Plant Physiology

Step 1: Define guttation.
Guttation is the exudation of liquid water from the tips or margins of leaves, especially during night or early morning, when transpiration is low but root pressure is high.
Step 2: Examine each statement.
- A: The term guttation was given by Stephan Hales → Correct.
- B: Caused due to root pressure, pushing water out through hydathodes → Correct.
- C: Occurs in the day → Wrong, as it occurs at night or early morning, not usually in the day.
- D: Exudation of water with dissolved salts and minerals through hydathodes → Correct.
Step 3: Conclusion.
Correct statements are A, B and D only.

Step 1: Function of stomata.
Stomata are pores on the leaf surface that regulate gas exchange and transpiration.
Their opening and closing depend on turgor pressure changes in guard cells.
Step 2: Role of Potassium.
Potassium ions (K ) play a key role in controlling stomatal movement.
- When K ions enter guard cells, water follows osmotically, guard cells become turgid, and stomata open.
- When K ions exit, guard cells lose water, become flaccid, and stomata close.
Step 3: Analysis of options.
- (A) Potassium: Correct, regulates stomatal opening and closing.
- (B) Nitrogen: Important for protein and chlorophyll synthesis, not stomatal movement.
- (C) Phosphorus: Involved in energy transfer (ATP), not directly in stomatal regulation.
- (D) Sulphur: Needed for amino acids, not related to stomata.
Step 4: Conclusion.
Thus, potassium is the essential nutrient responsible for regulating stomatal opening and closing.

Step 1: Background of Plant Physiology.
Plant Physiology deals with the study of functions and vital processes of plants such as photosynthesis, respiration, water relations, and mineral nutrition.
Step 2: Contribution of Stephen Hales.
Stephen Hales (1677–1761) is known as the “Father of Plant Physiology.”
His book ‘Vegetable Staticks’ (1727) described experiments on water uptake, transpiration, and gas exchange in plants.
Step 3: Analysis of options.
- (1) Shelford: Known as father of Animal Ecology, not Plant Physiology.
- (2) Stephen Hales: Correct, pioneer in plant physiological studies.
- (3) W. Kutins: Not associated with this field.
- (4) Fisher: Wrong, not credited as father of plant physiology.
Step 4: Conclusion.
Therefore, the father of plant physiology is Stephen Hales.

Step 1: Define photoperiodism.
Photoperiodism is the response of plants to the relative lengths of day and night. It affects flowering and other physiological processes.
Step 2: Long day plants.
Long day plants flower when the day length exceeds a certain critical value, typically more than 14 hours of light per day.
Examples include spinach, wheat, barley, lettuce, and radish.
Step 3: Checking options.
- 10 hours: Too short, this is suitable for short-day plants.
- 12 hours: Borderline neutral day length, not for long-day species.
- 14 hours: Minimum requirement, but most need slightly longer.
- More than 14 hours: Correct, fits the definition of long-day plants.
Step 4: Conclusion.
Thus, long-day plants require more than 14 hours of day length.