CBSE Class 12 Biology Question Paper 2024 (Set 1- 57/4/1) Available- Download Solution PDF with Answer Key

Solution:
• In a fertilized ovule of an angiosperm:
- n (haploid): Present in the antipodal cells.
- 2n (diploid): Present in the zygote formed through fertilization.
- 3n (triploid): Present in the endosperm formed via double fertilization.
• This pattern of ploidy levels is a defining feature of the angiosperm reproductive process.

Solution:
• Ovum: The egg cell that has not been fertilized (A), as depicted in the diagram.
• Morula: A solid mass of cells (E) formed during the early cleavage stages after fertilization.
• Blastocyst: A hollow structure (G) that develops early in mammalian development and later implants into the uterine wall.

Solution:
• A – The pill: Functions by preventing ovulation (III).
• B – Condom: Stops sperm from reaching the cervix (I).
• C – Vasectomy: Involves cutting or tying the vas deferens, leading to semen without sperm (IV).
• D – Copper-T: Prevents the fertilized egg from implanting in the uterus (II).

Solution: Examine the Pedigree Chart.
- Both males and females are affected, suggesting autosomal inheritance.
- The disorder manifests in siblings but not in the parents, which is typical of a recessive trait.
Final Answer: The genetic disorder shown is autosomal recessive.

Solution: Review the Human Genome Project-
- Chromosome 1 was the final human chromosome to be fully sequenced due to its large size and complexity. It contains the greatest number of genes and numerous repetitive sequences, making sequencing particularly difficult.
Final Answer: The last chromosome to be entirely sequenced was Chromosome 1.

Solution: Interpret the Anther Diagram-
- Connective tissue joins the two lobes of the anther.
- Endothecium forms the outer wall of the pollen sac.
- Pollen grains are present inside the pollen sac.
Final Answer: The correct identification is A – Connective, B – Endothecium, C – Pollen grain.

Solution: About Turner's Syndrome:
- Turner's syndrome is a chromosomal disorder caused by the presence of a single X chromosome (45, XO) instead of two sex chromosomes and a form of aneuploidy, which refers to the loss or gain of chromosomes.
Final Answer: Turner's syndrome is caused by aneuploidy.

Solution: The Central Dogma:
- Transcription (P): DNA to mRNA.
- mRNA (Q): Carries genetic information.
- Translation (R): mRNA to protein.
Final Answer: P – Transcription, Q – mRNA, R – Translation.

Solution: Evolutionary Theories are as follows-
Hugo de Vries proposed the mutation theory, which states that evolution occurs through sudden, heritable changes in an organism's genetic material and These mutations serve as raw material for natural selection.
Final Answer: The mutation theory was proposed by Hugo de Vries.

Solution: Match Bioactive Substances to Their Actions-
- Statin: Lowers blood cholesterol (III).
- Cyclosporin A: Acts as an immuno-suppressive agent (IV).
- Streptokinase: Removes clots from blood vessels (II).
- Lipase: Removes oil stains (I).
Final Answer: A – III, B – IV, C – II, D – І.

Solution: About Restriction Enzymes:
- Restriction enzymes, also known as molecular scissors, cut DNA at specific sequences.
- These enzymes are extensively used in genetic engineering and molecular biology.
Therefore, Restriction enzymes are referred to as molecular scissors.

Solution:
• ELISA (Enzyme-Linked Immunosorbent Assay) operates based on the principle of antigen-antibody binding to identify specific proteins or antibodies within a sample.
• The interaction between an enzyme-labeled antibody and its corresponding antigen is assessed by color change, which indicates the presence of the antigen.

Solution:
• Fig and wasp share a mutualistic relationship where each depends on the other for survival and reproduction.
• Wasps pollinate fig flowers while laying eggs, ensuring mutual benefit.

Solution:
• Plasmids are circular DNA molecules that can replicate independently.
• While they are found in prokaryotic cells, such as bacteria, they are not typically present in eukaryotic cells.
• These plasmids exist separately from chromosomal DNA in prokaryotes.
• Their ability to replicate autonomously allows for the transfer of genetic material between cells.
• Plasmids are essential tools in genetic engineering and biotechnology.

Solution:
• Patents are legal rights granted to inventors for exclusive use of their inventions.
• The purpose of patents is to prevent unauthorized commercial use and ensure the protection of intellectual property, which directly explains the reason provided.

Solution:
• Inverted biomass pyramids occur in aquatic ecosystems where the biomass of primary consumers exceeds that of producers.
• The energy transfer efficiency in trophic levels determines biomass, not the amount of energy required by higher trophic levels, which makes the reason valid but not explanatory for the assertion.

Correct Answer: Normal and lack of thickening
Solution:
• The graph shows:
- Woman 'X': Normal thickening of the uterine wall due to regular hormonal activity.
- Woman 'Y': Lack of thickening indicates a hormonal imbalance or insufficient estrogen/progesterone secretion.

Solution:
• Lactational amenorrhea prevents ovulation during intense lactation.
• Prolactin, the hormone responsible for milk production, suppresses gonadotropin release, thereby preventing the onset of ovulation.

Solution:
• To prevent misuse and ensure MTP is conducted only for genuine medical or legal reasons.
• Protects the health and rights of women.

Solution:
• Source: Pancreas of pigs and cows.
• Reason: Animal insulin caused allergic reactions in some patients due to structural differences from human insulin.

Solution:
• Human insulin is produced as proinsulin and requires processing to remove C-peptide.
• Eli Lilly produces ready-to-use recombinant insulin without requiring further processing.

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:
• Biodiversity hotspots are regions rich in endemic species but threatened by habitat loss.
• Protecting hotspots helps conserve numerous species, ensuring ecosystem stability and reducing extinction rates.

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

Answer: The diagram of a male gametophyte/microspore of an angiosperm should include:
Functions:
• Generative cell: Divides to form two male gametes.
• Tube cell: Grows into a pollen tube to facilitate fertilization.

Solution:
Punnett Square:

Solution: The ABO blood grouping is based on:
• The presence or absence of antigens (A and B) on the surface of red blood cells.
• The presence of antibodies (anti-A and anti-B) in the plasma.

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

Solution:
• (i) Australopithecus (ape-like)
• (ii) Homo erectus (man-like)

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.

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:
• Flocs: Aggregates of bacteria and fungi used in the secondary treatment to degrade organic matter in sewage.

Solution:
• Anaerobic sludge digester: Breaks down organic matter into methane, CO2, and water during the anaerobic digestion of sludge.

Solution:
• A: Denaturation of DNA at high temperatures.
• D: Amplification of DNA after 30 cycles.

Solution: Primer annealing is the process where primers bind to their complementary sequences on the single-stranded DNA template.
This occurs during the cooling phase of the PCR cycle, allowing the primers to stabilize the DNA template for the extension step.
The temperature at which primer annealing occurs is crucial for the specificity and efficiency of the PCR amplification.

Solution:
• C: Taq DNA polymerase.
• Source: Thermus aquaticus.

Solution:
• Used in Polymerase Chain Reaction (PCR) to amplify DNA for genetic testing, disease diagnosis, and forensic analysis.

Solution:
• Transgenic animals are engineered to produce important biological products like proteins and hormones.
• Example: Transgenic cows producing human lactoferrin, which has therapeutic applications.

Solution:
• Transgenic animals are used as models to study human diseases and their progression.
• Example: Transgenic mice are commonly used to study cancer, diabetes, and Alzheimer's disease.

Solution:
• Transgenic animals are used to test the safety of chemicals and drugs before they are approved for human use.
• Example: Transgenic mice are used to assess the toxicity of new pharmaceutical compounds.

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 2018B2019 (logistic growth) differs from curve 2018A2019 (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 2018A2019) 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:
• The RNA product is mRNA (messenger RNA).
• Enzyme responsible: RNA polymerase II.

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: One RNA polymerase is involved in transcription.
• Eukaryotes: Three RNA polymerases (RNA polymerase I, II, and III) are involved in transcription.

Solution:
• Prokaryotes: Transcription occurs in the cytoplasm.
• Eukaryotes: Transcription occurs in the nucleus.

Solution:
• Process: Spermatogenesis.
• Description: Spermatogenesis is the process of formation of sperm cells (spermatozoa) from the spermatogonial cells in the seminiferous tubules of the testes. It includes the following stages:
- Multiplication Phase: Mitotic division of spermatogonia to produce primary spermatocytes.
- Growth Phase: Enlargement of primary spermatocytes.
- Maturation Phase: Meiosis to produce haploid spermatids from secondary spermatocytes.
- Differentiation Phase: Spermatids transform into spermatozoa.

Solution:
• The cell is the Sertoli cell.
• Function: Sertoli cells provide nourishment and structural support to the developing sperm cells. They also secrete inhibin, which regulates spermatogenesis.

Solution:
• 'A': Chasmogamous flower.
• 'B': Cleistogamous flower.

Solution:
• Characteristic feature:
- Chasmogamous flowers: Open flowers, reproductive parts exposed.
- Cleistogamous flowers: Closed flowers, reproductive parts not exposed.
• Modes of pollination:
- Chasmogamous flowers: Cross-pollination facilitated by agents like wind, insects, or water.
- Cleistogamous flowers: Self-pollination occurs as flowers never open.

Solution:
• Out breeding devices:
- Self-incompatibility.
- Production of unisexual flowers.
• Explanation: These devices prevent self-pollination and promote cross-pollination, which enhances genetic diversity and adaptation.

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 develop in human blood and are taken up by a mosquito during a blood meal.
• Fertilization occurs in the mosquito's gut, forming a zygote.
• The zygote develops into an ookinete and then an oocyst.
• Sporozoites are released from the oocyst and migrate to the salivary glands, ready to infect another human.