum$ and is used as an immunosuppressive agent in organ transplant patients.
$Aspergillus$ $niger$ produces citric acid,not acetic acid.
$Clostridium$ $butyricum$ produces butyric acid,not citric acid.
$Streptococcus$ is used for clot busters (streptokinase),whereas statins are produced by $Monascus$ $purpureus$.

(A) Baculoviruses are pathogens that attack insects and other arthropods. The majority of baculoviruses used as biological control agents are in the genus $Nucleopolyhedrovirus$. These viruses are excellent candidates for species-specific,narrow-spectrum insecticidal applications. They have been shown to have no negative impacts on plants,mammals,birds,fish,or even non-target insects,making them ideal for integrated pest management $(IPM)$ programs.

(C) Bottled fruit juices are clearer than homemade juices because they are treated with enzymes like $Pectinase$ and $Proteases$. These enzymes break down the pectin and proteins present in the fruit pulp,which helps in clarifying the juice and removing turbidity.

(C) Flocs are masses of bacteria associated with fungal filaments to form mesh-like structures.
These structures are known as flocs.
They are formed during the secondary treatment of sewage,where aerobic microbes consume the organic matter in the effluent.
Therefore,flocs consist of fungi mycelium and microbes.

(C) The correct answer is $C$.
Mycorrhiza is a symbiotic association between a fungus and the roots of higher plants.
Many members of the genus $Glomus$ form mycorrhiza.
The fungal symbiont in these associations absorbs phosphorus from the soil and passes it to the plant.

(A) In the genetic code,there are $64$ codons,out of which $3$ codons do not code for any amino acid. These are known as stop codons or termination signals because they signal the end of the protein synthesis process. These three codons are $UAA$,$UAG$,and $UGA$.

(B) The process of protein synthesis involves two main steps: transcription and translation.
$1$. During transcription,the template strand of $DNA$ $(ACG)$ is transcribed into $mRNA$. According to the base-pairing rules ($A$ pairs with $U$,$T$ pairs with $A$,$C$ pairs with $G$,and $G$ pairs with $C$),the $mRNA$ codon will be $UGC$.
$2$. During translation,the $tRNA$ carries an anticodon that is complementary to the $mRNA$ codon.
$3$. Since the $mRNA$ codon is $UGC$,the complementary anticodon on the $tRNA$ will be $ACG$ ($U$ pairs with $A$,$G$ pairs with $C$,and $C$ pairs with $G$).
Therefore,the correct option is $B$.

(D) According to Chargaff's rule,in a double-stranded $DNA$ molecule,the amount of Adenine $(A)$ equals the amount of Thymine $(T)$,and the amount of Guanine $(G)$ equals the amount of Cytosine $(C)$.
Given: Total base pairs = $50$,so total nitrogen bases = $100$.
Number of Thymine $(T)$ = $20$.
Therefore,number of Adenine $(A)$ = $20$.
Number of $A-T$ pairs = $20$.
Number of $G-C$ pairs = Total base pairs - $A-T$ pairs = $50 - 20 = 30$.
Hydrogen bonds between $A$ and $T$ = $2 \times 20 = 40$.
Hydrogen bonds between $G$ and $C$ = $3 \times 30 = 90$.
Total hydrogen bonds = $40 + 90 = 130$.

(B) The process of identifying all the genes in a genome and determining their functions,including both coding and non-coding sequences,is known as $Sequence \ Annotation$. This is a crucial step in the Human Genome Project to understand the biological significance of the sequenced $DNA$.

(C) Sexual deceit is a specialized pollination strategy where a plant mimics the female of a specific insect species to attract the male of that species for pollination.
In the case of the Mediterranean orchid $(Ophrys)$,one petal of the flower bears an uncanny resemblance to the female of the bee species in size,color,and markings.
The male bee perceives the flower as a female and attempts to copulate with it,a process known as pseudocopulation.
During this attempt,pollen grains are dusted onto the bee's body,which are then transferred to another flower when the bee visits it,thus ensuring pollination.

(D) Parasitism is a type of population interaction where one organism,known as the parasite,derives nutrition and shelter from another organism,known as the host. In this interaction,the parasite is benefited $(+)$ while the host is harmed $(-)$. Therefore,it is a $(+, -)$ interaction.

(C) The correct answer is $C$.
Some organisms,such as bamboo,reproduce only once in their lifetime.
Bamboo species are known for their unique life history strategy where they grow vegetatively for many years (often $50-100$ years) and then flower and produce seeds only once before dying (monocarpic).

(A) Thalassemia is an autosomal recessive blood disorder.
$\alpha$-thalassemia is caused by mutations in the genes $HBA1$ and $HBA2$,which are located on chromosome $16$.
$\beta$-thalassemia is caused by mutations in the $HBB$ gene,which is located on chromosome $11$.
Therefore,the genes associated with $\alpha$-thalassemia and $\beta$-thalassemia are located on the $16^{\text{th}}$ and $11^{\text{th}}$ chromosomes,respectively.

(B) Mendelian disorders are primarily determined by alteration or mutation in a single gene.
$A$,$C$,and $D$ are chromosomal disorders caused by an excess,absence,or abnormal arrangement of chromosomes.
$B$ (Cystic fibrosis) is an autosomal recessive Mendelian disorder caused by a mutation in the $CFTR$ gene.
Therefore,the correct option is $B$.

(C) The $Law$ $of$ $Dominance$ states that in a heterozygous condition, only one allele (the dominant one) expresses its phenotype in the $F_1$ generation, masking the other (recessive) allele. However, during gamete formation, these alleles segregate, allowing the recessive trait to reappear in the $F_2$ generation when the recessive alleles pair up again. Thus, the appearance of only one trait in $F_1$ and both traits in $F_2$ is explained by the $Law$ $of$ $Dominance$.

(A) In bees,the process where an unfertilized egg develops into a new individual is called Parthenogenesis. In this system,the queen bee produces eggs by meiosis,and if an egg remains unfertilized,it develops into a male (drone) by parthenogenesis. This is a form of asexual reproduction occurring within a sexual species.

(A) In human blood group inheritance,the $ABO$ blood group system is controlled by the gene $I$. The gene $I$ has three alleles: $I^A$,$I^B$,and $i$.
When the father contributes the $I^B$ allele and the mother contributes the $I^A$ allele,the resulting genotype of the offspring is $I^A I^B$.
According to the principle of codominance,both $I^A$ and $I^B$ alleles are expressed equally in the presence of each other.
Therefore,the individual with the genotype $I^A I^B$ will have blood group $AB$.

(D) The Medical Termination of Pregnancy $(MTP)$ Act,$1971$,was enacted by the Government of India to reduce illegal abortions and maternal mortality.
$MTP$ is permitted in cases of contraceptive failure,rape,or when the pregnancy poses a risk to the life of the mother or the child.
However,the use of $MTP$ for sex-selective abortion (i.e.,if the embryo is female) is illegal and strictly prohibited under the Pre-Conception and Pre-Natal Diagnostic Techniques $(PCPNDT)$ Act,$1994$.

(A) $GIFT$ (Gamete Intra Fallopian Transfer) is the technique where an ovum collected from a donor is transferred into the fallopian tube of another female who cannot produce one,but can provide a suitable environment for fertilization and further development. Note: The original question mentioned 'testis',which is biologically incorrect for this procedure; it has been corrected to 'ovum'.

(D) The term $Test$ $Tube$ $Baby$ refers to the process of $In$ $Vitro$ $Fertilization$ $(IVF)$,where fertilization occurs outside the body in a laboratory setting.
After fertilization,the resulting zygote or early embryo (up to $8$ blastomeres) is transferred into the fallopian tube,a procedure known as $Zygote$ $Intra$ $Fallopian$ $Transfer$ $(ZIFT)$.
$GIFT$ ($Gamete$ $Intra$ $Fallopian$ $Transfer$) involves transferring gametes,not embryos,and is used when fertilization cannot occur in vivo.
$IUI$ ($Intra$ $Uterine$ $Insemination$) is a technique where sperm is placed directly into the uterus.
$ICSI$ ($Intra$ $Cytoplasmic$ $Sperm$ $Injection$) is a specialized procedure to form an embryo in the laboratory.
Therefore,$ZIFT$ is the specific method used to transfer the embryo formed via $IVF$ into the fallopian tube.

(A) Chlamydia,trichomoniasis,and syphilis are all examples of Sexually Transmitted Infections ($STI$s).
$STI$s are diseases or infections which are transmitted through sexual intercourse with an infected person.
$MTP$ stands for Medical Termination of Pregnancy,which is a procedure,not a disease.
$IUI$ stands for Intrauterine Insemination,which is an assisted reproductive technology.
Therefore,the correct option is $A$.

(A) Lactational amenorrhea refers to the natural absence of menstruation that occurs during the period of intense lactation following childbirth.
During this phase,high levels of prolactin inhibit the release of gonadotropin-releasing hormone $(GnRH)$ from the hypothalamus,which in turn prevents the secretion of follicle-stimulating hormone $(FSH)$ and luteinizing hormone $(LH)$.
As a result,ovulation does not occur,and the menstrual cycle is temporarily suspended.
This method is used as a natural contraceptive,effective for up to $6$ months postpartum.