UKPSC Biology: Plant Kingdom, Morphology, Photosynthesis & Plant Physiology (Solved PYQs & Notes)

UKPSC Biology (Unit 5): Plant Kingdom, Morphology, Photosynthesis & Plant Physiology

Part of the UKPSC General Science & Technology Revision Series.

1.High-Yield Micro-Notes

• Photosynthetic Energetics & Action Spectrum: Photosynthesis transforms radiant solar energy into stable chemical bond energy (6CO₂ + 12H₂O + Photons → C₆H₁₂O₆ + 6O₂ + 6H₂O), with atmospheric Carbon Dioxide (CO₂) acting as the primary carbon feedstock. Chlorophyll pigments (chiefly chlorophyll-a and chlorophyll-b) show maximum quantum absorption and action efficiency in the Red spectral band (660–680 nm), followed by the Blue band (430–450 nm), while reflecting green light. Cellulose, the structural polymer of plant cell walls, is an unbranched polysaccharide carbohydrate composed of beta-D-glucose units.
• Seed Physiology & Mineral Mobility: Successful seed germination requires three environmental factors: Moisture (water) for imbibition and enzymatic activation, Optimal ambient temperature for biocatalysis, and Oxygen (O₂) for aerobic cellular respiration; soil nutrients and direct sunlight are non-essential at this initial stage. Plant mineral transport varies by mobility: mobile nutrients (N, P, K, Mg) translocate from older tissues to young shoots, showing deficiency symptoms on lower leaves first, whereas immobile nutrients like Sulfur (S) and Calcium (Ca) cannot easily relocate, meaning sulfur deficiency (interveinal chlorosis) appears first on the youngest upper leaves.
• Comparative Plant Phylogeny & Chromosome Ploidy: Both Bryophytes and Pteridophytes are classified as Embryophytes, sharing the synapomorphic trait of embryo formation within maternal gametangia following syngamy. In Gymnosperms, the endosperm develops directly from the haploid megaspore prior to fertilization, making it haploid (n) (unlike the triploid (3n) endosperm of double-fertilized Angiosperms); if somatic leaf tissue is diploid (2n = 16), gymnosperm endosperm possesses n = 8 chromosomes. Among gymnosperms, the order Gnetales (Gnetum, Ephedra, Welwitschia) is the most phylogenetically advanced, uniquely sharing genuine xylem vessel elements and angiosperm-like floral envelopes.
• Economic Botany, Plant Adaptations & Morphology: Hydrophytic wetland plants rely on aerenchyma tissue (parenchyma packed with interconnected air cavities) to provide buoyancy and internal gas diffusion during flood surges. Turmeric (Curcuma longa) and Ginger (Zingiber officinale) are underground modified storage stems known as rhizomes that bear distinct nodes and internodes. Chilgoza refers to the edible, protein-dense seeds harvested from the gymnosperm conifer Pinus gerardiana. The ancient writing parchment Bhojpatra is harvested from the papery peeling bark of the high-altitude Himalayan Birch (Betula utilis). The parasitic Red Rust disease of tea is caused by the green alga Cephaleuros virescens, not by a fungal or viral pathogen.

2. Important facts you should know:

3. Master Questions

Q1. What specialized internal vegetative tissue allows hydrophytes and semi-aquatic plants to survive periodic submergence and seasonal water table fluctuations across wetlands and marshes?

[UKPSC Pre 2024] [Direct Fact]

(a) Specialized rhizomatous roots

(b) Anchoring submergent rootlets

(c) Spongy aerenchyma tissue

(d) Aerial rhizophore extensions

Q2. The fundamental bio-physicochemical process wherein green plants capture radiant photon flux to transform it into chemical bond energy utilizes which of the following atmospheric gases?

[UKPSC Pre 2002-03 | UKPSC Pre 2006-07] [Direct Fact]

(a) Gaseous Ammonia

(b) Carbon Dioxide (CO₂)

(c) Diatomic Chlorine

(d) Sulfur Dioxide

Q3. Cellulose, the structural fibrous macromolecule constituting primary plant cell walls, belongs biochemically to the family of:

[UKPSC Pre 2021] [Direct Fact]

(a) Polysaccharide Carbohydrates

(b) Globular Storage Proteins

(c) Structural Lipids

(d) Polynucleotide Nucleic Acids

Q4. Because of the immobility of certain structural mineral ions within vegetative vascular systems, visual symptoms of Sulfur deficiency appear:

[UKPSC Mains 2004-05] [Direct Fact]

(a) Exclusively on basal lower leaves

(b) Uniformly across lower and middle foliage

(c) Confined to intermediate mature leaves

(d) First and foremost on the youngest upper leaves

Q5. Which triad of environmental conditions is essential for terminating seed dormancy and initiating successful germination?

[UKPSC UDA/LDA Pre 2003] [Direct Fact]

(a) Humus Soil, Moisture, and Free Oxygen

(b) Water (Moisture), Optimal Ambient Temperature, and Oxygen

(c) Optimal Temperature, Ambient Oxygen, and Carbon Dioxide

(d) Elevated Temperature, Oxygen, and Direct Solar Radiation

Q6. The destructive ‘Red-Rust’ disease that produces velvety foliar lesions on commercial tea plantations (Camellia sinensis) is a/an:

[UKPSC RO/ARO Pre 2022] [Direct Fact]

(a) Obligate fungal blight

(b) Parasitic algal disease

(c) Systemic bacterial wilt

(d) Sub-microscopic viral infection

Q7. Which of the following fundamental embryological characteristics is shared by both Bryophytes and Pteridophytes?

[UKPSC RO/ARO Pre 2022] [Direct Fact]

(a) Presence of lignified vascular xylem and phloem

(b) Completely undifferentiated thalloid gametophytic plant body

(c) Retention of the fertilized zygote and embryo formation within parental tissues

(d) Dominant, perennial haploid free-living plant phase

Q8. If the somatic diploid leaf cells of a gymnospermous tree contain 16 chromosomes (2n = 16), the chromosome number present within its endosperm tissue is:

[UKPCS Lower Pre 2021] [Statement-Based]

(a) Eight (8)

(b) Thirty-two (32)

(c) Sixty-four (64)

(d) Twenty (20)

Q9. Which taxonomic order within the division Gymnospermae is recognized as the most phylogenetically advanced, sharing vessels in the secondary xylem with angiosperms?

[UKPSC FRO/ACF Pre 2021] [Direct Fact]

(a) Cycadales

(b) Coniferales

(c) Gnetales

(d) Taxales

Q10. The edible dry fruit commercially marketed under the name ‘Chilgoza’ is the seed of a/an:

[UKPSC APS Mains 2017] [Direct Fact]

(a) Monocotyledonous Angiosperm

(b) Terrestrial Bryophyte

(c) Non-flowering Pteridophyte

(d) Gymnosperm (Pinus gerardiana)

Q11. During oxygenic terrestrial photosynthesis, the photosynthetic pigments of green plants absorb and utilize light energy most effectively in the:

[UKPSC RO/ARO Mains 2006 | UKPSC Pre 2011] [Direct Fact]

(a) Red wavelength band

(b) Yellow wavelength band

(c) Green wavelength band

(d) Ultraviolet band

Q12. In agricultural horticulture and nursery propagation, a ‘Poly-house’ structure is primarily constructed to:

[UKPSC Mains 2006] [Direct Fact]

(a) Grow tender and exotic crop plants under controlled climatic conditions

(b) Store harvested cereal grains in an airtight dry space

(c) Store fresh perishables under cold refrigeration

(d) Extract aromatic essential oils from flower petals

Q13. Botanically, the culinary rhizome from which the spice Turmeric (Curcuma longa) is harvested constitutes a modified:

[UKPSC Forest Ranger Pre 2012 | UKPSC Polytechnic Lecturer 2015-16] [Direct Fact]

(a) Tap root

(b) Underground stem (Rhizome)

(c) Modified foliar leaf base

(d) Inflorescence axis

Q14. The historical writing parchment known as ‘Bhojpatra’, used for ancient Himalayan manuscripts, is harvested from the exfoliated bark of:

[UKPSC CFO 2021] [Direct Fact]

(a) Rhododendron arboreum

(b) Himalayan Birch (Betula utilis)

(c) Populus ciliata

(d) Himalayan Oak (Quercus leucotrichophora)

Q15. The renowned, commercially prized horticultural cultivar designated as ‘Alphonso’ (Hapoos) belongs to:

[UKPSC APO 2015] [Direct Fact]

(a) Banana (Musa paradisiaca)

(b) Apple (Malus domestica)

(c) Mango (Mangifera indica)

(d) Guava (Psidium guajava)

4. Master Explanations & Answer Key

1. Ans. (c)

• Direct Answer: Aerenchyma is a specialized spongy plant tissue characterized by thin-walled cells enclosing large, continuous intercellular gas channels that provide buoyancy and facilitate internal gas transport in hydrophytes.
• Exam Trap / Distractor Alert: Rhizophores are specialized leafless branching structures that produce adventitious roots in mangrove plants (e.g., Rhizophora), while aerenchyma is the internal anatomical adaptation that keeps aquatic and marsh plants buoyant and oxygenated.
• High-Yield Extra Facts: In deepwater floating plants (such as Eichhornia crassipes / Water Hyacinth), swollen petioles are packed with aerenchyma, allowing the plant to remain buoyant and ride fluctuating water tables.

2. Ans. (b)

• Direct Answer: Oxygenic photosynthesis captures atmospheric carbon dioxide (CO₂) during the light-independent Calvin cycle (catalyzed by the enzyme RuBisCO) to synthesize hexose sugars using chemical energy (ATP and NADPH) generated during the light reactions.
• Exam Trap / Distractor Alert: Oxygen (O₂) is a byproduct evolved from the photolysis (water-splitting) reaction at Photosystem II, not the input carbon source; CO₂ is the essential gas consumed to build carbohydrates.
• High-Yield Extra Facts: Corn, sugarcane, and sorghum utilize the C4 Hatch-Slack pathway, using the enzyme PEP carboxylase to fix carbon dioxide without the photorespiratory losses common to standard C3 plants.

3. Ans. (a)

• Direct Answer: Cellulose is an unbranched, structural homopolysaccharide carbohydrate consisting of repeating D-glucose units linked by beta-1,4-glycosidic bonds.
• Exam Trap / Distractor Alert: While cell membranes contain lipids and proteins, the rigid, load-bearing outer cell wall of green plants is composed primarily of cellulose, hemicellulose, and pectin.
• High-Yield Extra Facts: Cotton fibers represent the purest natural form of cellulose (over 90% dry weight); humans lack the digestive enzyme cellulase to hydrolyze beta-1,4-glycosidic bonds, so dietary cellulose passes through the gut as insoluble dietary fiber.

4. Ans. (d)

• Direct Answer: Sulfur is relatively immobile once integrated into structural amino acids (cysteine and methionine) within mature plant tissues; because it cannot be readily remobilized to newer growth, sulfur deficiency symptoms appear first on the youngest upper leaves.
• Exam Trap / Distractor Alert: Mobile elements like Nitrogen (N), Phosphorus (P), Potassium (K), and Magnesium (Mg) readily relocate from older senescing foliage to young tissues, so their deficiency symptoms (such as chlorosis) manifest on the lower, older leaves first.
• High-Yield Extra Facts: Calcium (Ca) is another immobile nutrient; its deficiency causes localized tissue necrosis, “blossom end rot” in tomatoes, and apical bud death in growing tips.

5. Ans. (b)

• Direct Answer: Non-dormant viable seeds require water (to rehydrate desiccated cellular tissues and trigger hydrolytic enzymes), optimal ambient temperature (to support metabolic enzymes), and oxygen (for aerobic ATP synthesis via cellular respiration).
• Exam Trap / Distractor Alert: Most non-photoblastic agricultural seeds do not require light or soil to germinate; seeds germinate in complete darkness on moist, aerated paper, drawing energy from stored cotyledon reserves.
• High-Yield Extra Facts: Imbibition of water expands seed volume and ruptures the protective seed coat (testa), allowing the embryonic radicle to emerge and establish the primary root system.

6. Ans. (b)

• Direct Answer: Red Rust of tea is an uncommon plant disease caused by a parasitic green alga (Cephaleuros virescens), which forms velvety orange-red or brownish algal patches on tea leaves and stems.
• Exam Trap / Distractor Alert: While most agricultural rusts (e.g., Black Rust of wheat, caused by Puccinia graminis) are basidiomycete fungal infections, Red Rust of tea is caused by an alga.
• High-Yield Extra Facts: Cephaleuros virescens also infects other commercial plantation crops, including mango, coffee, and guava, causing foliar chlorosis and twig dieback.

7. Ans. (c)

• Direct Answer: Both Bryophytes and Pteridophytes are classified as Embryophytes; their diploid zygotes are retained and nourished within the multicellular female sex organ (archegonium) to develop into an embryo.
• Exam Trap / Distractor Alert: Vascular tissues (xylem and phloem) are found only in Pteridophytes, Gymnosperms, and Angiosperms (Tracheophytes); Bryophytes lack vascular bundles, but they share protected embryo formation with Pteridophytes.
• High-Yield Extra Facts: Both groups exhibit heteromorphic alternation of generations; however, the haploid gametophyte dominates in Bryophytes, whereas the diploid sporophyte dominates in Pteridophytes.

8. Ans. (a)

• Direct Answer: In gymnosperms, the endosperm is the female gametophyte, which forms before fertilization directly from a functional haploid megaspore (n). If the diploid vegetative leaf cell has 2n = 16, the endosperm is haploid with n = 8 chromosomes.
• Exam Trap / Distractor Alert: In angiosperms (flowering plants), the endosperm forms after double fertilization when a haploid sperm fuses with two polar nuclei, producing a triploid (3n = 24) tissue. In gymnosperms, endosperm is haploid (n = 8).
• High-Yield Extra Facts: Because gymnosperm endosperm forms before syngamy, it represents maternal haploid tissue that develops regardless of whether fertilization is ultimately successful.

9. Ans. (c)

• Direct Answer: The order Gnetales (comprising the three distinct genera Gnetum, Ephedra, and Welwitschia) is considered the most evolutionarily advanced group of gymnosperms.
• Exam Trap / Distractor Alert: Coniferales (pines, spruces) and Cycadales (cycads) possess only primitive xylem tracheids; Gnetales have evolved true vessel elements in their secondary xylem, mimicking the vascular efficiency of angiosperms.
• High-Yield Extra Facts: Gnetales also display angiosperm-like features such as opposite broad leaves with reticulate venation (Gnetum) and compound, flower-like reproductive cones surrounded by sterile bracts.

10. Ans. (d)

• Direct Answer: Chilgoza is the edible, protein- and lipid-rich seed obtained from the evergreen gymnosperm conifer Pinus gerardiana (commonly called the Chilgoza pine), native to the dry temperate valleys of the northwestern Himalayas.
• Exam Trap / Distractor Alert: Because gymnosperms do not form an ovary, they cannot produce true botanical fruits; the commercial “nut” is a naked seed shed from female woody cones.
• High-Yield Extra Facts: In India, natural Pinus gerardiana stands are largely restricted to the dry, high-altitude gorges of Himachal Pradesh (Kinnaur) and parts of Jammu and Kashmir.

11. Ans. (a)

• Direct Answer: The action spectrum of photosynthesis shows that chlorophyll pigments absorb and utilize photons most efficiently in the red spectral band (around 660–680 nm), followed by blue light (around 430–450 nm).
• Exam Trap / Distractor Alert: While blue light photons carry higher quantum energy than red light photons, chlorophylls show peak quantum yield (the efficiency of carbon fixed per absorbed photon) in the red band. Green light is largely reflected, which is why healthy foliage appears green.
• High-Yield Extra Facts: The German botanist T.W. Engelmann demonstrated this action spectrum in 1883 by illuminating filaments of the green alga Spirogyra with a prism-split light spectrum, observing that aerobic bacteria clustered primarily around the red and blue illuminated zones.

12. Ans. (a)

• Direct Answer: A poly-house (or polyethylene-covered greenhouse) is an agricultural framing structure clad in translucent plastic, designed to grow vegetables, flowers, and nursery seedlings under regulated microclimatic conditions (temperature, humidity, and ventilation).
• Exam Trap / Distractor Alert: Poly-houses are protected cultivation structures used for growing living crops, not post-harvest grain silos or refrigerated cold-storage rooms.
• High-Yield Extra Facts: In the hilly Himalayan terrain of Uttarakhand, poly-houses help counter low winter temperatures and hail damage, supporting off-season cultivation of high-value crops like capsicum, cherry tomatoes, and carnations.

13. Ans. (b)

• Direct Answer: The commercially valuable spice turmeric (Curcuma longa) is the prepared, dried rhizome—a modified horizontal underground storage stem that bears distinct nodes, internodes, and scale leaves.
• Exam Trap / Distractor Alert: Although buried underground, rhizomes are true stems rather than roots; they are distinguished from roots by the presence of nodes, internodes, axillary buds, and scale leaves.
• High-Yield Extra Facts: The yellow pigment in turmeric is the polyphenol curcumin, which possesses anti-inflammatory and antioxidant properties; the ginger family (Zingiberaceae) also includes ginger and cardamom.

14. Ans. (b)

• Direct Answer: Bhojpatra (birch bark) is harvested from the Himalayan Birch (Betula utilis, locally called Bhojpatra), an alpine deciduous tree native to the sub-alpine timberline of the Himalayas.
• Exam Trap / Distractor Alert: While Rhododendron arboreum (Buransh, the state tree of Uttarakhand) produces scarlet flowers used for juices, its bark is not papery and cannot be peeled for writing; Bhojpatra is harvested specifically from Betula utilis.
• High-Yield Extra Facts: Bhojpatra bark consists of thin, parchment-like layers infused with betulin, making it durable and naturally resistant to fungal decay, which helped preserve ancient sacred Sanskrit texts for centuries.

15. Ans. (c)

• Direct Answer: Alphonso (locally known as Hapoos) is a premium commercial mango (Mangifera indica) cultivar prized for its low fiber content, sweet taste, rich golden-yellow pulp, and aromatic fragrance.
• Exam Trap / Distractor Alert: Alphonso is a classic drupe fruit of the mango tree; other notable Indian mango varieties include Dasheri, Langra, Chausa, and Kesar.
• High-Yield Extra Facts: Grown along the Konkan belt of western India (including Ratnagiri, Sindhudurg, and Raigad), the Alphonso mango holds Geographical Indication (GI) status in India.

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Hemant Bhatt

Chief Mentor at Oracle IAS

Hemant Bhatt is a B. Tech from Pantnagar University and has studied Social Sciences at SciencesPo, Paris. He teaches at Oracle IAS, Dehradun. He has given 5 UPSC mains back to back along with 2 interviews.
He is a bibliophile,accomplished writer and a fitness enthusiast.

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