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Q1. The transverse section of a plant shows the following anatomical features:
(a) Large number of scattered vascular bundles surrounded by bundle sheath.
(b) Large conspicuous parenchymatous ground tissue.
(c) Vascular bundles conjoint and closed.
(d) Phloem parenchyma absent.
Identify the category of plant and its part:
(1) Dicotyledonous root
(2) Monocotyledonous stem
(3) Monocotyledonous root
(4) Dicotyledonous stem
Answer: (2) Monocotyledonous stem
Explanation:
- Scattered vascular bundles with bundle sheaths:
Monocot stems are characterized by vascular bundles scattered throughout the ground tissue, each surrounded by a sclerenchymatous bundle sheath. This contrasts with dicot stems, where vascular bundles are arranged in a ring. - Parenchymatous ground tissue:
The presence of a large, prominent parenchyma-rich ground tissue (as seen in plants like maize) is typical of monocot stems. - Conjoint and closed vascular bundles:
Conjoint bundles (xylem and phloem in the same bundle) that are closed (lacking cambium, meaning no secondary growth) are a hallmark of monocots. - Absence of phloem parenchyma:
Monocot vascular bundles lack phloem parenchyma, which is replaced by sclerenchyma in the bundle sheath for structural support.
Conclusion: These features collectively confirm the plant as a monocotyledonous stem.
Q2. Which of the following would help in prevention of diuresis?
- Decrease in secretion of renin by JG cells
- More water reabsorption due to under-secretion of ADH
- Reabsorption of Na⁺ and water from renal tubules due to aldosterone
- Atrial natriuretic factor causes vasoconstriction
The question asks which factor helps prevent diuresis (excessive urine production). Here’s the analysis:
Answer: (3) Reabsorption of Na+ and water from renal tubules due to aldosterone
Explanation:
- Aldosterone’s Role:
Aldosterone, a hormone produced by the adrenal glands, enhances sodium (Na⁺) reabsorption in the distal tubules and collecting ducts of the kidneys. Increased Na⁺ reabsorption is followed by passive water reabsorption, reducing urine output and preventing diuresis. This mechanism counteracts fluid loss and maintains blood pressure. - Why Other Options Are Incorrect:
- (1) Decrease in renin secretion: Reduced renin lowers angiotensin II and aldosterone levels, leading to less Na⁺/water reabsorption and increased diuresis.
- (2) Under-secretion of ADH: Antidiuretic hormone (ADH) promotes water reabsorption. Low ADH causes water loss (e.g., diabetes insipidus), increasing diuresis.
- (4) Atrial natriuretic factor (ANF): ANF promotes Na⁺/water excretion (natriuresis) and causes vasodilation, not vasoconstriction. This increases diuresis.
Key Mechanism:
Aldosterone directly opposes diuresis by retaining Na⁺ and water, making option (3) the correct choice.
Q3. Which of the following statements is not correct?
- Genetically engineered insulin is produced in E. coli.
- In humans, insulin is synthesised as proinsulin.
- Proinsulin has an extra peptide called C-peptide.
- Functional insulin has A and B chains linked together by hydrogen bonds.
Answer: (4) Functional insulin has A and B chains linked together by hydrogen bonds.
Explanation:
Correct Statements:
- Genetically engineered insulin in E. coli:
Recombinant human insulin is predominantly produced in E. coli (and yeast) using engineered genes. For example, E. coli expresses insulin precursors as inclusion bodies, which are later refolded into functional insulin. - Proinsulin synthesis in humans:
Human insulin is initially synthesized as proinsulin, a precursor molecule containing the A and B chains connected by a C-peptide. - C-peptide in proinsulin:
The C-peptide is a connecting peptide in proinsulin that is enzymatically removed during maturation to yield active insulin.
Incorrect Statement:
- A and B chains linked by hydrogen bonds:
Functional insulin’s A and B chains are covalently linked by disulfide bonds (not hydrogen bonds). These bonds are critical for insulin’s structural integrity and biological activity. Hydrogen bonds are weaker interactions that stabilize protein folding but do not directly link the chains.
Conclusion: Statement (4) is incorrect because disulfide bonds, not hydrogen bonds, connect insulin’s A and B chains.
Q4. Which of the following statements is not correct?
- Genetically engineered insulin is produced in E. coli.
- In humans, insulin is synthesized as proinsulin.
- Proinsulin has an extra peptide called C-peptide.
- Functional insulin has A and B chains linked together by hydrogen bonds.
Answer: (4) Functional insulin has A and B chains linked together by hydrogen bonds.
Explanation:
- Genetically engineered insulin in E. coli:
Recombinant human insulin is predominantly produced in E. coli (and yeast) using engineered genes. For example, E. coli expresses insulin precursors as inclusion bodies, which are later refolded into functional insulin. - Proinsulin synthesis in humans:
Human insulin is initially synthesized as proinsulin, a precursor molecule containing the A and B chains connected by a C-peptide. - C-peptide in proinsulin:
The C-peptide is a connecting peptide in proinsulin that is enzymatically removed during maturation to yield active insulin.
Incorrect Statement:
- A and B chains linked by hydrogen bonds:
Functional insulin’s A and B chains are covalently linked by disulfide bonds (not hydrogen bonds). These bonds are critical for insulin’s structural integrity and biological activity.
Conclusion: Statement (4) is incorrect because disulfide bonds, not hydrogen bonds, connect insulin’s A and B chains.
Q5. Which of the following disapproved embryological support for evolution?
- Oparin
- Karl Ernst von Baer
- Alfred Wallace
- Charles Darwin
Answer: (2) Karl Ernst von Baer
Explanation:
Karl Ernst von Baer disapproved embryological support for evolution by rejecting the idea that embryonic development recapitulates evolutionary history (a concept known as “recapitulation theory” proposed by Ernst Haeckel). Von Baer argued that embryos of different species do not resemble each other at all stages of development but instead diverge as they develop, which contradicted Haeckel’s claims that embryology provides direct evidence for evolution.
Q6. Goblet cells of the alimentary canal are modified from:
- Compound epithelial cells
- Squamous epithelial cells
- Columnar epithelial cells
- Chondrocytes
Answer: (3) Columnar epithelial cells
Explanation:
- Goblet Cells and Their Function:
Goblet cells are specialized epithelial cells found in the lining of the respiratory and gastrointestinal tracts. They secrete mucus, which acts as a protective and lubricating layer. - Origin of Goblet Cells:
Goblet cells are derived from simple columnar epithelial cells. These columnar cells undergo differentiation to form goblet cells, which are characterized by their goblet-like shape due to the accumulation of mucus granules in their apical region. - Why Other Options Are Incorrect:
- Compound epithelial cells: These are multicellular structures, not individual cells like goblet cells.
- Squamous epithelial cells: These are flat, thin cells that do not differentiate into goblet cells.
- Chondrocytes: These are cartilage-producing cells and have no role in the formation of goblet cells.
Conclusion: Goblet cells originate from columnar epithelial cells, making option (3) the correct answer.
Q7. The QRS complex in a standard ECG represents:
- Repolarization of ventricles
- Repolarization of auricles
- Depolarization of auricles
- Depolarization of ventricles
Answer: (4) Depolarization of ventricles
Explanation:
- What is the QRS Complex?
The QRS complex is the most prominent waveform in a standard ECG and represents the depolarization of the ventricles, which initiates ventricular contraction (systole). It follows the P wave (which represents atrial depolarization) and precedes the T wave (which represents ventricular repolarization). - Components of the QRS Complex:
- Q wave: A small downward deflection representing depolarization of the interventricular septum.
- R wave: A sharp upward deflection representing depolarization of the main ventricular mass.
- S wave: A downward deflection following the R wave, representing depolarization of the basal parts of the ventricles.
- Why Other Options Are Incorrect:
- (1) Repolarization of ventricles: This is represented by the T wave, not the QRS complex.
- (2) Repolarization of auricles: This occurs during the QRS complex but is masked by ventricular depolarization and is not separately visible on an ECG.
- (3) Depolarization of auricles: This is represented by the P wave, not the QRS complex.
- Clinical Significance:
The duration and morphology of the QRS complex are crucial for diagnosing heart conditions such as bundle branch blocks, ventricular hypertrophy, and arrhythmias.
Conclusion: The QRS complex specifically indicates ventricular depolarization, making option (4) correct.
Q8. In light reactions, plastoquinone facilitates the transfer of electrons from:
- PS-I to ATP synthase
- PS-II to cytb₆f complex
- Cytb₆f complex to PS-I
- PS-I to NADP+
Correct Answer: (2) PS-II to Cyt b₆f complex.
In the light-dependent reactions of photosynthesis, plastoquinone (PQ) plays a critical role in shuttling electrons from Photosystem II (PSII) to the cytochrome b₆f complex. This lipid-soluble molecule transfers electrons through the thylakoid membrane as part of the electron transport chain.
Key Explanation:
- Electron Flow Pathway:
- Light energy excites electrons in PSII, which are then passed to plastoquinone.
- Plastoquinone carries these electrons to the cytochrome b₆f complex, where proton pumping occurs to establish the electrochemical gradient used for ATP synthesis.
- Why Other Options Are Incorrect:
- (1) PS-I to ATP synthase: ATP synthase is involved in ATP production via chemiosmosis, not direct electron transfer from PSI.
- (3) Cyt b₆f complex to PS-I: Electrons move from cytochrome b₆f to PSI via plastocyanin, not plastoquinone.
- (4) PS-I to NADP+: PSI transfers electrons to ferredoxin, which then reduces NADP+ to NADPH; plastoquinone is not involved here.
Correct Answer: (2) PS-II to Cyt b₆f complex.
Q9. The product(s) of the reaction catalyzed by nitrogenase in root nodules of leguminous plants is/are:
- Ammonia and hydrogen
- Ammonia alone
- Nitrate alone
- Ammonia and oxygen
Correct Answer: (1) Ammonia and hydrogen
Explanation:
Nitrogenase, the enzyme responsible for nitrogen fixation in root nodules, catalyzes the reduction of atmospheric nitrogen gas (N₂) into ammonia (NH₃). However, this reaction also produces hydrogen gas (H₂) as a byproduct. Here’s why:
- Key Reaction Mechanism:
- Nitrogenase reduces N₂ to NH₃ through a process requiring ATP and electrons.
- A side reaction reduces protons (H⁺) to H₂, even when N₂ is available. This occurs because nitrogenase cannot fully suppress proton reduction during N₂ fixation.
- Evidence from Search Results:
- Root nodules convert atmospheric N₂ into ammonia, which is assimilated into amino acids and nucleotides.
- Hydrogen gas production is inherent to nitrogenase activity, as observed in studies on legume nodules and other nitrogen-fixing systems.
- Oxygen is not a product; instead, it is strictly regulated (via leghaemoglobin) to protect oxygen-sensitive nitrogenase.
- Why Other Options Are Incorrect:
- (2) Ammonia alone: Excludes H₂, a proven byproduct.
- (3) Nitrate alone: Nitrate is not produced by nitrogenase; it is generated via nitrification in soil.
- (4) Ammonia and oxygen: Oxygen inhibits nitrogenase and is actively excluded from nodules.
Q10. Match the following stages of meiosis with their corresponding events:
List I List II
(a) Zygotene (i) Terminalization
(b) Pachytene (ii) Chiasmata
(c) Diplotene (iii) Crossing over
(d) Diakinesis (iv) Synapsis
Options:
- (a)-(ii), (b)-(iv), (c)-(iii), (d)-(i)
- (a)-(iii), (b)-(iv), (c)-(i), (d)-(ii)
- (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
- (a)-(i), (b)-(ii), (c)-(iv), (d)-(iii)
Correct Answer: (3) (a)-(iv), (b)-(iii), (c)-(ii), (d)-(i)
Explanation:
Matching Stages and Events:
- Zygotene (a) → Synapsis (iv)
- During zygotene, homologous chromosomes pair up via synapsis, facilitated by the synaptonemal complex.
- Pachytene (b) → Crossing over (iii)
- Crossing over (exchange of genetic material between non-sister chromatids) occurs at recombination nodules during pachytene.
- Diplotene (c) → Chiasmata (ii)
- In diplotene, homologous chromosomes begin to separate but remain connected at chiasmata (sites of crossing over).
- Diakinesis (d) → Terminalization (i)
- Diakinesis marks the terminalization of chiasmata (movement of chiasmata toward chromosome ends) and breakdown of the nuclear envelope.
Why Other Options Are Incorrect:
- Option (1): Incorrectly assigns chiasmata to zygotene and synapsis to pachytene.
- Option (2): Links crossing over to zygotene and terminalization to diplotene, which contradicts the sequence of events.
- Option (4): Associates terminalization with zygotene and synapsis with diplotene, reversing key processes.