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.
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 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.
Guttation in plants occurs due to:
A
Transpiration
B
Root pressure and high humidity conditions
C
Photorespiration
D
Osmotic stress
Correct Answer:
B. Root pressure and high humidity conditions
Explanation:
Guttation is the exudation of xylem sap through hydathodes, caused by positive root pressure, especially in early morning when transpiration is low.
The quantum yield of photosynthesis (φ) represents:
A
The number of CO₂ molecules fixed per photon absorbed
B
The wavelength of light absorbed
C
The rate of electron transport
D
The concentration of chlorophyll
Correct Answer:
A. The number of CO₂ molecules fixed per photon absorbed
Explanation:
Quantum yield is the ratio of CO₂ fixed to photons absorbed, typically 0.05-0.1 (5-10 CO₂ per 100 photons).
The casparian strip in plant roots is composed primarily of:
A
Cellulose and pectin
B
Suberin and lignin
C
Chitin and protein
D
Keratin and elastin
Correct Answer:
B. Suberin and lignin
Explanation:
The casparian strip is a hydrophobic barrier of suberin and lignin in the endodermis that prevents apoplastic transport and regulates ion uptake.
Mycorrhizal associations in plants primarily enhance the uptake of which nutrients?
A
Nitrogen and potassium
B
Phosphorus and micronutrients
C
Calcium and magnesium
D
Sulfur and iron
Correct Answer:
B. Phosphorus and micronutrients
Explanation:
Arbuscular mycorrhizal fungi increase plant access to phosphorus and micronutrients (Zn, Cu) through their extensive hyphal networks in soil.
The phenomenon where plants show reduced photosynthesis when exposed to high oxygen concentrations is called:
A
Warburg effect
B
Crabtree effect
C
Pasteur effect
D
Joule effect
Correct Answer:
A. Warburg effect
Explanation:
The Warburg effect in plants refers to photorespiration, where high O₂ competes with CO₂ for Rubisco binding, reducing net photosynthesis.
The calcium pump in plant cell vacuole membrane is primarily involved in:
A
Maintaining osmotic potential
B
Regulating turgor pressure
C
Sequestering calcium ions for cellular signaling
D
Photosynthesis regulation
Correct Answer:
C. Sequestering calcium ions for cellular signaling
Explanation:
Calcium pumps actively transport Ca²⁺ into vacuoles, serving as a calcium reservoir for second messenger signaling in plant cells.
In woody dicots, the wood primarily consists of:
A
Secondary phloem fibers
B
Secondary xylem
C
Primary xylem elements
D
Cortical cells
Correct Answer:
B. Secondary xylem
Explanation:
Wood is composed of secondary xylem with thick-walled tracheids and vessel elements that provide mechanical support and water transport. Annual rings visible in wood represent secondary xylem produced by vascular cambium.
