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Plant Life - Comparison of Photosynthesis and Respiration

Grade 7ICSE

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

🔑Concepts

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Photosynthesis is an anabolic (building-up) process where green plants manufacture food in the form of glucose (C6H12O6C_6H_{12}O_6) using carbon dioxide (CO2CO_2) and water (H2OH_2O) in the presence of sunlight and chlorophyll.

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Respiration is a catabolic (breaking-down) process where living cells oxidize glucose (C6H12O6C_6H_{12}O_6) to release energy in the form of ATPATP (AdenosineAdenosine TriphosphateTriphosphate), with carbon dioxide (CO2CO_2) and water (H2OH_2O) as by-products.

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The primary site for photosynthesis is the chloroplast, whereas aerobic respiration occurs mainly in the mitochondria of the cell.

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Photosynthesis occurs only during the daytime (in the presence of light), while respiration is a continuous process that occurs both day and night in all living cells.

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During the day, the rate of photosynthesis is much higher than the rate of respiration; therefore, there is a net release of oxygen (O2O_2) and intake of carbon dioxide (CO2CO_2).

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At night, photosynthesis stops due to the absence of light, but respiration continues, leading to the intake of oxygen (O2O_2) and the release of carbon dioxide (CO2CO_2).

📐Formulae

6CO2+6H2O→ChlorophyllSunlightC6H12O6+6O26CO_2 + 6H_2O \xrightarrow[\text{Chlorophyll}]{\text{Sunlight}} C_6H_{12}O_6 + 6O_2

C6H12O6+6O2→6CO2+6H2O+Energy (ATP)C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (ATP)}

💡Examples

Problem 1:

A plant is kept in a sealed glass container in the sunlight. After a few hours, the level of O2O_2 inside the container increases. Why?

Solution:

The level of O2O_2 increases because the rate of photosynthesis is greater than the rate of respiration.

Explanation:

In sunlight, the plant performs both photosynthesis and respiration. Photosynthesis produces O2O_2 as a byproduct, while respiration consumes it. Since photosynthesis occurs at a faster rate during the day, more O2O_2 is released into the container than is consumed.

Problem 2:

What is the 'Compensation Point' in terms of gas exchange in plants?

Solution:

The Compensation Point is the light intensity at which the rate of photosynthesis exactly equals the rate of respiration.

Explanation:

At this point, the amount of CO2CO_2 consumed in photosynthesis is equal to the amount of CO2CO_2 produced during respiration, and the amount of O2O_2 produced is equal to the amount of O2O_2 consumed. There is no net exchange of gases with the environment.