Botany
The turgor pressure in plant cells is maintained by which osmotically active substances?
A Cellulose and starch
B Soluble sugars, organic acids, and mineral ions
C Proteins and lipids
D Chlorophyll and carotenoids
Correct Answer:
B. Soluble sugars, organic acids, and mineral ions Explanation:
Osmotically active solutes like glucose, sucrose, malate, and K⁺ ions accumulate in vacuoles to maintain turgor pressure and cell rigidity.
Which of the following statements about stomatal conductance is correct?
A It remains constant regardless of humidity
B It increases with decreasing light intensity
C It is directly proportional to stomatal aperture and inversely related to diffusion path length
D It is independent of guard cell turgor pressure
Correct Answer:
C. It is directly proportional to stomatal aperture and inversely related to diffusion path length Explanation:
Stomatal conductance (gs) is the rate of gas diffusion through stomata, dependent on aperture width and inversely on distance (g = A/L).
The Hatch-Slack cycle in C4 plants first produces which compound?
A Oxaloacetate (4-carbon)
B 3-Phosphoglycerate (3-carbon)
C Malate (4-carbon)
D Pyruvate (3-carbon)
Correct Answer:
A. Oxaloacetate (4-carbon) Explanation:
In C4 photosynthesis, CO₂ combines with phosphoenolpyruvate (PEP) to form oxaloacetate (4-carbon), catalyzed by PEP carboxylase.
The phenomenon of etiolation in plants is characterized by:
A Increased chlorophyll synthesis in darkness
B Elongated internodes, pale color, and reduced photosynthetic capacity
C Increased leaf area in low light
D Enhanced root development
Correct Answer:
B. Elongated internodes, pale color, and reduced photosynthetic capacity Explanation:
Etiolation is the adaptation to grow in darkness: shoots elongate, leaves remain pale (no chlorophyll), and seedlings appear yellowish.
The transpiration pull mechanism in xylem transport depends on which principle?
A Osmotic gradient
B Cohesion-tension theory and water's high surface tension
C Active transport of ions
D Pressure exerted by companion cells
Correct Answer:
B. Cohesion-tension theory and water's high surface tension Explanation:
Transpiration creates negative pressure (tension) in xylem; water cohesion allows continuous columns to be pulled upward against gravity.
Which plant hormone promotes fruit ripening and is commercially used in India for tomato and mango maturation?
A Gibberellin
B Ethylene
C Cytokinin
D Auxin
Correct Answer:
B. Ethylene Explanation:
Ethylene (C₂H₄) is the ripening hormone that triggers color change, softening, and aroma development in climacteric fruits.
The non-cyclic photophosphorylation in photosystem II produces:
A ATP only
B NADPH only
C Both ATP and NADPH, and releases O₂
D Glucose directly
Correct Answer:
C. Both ATP and NADPH, and releases O₂ Explanation:
Non-cyclic photophosphorylation involves PSII and PSI, producing ATP, NADPH, and O₂ from water photolysis.
In the electron transport chain of chloroplasts, which complex transfers electrons from water to plastoquinone?
A Cytochrome b₆f complex
B Photosystem II (PSII)
C Photosystem I (PSI)
D ATP synthase
Correct Answer:
B. Photosystem II (PSII) Explanation:
PSII catalyzes photolysis of water at the oxygen-evolving complex, transferring electrons to plastoquinone in the thylakoid membrane.
The double fertilization process unique to angiosperms results in the formation of:
A Embryo and endosperm
B Seed coat and hilum
C Ovule and integuments
D Pollen and stigma
Correct Answer:
A. Embryo and endosperm Explanation:
One sperm nucleus fertilizes the egg (embryo), another fuses with polar nuclei (endosperm); this endosperm provides nutritive tissue for the developing embryo.
Which of the following is the primary pigment responsible for capturing light energy in photosynthesis?
A Chlorophyll a
B Chlorophyll b
C Xanthophyll
D Carotenoid
Correct Answer:
A. Chlorophyll a Explanation:
Chlorophyll a is the primary pigment that directly participates in the light reactions of photosynthesis and forms the reaction centre of both photosystems.
