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Plant Life - Respiration in Plants

Grade 7ICSE

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

🔑Concepts

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Respiration is a vital biochemical process in which living cells break down glucose (C6H12O6C_6H_{12}O_6) to release energy in the form of ATPATP (Adenosine Triphosphate).

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Aerobic Respiration: This occurs in the presence of Oxygen (O2O_2). It results in the complete breakdown of glucose into Carbon dioxide (CO2CO_2), Water (H2OH_2O), and a large amount of energy (3838 ATPATP molecules).

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Anaerobic Respiration: This occurs in the absence of Oxygen (O2O_2). In plants (like yeast or germinating seeds in water-logged soil), it produces Ethanol (C2H5OHC_2H_5OH), Carbon dioxide (CO2CO_2), and very little energy (22 ATPATP molecules).

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Gas Exchange in Plants: Plants do not have respiratory organs. They exchange gases through StomataStomata in leaves, LenticelsLenticels in woody stems, and general surfaces of the roots.

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Comparison with Photosynthesis: While Photosynthesis is an anabolic process (building food) that occurs only in the presence of sunlight, Respiration is a catabolic process (breaking down food) that occurs continuously (24/724/7) in all living cells.

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The energy released during respiration is used for various metabolic activities like growth, mineral absorption, and cell division.

📐Formulae

C6H12O6+6O2→enzymes6CO2+6H2O+38 ATP (Energy)C_6H_{12}O_6 + 6O_2 \xrightarrow{\text{enzymes}} 6CO_2 + 6H_2O + 38\text{ ATP (Energy)}

C6H12O6→absence of O22C2H5OH+2CO2+2 ATP (Energy)C_6H_{12}O_6 \xrightarrow{\text{absence of } O_2} 2C_2H_5OH + 2CO_2 + 2\text{ ATP (Energy)}

Glucose→Ethyl Alcohol+Carbon dioxide+Energy (Anaerobic)\text{Glucose} \rightarrow \text{Ethyl Alcohol} + \text{Carbon dioxide} + \text{Energy (Anaerobic)}

💡Examples

Problem 1:

Calculate the number of Carbon dioxide (CO2CO_2) molecules produced when 55 molecules of Glucose (C6H12O6C_6H_{12}O_6) are completely oxidized during aerobic respiration.

Solution:

3030 molecules of CO2CO_2.

Explanation:

According to the balanced chemical equation for aerobic respiration, 11 molecule of C6H12O6C_6H_{12}O_6 yields 66 molecules of CO2CO_2. Therefore, 55 molecules of glucose will yield 5×6=305 \times 6 = 30 molecules of CO2CO_2.

Problem 2:

Why do potted plants sometimes die if they are overwatered for a long duration?

Solution:

Due to the lack of oxygen reaching the roots, leading to anaerobic respiration.

Explanation:

Overwatering displaces the air in the soil spaces. The roots are unable to get O2O_2 for aerobic respiration and switch to anaerobic respiration. This produces Ethanol (C2H5OHC_2H_5OH), which is toxic to the plant and can lead to root rot and death.

Problem 3:

During an experiment to show that heat is evolved during respiration, why are thermos flasks used?

Solution:

To prevent the exchange of heat with the environment.

Explanation:

Thermos flasks are vacuum-insulated. Using them ensures that any rise in temperature measured by the thermometer is strictly due to the heat energy released during the respiration of the germinating seeds, rather than external environmental factors.