CBSE Class 12 Biology Question Paper 2024 (Set 3- 57/4/3) Available- Download Solution PDF with Answer Key

Solution:
• n (haploid): Present in the antipodal cells.
• 2n (diploid): Present in the zygote formed during fertilization.
• 3n (triploid): Present in the endosperm formed through double fertilization.
• This specific distribution of ploidy levels is a distinctive feature of the reproductive process in angiosperms.

Solution:
• A – Connective: Tissue that connects the two lobes of the anther.
• B – Endothecium: The outer layer of the pollen sac that provides structural support.
• C – Pollen grain: The male gametophyte developed within the pollen sac.

Solution:
• The disorder is seen in both males and females, indicating autosomal inheritance.
• It skips generations, suggesting recessive inheritance.
• The affected offspring have parents who are carriers of the recessive allele.

Solution:
• Transcription (P): The process by which mRNA is synthesized from a DNA template.
• mRNA (Q): Acts as a blueprint for the synthesis of proteins.
• Translation (R): The process in which the mRNA sequence is translated into a protein.
• The Central Dogma explains the transfer of genetic information from DNA to RNA and then to protein.

Solution: Hugo de Vries observed sudden heritable changes (mutations) while working with the evening primrose plant- Oenothera lamarckiana. His mutation theory proposed that these sudden changes serve as the basis for evolution, introducing new traits into populations.

Solution: The correct matches between the organisms and the products they produce are:
• Lactobacillus – Cheese.
• Saccharomyces cerevisiae – Curd.
• Aspergillus niger – Citric acid.
• Acetobacter aceti – Acetic acid.

Solution: The contraceptives and their corresponding modes of action are:
• A. The pill – III. Inhibits ovulation.
• B. Condom – I. Prevents sperm from reaching the cervix.
• C. Vasectomy – IV. Semen contains no sperm.
• D. Copper-T – III. Prevents implantation.

Solution:
• Ovum (A): The egg cell that has not been fertilized.
• Morula (E): A solid cluster of cells formed after several rounds of mitotic division.
• Blastocyst (G): A hollow structure formed during early embryonic development that attaches to the uterine wall.

Solution: BAC (Bacterial Artificial Chromosome) and YAC (Yeast Artificial Chromosome) were used as vectors in the Human Genome Project due to their capacity to clone large fragments of DNA efficiently.

Solution: Turner's syndrome is caused by the absence of one X chromosome, resulting in a 45, XO chromosomal pattern. This is a type of aneuploidy, which refers to the presence of an abnormal number of chromosomes.

Solution: ELISA (Enzyme-Linked Immunosorbent Assay) detects and quantifies antigens or antibodies using the principle of antigen-antibody interaction. This method is widely used for diagnostic purposes in medical and research fields.

Solution: Restriction enzymes, also known as molecular scissors, cut DNA at specific sequences called recognition sites. These enzymes are essential tools in genetic engineering and molecular biology.

Solution: Plasmids are autonomously replicating circular DNA molecules found in prokaryotic cells, not eukaryotic cells. These plasmids are widely used as vectors in genetic engineering.

Solution: The mutualistic relationship between figs and fig wasps involves the wasp pollinating the fig flowers while depositing eggs. This ensures species-specific pollination.

Solution: Inverted biomass pyramids comes under in aquatic ecosystems because the biomass of primary producers (phytoplankton) is smaller but reproduces rapidly, supporting higher trophic levels. The reason provided is true, but it is not the correct explanation for inverted biomass pyramids. Energy typically decreases with increasing trophic levels, but rapid reproduction of primary producers compensates for their low biomass.

Solution: Patents are legal rights granted to inventors to protect their innovations, preventing unauthorized commercial use by others. The reason correctly explains the assertion.

Solution: Rosie was the first transgenic cow developed in 1997. It produced milk enriched with human protein (alpha-lactalbumin), making it more nutritionally suitable for infants.

Solution: Rosie's milk was enriched with human alpha-lactalbumin, making it nutritionally superior. This milk provided essential proteins required for infant growth and development.

Solution: The graph shows:
• In woman 'X,' the uterine wall continues to thicken after ovulation, indicating successful implantation and pregnancy.
• In woman 'Y,' the uterine wall thickness reduces after ovulation, indicating no fertilization, leading to menstruation.

Solution: Step 1: HIV Transmission.
HIV can be transmitted through sexual contact with an infected person, particularly if there is exposure to infected bodily fluids like semen or blood. Sharing needles used for drug injection can also transmit HIV.
Step 2: Hepatitis-B Transmission.
Hepatitis-B can be transmitted in similar ways, including through unprotected sex with an infected person or through contact with contaminated blood, such as sharing needles.

Solution:
• HIV and Hepatitis-B can spread through unprotected sexual contact, blood transfusion, or contaminated syringes.
• Early detection helps in timely management, reduces transmission risk, and improves patient outcomes.

Solution:
• Biodiversity hotspots are regions with a high level of species richness and endemic species under threat due to human activities.
• Protection efforts such as habitat restoration, creating reserves, and sustainable practices help in preserving these species.

Solution:
• Western Ghats.
• Indo-Burma region.

Solution:
• Grazing food chain: Begins with producers consumed by herbivores. (e.g., Grass → Deer → Lion)
• Detritus food chain: Begins with decomposers breaking down organic matter. (e.g., Dead leaves → Fungi → Earthworm)

Solution:
• Brood parasitism: A reproductive strategy where one species lays eggs in the nest of another species.
• Example: Cuckoo lays eggs in crow nests; cuckoo chicks outcompete crow chicks for food.

Solution: The diagram of the 'E.coli' vector pBR322 should include:

Solution:
• A nematode-specific gene is introduced into the tobacco plant using Agrobacterium tumefaciens.
• The plant produces double-stranded RNA (dsRNA), initiating RNA interference (RNAi).
• RNAi silences the vital genes of Meloidogyne incognita, reducing infestation and damage.

Solution:
• Flocs: These are masses of aerobic bacteria and fungi that degrade organic matter, reducing BOD (Biochemical Oxygen Demand) in sewage water.

Solution:
• Anaerobic sludge digester: It processes the settled sludge from the primary treatment under anaerobic conditions, producing biogas (methane, carbon dioxide) as a by-product.

Solution:
• Skull A: Homo sapiens.
• Skull B: Neanderthals.
• Skull C: Australopithecus.
• Skulls A and B (Homo sapiens and Neanderthals) are more similar to each other.

Solution:
• (i) Ape-like: Australopithecus.
• (ii) Man-like: Homo erectus.

Solution: -Steroids are the drugs whose skeletal molecule is given. -They are characterized by a four-ring carbon structure. -Steroids can be classified into anabolic steroids, which promote muscle growth, and corticosteroids, which are used to treat inflammation and immune disorders.

Solution: -These drugs are consumed orally, injected, or applied topically.
-They can have various therapeutic uses, such as treating inflammation, hormone imbalances, and autoimmune diseases.
-However, prolonged or excessive use can lead to side effects, including liver damage, hormonal imbalances, and increased risk of cardiovascular diseases.

Solution: Liver is affected by the consumption of steroids. Prolonged use of steroids can lead to liver toxicity, causing conditions like jaundice, liver damage, and in severe cases, liver failure. Steroids can also increase the risk of developing liver tumors or cysts due to their impact on liver function and metabolism.

Solution:
• Antibodies are Y-shaped molecules produced by B-lymphocytes.
• Chemical Nature: Proteins made of light and heavy polypeptide chains.

Solution: The first generation (F1) produced only purple-flowered plants because purple is dominant. In the second generation (F2), the ratio of purple to white flowers is approximately 3:1.
P : PP(purple) × pp(white) F1: All Pp (purple)
F2 generation cross:
Pp × Pp gives: PP, Pp, Pp, pp.
Phenotypic ratio: 3 (purple):1 (white).

Correct Answer: The diagram should include:

Solution: mRNA is transcribed from DNA and carries the genetic information for protein synthesis. RNA polymerase II is responsible for transcribing protein-coding genes in eukaryotes. This process is called transcription.

Solution:
• Process: Splicing.
• Explanation: During splicing, non-coding regions (introns) are removed from the pre-mRNA, leaving only coding regions (exons) to form mature mRNA. This ensures the correct sequence for translating into a 400 amino acid polypeptide.

Solution: - Prokaryotes rely on a single RNA polymerase for synthesizing all types of RNA (mRNA, tRNA, and rRNA).
- Eukaryotes have specialized RNA polymerases:
- RNA polymerase I synthesizes rRNA.
- RNA polymerase II synthesizes mRNA.
- RNA polymerase III synthesizes tRNA and some small RNAs.

Solution: - Prokaryotes lack a defined nucleus, so transcription occurs directly in the cytoplasm where translation can occur simultaneously.
- Eukaryotes have a defined nucleus where transcription occurs, separating it from translation which happens in the cytoplasm.

Solution: Exponential growth occurs under unlimited resources, showing a J-shaped curve. Logistic growth accounts for environmental constraints and levels off at the carrying capacity (K), forming an S-shaped curve.

Solution:
• The dotted line represents the carrying capacity (K).
• Importance: Carrying capacity is the maximum population size that an environment can sustain indefinitely. It is determined by resource availability and environmental factors.

Solution:
• Curve (logistic growth) differs from curve (exponential growth) because it incorporates the concept of limited resources and environmental resistance.
• Logistic growth considers population stabilization when reaching the carrying capacity, making it more realistic.

Solution:
• Curve (logistic growth) is more realistic because populations are subject to resource limitations, predation, and environmental constraints.
• Curve (exponential growth) assumes unlimited resources, which is rarely the case in natural ecosystems.

Solution:
• The exponential growth curve (Curve 2018-2019) is more relevant because the human population continues to grow at a rapid rate, often exceeding the carrying capacity temporarily.
• However, environmental resistance like resource depletion and climate change will eventually necessitate stabilization, transitioning to a logistic growth model.

Solution:
• Polarity: 5' to 3' direction.
• Number of additional amino acids: Depends on the number of codons left untranslated on the mRNA.
• Reason: Each codon corresponds to one amino acid, and translation stops when a stop codon is encountered.

Solution:
• Initiating codon: AUG.
• Anticodon: UAC.
• Amino acid: Methionine.

Solution:
• Charging of tRNA: Aminoacyl-tRNA synthetase attaches a specific amino acid to its corresponding tRNA, forming aminoacyl-tRNA.
• Importance: Charged tRNA ensures accurate addition of amino acids to the growing polypeptide chain during translation.

Solution:
• The disorder causes red blood cells to assume a sickle shape under low oxygen conditions, leading to its name.

Solution:
• It is caused by a point mutation in the -globin gene, where glutamic acid is replaced by valine at the sixth position of the haemoglobin protein.
• The mutated haemoglobin (HbS) polymerizes under low oxygen conditions, leading to cell deformation.

Solution:
• When both parents are carriers (HbA HbS), the offspring have a 25% chance of inheriting two sickle-cell alleles (HbS HbS), causing the disorder.

Solution:
• Entry: HIV enters host cells (CD4+ T-cells) via surface receptors.
• Reverse transcription: Viral RNA is converted into DNA by reverse transcriptase.
• Integration: Viral DNA integrates into the host genome via integrase enzyme.
• Replication: Host machinery synthesizes viral components.
• Assembly and release: New viral particles are assembled and released, infecting other cells.
• Progression to AIDS: Gradual destruction of CD4+ cells leads to weakened immunity and opportunistic infections, culminating in AIDS.

Solution:
• Symptoms:
- High fever with chills.
- Sweating and headache.
- Nausea and vomiting.
• Cause: The symptoms are caused by the rupture of red blood cells during the release of merozoites and the immune response to parasitic toxins.

Solution:
• Gametocytes: Male and female gametocytes are ingested by a mosquito during a blood meal.
• Fertilization: Gametocytes fuse in the mosquito's gut to form a zygote.
• Development: The zygote develops into an ookinete, which penetrates the gut wall and forms an oocyst.
• Sporozoites: The oocyst releases sporozoites that migrate to the mosquito's salivary glands, ready to infect a new host.

Solution: Artificial hybridization is used in plant breeding to combine the best traits from different plant varieties, improving crop quality and yield. To obtain desired traits such as disease resistance, higher yield, or improved quality in plants by crossing two genetically different plants.

Solution: The steps in artificial hybridisation are:
• Emasculation: Removal of stamens from the bisexual flowers of the female parent to prevent self-pollination.
• Bagging: Covering the emasculated flower with a bag to prevent contamination from unwanted pollen.
• Pollination: Dusting pollen from the male parent onto the stigma of the female parent.
• Re-bagging: Re-covering the flower to ensure fertilization occurs without external interference.

Solution: -The placenta develops from the chorionic villi of the embryo and the uterine tissue of the mother. It establishes a structural and functional connection between the fetus and the mother.
-The placenta facilitates the exchange of nutrients, gases, and waste products between the maternal and fetal blood.
-It also produces hormones like human chorionic gonadotropin (hCG), progesterone, and estrogen to support pregnancy.

Solution: The placenta performs the following functions:
• Facilitates exchange of nutrients, gases, and waste products between the mother and fetus.
• Produces hormones such as hCG, progesterone, and estrogens to maintain pregnancy.
• Acts as a barrier to certain harmful substances while allowing essential nutrients to pass through.