Q1. A researcher is studying the Meselson-Stahl experiment. Instead of the standard protocol, they first grow *E. coli* in a medium containing ¹⁴N for many generations and then transfer it to a medium containing ¹⁵N. What would be the expected ratio of DNA densities (Light:Hybrid:Heavy) in the centrifuge tube after THREE generations in the ¹⁵N medium?
Correct Answer: Option A (0 : 1 : 7)
Explanation: Detailed explanation will be updated shortly.
Q2. In a particular ecosystem, the removal of a detritivore species that primarily performs fragmentation leads to a significant slowdown in decomposition. Which of the following processes would be most directly and immediately hampered as a result?
Correct Answer: Option A (Mineralisation by bacteria)
Explanation: Detailed explanation will be updated shortly.
Q3. A pedigree chart for a rare genetic condition shows that an affected father passes the trait to all of his daughters, but to none of his sons. Affected mothers pass the trait to half of their sons and half of their daughters. What is the most probable mode of inheritance?
Correct Answer: Option A (Autosomal Dominant)
Explanation: Detailed explanation will be updated shortly.
Q4. In an effort to create a "super-ovulating" cow for a MOET program, a veterinarian administers a hormone. Which of the following correctly identifies the hormone and its primary target?
Correct Answer: Option A (LH, targeting the corpus luteum to prevent its degeneration.)
Explanation: Detailed explanation will be updated shortly.
Q5. A circular plasmid of 6000 base pairs (bp) is digested. Gel electrophoresis analysis shows a single band of 6000 bp when digested with EcoRI, and two bands of 2000 bp and 4000 bp when digested with BamHI. When digested with both enzymes simultaneously, what banding pattern is expected?
Correct Answer: Option A (Two bands: 2000 bp and 4000 bp)
Explanation: Detailed explanation will be updated shortly.
Q6. In the context of the *lac* operon, consider a mutant *E. coli* strain where the operator site (O) has a mutation that prevents the repressor protein from binding. What would be the expression profile of the structural genes (*z, y, a*) in a medium containing high glucose and high lactose?
Correct Answer: Option A (The genes will be expressed constitutively.)
Explanation: Detailed explanation will be updated shortly.
Q7. Myasthenia gravis is an autoimmune disorder characterized by muscle weakness. The underlying mechanism involves the body producing antibodies that target and block or destroy specific receptors at the neuromuscular junction. Which receptors are primarily affected?
Correct Answer: Option A (GABA receptors on the postsynaptic membrane)
Explanation: Detailed explanation will be updated shortly.
Q8. In a plant breeding experiment, a cross between two pure-line parents (AABB x aabb) produces an F1 generation. The F1 is self-pollinated, and the resulting F2 generation shows a phenotypic ratio of 9:3:4. This deviation from the classic 9:3:3:1 ratio is a classic example of:
Correct Answer: Option A (Co-dominance)
Explanation: Detailed explanation will be updated shortly.
Q9. The barnacle *Balanus* is a superior competitor and can exclude the smaller barnacle *Chthamalus* from the lower intertidal zone. However, *Chthamalus* thrives in the upper intertidal zone where *Balanus* cannot survive due to desiccation stress. This scenario is a textbook example of:
Correct Answer: Option A (Mutualism)
Explanation: Detailed explanation will be updated shortly.
Q10. A patient is diagnosed with a genetic disorder caused by a single point mutation leading to the substitution of glutamic acid by valine at the sixth position of a polypeptide chain. Despite this being a molecular-level change, it has severe physiological consequences. This condition is:
Correct Answer: Option A (Phenylketonuria)
Explanation: Detailed explanation will be updated shortly.
Q11. During the secondary treatment of sewage, aeration tanks are vigorously agitated. If the practice of recycling a small part of the activated sludge back into the aeration tank is stopped, what would be the most immediate consequence?
Correct Answer: Option A (A rapid increase in the biochemical oxygen demand (BOD) of the effluent.)
Explanation: Detailed explanation will be updated shortly.
Q12. To induce parthenocarpy in tomatoes and prevent the need for pollination, a commercial grower should spray the flowers with a synthetic version of which plant growth regulator?
Correct Answer: Option A (Abscisic Acid)
Explanation: Detailed explanation will be updated shortly.
Q13. In the context of biodiversity conservation, the Amazon rainforest is often referred to as the 'lungs of the planet'. If a large portion of this forest is cleared for cattle ranching, which component of the 'Evil Quartet' is most prominently represented?
Correct Answer: Option A (Co-extinctions)
Explanation: Detailed explanation will be updated shortly.
Q14. In a PCR reaction, the thermal cycler was mis-programmed. After the initial denaturation step at 95°C, the temperature was immediately set to 72°C for an extended period, completely skipping the 55°C annealing step. What is the most likely outcome after one cycle?
Correct Answer: Option A (The primers will anneal to the template DNA, but no extension will occur.)
Explanation: Detailed explanation will be updated shortly.
Q15. A man with blood group AB marries a woman with blood group O. They have a daughter. What is the probability that this daughter will have the same blood group as her mother?
Correct Answer: Option A (0%)
Explanation: Detailed explanation will be updated shortly.
Q16. The seeds of a citrus fruit are dissected and found to contain multiple embryos (polyembryony). One embryo originated from the zygote, while the others are nucellar embryos. What is the genetic relationship between the nucellar embryos and the maternal plant?
Correct Answer: Option A (They are genetically identical to the maternal plant (clones).)
Explanation: Detailed explanation will be updated shortly.
Q17. If the Sertoli cells in the testes of a healthy adult male were selectively destroyed by a toxin, which of the following hormonal changes would be most expected?
Correct Answer: Option A (A sharp decrease in both FSH and LH levels.)
Explanation: Detailed explanation will be updated shortly.
Q18. A food chain consists of Algae → Copepods → Small Fish → Large Fish. If a persistent, non-biodegradable pesticide like DDT is introduced into this aquatic system, which statement is correct?
Correct Answer: Option A (The concentration of DDT will be highest in the algae.)
Explanation: Detailed explanation will be updated shortly.
Q19. An inverted pyramid of biomass is a rare ecological phenomenon. In which of the following ecosystems is it most likely to be observed?
Correct Answer: Option A (A dense tropical rainforest)
Explanation: Detailed explanation will be updated shortly.
Q20. RNA interference (RNAi) is used to protect tobacco plants from the nematode *Meloidegyne incognita*. The mechanism involves the host plant producing a specific dsRNA. How does this lead to the death of the nematode?
Correct Answer: Option A (The dsRNA blocks the transcription of the nematode's vital genes.)
Explanation: Detailed explanation will be updated shortly.