General Q&A for Class 12 · Page 240
5,215 free answers in General for Class 12 students, across CBSE, ICSE and State boards.
Question & Answer
Questions
- GeneralClass 12All
Define balanced solution.
A balanced solution is a nutrient medium containing all the essential mineral elements in optimal concentrations required for normal plant growth and development. Such solutions are used in hydroponics and experimental plant nutrition studies to ensure plants receive complete mineral nutrition without deficiencies or toxicities.
- GeneralClass 12All
Name the micronutrient which is the constituent of nitrate reductase.
Answer:Molybdenum (Mo) is the essential micronutrient that forms a critical component of the enzyme nitrate reductase, which catalyzes the reduction of nitrate (NO₃⁻) to nitrite (NO₂⁻) during nitrogen assimilation in plants.
- GeneralClass 12All
Why do well-watered plants transpire more during sunny and windy days than in cool and calm morning? Why it is important to plants?
Effect of Environmental Factors on Transpiration Well-watered plants exhibit significantly higher transpiration rates on sunny, windy days compared to cool, calm mornings due to the combined influence of multiple environmental factors on stomatal behavior and evaporative demand. Factors Causing Increased Transpiration on Sunny, Windy Days: 1. Light (Sunlight) <p
- GeneralClass 12All
What will happen if we remove a ring of bark leaving a narrow strip in a plant?
Girdling (Ringing) Experiment: Effects Removing a ring of bark (including phloem, cortex, and cork) from a tree trunk while leaving the xylem intact demonstrates the unidirectional translocation of organic nutrients in phloem. What Happens: Immediate Effects (Hours to Days): Upward Water Transport Unaffected:</
- GeneralClass 12All
hat role does active transport play in transport of substances in living cell?
Active Transport: Definition and Significance Active transport is the energy-dependent movement of molecules or ions against their concentration gradient (from low concentration → high concentration) across biological membranes. Key Characteristics: Energy source: ATP (adenosine triphosphate) Direction: Against gradient (uphill tr
- GeneralClass 12All
How are C₄ plants more efficient than C₃ plants?
C₄ plants are photosynthetically more efficient than C₃ plants, particularly under conditions of: High temperature High light intensity Water scarcity Efficiency Comparison: Parameter C₃ Plants <td width
- GeneralClass 12All
What is the principle of mass flow or pressure flow system of food translocation in plants?
Pressure Flow Hypothesis: Principle The mass flow (or pressure flow) hypothesis, proposed by Ernst Münch (1930), explains how organic solutes (primarily sucrose) are translocated from source to sink through phloem tissue. Core Principle: Organic solutes move en masse (in bulk) through phloem sieve
- GeneralClass 12All
How can you say that transpiration is a compromise for plants in a way, to carry out photosynthesis?
Transpiration is often called a "necessary evil" because it represents a compromise between two conflicting needs: The Dilemma: Benefit (For Photosynthesis) Cost (Water Loss) Stomata must open to allow CO₂ entry for photosynthesis <td
- GeneralClass 12All
Why are minerals remobilised in plants? Mention any two minerals which are remobilised.
Mineral Remobilization: Definition and Purpose Mineral remobilization is the process by which plants redistribute mineral nutrients from older, senescing tissues to younger, actively growing regions. This ensures efficient nutrient use and plant survival. Why Remobilization Occurs: Resource Conservation: Before leaves/flowers shed, va
- GeneralClass 12All
Discuss four plant factors that influence the rate of transpiration.
Internal (Plant) Factors Affecting Transpiration: 1. Frequency and Distribution of Stomata Definition: Number of stomata per unit leaf area (stomatal density) Typical Range: 100-1000 stomata/mm² Relationship: Generally, higher stomatal density → higher transpiration Exceptions: Xerophytes have numerou
- GeneralClass 12All
Give difference between turgid and flaccid cells.
Characteristic Turgid Cell Flaccid Cell Water Movement Endosmosis (water entry) occurs No net movement (equilibrium)
- GeneralClass 12All
How can you demonstrate by an experiment that transpiration takes place in plants?
Experiment: Demonstration of Transpiration Objective: To prove that plants lose water vapor through transpiration Materials Required: Healthy potted plant Bell jar (glass/transparent) Oil cloth/plastic sheet Glass plate Anhydrous cobalt chloride paper (blue) Vaseline Procedure: Setup: Wat
- GeneralClass 12All
Differentiate between active water absorption and passive water absorption.
Parameter Active Water Absorption Passive Water Absorption Energy Requirement Requires metabolic energy (ATP) No energy required (passive process) </tr
- GeneralClass 12All
How imbibition pressure helps in germination of seeds?
Imbibition plays a crucial role in seed germination through the following mechanism: Step-by-Step Process: Dry Seed Characteristics: Extremely negative water potential (Ψ<sub>w</sub> ≈ –100 to –300 MPa) High concentration of hydrophilic colloids (proteins, starch) Strong affinity for water
- GeneralClass 12All
How solute potential, water potential and pressure potential of a cell (plant) vary when kept in hypotonic solution?
When a plant cell is placed in a hypotonic solution (solution with higher water potential than the cell): Sequential Changes: Stage Water Movement Ψ<sub>p</sub> Ψ<sub>s</sub> <td widt
- GeneralClass 12All
What will be the water potential of solution B, if its solute potential Ψs at atmospheric pressure is –200 Pa?
At atmospheric pressure, the pressure potential (Ψ<sub>p</sub>) = 0 Using the formula: Ψ<sub>w</sub> = Ψ<sub>s</sub> + Ψ<sub>p</sub> Ψ<sub>w</sub> = (–200 Pa) + 0 = –200 Pa Therefore, the water potential of solution B = –200 Pa Key Principle: At atmospheric
- GeneralClass 12All
Give any two characteristic features of transport through special proteins in facilitated diffusion.
Facilitated diffusion uses membrane carrier proteins (transporters) or channel proteins to move substances across membranes along their concentration gradient. Two key characteristics: Feature Explanation 1. Specificity E
- GeneralClass 12All
Name the two factors on which water potential depends? Also give its relationship with them.
Water potential (Ψ<sub>w</sub>) depends on two components: Factor Symbol Nature Effect on Ψ<sub>w</sub> Solute Potential (Osmotic Potential) <td
- GeneralClass 12All
What is turgor pressure? Give its one significance to plants.
Turgor pressure (Ψ<sub>p</sub>) is the hydrostatic pressure exerted by the cell contents (protoplast) against the rigid cell wall when water enters the cell through osmosis. Mechanism: Cell placed in hypotonic solution Water enters by osmosis Vacuole swells, protoplast pushes against cell wall Cell wall resists, creating wall pressure (equal
- GeneralClass 12All
What are the two conditions for imbibition to occur?
Imbibition is the passive absorption of water by hydrophilic colloids, causing them to swell. Two essential conditions are: Condition Explanation 1. Water Potential Gradient There must exist a water potential gradient between the