Section B
[1 Marks]
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(A) pentamer
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(B) heptomer
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(C) hexamer
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(D) octamer
Explanation: The correct answer is 'octamer' because the context states that histones are organised to form a unit of eight molecules known as a histone octamer. Nucleosomes are formed when negatively charged DNA wraps around this positively charged histone octamer.
[1 Marks]
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(A) (ii), (iv) and (v)
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(B) (i), (ii) and (iv)
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(C) (ii), (iii) and (v)
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(D) (i), (iii) and (iv)
Explanation: The correct option is (i), (iii) and (iv). Statement (i) is correct because the myometrium is known for its strong contractions during childbirth. Statement (iii) is correct as the cervical canal and the vagina constitute the birth canal. Statement (iv) is correct as the outer layer of the uterus is indeed referred to as the perimetrium. Statement (ii) is incorrect since the uterus opens into the vagina via the cervix, not the other way around, and statement (v) is also incorrect as the uterus is supported by ligaments, not tendons.
[1 Marks]
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(A) Ribonucleotide triphosphate
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(B) Deoxyribonucleoside triphosphate
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(C) Ribonucleoside triphosphate
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(D) Deoxyribonucleotide triphosphate
Explanation: The correct answer is 'Ribonucleotide triphosphate' because during transcription, RNA polymerase utilizes ribonucleotide triphosphates (NTPs) as substrates to synthesize RNA, pairing them with the complementary bases in the DNA template strand. This is supported by the reference to RNA polymerase using nucleoside triphosphates as substrates while catalyzing RNA synthesis.
[1 Marks]
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(A) Turner’s syndrome
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(B) Klinefelter’s syndrome
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(C) Down’s syndrome
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(D) Phenylketonuria
Explanation: Phenylketonuria is not an example of aneuploidy as it is caused by a mutation in a single gene, rather than an abnormal number of chromosomes. In contrast, Turner’s syndrome, Klinefelter’s syndrome, and Down’s syndrome are all characterized by an abnormal number of chromosomes, classifying them as types of aneuploidy.
[1 Marks]
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(A) IgA
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(B) IgG
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(C) IgD
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(D) IgE
Explanation: The correct answer is IgA. The context mentions that the yellowish fluid colostrum secreted by the mother during the initial days of lactation has abundant antibodies, specifically IgA, which are essential to protect the newborn infant.
[1 Marks]
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(A) (i) and (iv)
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(B) (iii) and (iv)
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(C) (ii) and (iii)
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(D) (i) and (ii)
Explanation: The correct options are (iii) and (iv). Statement (iii) is correct because the context states that in most water-pollinated species, pollen grains have a mucilaginous coating that protects them from wetting. Statement (iv) is also correct as it specifies that pollination by water is quite rare and limited to about 30 genera of flowering plants, which is directly supported by the provided context.
[1 Marks]
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(A) Bobcat Lemur
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(B) Numbat Anteater
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(C) Tasmanian tiger cat Anteater
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(D) Lemur Spotted cuscus
Explanation: The correct answer is 'Numbat Anteater'. This combination illustrates convergent evolution as the numbat (a marsupial) and the anteater (a placental mammal) have evolved similar adaptations to feed on ants and termites, despite belonging to different evolutionary lineages. This aligns with the provided context, which discusses how marsupials and placental mammals in Australia exhibit similar characteristics due to adaptive radiation in an isolated geographical area.
[1 Marks]
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(A) Protease
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(B) Lysozyme
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(C) Cellulase
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(D) Chitinase
Explanation: The correct option is Chitinase. Chitinase is an enzyme that specifically breaks down chitin, which is a component of the fungal cell wall. According to the context provided, the isolation of DNA from cells, including fungal cells, can be achieved through the use of specific enzymes designed to break down cellular components, and chitinase is the appropriate enzyme for fungi.
[1 Marks]
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(A) TT Tt
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(B) tt tt
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(C) Tt tt
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(D) Tt Tt
Explanation: The correct option is 'TT, tt'. In a monohybrid cross between a true-breeding tall plant (TT) and a true-breeding dwarf plant (tt), the offspring will have a 1:1 ratio of tall (Tt) and dwarf (tt) plants in the F2 generation. This aligns with Mendel's principles where TT represents the genotype for the tall parent and tt represents the genotype for the dwarf parent.
[1 Marks]
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(A) A polypeptide of 50 amino acids will be formed.
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(B) A polypeptide of 49 amino acids will be formed.
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(C) A polypeptide of 25 amino acids will be formed.
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(D) A polypeptide of 24 amino acids will be formed.
Explanation: If a gene encoding a 50 amino acid polypeptide has its 25th codon (UAU) mutated to UAA, the polypeptide chain will terminate prematurely at the 25th codon. This is because UAA is a stop codon, which signals the end of translation. Therefore, a shorter polypeptide of only 24 amino acids will be produced
[1 Marks]
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(A) Aspergillus sp.
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(B) Trichoderma sp.
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(C) Streptococcus sp.
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(D) Clostridium sp.
Explanation: The correct answer is Clostridium sp. This is because Clostridium butylicum, a bacterium mentioned in the context, is specifically known for producing butyric acid on an industrial scale.
[1 Marks]
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(A) No Radioactive (35S) detected in cells + Radioactive (35S) detected in supernatant. Radioactive (32P) detected in cells + No Radioactivity detected in supernatant.
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(B) No Radioactive (35S) detected in cells + No Radioactivity detected in supernatant. Radioactive (32P) detected in cells + Radioactive (35S) detected in supernatant.
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(C) Radioactive (35S) detected in cells + Radioactive (35S) detected in supernatant. No Radioactive (32P) detected in cells + No Radioactivity detected in supernatant.
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(D) Radioactive (35S) detected in cells + No Radioactivity detected in supernatant. No Radioactive (32P) detected in cells + Radioactive (35S) detected in supernatant.
Explanation: The correct answer is 'Radioactive (32P) detected in cells + No Radioactivity detected in supernatant.' This is because in the Hershey-Chase experiment, when bacteriophages with radioactive DNA (labelled with 32P) infected the bacteria, the DNA entered the bacterial cells while the protein coats (labelled with 35S) remained outside, leading to no radioactivity detected in the supernatant.
[1 Marks]
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(A) Assertion (A) is true, but Reason (R) is false.
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(B) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
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(C) Assertion (A) is false, but Reason (R) is true.
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(D) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
Explanation: The correct answer is 'Assertion (A) is false, but Reason (R) is true.' Totipotency refers to the ability of a single cell to develop into a whole organism or plant, not just a part. Therefore, the assertion is incorrect. However, the reason correctly states that specific nutrient media and sterile conditions are necessary for the successful culture and division of cells in explants, making it true.
[1 Marks]
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(A) Assertion (A) is false, but Reason (R) is true.
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(B) Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A).
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(C) Both Assertion (A) and Reason (R) are true, but Reason (R) is not the correct explanation of the Assertion (A).
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(D) Assertion (A) is true, but Reason (R) is false.
Explanation: Both Assertion (A) and Reason (R) are true and Reason (R) is the correct explanation of the Assertion (A). Biogas plants are commonly built in rural areas because cattle dung, which contains Methanobacterium, is readily available there, enabling the production of biogas.
Section C
[2 Marks]
Answer: An antibody molecule, produced by B-lymphocytes, typically has a Y-shaped structure consisting of four polypeptide chains—two heavy chains and two light chains. These chains are linked by disulfide bonds. The antibody has two binding sites at the tips of the Y, allowing it to attach to specific antigens on pathogens. The constant region of the antibody defines its class (e.g., IgA, IgG), while the variable region allows for antigen specificity, enabling the immune system to neutralize pathogens effectively.
[2 Marks]
Answer: To prevent the spread of HIV infection, several measures have been implemented by NACO, WHO, and NGOs. Firstly, making blood safe from HIV through rigorous screening in blood banks is essential. Secondly, ensuring the use of only disposable needles and syringes in healthcare settings helps reduce transmission. Thirdly, free distribution of condoms promotes safe sex practices. Lastly, controlling drug abuse and advocating for regular check-ups within high-risk populations are crucial in reducing HIV infections.
[2 Marks]
Answer: The correct representation of the replicating fork of DNA replication in E. coli is diagram (i). It accurately depicts the direction of synthesis for both leading and lagging strands, illustrating that DNA polymerase synthesizes new DNA complementary to the template strand. The enzyme responsible for joining the newly synthesized fragments of DNA, known as Okazaki fragments, is DNA ligase, which connects these discontinuously synthesized sections.
[2 Marks]
Answer: Amniocentesis is a medical procedure used to collect a small amount of amniotic fluid surrounding a fetus for testing. This technique helps identify genetic disorders and congenital disabilities. In India, amniocentesis is misused primarily for sex determination, leading to illegal abortions if the baby is female. This practice has contributed to the rising incidence of female foeticides, which is both unethical and dangerous for the health of the mother and fetus.
[2 Marks]
Answer: Two sexually transmitted diseases (STDs) that can occur in human females are gonorrhea and chlamydia. If left untreated, these infections can lead to several complications, which include pelvic inflammatory disease (PID) and infertility. PID can cause chronic pain and damage to reproductive organs, while infertility can prevent successful conception in the future.
[2 Marks]
Answer: The specific enzyme used to make multiple copies of foreign DNA before Step-1 of the recombinant DNA technology process is DNA polymerase. This enzyme synthesizes new DNA strands by adding nucleotides complementary to the template strand, allowing for amplification of the desired DNA fragment.
[2 Marks]
Answer: The interaction between fig trees and their pollinator wasps exemplifies mutualism, where both species benefit. The fig provides a habitat and food source for the wasp's larvae by offering its seeds. In return, the wasp pollinates the fig's flowers while laying its eggs. This one-to-one relationship means that each fig species is specifically adapted to a particular wasp species, ensuring successful reproduction for both organisms. Thus, they co-evolve, benefiting mutually from their interaction.
[2 Marks]
Answer: In the ecological pyramid of numbers, the first trophic level consists of one banyan tree, the producer. This level supports 20 insects that feed on the tree (second trophic level). At the third trophic level, 32 birds depend on these insects. This structure resembles a pyramid, broad at the base with the tree, narrowing as it rises to the apex with the birds. The pyramid clearly illustrates the decrease in numbers at higher trophic levels.
Section D
[3 Marks]
Answer: Parturition, the process of childbirth, is regulated by a complex neuroendocrine mechanism initiated by signals from the fully developed fetus and the placenta. This leads to the activation of the fetal ejection reflex which triggers the release of oxytocin from the maternal pituitary gland. Oxytocin enhances uterine contractions, inducing further release of this hormone, creating a positive feedback loop. Resulting strong, rhythmic contractions lead to the expulsion of the baby through the birth canal, followed by the placenta. Additionally, hormones such as cortisol and estrogens play crucial roles in preparing the uterus for these contractions and facilitating childbirth.
[3 Marks]
Answer: The disorder that the infant is suffering from is known as Down’s Syndrome, or trisomy 21, characterized by the presence of an extra copy of chromosome number 21. This genetic condition results in various physical and cognitive symptoms that can significantly affect the individual’s development. Common physical features include a short stature, a small round head, and a flat facial profile. Additionally, children with Down's syndrome often have a furrowed tongue and a partially open mouth. As they grow older, they may experience challenges such as delayed speech and language development, lower cognitive abilities, and an increased risk of heart defects and other health issues, including vision and hearing problems. Early intervention and supportive therapies can help manage these symptoms and improve quality of life.
[3 Marks]
Answer: The full form of BOD is Biochemical Oxygen Demand. BOD is defined as the amount of oxygen required by microorganisms to decompose organic matter in water at a specified temperature over a fixed period, typically five days. It serves as an important measure of organic pollution in water bodies. Higher BOD values indicate a greater amount of organic matter present, which suggests more oxygen is consumed by microbes for decomposition. As waste water treatment progresses, microorganisms break down organic pollutants, consequently reducing the BOD—indicating an improvement in water quality.
[3 Marks]
Answer: Genetically modified (GM) plants offer several advantages that enhance agricultural productivity and sustainability. Firstly, they increase crop yields by providing resistance to various environmental stresses such as drought, heat, and salinity, thus ensuring that crops thrive under adverse conditions. Secondly, GM plants reduce reliance on chemical pesticides by being engineered for pest resistance, which not only lowers production costs but also minimizes the environmental impact of agriculture. Lastly, these plants demonstrate improved nutritional value, as evidenced by developments like golden rice, which is enriched with Vitamin A, helping address nutritional deficiencies in populations that rely heavily on rice as a staple food.
[3 Marks]
Answer: In humans, three alleles determine blood grouping: A, B, and O. The inheritance type for the AB blood group, which showcases both A and B alleles, is called co-dominance. To illustrate the possible blood types of the offspring in a cross between a man with A blood group (genotype I^A I^O) and a woman with B blood group (genotype I^B I^O), we create a Punnett square. The outcomes from this cross include potential blood groups A (I^A I^O), B (I^B I^O), AB (I^A I^B), and O (I^O I^O), indicating they can indeed have a child with O blood group.
[3 Marks]
Answer: The loss of habitat and fragmentation significantly contribute to the extinction of both plants and animals. In tropical rain forests, a prime example is the Amazon, which once spanned over 14% of Earth's land but now covers only about 6%. Human activities like agriculture and cattle ranching lead to widespread habitat destruction. Fragmentation results in smaller, isolated patches of habitat that can severely impact species needing large territories, such as certain mammals and migrating birds, leading to declining populations. These isolated groups struggle to find mates and resources, intensifying their risk of extinction. Habitat degradation further threatens species survival, establishing a dire need for conservation efforts to protect biodiversity.
[3 Marks]
Answer: Cross-pollination provides several advantages to flowering plants. It enhances genetic diversity, which increases the resilience of plant populations against diseases and environmental changes. By promoting hybrid vigor, cross-pollination allows for offspring that are better adapted to survive and reproduce. Moreover, varied genetic combinations can lead to improved traits such as higher yield and better nutritional profiles. Regarding geitonogamy, while it is a form of cross-pollination with pollen from the same plant, it is not advantageous as it does not increase genetic diversity. Therefore, although possible, geitonogamy does not provide the same benefits as true cross-pollination from different plants.
Section E
[5 Marks]
Answer: Transgenic animals are those genetically modified organisms that contain a gene or genes from another species, typically achieved through gene transfer technologies. These modifications allow scientists to create animals with desirable traits, enabling both research and practical applications in various fields. One area of benefit is the study of normal physiology and development; for example, transgenic mice can be engineered to produce human proteins like α-1-antitrypsin, which helps in treating emphysema. Another significant use is in disease modeling; transgenic animals can mimic human diseases allowing researchers to understand mechanisms of diseases like cancer, cystic fibrosis, and Alzheimer’s, facilitating the development of new therapies. Transgenic animals can also produce biological products; for instance, they can be engineered to produce proteins for pharmaceuticals at lower costs. Lastly, transgenic animals are valuable in agricultural enhancements, leading to improved livestock that can resist diseases, produce more milk or meat, and require fewer resources. These advancements demonstrate the potential of transgenic technology to enhance human health, understanding of diseases, and agricultural sustainability.
[5 Marks]
Answer: A sparged stirred-tank bioreactor is a cylindrical vessel designed to facilitate the cultivation of microorganisms or cells in a controlled environment. Its structure includes several essential components: a stirrer for mixing, a sparger for air delivery, a foam control system, and systems for temperature, pH, and nutrient control. The stirrer ensures uniform mixing and oxygen distribution, which is crucial for cell growth. To enhance oxygen transfer, sterile air or oxygen is sparged through the liquid culture via the sparger, forming bubbles that increase the surface area for gas exchange. The foam control system prevents excessive foam formation, which can impede operation. Additionally, sampling ports allow for periodic withdrawal of the culture to monitor growth and product formation. Overall, the combination of mixing and sparging in this bioreactor type promotes optimal growth conditions, thus maximizing the production yield of desired metabolites or cells.
[5 Marks]
Answer: In nature, when a population has unlimited resources, it experiences exponential growth, characterized by an unrestricted increase in numbers. This growth continues until environmental limitations arise, but in theory, it accelerates indefinitely due to the endless provision of food and space. The equation representing this growth is dN/dt = rN, where N represents the population size, r is the intrinsic rate of increase, and t is time. Graphically, this growth curve is plotted as a J-shaped curve, reflecting the rapid increase in population without restrictions. The growth curve showcases how populations can potentially flourish under ideal conditions, illustrating the concept of exponential growth. However, it is important to note that in nature, such ideal conditions are rarely sustained long-term due to various limiting factors that ultimately affect population dynamics.
[5 Marks]
Answer: Alexander von Humboldt's explorations in South America led him to conclude that species richness, or the number of species in a given area, increases with the size of the explored area, though only up to a certain point. This observation is encapsulated in the Species-Area relationship. It is described mathematically by the equation: log S = log C + Z log A, where S represents species richness, A is the area, C is the y-intercept, and Z is the slope of the line. A graphical representation of this relationship shows a growth pattern where species richness rises as area increases, suggesting that larger areas tend to support more diverse ecosystems. This relationship is crucial for understanding biodiversity, as well as for conservation efforts by highlighting areas of high species richness. The graph typically takes the form of a rectangular hyperbola, illustrating how richness plateaus at larger areas. Thus, Humboldt's findings laid the foundational principles of ecology and the importance of habitat size in determining diversity.
[5 Marks]
Answer: A typical monocotyledonous embryo consists of a single cotyledon, an embryonal axis, and two primary components: the plumule and the radicle. The cotyledon is the leaf-like structure that absorbs nutrients and supports early growth. The embryonal axis contains the plumule, which develops into the shoot and contributes to the stem, and the radicle, which becomes the root and anchors the plant. Upon fertilization, the ovary transforms into fruit while the ovules develop into seeds. In citrus fruits, multiple embryos can form through a mechanism known as polyembryony. This occurs when the nucellar cells surrounding the embryo sac divide, protruding into the sac and forming multiple embryos. Each ovule can then house several embryos of varying sizes and shapes. This form of reproduction allows for genetic variability and is beneficial in ensuring successful seed germination in varying conditions. Apomixis, where seeds form without fertilization, can also lead to similar reproductive outcomes, becoming an important aspect in horticulture and agriculture.
[5 Marks]
Answer: The male sex accessory ducts in the human reproductive system consist of several critical structures: the rete testis, vasa efferentia, epididymis, and vas deferens. The rete testis is a network of tubules that carries sperm from the seminiferous tubules to the vasa efferentia, which are a series of small tubes that transport sperm from the testis to the epididymis. The epididymis is a coiled tube where sperm mature and are stored. The vas deferens then transports mature sperm to the ejaculatory duct. These ducts facilitate the transport and maturation of sperm, contributing significantly to male fertility.\n\nGonadotropin FSH (Follicle-Stimulating Hormone) plays a vital role in spermatogenesis, which is the process of sperm formation. FSH acts primarily on Sertoli cells located within the seminiferous tubules. Upon stimulation by FSH, Sertoli cells secrete several factors that support the development and maturation of spermatogenic cells. These factors include androgen-binding protein and various growth factors that enhance the process of spermiogenesis. Thus, FSH is crucial for the adequate development of sperm and the overall regulation of the male reproductive system.
[1 Marks]