Numericals & Tricks

JEE Mains and Advanced

• Light reactions:

• Efficiency of photosynthesis: ~2/100 rule: Efficiency (approximately 1%) = (2 units of energy harvested by chloroplast) / (100 units of light energy incident on leaves).

• Quantum yield: ~8 per 4 quanta rule: For every four quanta of light energy absorbed, about eight molecules of oxygen (O2) are released during photosynthesis, indicating a high efficiency of the process.

• Action spectrum: Remember the peaks: Two prominent peaks in the action spectrum correspond to red light (around 680 nm) and blue light (around 450 nm), indicating their effectiveness in driving photosynthesis.

• Red drop: High light blues: The red drop phenomenon occurs at high light intensities due to the saturation of photosystem II, making blue light relatively more efficient in driving photosynthesis under such conditions.

Calvin Cycle (Dark Reactions):

• Rate of carbon dioxide fixation: ~30 per mg Chl per hr rule: The typical range for the rate of CO2 fixation is 10-30 µmol CO2/mg Chl/hr, reflecting the activity of the Calvin cycle in converting CO2 into organic compounds.

• ATP requirement: ~3 ATP per CO2 molecule rule: Each molecule of CO2 fixed during the Calvin cycle requires approximately 3 ATP molecules to drive the reactions involved in carbon assimilation.

• NADPH requirement: ~2 NADPH per CO2 molecule rule: Similar to ATP, each CO2 molecule fixed during the Calvin cycle also requires about 2 NADPH molecules as a source of reducing power.

Photorespiration:

• Rate of photorespiration: ~50% of photosynthesis rate: Typically, photorespiration can account for up to 20-50% of the rate of photosynthesis, highlighting the importance of managing this process to improve plant productivity.

• Compensation point: ~10% of full sunlight: The compensation point is the light intensity at which the rate of photosynthesis balances the rate of photorespiration. It commonly occurs at around 10% of full sunlight.

Transpiration:

• Rate of transpiration: ~1-2 mmol H2O/dm2 leaf area/hr rule: Transpiration rates typically fall within the range of 1-2 mmol H2O/dm2 leaf area/hr, providing insights into water loss and plant water relations.

• Water use efficiency: ~1-2 g per kg H2O transpired: Water use efficiency quantifies the amount of dry matter produced per unit of water transpired. Plants with higher water use efficiency are better adapted to water scarcity.

Mineral Nutrition:

• Macronutrients: ~NPK rule: The most commonly remembered macronutrients are nitrogen (N), phosphorus (P), and potassium (K), which are crucial for plant growth and metabolism.

• Micronutrients: ~FeCuZnMn rule: Micronutrients such as iron (Fe), copper (Cu), zinc (Zn), and manganese (Mn) play essential roles in various plant physiological processes despite being required in smaller amounts.

CBSE Board Exams

Photosynthesis:

• Equation of photosynthesis: ~6CO2,6H2O,1 glucose rule: Remember the 6’s: The balanced equation for photosynthesis involves 6 molecules of CO2, 6 molecules of H2O, and produces 1 molecule of glucose (C6H12O6), along with 6 molecules of O2.

Respiration:

• Equation of respiration: ~6CO2, 6H2O, energy rule: Respiration is essentially the reverse of photosynthesis, where 1 molecule of glucose (C6H12O6) reacts with 6 molecules of O2 to produce 6 molecules of CO2, 6 molecules of H2O, and releases energy.

Transpiration:

• Factors affecting transpiration: ~THWL rule: The key factors influencing transpiration are temperature (T), humidity (H), wind speed (W), and light intensity (L).

Mineral Nutrition:

• Functions of essential elements: Nitrogen, Potassium, Water: Remember “NPK + W” for the major essential elements necessary for plant growth and health.