DHR - BRET PYQs Dec 2020

Immunology & Physiology

Frogs have the ability to change the colour to hide them from their enemies. This protective coloration is known as:

Although often termed camouflage, some sources classify frog colour change as mimicry mimicking surroundings to avoid predators. Pigment dispersion in chromatophores enables concealment. Aestivation and hibernation are dormancy strategies, not colour change mechanisms.

Ref: Cott, Adaptive Coloration in Animals, Oxford University Press, 1940, and Stebbins and Cohen, A Natural History of Amphibians, Princeton University Press, Chapter 2, discuss protective coloration, chromatophore based mimicry, concealment and camouflage in frogs.

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Immunology & Physiology

Ranikhet disease is a viral disease of:

Ranikhet disease, also termed Newcastle disease, caused by avian paramyxovirus type-1, is highly contagious in poultry leading to respiratory, nervous symptoms and high mortality. Bovine, equine and ovine are affected by different viruses, not Ranikhet.

Ref: OIE Manual of Diagnostic Tests and Vaccines for Terrestrial Animals, Chapter 2.3.14, and Swayne et al., Diseases of Poultry, 13th Edition, Chapter 3, describe Newcastle disease Ranikhet virus, avian paramyxovirus pathology in poultry, published by Wiley Blackwell.

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Immunology & Physiology

Which of the following is not a ruminant?

Pigs are monogastric omnivores lacking four-chambered ruminant stomach with rumen fermentation; they cannot regurgitate cud. Cows, goats and giraffes are true ruminants possessing rumen, reticulum, omasum and abomasum for cellulose digestion via symbiotic microbes.

Ref: Dyce, Sack and Wensing, Textbook of Veterinary Anatomy, 4th Edition, Chapter 3, explains ruminant digestive anatomy, four chambered stomach, differences between ruminants and monogastric pig digestion and comparative gastrointestinal physiology, published by Saunders Elsevier.

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Immunology & Physiology

Which of the following insect can be used for production of formic acid?

Red ants, particularly Formica rufa, possess acid glands secreting formic acid as defense. Distillation of ant bodies historically yielded formic acid. Bed bugs, crickets and locusts lack such concentrated formic acid glands for industrial use.

Ref: Holldobler and Wilson, The Ants, Harvard University Press, 1990, Chapter 3, discusses formic acid gland, chemical defense in Formica rufa, red ant secretion chemistry and historical formic acid production from ants, evolutionary significance and ecology.

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Immunology & Physiology

Silk is harvested from which of the following?

Bombyx mori, the domestic silkmoth, spins cocoon composed of fibroin protein coated with sericin during pupation. Sericulture harvests these cocoons for commercial silk. Chironomus is midge, Vespula wasp and Drosophila fruit fly not silkworms.

Ref: Gullan and Cranston, The Insects: An Outline of Entomology, 5th Edition, Chapter 1 and 14, describes Bombyx mori biology, silk gland fibroin production, sericulture history and commercial silk harvesting methods, published by Wiley Blackwell.

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Immunology & Physiology

Which tissue conducts food in plants?

Phloem conducts photosynthates as sucrose from source to sink via sieve elements and companion cells driven by pressure-flow hypothesis. Xylem transports water and minerals, parenchyma stores nutrients and sclereids provide mechanical support only.

Ref: Raven, Evert and Eichhorn, Biology of Plants, 8th Edition, Chapter 23, explains phloem transport, source sink relationship, pressure flow model, sieve tubes and comparison with xylem water conduction, published by W.H. Freeman.

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Immunology & Physiology

Which of the following is a chill-tolerant plant:

Arabidopsis thaliana is a model chill-tolerant plant that undergoes cold acclimation via CBF transcription factors and antifreeze proteins, tolerating freezing. Coleus, Dieffenbachia and Croton are tropical ornamentals highly sensitive to low temperature chilling injury.

Ref: Taiz, Zeiger, Møller and Murphy, Plant Physiology and Development, 6th Edition, Chapter 10, explains cold acclimation, chill tolerance, Arabidopsis model, CBF regulon, frost resistance versus tropical chilling sensitive species, published by Sinauer Associates.

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Immunology & Physiology

The enzyme RuBisCO is involved in which part of photosynthesis:

RuBisCO, ribulose-1,5-bisphosphate carboxylase/oxygenase, catalyzes CO2 fixation to ribulose bisphosphate forming 3-phosphoglycerate, the first step of Calvin-Benson cycle in stroma. Light reactions and Z-scheme generate ATP and NADPH supporting this dark reaction.

Ref: Berg, Tymoczko, Gatto and Stryer, Biochemistry, 8th Edition, Chapter 20, covers photosynthesis, Calvin-Benson cycle, RuBisCO structure, carbon fixation mechanism and Rubisco activase regulation, published by W.H. Freeman.

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Immunology & Physiology

Continuity of cytoplasm from cell to cell is maintained through cytoplasmic connections in plants called:

Plasmodesmata are cytoplasmic channels traversing cell walls, connecting protoplasts and containing desmotubule derived from ER, enabling symplastic transport of metabolites and signals. Tight and gap junctions are animal-specific; ER alone is not intercellular.

Ref: Taiz, Zeiger, Møller and Murphy, Plant Physiology and Development, 6th Edition, Chapter 1, describes plant cell structure, plasmodesmata function, symplastic continuity, desmotubule and intercellular communication, published by Sinauer Associates.

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Immunology & Physiology

Bicollateral vascular bundles are found in:

Bicollateral bundles possess phloem on both outer and inner sides of xylem, typically with two cambium strips. This arrangement characterizes Cucurbitaceae stems such as pumpkin, while Fabaceae, Solanaceae and Poaceae generally exhibit collateral or closed bundles.

Ref: Esau's Plant Anatomy by Ray Evert, 3rd Edition, Chapter 10, details vascular bundle types, bicollateral bundles, phloem distribution, Cucurbitaceae anatomy and comparative plant structure, published by John Wiley and Sons.

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Immunology & Physiology

Which environmental problem is the result of chemical reactions in the atmosphere that involves sulphur dioxide?

Sulfur dioxide oxidizes in atmosphere to sulfuric acid, mixing with rain forming acid rain with pH below 5.6. It damages forests, buildings and aquatic systems. Melting glaciers and global warming relate to CO2 and greenhouse gases, not sulfur chemistry.

Ref: Botkin and Keller, Environmental Science: Earth as a Living Planet, 9th Edition, Chapter 20, explains sulfur dioxide emission, atmospheric oxidation to sulfuric acid, acid rain formation, pH effects and ecosystem damage, published by Wiley.

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Immunology & Physiology

Which of the following relates to ‘sustainable development'?

Brundtland Report titled Our Common Future, 1987, coined sustainable development defined as development meeting present needs without compromising future generations. Montreal Protocol addresses ozone, Kyoto and Paris agreements climate change, distinct from sustainable development concept.

Ref: World Commission on Environment and Development, Our Common Future, 1987, Oxford University Press, Chapter 2, coined sustainable development definition emphasizing intergenerational equity, resource use, environmental policy framework and global governance principles for sustainability.

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