• In transcription, the sequence of the coding strand determines the mRNA sequence. Uracil (U) replaces thymine (T).
• Given coding strand: 5’–ATGAATG–3’
• mRNA transcript: 5’–AUGAAUG–3’

• Each nucleosome contains approximately 200 base pairs of DNA.
• For 20 nucleosomes: 20 × 200 = 4000 base pairs.

• Trisomy of chromosome 21 causes Down syndrome.
• Common features include furrowed tongue (i) and characteristic palm crease (ii).
• Other physical and developmental traits may vary among individuals.

• Saltation refers to a sudden, large-scale mutation causing significant evolutionary changes.
• It leads to speciation, bypassing the gradual evolutionary process.

• The diagram shows Intracytoplasmic Sperm Injection (ICSI).
• A single sperm is injected into the egg’s cytoplasm using a fine needle.
• This technique is used in cases of male infertility or low sperm motility.

• ‘i’ gene: Produces the repressor protein (iii).
• ‘z’ gene: Produces β-galactosidase (i), which breaks down lactose.
• ‘a’ gene: Produces transacetylase (iv).
• ‘y’ gene: Produces lac permease (ii), which facilitates lactose entry into the cell.

• Fungal cells have a cell wall composed of chitin.
• Chitinase is an enzyme that breaks down chitin, enabling the release of DNA and other macromolecules.

• Flocs are aggregates of bacteria and fungal filaments formed during the secondary treatment of sewage.
• They play a crucial role in breaking down organic matter, thereby reducing the Biochemical Oxygen Demand (BOD) in wastewater.

• Humus is an amorphous, colloidal, and dark-coloured substance formed during the final stages of detritus decomposition.
• It has high resistance to microbial action and plays a significant role in soil fertility by improving its water and nutrient retention capacity.
• Light-coloured humus is not a characteristic feature.

• Interferons are proteins produced by virus-infected cells as part of the innate immune response.
• They inhibit viral replication and activate immune cells such as macrophages and natural killer cells.
• Interferons also signal neighboring cells to enhance their antiviral defense mechanisms.

• In the fertilised embryo sac:
  • A represents degenerating synergids, which are no longer needed post-fertilization.
  • B is the zygote, formed by the fusion of male and female gametes.
  • C is the Primary Endosperm Nucleus (PEN), which divides to form the endosperm, a nutritive tissue.
  • D shows degenerating antipodal cells that have no role after fertilization.

• The disorder is autosomal recessive based on:
  • The trait skips generations, as unaffected parents can pass the recessive allele to offspring.
  • Both males and females are equally affected, indicating autosomal inheritance.
  • The condition appears only in individuals inheriting two recessive alleles, one from each parent.

• Communities with higher species diversity are more stable due to greater ecological balance and resource utilization efficiency.
• Reason (R) explains Assertion (A) as higher diversity reduces biomass variation, providing stability against environmental changes.

• DNA strands are anti-parallel, meaning one strand runs in a 5’ to 3’ direction while the complementary strand runs in a 3’ to 5’ direction.
• Reason (R) explains this anti-parallel arrangement, as the phosphor-diester bonds in the strands have opposite orientations.

• A probe is a labeled DNA or RNA strand used in molecular diagnosis to identify specific sequences.
• It hybridizes with its complementary DNA, confirming the explanation of Assertion (A) by Reason (R).

• Assertion (A) is true as AIDS (Acquired Immunodeficiency Syndrome) is caused by HIV (Human Immunodeficiency Virus).
• Reason (R) is false because AIDS is not genetic material; it is a condition caused by HIV, which contains RNA as its genetic material.

Correct Answer:
• X: Slurry tank, which stores organic waste mixed with water.
• Y: Gas outlet, releasing methane-rich biogas.
• Z: Digester, where anaerobic bacteria decompose organic material to produce biogas and nutrient-rich slurry.

• Explanation: The digester is the central component of a biogas plant, enabling biogas production and recycling of organic waste into agricultural manure.

Correct Answer:
Dung is rich in organic matter and cellulose, which are ideal for methanogenic bacteria. It is affordable, abundant, and sustainable, producing renewable energy and nutrient-rich slurry for agriculture.

• Explanation: Dung not only serves as a raw material for biogas but also minimizes methane emissions, contributing to sustainable waste management and climate change mitigation.

Correct Answer:
• Adenine pairs with thymine, so A + T = 31% + 31% = 62%.
• Cytosine pairs with guanine, and C + G = 100% - (A + T) = 38%.
• Therefore, cytosine is 19%.

• Explanation: DNA follows Chargaff’s rule, where A pairs with T and C pairs with G in equal proportions. This complementary base-pairing ensures the sum of bases equals 100%.

Correct Answer:
• Apomictic seeds are genetically identical to the parent plant, ensuring trait stability.
• They eliminate the need for farmers to purchase new seeds annually, reducing costs.

• Explanation: Apomictic seeds guarantee uniformity and preservation of desirable traits across generations without the variability seen in hybrid seeds.

Correct Answer:
• Advantage: Early detection of genetic or chromosomal disorders during pregnancy.
• Disadvantage: Misuse for sex determination increases the risk of female feticide, raising ethical concerns.

• Explanation: While amniocentesis is a valuable diagnostic tool, it must be regulated to prevent unethical practices such as gender-biased abortions.

Correct Answer:
• Growth curve ‘A’ (Exponential growth): Occurs under ideal conditions with unlimited resources.
• Growth curve ‘B’ (Logistic growth): Occurs when resources are limited, and environmental resistance impacts growth.

• Explanation: Exponential growth represents idealized scenarios, while logistic growth accounts for real-world resource constraints and carrying capacity.

Correct Answer:
‘K’ represents the carrying capacity of the environment, the maximum population size that available resources can sustain.

• Explanation: Carrying capacity depends on factors like food, habitat space, and environmental conditions, which limit population growth.

Correct Answer:
• Adenine (A) pairs with Thymine (T), so A + T = 31% + 31% = 62%.
• Cytosine (C) pairs with Guanine (G), and C + G = 100% - (A + T) = 38%.
• Cytosine is therefore 19%.

• Explanation: DNA follows Chargaff’s rule, ensuring A pairs with T and C pairs with G in a 1:1 ratio. This complementary base-pairing maintains the double-helix structure.

Correct Answer:
• Grazing food chain: Starts with living producers like plants, transferring energy to herbivores and carnivores.
• Detritus food chain: Begins with decomposed organic matter, transferring energy to detritivores (e.g., earthworms) and decomposers (e.g., fungi).

• Explanation: The grazing food chain depends on photosynthesis, while the detritus food chain utilizes organic waste for energy transfer and nutrient recycling.

Correct Answer:
Dead plants and organic detritus are decomposed by microorganisms, releasing nutrients absorbed by plants (producers in the grazing food chain). Organisms like earthworms feed on detritus and are eaten by higher trophic-level organisms, linking the two chains.

• Explanation: The connection between the detritus and grazing food chains ensures efficient energy flow and nutrient recycling within ecosystems.

Correct Answer:
• Endosperm: 30 chromosomes (3n, triploid).
• Zygote: 20 chromosomes (2n, diploid).

• Explanation: Double fertilization in angiosperms ensures simultaneous embryo and endosperm formation:
  • One sperm nucleus fertilizes the egg cell, forming the diploid zygote.
  • Another sperm nucleus fuses with two polar nuclei, forming the triploid endosperm, which provides nutrients to the developing embryo.

Correct Answer:
• Competency is necessary to enable cells to take up foreign DNA during transformation.
• Calcium ions neutralize the negative charges of DNA and the cell membrane, reducing repulsion and facilitating DNA entry into the cell.

• Explanation: Competent cells are critical for successful genetic engineering, allowing the introduction of recombinant DNA for cloning and gene expression studies.

Correct Answer:
• The biolistic gun delivers DNA into plant cells by bombarding them with high-velocity microprojectiles coated with DNA.
• This tool is widely used in genetic engineering to create transgenic plants, particularly in species with thick cell walls.

• Explanation: The biolistic gun is a vital tool in agricultural and biotechnological research for gene transfer, crop improvement, and transgenic studies.

Correct Answer:
• DNA polymerase synthesizes DNA in the 5’ to 3’ direction.
• At the replication fork:

• The leading strand is synthesized continuously in the direction of fork movement.
• The lagging strand is synthesized discontinuously using Okazaki fragments, which are later joined by DNA ligase.

• Explanation: Replication forks optimize accuracy and efficiency, ensuring proper sequence matching and error correction.

Correct Answer:•Leading strand:
Synthesized continuously in the 5’ to 3’ direction.
•Lagging strand:
Synthesized discontinuously in Okazaki fragments, later joined by DNA ligase.

• Explanation: The antiparallel nature of DNA and the unidirectional activity of DNA polymerase result in this semi-discontinuous mechanism.
  

Correct Answer:

• Explanation: These modes of gene expression highlight variations in inheritance patterns, demonstrating the diversity of phenotypic traits in organisms.

Correct Answer:

• Explanation: These factors collectively make tropical regions biodiversity hotspots, supporting the greatest variety of species on Earth.

Correct Answer:

• Explanation: Energy pyramids are always upright, while biomass and number pyramids vary based on ecosystem type, providing insights into energy flow and ecosystem structure.

Correct Answer:

• Explanation: The shape of the ecological pyramid depends on the ecosystem’s structure and the flow of energy or biomass.

• Explanation: These microorganisms and their bioactive molecules are significant in medicine, agriculture, and industry, contributing to human welfare and sustainable development.

Correct Answer:
• (1) Sporozoite – The infective stage that enters the human body.
• (2) Gametocytes – The stage that enters the mosquito during a blood meal.

• Explanation: The sporozoite stage infects humans, while gametocytes ensure parasite transmission to mosquitoes.

Correct Answer:
• The sporozoites take time to multiply in liver cells and then infect red blood cells, leading to symptoms.
• Symptoms like fever, chills, and sweating appear after the parasites rupture red blood cells.

• Explanation: The incubation period allows the parasites to develop within the liver before causing symptoms.

Correct Answer:
• Gametocytes of Plasmodium enter the mosquito’s gut with the blood meal.
• In the gut, gametocytes develop into gametes, fuse to form zygotes, and subsequently develop into sporozoites.
• Sporozoites migrate to the mosquito’s salivary glands, preparing it to infect another host.

• Explanation: Plasmodium undergoes sexual reproduction inside the mosquito to complete its life cycle.

Correct Answer:
• Mosquito: Aedes aegypti.
• Disease: Dengue or Zika virus.

• Explanation: Aedes aegypti is a vector for several diseases, including Dengue, Zika, and Chikungunya.

Correct Answer:
• Hormones: Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH).
• Source organ: Pituitary gland.

• Explanation: FSH and LH regulate ovarian follicle development and ovulation during the menstrual cycle.

Correct Answer:
• Phase: Luteal phase (Day 15–28).
• Reason: During this phase, the endometrium is thick and rich in blood supply, making it ideal for implantation and embryo nourishment.

• Explanation: The luteal phase ensures optimal uterine conditions for embryo implantation due to high progesterone levels.

Correct Answer:
• Hormone: Estrogen.
• Source organ: Ovaries (developing follicles).
• Event: Estrogen repairs and thickens the uterine lining, preparing it for potential implantation.

• Explanation: Estrogen is essential for regenerating the uterine lining during the proliferative phase of the menstrual cycle.

Correct Answer:
• If the ovum is not fertilised, the corpus luteum degenerates, leading to a drop in progesterone levels.
• This hormonal change causes the breakdown and shedding of the uterine lining as menstrual blood.

• Explanation: Menstruation is triggered by the absence of fertilisation, causing hormonal changes that lead to the shedding of the uterine lining.

Correct Answer:
• The graph depicts Directional Selection, which occurs when one extreme phenotype is favored over others due to environmental pressures.

• Explanation: Directional selection shifts population traits toward one extreme, favoring individuals with advantageous traits, as seen during industrial melanism in moths.

Correct Answer:
• Pre-industrialization: White-winged moths blended with light-colored tree barks, avoiding predation.
• Post-industrialization: Pollution darkened tree barks, making white moths visible and vulnerable, while dark-winged moths became camouflaged and had higher survival rates.

• Explanation: This phenomenon, called Industrial Melanism, is a classic example of directional selection caused by environmental changes.

Correct Answer:
• Human activities create strong selective pressures that accelerate evolution, such as:
• Antibiotic resistance: Overuse of antibiotics leads to the survival of resistant bacterial strains.
• Pesticide resistance: Pests evolve resistance to pesticides.
• Industrial melanism: Pollution favored darker phenotypes in species like the peppered moth.

• Explanation: Anthropogenic actions drive evolution by altering environmental pressures, emphasizing the need for sustainable practices.

Correct Answer:

• Explanation: Sertoli cells provide structural and nutritional support, ensuring sperm maturation over 64–74 days in humans.

Correct Answer:

• Explanation: Hormonal coordination is crucial for initiating and maintaining spermatogenesis.

Correct Answer:
The diploid megaspore mother cell undergoes meiosis to form four haploid megaspores, of which only one survives. The surviving megaspore undergoes three mitotic divisions, forming an eight-nucleate, seven-celled embryo sac.

• Explanation: The mature embryo sac includes three antipodal cells, two synergids, one egg cell, and a central cell with two polar nuclei.

Correct Answer:

• Explanation: Geitonogamy is functionally cross-pollination but involves the same genotype, unlike xenogamy.

Correct Answer:
Cleistogamous flowers are invariably autogamous. These flowers do not open, ensuring self-pollination and reproductive success under unfavorable conditions.

• Explanation: Cleistogamy guarantees seed production even in the absence of pollinators.

Correct Answer:
The diagram of pBR322 includes the following features:
•BamHI site:
Restriction site for inserting foreign DNA.
•Ampicillin resistance gene:
Enables selection of transformed cells.
•Ori:
Origin of replication ensures plasmid duplication in host cells.
•Rop gene:
Regulates plasmid copy number.

• Explanation: pBR322 is a widely used vector for molecular cloning due to its efficiency and multiple selection markers.

Correct Answer:
The rop gene regulates plasmid replication, maintaining a low copy number and preventing stress on host cells.

• Explanation: By modulating plasmid replication, the rop gene ensures stability and successful cloning experiments.

Correct Answer:

• Non-recombinant cells may outgrow recombinant ones, complicating identification.
• Alternative methods like PCR or sequencing are required, increasing cost and time.

• Explanation: Selectable markers simplify identification by allowing only transformed cells to grow under specific conditions, such as antibiotic resistance.

Correct Answer:
Insertional inactivation involves disrupting a functional gene by inserting foreign DNA, providing a visual distinction between recombinant and non-recombinant colonies.

• Advantages:
  • Biosafety: Avoids the use of antibiotic resistance genes, reducing environmental risks.
  • Simple identification: Recombinant colonies are visually identifiable (e.g., loss of color in the disrupted gene).
  • Cost-effective: Reduces the need for antibiotics and additional screening.
• Explanation: Insertional inactivation is a safe and efficient method for identifying recombinant DNA in host cells.

Correct Answer:
• Nematode: Meloidogyne incognita (root-knot nematode).

• Explanation: This nematode infects tobacco plant roots, causing galls that disrupt nutrient and water absorption, leading to stunted growth and reduced yield.

Correct Answer:
• Vector: Agrobacterium tumefaciens

• Explanation: Agrobacterium tumefaciens contains a modified Ti plasmid, used to transfer nematode-specific genes into tobacco plants. This process triggers RNA interference (RNAi), silencing critical nematode genes and preventing infestation.

Correct Answer:

• Explanation: This mechanism, called RNA interference (RNAi), silences specific genes and is widely used to control pests and pathogens in transgenic plants.

Correct Answer:
• Transgenic tobacco plants produce double-stranded RNA (dsRNA) that targets essential genes in nematodes.
• RNA interference (RNAi) silences critical genes, preventing the parasite from surviving or reproducing.

• Explanation: RNAi technology provides an eco-friendly and specific approach to pest control, protecting crops without harming beneficial organisms.