In the Calvin cycle, how many ATP and NADPH molecules are required to fix one molecule of CO2?
A1 ATP, 1 NADPH
B3 ATP, 2 NADPH
C2 ATP, 1 NADPH
D6 ATP, 3 NADPH
Correct Answer:
B. 3 ATP, 2 NADPH
Explanation:
The reduction phase of Calvin cycle requires 3 ATP per CO2 fixed. NADPH requirement is 2 molecules per CO2. These are stoichiometric ratios essential for understanding photosynthetic efficiency.
The phenomenon of senescence in plants is primarily controlled by which plant hormone?
AAuxin
BGibberellin
CEthylene
DCytokinin
Correct Answer:
C. Ethylene
Explanation:
Ethylene is the senescence hormone that promotes leaf yellowing, abscission, and fruit ripening. Cytokinins antagonize ethylene effects. This hormone physiology is important for understanding plant development.
The phenomenon where certain seeds require light for germination is called:
APhototropism
BPhotomorphogenesis
CPhotoperiodism
DHeliotropism
Correct Answer:
B. Photomorphogenesis
Explanation:
Photomorphogenesis refers to light-dependent development processes including light-mediated seed germination. Phytochrome is the photoreceptor involved. This is distinct from photoperiodism (flowering response to day length).
In C4 photosynthesis, the first stable compound formed after CO2 fixation is:
A3-Phosphoglycerate (3-PGA)
BOxaloacetate
CRibulose-1,5-bisphosphate
DGlucose
Correct Answer:
B. Oxaloacetate
Explanation:
In C4 plants, PEP carboxylase fixes CO2 into oxaloacetate (4-carbon compound), unlike C3 plants where RuBisCO produces 3-PGA. This adaptation reduces photorespiration and is efficient in hot climates.
Which of the following pigments is primarily responsible for absorbing light in the red and far-red regions of the spectrum in photosynthesis?
AChlorophyll a
BPhytochrome
CCarotenoids
DXanthophyll
Correct Answer:
B. Phytochrome
Explanation:
Phytochrome exists in two interconvertible forms (Pr and Pfr) and absorbs maximally in red (~660 nm) and far-red (~730 nm) regions. It's crucial for seed germination and photoperiodism - important for UPSC agriculture-related questions.
The root pressure phenomenon in plants is primarily due to which of the following?
ATranspiration pull alone
BCapillary action in soil
CActive transport of mineral ions into xylem, creating osmotic gradient
DGravitational force on water column
Correct Answer:
C. Active transport of mineral ions into xylem, creating osmotic gradient
Explanation:
Root pressure is generated by active transport of mineral ions into the xylem sap, creating a concentration gradient that draws water in osmotically. This is distinct from transpiration pull and is a key concept in plant physiology.
A plant cell is placed in a hypertonic solution. Which physical phenomenon occurs, and what is the correct term for it?
APlasmolysis - protoplasm shrinks away from cell wall
BDeplasmolysis - cell regains water
CTurgor pressure increases
DCell wall becomes permeable
Correct Answer:
A. Plasmolysis - protoplasm shrinks away from cell wall
Explanation:
In hypertonic solutions, water moves out of the cell due to osmosis, causing protoplasm to shrink away from the cell wall - this is plasmolysis. This is a fundamental osmotic principle tested in SSC/Railway exams.
