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Plant Life - Factors affecting Photosynthesis

Grade 7ICSE

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Photosynthesis is the process by which green plants manufacture food (glucose) using carbon dioxide (CO2CO_2) and water (H2OH_2O) in the presence of sunlight and chlorophyll.

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Light Intensity: The rate of photosynthesis increases with an increase in light intensity up to a certain point, after which it becomes constant. If light is too intense, it may damage the chlorophyll.

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Carbon Dioxide (CO2CO_2) Concentration: Since the atmosphere contains only about 0.03%0.03\% to 0.04%0.04\% of CO2CO_2, increasing this concentration generally increases the rate of photosynthesis.

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Temperature: Photosynthesis occurs optimally between 25∘C25^{\circ}C and 35∘C35^{\circ}C. Temperatures above 40∘C40^{\circ}C inhibit the process because the enzymes involved are destroyed by heat.

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Water Availability: Water is a vital raw material. A lack of H2OH_2O causes the stomata to close to prevent transpiration, which in turn stops the entry of CO2CO_2 and slows down photosynthesis.

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Chlorophyll: This green pigment is essential for absorbing solar energy. Leaves with variegated patches (like Croton) only perform photosynthesis in the green areas where chlorophyll is present.

📐Formulae

6CO2+6H2O→ChlorophyllSunlightC6H12O6+6O26CO_{2} + 6H_{2}O \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} C_{6}H_{12}O_{6} + 6O_{2}

Rate of Photosynthesis∝Light Intensity (up to a limit)\text{Rate of Photosynthesis} \propto \text{Light Intensity (up to a limit)}

Rate of Photosynthesis∝[CO2] concentration\text{Rate of Photosynthesis} \propto [CO_{2}] \text{ concentration}

💡Examples

Problem 1:

During an experiment, a plant is provided with water enriched with a 0.1%0.1\% solution of Sodium Bicarbonate (NaHCO3NaHCO_{3}). How does this affect the rate of photosynthesis?

Solution:

The rate of photosynthesis will increase.

Explanation:

NaHCO3NaHCO_{3} releases extra CO2CO_{2} into the water. Since CO2CO_{2} is a limiting factor and a raw material for photosynthesis, increasing its concentration accelerates the production of glucose (C6H12O6C_{6}H_{12}O_{6}).

Problem 2:

Explain why a plant kept in a glass greenhouse often grows faster than one outside in a cold climate.

Solution:

The greenhouse creates an optimal environment by trapping heat (increasing temperature to 25∘C−30∘C25^{\circ}C - 30^{\circ}C) and providing sufficient light.

Explanation:

Photosynthesis is temperature-dependent. The greenhouse effect maintains a temperature closer to the optimal range for plant enzymes, unlike the cold external environment which slows down molecular movement and enzyme activity.

Problem 3:

If a leaf is tested with iodine and only the green parts turn blue-black, what does this conclude regarding the factors of photosynthesis?

Solution:

This concludes that chlorophyll is essential for photosynthesis.

Explanation:

Iodine turns blue-black in the presence of starch. Starch is the stored form of glucose (C6H12O6C_{6}H_{12}O_{6}). The fact that only green areas (containing chlorophyll) produced starch proves that light energy cannot be converted to chemical energy without chlorophyll.

Factors affecting Photosynthesis - Revision Notes & Key Formulas | ICSE Class 7 Science