Question 1
Plants follow different pathways in response to environment or phases of life to form different kinds of structures. This ability is called plasticity. Which of the following plants displays environmental heterophilly?[cite: 8]
✅ Correct Answer: Buttercup
Explanation: According to NCERT, heterophilly due to phases of life (developmental) is seen in cotton, coriander, and larkspur[cite: 8]. On the other hand, the buttercup (Ranunculus) shows environmental heterophilly, where the leaves formed in air look distinctly different from those submerged in water[cite: 8].
Question 2
Select the animal phylum that is exclusively marine, exhibits radial symmetry in adults, is triploblastic, and possesses a unique water vascular system used for locomotion and food capture:[cite: 8]
✅ Correct Answer: Echinodermata
Explanation: Echinoderms are exclusively marine, triploblastic, and coelomate animals[cite: 8]. Adult echinoderms show radial symmetry while larvae show bilateral symmetry[cite: 8]. Their most distinctive feature is the presence of a water vascular system which helps in locomotion, capture and transport of food, and respiration[cite: 8].
Question 3
In grasses, certain adaxial epidermal cells along the veins modify themselves into large, empty, colorless cells. When they are flaccid due to water stress, they make the leaves curl inwards to minimize water loss. These specialized cells are known as:[cite: 8]
✅ Correct Answer: Bulliform cells
Explanation: In isobilateral (monocot) leaves like grasses, specific adaxial epidermal cells turn into bulliform cells[cite: 8]. When they absorb water and are turgid, the leaf surface is exposed[cite: 8]. Under water stress, they lose turgidity and become flaccid, causing the leaf to roll inward to decrease transpiration[cite: 8].
Question 4
The human inner ear contains a highly complex organ located on the basilar membrane which contains rows of hair cells acting as the primary auditory receptors. This organ is called the:[cite: 8]
✅ Correct Answer: Organ of Corti
Explanation: The organ of Corti is a structure located on the basilar membrane of the cochlea in the human inner ear[cite: 8]. It contains hair cells that possess stereocilia and function as auditory receptors by converting sound-induced mechanical vibrations into nerve impulses[cite: 8].
Question 5
During which specific stage of meiotic cell division do homologous chromosomes separate while sister chromatids remain associated at their respective centromeres?[cite: 8]
✅ Correct Answer: Anaphase I of Meiosis
Explanation: In Anaphase I, the homologous chromosome pairs separate and move toward opposite poles of the cell[cite: 8]. Crucially, the centromeres do not split during Anaphase I, meaning sister chromatids remain attached[cite: 8]. Centromere splitting and sister chromatid separation only happen in Anaphase II or mitotic Anaphase[cite: 8].
Question 6
While the membranes of the grana thylakoids possess both Photosystem I (PS I) and Photosystem II (PS II), the unstacked stroma lamellae membranes lack:[cite: 8]
✅ Correct Answer: PS II and NADP reductase
Explanation: According to NCERT, the stroma lamellae membranes lack both Photosystem II and the NADP reductase enzyme[cite: 8]. Because they lack PS II (which provides electrons via water splitting) and NADP reductase, they can only perform cyclic photophosphorylation, where electrons loop back through PS I to generate ATP without creating NADPH[cite: 8].
Question 7
In his classic dihybrid crosses involving eye color and wing size in Drosophila melanogaster, T.H. Morgan observed a recombination frequency of 37.2%. This specific percentage indicates that:[cite: 8]
✅ Correct Answer: The two genes are loosely linked on the same chromosome.
Explanation: In Drosophila, the genes for white eye and miniature wing are located on the same chromosome (X-chromosome) but are quite far apart[cite: 8]. This loose linkage allows for a high crossover rate, yielding 37.2% recombinants and 62.8% parental types, in contrast to tightly linked genes like yellow body and white eye (which show only 1.3% recombination)[cite: 8].
Question 8
The Mediterranean orchid Ophrys achieves pollination by employing a unique evolutionary mechanism where one petal of its flower closely mimics the size, color, and markings of a female bee. This interaction is a classic example of:[cite: 8]
✅ Correct Answer: Mutualism involving sexual deceit
Explanation: The relationship is a co-evolved mutualism[cite: 8]. The orchid flower uses "sexual deceit" to get pollinated by a male bee (Colpa), which attempts to "pseudocopulate" with the flower petal that mimics a female bee[cite: 8]. During this act, pollen is transferred[cite: 8].
Question 9
Assertion (A): The toxic insecticidal Bt protein crystals produced by Bacillus thuringiensis do not damage or kill the bacterium itself.
Reason (R): The toxin is synthesized as an inactive protoxin within the bacterium and only converts into its active form in the alkaline pH of the insect gut.[cite: 8]
✅ Correct Answer: Both A and R are true and R is the correct explanation of A.
Explanation: Bacillus thuringiensis forms protein crystals during a particular phase of growth containing an insecticidal protein[cite: 8]. It does not kill the bacterium because it exists as an inactive protoxin[cite: 8]. Once ingested by an insect, the protoxin is solubilized due to the alkaline pH of the insect's gut, turning it into an active, pore-forming toxin[cite: 8].
Question 10
Assertion (A): During human fertilization, normally only a single sperm can successfully penetrate and fertilize a secondary oocyte.
Reason (R): The contact of a sperm with the zona pellucida layer induces depolarization and structural changes that effectively block the entry of additional sperms.[cite: 8]
✅ Correct Answer: Both A and R are true and R is the correct explanation of A.
Explanation: When a sperm makes contact with the zona pellucida layer of the ovum, it triggers a reaction that alters the membrane's chemical and electrical properties[cite: 8]. This cortical and zona reaction ensures the prevention of polyspermy, ensuring that only one sperm can fertilize the egg[cite: 8]. Therefore, Reason (R) perfectly explains the assertion[cite: 8].
Question 11
Read the following statements regarding transcription in eukaryotic cells...[cite: 8]
✅ Correct Answer: Both Statement I and Statement II are correct.
Explanation: Eukaryotic division of labor among RNA polymerases is highly specific: RNA Polymerase I transcribes rRNAs (28S, 18S, 5.8S); RNA Polymerase II transcribes the precursor of mRNA (hnRNA); and RNA Polymerase III transcribes tRNA, 5S rRNA, and snRNAs[cite: 8]. Both given statements are entirely accurate based on NCERT[cite: 8].
Question 12
Consider the following statements regarding the types of placentation in flowering plants...[cite: 8]
✅ Correct Answer: Both Statement I and Statement II are correct.
Explanation: Free central placentation has ovules on a central axis without partitioning walls (septa), with Dianthus and Primrose as classic examples[cite: 8]. Basal placentation occurs at the base of the ovary with one solitary ovule, typical of the Asteraceae family (sunflower, marigold)[cite: 8]. Both statements match NCERT descriptions exactly[cite: 8].
Question 13
An mRNA strand contains a coding sequence of exactly 450 nucleotides... If a point mutation changes the 51st codon from UGG to the nonsense termination codon UAA, what will be the total number of amino acids in the resulting truncated polypeptide chain?[cite: 8]
✅ Correct Answer: 50 amino acids
Explanation: The 450 nucleotides code for $450/3=150$ amino acids[cite: 8]. The mutation alters the 51st codon into a stop codon (UAA)[cite: 8]. During translation, the ribosome reads codons sequentially. It successfully links the first 50 amino acids[cite: 8]. When it arrives at the 51st codon (now a stop codon), release factors bind, and translation terminates immediately. The 51st amino acid is not added. Thus, the chain contains exactly 50 amino acids[cite: 8].
Question 14
In a temperate forest ecosystem, the Gross Primary Productivity (GPP) of the primary producers is measured to be $250 \text{ g m}^{-2} \text{ yr}^{-1}$. If the total respiratory loss (R) of these plants is determined to be $50 \text{ g m}^{-2} \text{ yr}^{-1}$, what is the Net Primary Productivity (NPP) available to the primary consumers?[cite: 8]
✅ Correct Answer: $200 \text{ g m}^{-2} \text{ yr}^{-1}$
Explanation: Net Primary Productivity (NPP) represents the biomass storage left over after accounting for the plant's own respiratory needs[cite: 8]. The standard formula is: $\text{NPP} = \text{GPP} - R$[cite: 8]. Substituting the values: $\text{NPP} = 250 - 50 = 200 \text{ g m}^{-2} \text{ yr}^{-1}$[cite: 8].
Question 15
A diploid somatic cell of an animal has 24 chromosomes ($2n=24$). How many total sister chromatids and how many functional centromeres are present inside this cell during the $G_2$ phase of interphase?[cite: 8]
✅ Correct Answer: 48 sister chromatids and 24 centromeres
Explanation: During the S phase of interphase, DNA replication takes place, which doubles the DNA content[cite: 8]. However, the total chromosome count remains identical ($2n=24$)[cite: 8]. Consequently, during the subsequent $G_2$ phase, every individual chromosome consists of 2 distinct sister chromatids attached together[cite: 8]. Total sister chromatids = $24 \times 2 = 48$[cite: 8]. Because they are still joined at their central points, the chromosome count is determined by the number of centromeres, which remains 24[cite: 8].
Question 16
Match the following microbial bioactive molecules with their direct clinical or industrial applications...[cite: 8]
✅ Correct Answer: a-ii, b-iii, c-i, d-iv
Explanation: Cyclosporin A (from Trichoderma polysporum) is an immunosuppressive agent[cite: 8]. Statins (from Monascus purpureus) competitively inhibit cholesterol synthesis[cite: 8]. Streptokinase (from Streptococcus) acts as a clot buster[cite: 8]. Lipases are used in detergent formulations to digest fats/oils[cite: 8].
Question 17
A sudden, acute drop in glomerular blood pressure and Glomerular Filtration Rate (GFR) immediately activates the juxtaglomerular (JG) cells of the kidney to release renin. Which of the following events occurs downstream within the RAAS cascade?[cite: 8]
✅ Correct Answer: Angiotensin II stimulates the adrenal cortex to secrete aldosterone, promoting $Na^+$ and water reabsorption in the distal tubules.
Explanation: Released renin converts angiotensinogen in the blood to angiotensin I, which is converted to angiotensin II by ACE[cite: 8]. Angiotensin II is a potent vasoconstrictor that raises glomerular blood pressure and stimulates the adrenal cortex to secrete aldosterone[cite: 8]. Aldosterone increases $Na^+$ and water reabsorption from the distal parts of the nephron, expanding blood volume and correcting GFR[cite: 8].
Question 18
According to the well-established sliding filament theory of skeletal muscle contraction, when a muscle fiber receives an activating nerve impulse from a motor neuron, which of the following bands/zones shortens or disappears?[cite: 8]
✅ Correct Answer: The H-zone and I-band shorten, while the length of the A-band remains completely unchanged.
Explanation: During muscle contraction, actin (thin) filaments slide over myosin (thick) filaments[cite: 8]. The sarcomere shortens[cite: 8]. The I-bands (containing only actin) decrease in width, and the H-zone (the central area containing only myosin) narrows or completely disappears as actin moves inward[cite: 8]. Crucially, the length of the A-band (determined by the full length of the thick myosin filaments) remains completely constant[cite: 8].
Question 19
Hormones interact with target tissues by binding to specific receptor molecules. Which of the following hormones is lipid-soluble, passes through the plasma membrane, binds to an intracellular receptor, and directly regulates gene expression by interacting with the cell's genome?[cite: 8]
✅ Correct Answer: Cortisol
Explanation: Cortisol is a steroid hormone derived from cholesterol[cite: 8]. Steroid hormones and thyroid hormones are lipid-soluble and diffuse freely across the cell membrane to bind to intracellular receptors (mostly nuclear receptors)[cite: 8]. The resulting hormone-receptor complex interacts with DNA to alter transcription[cite: 8]. Epinephrine, insulin, and glucagon are water-soluble peptide/amino-acid derivatives that must bind to external membrane receptors[cite: 8].
Question 20
Gymnosperms exhibit unique morphological adaptations and reproductive variations. Considering Cycas and Pinus, which of the following statements represents an accurate morphological exception/feature described in NCERT?[cite: 8]
✅ Correct Answer: In Cycas, male cones and megasporophylls are borne on separate plants (dioecious), and the megasporophylls do not associate into true female cones.
Explanation: Pinus is monoecious (male and female cones on the same tree) and has branched stems[cite: 8]. Cycas is dioecious (male and female structures on completely separate trees) and has an unbranched stem[cite: 8]. Furthermore, while Cycas males produce a well-defined, compact cone, its female reproductive structures are lax megasporophylls that do not aggregate into a true compact female cone[cite: 8].
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