All living organisms need food for energy, but to use that energy, they must first release it through respiration.
In plants, food is created through photosynthesis, which uses captured light energy to convert carbon dioxide and water into complex molecules like glucose and starch. These compounds are stored in plants, but the energy is not immediately available. Respiration allows plants to tap into that stored energy to power growth and other biological processes.
In this blog post, we’ll explain how respiration works, why it matters and which factors affect it.
Respiration and energy metabolism
Respiration is the process of breaking carbon–carbon (C–C) bonds in complex compounds through oxidation within cells. While glucose is the primary compound used, fats, proteins and organic acids are also metabolized under certain conditions.[1]
This oxidation releases a large amount of energy, but not in a form that cells can immediately use. Instead, the energy is used to synthesize adenosine triphosphate (ATP)[2] through a series of reactions. ATP is known as the “energy currency of life” because it stores and releases energy as needed, driving metabolic activities like growth, nutrient uptake and cellular maintenance.
In addition to glucose, respiration requires oxygen, which is taken in from the atmosphere and reduced to water in a process called aerobic respiration. Via anaerobic respiration, which can occur under oxygen-deficient conditions such as waterlogged roots, plants can also respire without oxygen. However, anaerobic respiration is far less efficient, generating just two molecules of ATP per glucose molecule compared to up to 38 molecules from aerobic respiration. The equations for respiration are as follows:[3]
Respiration and energy metabolism
Respiration is the process of breaking carbon–carbon (C–C) bonds in complex compounds through oxidation within cells. While glucose is the primary compound used, fats, proteins and organic acids are also metabolized under certain conditions.[1]
This oxidation releases a large amount of energy, but not in a form that cells can immediately use. Instead, the energy is used to synthesize adenosine triphosphate (ATP)[2] through a series of reactions. ATP is known as the “energy currency of life” because it stores and releases energy as needed, driving metabolic activities like growth, nutrient uptake and cellular maintenance.
Respiration and energy metabolism
Respiration is the process of breaking carbon–carbon (C–C) bonds in complex compounds through oxidation within cells. While glucose is the primary compound used, fats, proteins and organic acids are also metabolized under certain conditions.[1]
This oxidation releases a large amount of energy, but not in a form that cells can immediately use. Instead, the energy is used to synthesize adenosine triphosphate (ATP)[2] through a series of reactions. ATP is known as the “energy currency of life” because it stores and releases energy as needed, driving metabolic activities like growth, nutrient uptake and cellular maintenance.
In addition to glucose, respiration requires oxygen, which is taken in from the atmosphere and reduced to water in a process called aerobic respiration. Via anaerobic respiration, which can occur under oxygen-deficient conditions such as waterlogged roots, plants can also respire without oxygen. However, anaerobic respiration is far less efficient, generating just two molecules of ATP per glucose molecule compared to up to 38 molecules from aerobic respiration. The equations for respiration are as follows:[3]
- Aerobic: C6H12O6 (glucose) + 6 O2 (oxygen) ® 6 CO2 (carbon dioxide) + 6 H2O (water) + ~38 ATP (energy)
- Anaerobic: C6H12O6 (glucose) + NAD+ (nicotinamide adenine dinucleotide) ® NADH (nicotinamide adenine dinucleotide hydrogen) + 2 ATP (energy) + various waste products
In addition to glucose, respiration requires oxygen, which is taken in from the atmosphere and reduced to water in a process called aerobic respiration. Via anaerobic respiration, which can occur under oxygen-deficient conditions such as waterlogged roots, plants can also respire without oxygen. However, anaerobic respiration is far less efficient, generating just two molecules of ATP per glucose molecule compared to up to 38 molecules from aerobic respiration. The equations for respiration are as follows:[3]
- Aerobic: C6H12O6 (glucose) + 6 O2 (oxygen) ® 6 CO2 (carbon dioxide) + 6 H2O (water) + ~38 ATP (energy)
- Anaerobic: C6H12O6 (glucose) + NAD+ (nicotinamide adenine dinucleotide) ® NADH (nicotinamide adenine dinucleotide hydrogen) + 2 ATP (energy) + various waste products
Three stages of respiration
Respiration occurs in three stages. While biologists differ slightly in how they define these stages, the process can be distilled into three metabolic steps: glycolysis, the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC), also known as oxidative phosphorylation.
Three stages of respiration
Respiration occurs in three stages. While biologists differ slightly in how they define these stages, the process can be distilled into three metabolic steps: glycolysis, the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC), also known as oxidative phosphorylation.
Three stages of respiration
Respiration occurs in three stages. While biologists differ slightly in how they define these stages, the process can be distilled into three metabolic steps: glycolysis, the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC), also known as oxidative phosphorylation.
Glycolysis
Glycolysis is the first step, when glucose is broken down into two pyruvate molecules, generating ATP and NADH in the process. The pyruvates are then used in the TCA cycle.[4]
TCA cycle
Also called the Krebs or citric acid cycle, the TCA cycle is an eight-step process that occurs within the cell’s mitochondria. It generates energy throughout the cycle, most of which is captured by coenzymes NAD+ and flavin adenine dinucleotide (FAD), which are later converted into ATP.[5] The pyruvates from glycolysis are oxidized into acetyl coenzyme A (CoA), which enters the cycle.[6]
The TCA cycle produces carbon dioxide, NADH and the reduced form of FAD (FADH2), all of which transfer their energy to the ETC.[7]
ETC
In the ETC, NADH and FADH2 donate their electrons through a series of proteins in a process called oxidative phosphorylation. This transfer releases energy that produces a large amount of ATP.[8] A byproduct of this process is reactive oxygen species, which can cause oxidative stress in plant cells if not properly regulated.[9]
Role of respiration in plant metabolism
Respiration plays a central role in plant development. Many of the products formed during respiration are used to synthesize essential molecules like amino acids, lipids and nucleotides,[10] supporting biosynthesis. The balance between respiration and photosynthesis influences the rate of biomass accumulation.[11] Since younger tissues grow more rapidly, they also exhibit higher rates of respiration.[12]
Respiration also facilitates the movement of nutrient ions across membranes[13] and helps plants respond to both abiotic and biotic stress, enabling them to acclimate to harsh conditions.[14]
Factors affecting respiration
While respiration is influenced by internal factors like tissue nitrogen concentration, plant age and size, several external conditions also affect the process:
- Temperature: Respiration increases as temperatures rise. However, if temperatures climb too high, respiration may outpace photosynthesis, slowing plant growth.[15]
- Oxygen: Oxygen availability influences aerobic respiration and is especially important in hydroponics, where dissolved oxygen levels in the root zone can affect root respiration. Research shows that low oxygen levels reduce ATP production compared to well-oxygenated roots.[16]
- Water: Severe drought can suppress respiration, while mild water stress may increase it.[17]
- Photosynthesis: Although photosynthesis is an internal factor, it is influenced by light and carbon dioxide, two external conditions that also indirectly affect respiration.
Factors affecting respiration
While respiration is influenced by internal factors like tissue nitrogen concentration, plant age and size, several external conditions also affect the process:
- Temperature: Respiration increases as temperatures rise. However, if temperatures climb too high, respiration may outpace photosynthesis, slowing plant growth.[15]
- Oxygen: Oxygen availability influences aerobic respiration and is especially important in hydroponics, where dissolved oxygen levels in the root zone can affect root respiration. Research shows that low oxygen levels reduce ATP production compared to well-oxygenated roots.[16]
Factors affecting respiration
While respiration is influenced by internal factors like tissue nitrogen concentration, plant age and size, several external conditions also affect the process:
- Temperature: Respiration increases as temperatures rise. However, if temperatures climb too high, respiration may outpace photosynthesis, slowing plant growth.[15]
- Oxygen: Oxygen availability influences aerobic respiration and is especially important in hydroponics, where dissolved oxygen levels in the root zone can affect root respiration. Research shows that low oxygen levels reduce ATP production compared to well-oxygenated roots.[16]
- Water: Severe drought can suppress respiration, while mild water stress may increase it.[17]
- Photosynthesis: Although photosynthesis is an internal factor, it is influenced by light and carbon dioxide, two external conditions that also indirectly affect respiration.
- Water: Severe drought can suppress respiration, while mild water stress may increase it.[17]
- Photosynthesis: Although photosynthesis is an internal factor, it is influenced by light and carbon dioxide, two external conditions that also indirectly affect respiration.
Nutrient impact
Several macro- and micronutrients are involved in respiration, making balanced nutrition essential.
Of the macronutrients, nitrogen is particularly important. It helps form amino acids and enzymes, which are vital for metabolic reactions. Tissue nitrogen concentration is closely linked to respiration rate, as high-nitrogen proteins, enzymes and compounds like chlorophyll boost metabolic activity and meet the demand for ATP and NADPH.[18]
Phosphorus is also important, as it is a core component of ATP and supports the conversion of food energy into chemical energy during oxidative phosphorylation.
Of the micronutrients, sulfur and iron participate in the ETC by forming part of the proteins that transfer electrons. Magnesium supports respiration by catalyzing ATP synthesis.[19]
Conclusion
Respiration fuels the growth and development of all living organisms. In plants, high respiration rates indicate vigor and yield potential. Growers can support respiration in hydroponic systems by maintaining an appropriate temperature, promoting photosynthesis with adequate carbon dioxide and light, supplying oxygen to the roots and providing the right balance of essential nutrients.
Emerald Harvest Team
[1] Ministry of Education Government of India. n.d. “Chapter 14 Respiration in Plants.” Accessed May 20, 2025. https://icar.iitk.ac.in/sathee-icar/student-corner/ncert-books/class-11/nb-bio-11/bio-11-chapter-14-respiration-in-plants/.
[2] Ibid.
[3] Bartee, Lisa, and Christine Anderson. 2016. “Chapter VII: How cells obtain energy.” In Mt Hood Community College Biology 101. Open Oregon Educational Resources. https://openoregon.pressbooks.pub/mhccbiology101/chapter/overview-of-cellular-respiration/.
[4] Chaudhry, Raheel, and Matthew A. Varacallo. 2023. “Biochemistry, Glycolysis.” Last updated August 8. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK482303/.
[5] Britannica. 2025. “Tricarboxylic acid cycle.” Last updated March 27. https://www.britannica.com/science/glycolysis.
[6] Ahmad, Maria, Adam Wolberg, and Chadi I. Kahwaji. 2023. “Biochemistry, Electron Transport Chain.” Last updated September 4. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK526105/.
[7] Britannica. 2025. “Tricarboxylic acid cycle.” Last updated March 27. https://www.britannica.com/science/glycolysis.
[8] Ahmad, Maria, Adam Wolberg, and Chadi I. Kahwaji. 2023. “Biochemistry, Electron Transport Chain.” Last updated September 4. StatPearls Publishing. https://www.ncbi.nlm.nih.gov/books/NBK526105/.
[9] Sharma, Pallavi, Ambuj Bhushan Jha, Rama Shanker Dubey, and Mohammad Pessarakli. 2012. “Reactive Oxygen Species, Oxidative Damage, and Antioxidative Defense Mechanism in Plants Under Stressful Conditions.” Journal of Botany. https://doi.org/10.1155/2012/217037.
[10] Alberts, B., A. Johnson, J. Lewis, et. al. 2002. “How Cells Obtain Energy from Food.” In Molecular Biology of the Cell, Fourth Edition. Garland Science. https://www.ncbi.nlm.nih.gov/books/NBK26882/.
[11] Millar, A. Harvey, James Whelan, Kathleen L. Soole, and David A. Day. 2011. “Organization and Regulation of Mitochondrial Respiration in Plants.” Annual Review of Plant Biology 62: 79-104. https://doi.org/10.1146/annurev-arplant-042110-103857.
[12] Bulut, Mustafa, Saleh Alseekh, and Alisdair R. Fernie. 2022. “Natural Variation of Respiration-Related Traits in Plants.” Plant Physiology 191 (4): 2120-2132. https://doi.org/10.1093/plphys/kiac593.
[13] Waring, Richard H., and Steven W. Running. 2007. “Chapter 3 – Carbon Cycle.” In Forest Ecosystems (Third Edition). Academic Press. https://doi.org/10.1016/B978-012370605-8.50008-6.
[14] Jethva, Jay, Romy R. Schmidt, Margret Sauter, and Jennifer Selinski. 2022. “Try or Die: Dynamics of Plant Respiration and How to Survive Low Oxygen Conditions.” Plants 11 (2): 205. https://doi.org/10.3390/plants11020205.
[15] VanDerZanden, Ann Marie. 2008. “Environmental Factors Affecting Plant Growth.” Oregon State University Extension Service. https://extension.oregonstate.edu/gardening/techniques/environmental-factors-affecting-plant-growth.
[16] Tan, Jiehui, Haozhao Jiang, Yamin Li, et. al. 2023. “Growth, Phytochemicals, and Antioxidant Activity of Kale Grown Under Different Nutrient-Solution Depths in Hydroponic.” Horticulturae 9 (1): 53. https://doi.org/10.3390/horticulturae9010053.
[17] Seleiman, Mahmoud F., Nasser Al-Suhaibani, Nawab Ali, et. al. 2021. “Drought Stress Impacts on Plants and Different Approaches to Alleviate Its Adverse Effects.” Plants 10 (2): 259. https://doi.org/10.3390/plants10020259.
[18] Schmiege, Stephanie C, Mary Heskel, Yuzhen Fan, and Danielle A Way. 2023. “It’s Only Natural: Plant Respiration in Unmanaged Systems.” Plant Physiology 192 (2): 710-727. https:doi.org/10.1093/plphys/kiad167.
[19] Ahmed, Nazir, Baige Zhang, Bilquees Bozdar, et. al. 2023. “The Power of Magnesium: Unlocking the Potential for Increased Yield, Quality, and Stress Tolerance of Horticultural Crops.” Frontiers in Plant Science 14: 1285512. https://doi.org/10.3389/fpls.2023.1285512.
