Difference Between Photosynthesis and Cellular Respiration: Types, Transformation, Comparison, Chart

Edited By Irshad Anwar | Updated on Jul 02, 2025 06:57 PM IST

What Are Photosynthesis And Cellular Respiration?

Photosynthesis and cellular respiration are the biological activities that keep life going on Earth. In photosynthesis, light energy is converted into chemical energy in which glucose and oxygen become the byproducts of carbon dioxide and water in green plants, algae, and some bacteria. It goes on in the chloroplasts of these organisms.

On the other hand, cellular respiration is when cells convert glucose and oxygen into energy, carbon dioxide, and water. It mostly happens in the mitochondria of eukaryote cells. In both processes, there is the flow of energy in biological systems: photosynthesis captures it and stores it from sunlight, while cellular respiration releases this stored energy for use by the organism. Together they are the cycle that feeds the activities of living organisms and at the same time balances the gases in the atmosphere.

Photosynthesis

Photosynthesis is a process in which green plants, algae, and some bacteria transform light energy into chemical energy; it produces glucose and oxygen from carbon dioxide and water. This key process takes place in plant cells and other photosynthetic organisms in organelles called chloroplasts. Photosynthesis can be split into two major steps: light-dependent reactions and the Calvin cycle.

In light-dependent reactions, sunlight is absorbed by pigments like chlorophyll and others, which starts the production of ATP and NADPH through the splitting of water molecules into oxygen gas. The Calvin cycle involves using this ATP and NADPH to turn carbon dioxide into glucose, an energy-rich molecule needed by living organisms to sustain life. Photosynthesis is of prime importance to life here on Earth because it is the source of energy.

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Cellular Respiration

Cellular respiration refers to that major metabolic process which involves converting glucose and oxygen into energy in the form of ATP, carbon dioxide, and water. The process mainly takes place within the mitochondria of eukaryotic cells. This process is crucial in providing the energy to maintain the various activities in the cell and is summarized in three stages or steps: glycolysis, citric acid cycle, and oxidative phosphorylation.

In glycolysis, glucose is broken down into pyruvate within the cytoplasm, producing a small amount of ATP. The pyruvate formed subsequently enters the mitochondria, where, via the citric acid cycle, electron carriers are produced. These carriers transport electrons to the electron transport chain, where most ATPs are produced during the process of oxidative phosphorylation. Cellular respiration is important for the survival of aerobic organisms because it is an effective way of extracting energy from organic molecules to power cellular functions.

Comparison Of Photosynthesis And Cellular Respiration

Aspect	Photosynthesis	Cellular Respiration
Energy Flow	Converts light energy into chemical energy	Converts chemical energy into usable ATP
Electron Carriers	NADP+ to NADPH	NAD+ to NADH, FAD to FADH2
Organisms Involved	Autotrophs (plants, algae, some bacteria)	All living organisms
Chemical Equations	6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂	C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP

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Frequently Asked Questions (FAQs)

1. What are the main differences between photosynthesis and cellular respiration?

Photosynthesis is an anabolic process that transforms the energy of light into chemical energy and produces glucose and oxygen. Cellular respiration is a process of catabolism in which glucose is broken down into water, carbon dioxide, and ATP.

2. Why are both photosynthesis and cellular respiration essential for life on Earth?

Photosynthesis provides the oxygen and the glucose to feed cellular respiration which provides the ATP for all cellular activities. They jointly maintain the balance of oxygen and carbon dioxide in the atmosphere.

3. How do light-dependent reactions and the Calvin Cycle differ?

Light-dependent reactions take place in thylakoid membranes to convert light energy into chemical energy in the form of ATP and NADPH. The Calvin Cycle goes on in the stroma and links carbon dioxide to form glucose using the products from light-dependent reactions, namely ATP and NADPH.

4. What roles do NADH and FADH2 play in cellular respiration?

Major electron carriers carry these electrons to the electron transport chain which would drive the formation of a proton gradient to make ATP.

5. How do environmental factors affect the rate of photosynthesis and cellular respiration?

Photosynthesis is affected by Light/CO2 amount and temperature. Oxygen availability, glucose amount availability, temperature.

6. What role does ATP play in photosynthesis and cellular respiration?

In photosynthesis, ATP is produced during the light-dependent reactions and then used in the Calvin cycle to synthesize glucose. In cellular respiration, ATP is the main product, generated through oxidative phosphorylation and substrate-level phosphorylation, providing energy for cellular processes.

7. How does cellular respiration differ in aerobic and anaerobic conditions?

Aerobic respiration occurs in the presence of oxygen and produces more ATP through the complete breakdown of glucose. Anaerobic respiration occurs without oxygen, producing less ATP and resulting in fermentation products like lactic acid or ethanol, depending on the organism.

8. How do photosynthesis and cellular respiration contribute to the global carbon cycle?

Photosynthesis removes CO2 from the atmosphere, incorporating it into organic compounds. Cellular respiration releases CO2 back into the atmosphere by breaking down these compounds. This balance helps regulate atmospheric CO2 levels and maintains the global carbon cycle.

9. What is the relationship between photosynthesis and cellular respiration in terms of energy flow?

Photosynthesis captures and stores solar energy in chemical bonds, while cellular respiration releases this stored energy for cellular use. This relationship forms the basis of energy flow in most ecosystems, with photosynthetic organisms supporting the energy needs of non-photosynthetic organisms.

10. How do the rates of photosynthesis and cellular respiration vary throughout the day in plants?

Photosynthesis rates are highest during daylight hours, peaking at midday when light intensity is strongest. Cellular respiration occurs continuously but may increase at night when photosynthesis stops. The balance between these processes changes with light availability and plant energy demands.

11. What is the fundamental difference between photosynthesis and cellular respiration?

Photosynthesis is an anabolic process that converts light energy into chemical energy, producing glucose from CO2 and H2O. Cellular respiration is a catabolic process that breaks down glucose to release energy in the form of ATP. Photosynthesis stores energy, while respiration releases it.

12. Why do plants perform both photosynthesis and cellular respiration?

Plants perform both processes because they have different purposes. Photosynthesis produces glucose for energy storage and building materials, while cellular respiration breaks down glucose to provide immediate energy for cellular activities. Plants need both processes to maintain their metabolism and growth.

13. How does the location of photosynthesis and cellular respiration differ in plant cells?

Photosynthesis primarily occurs in the chloroplasts of plant cells, specifically in the thylakoid membranes. Cellular respiration takes place mainly in the mitochondria, with some steps occurring in the cytoplasm. This spatial separation allows for efficient energy management within the cell.

14. How do the reactants and products of photosynthesis and cellular respiration compare?

Photosynthesis uses CO2 and H2O as reactants to produce glucose and O2. Cellular respiration uses glucose and O2 as reactants to produce CO2, H2O, and ATP. The products of one process are the reactants of the other, creating a cyclical relationship between the two.

15. How do the electron transport chains in photosynthesis and cellular respiration differ?

Both processes use electron transport chains, but they serve different purposes. In photosynthesis, the chain generates a proton gradient to produce ATP and NADPH for glucose synthesis. In respiration, the chain creates a proton gradient to drive ATP synthesis through oxidative phosphorylation.

16. What are the main types of photosynthesis, and how do they differ?

The main types are C3, C4, and CAM photosynthesis. C3 is the most common, using rubisco to fix CO2 directly. C4 uses PEP carboxylase to pre-fix CO2 before rubisco, reducing photorespiration. CAM temporally separates CO2 fixation and the Calvin cycle, adapting plants to arid conditions.

17. What is the significance of the light-dependent and light-independent reactions in photosynthesis?

The light-dependent reactions capture light energy to produce ATP and NADPH, which are then used in the light-independent reactions (Calvin cycle) to fix CO2 and produce glucose. This division allows plants to continue fixing carbon even when light is not available, using stored energy.

18. What is photorespiration, and why is it considered inefficient?

Photorespiration is a process where rubisco fixes oxygen instead of CO2, producing no net energy or carbohydrates. It's considered inefficient because it consumes ATP and reduces the overall efficiency of photosynthesis, especially in C3 plants under high temperature and low CO2 conditions.

19. What is the role of chlorophyll in photosynthesis, and is there an equivalent in cellular respiration?

Chlorophyll is crucial in photosynthesis for capturing light energy and initiating electron flow. There is no direct equivalent in cellular respiration, but electron carriers like NAD+ and FAD play important roles in transferring electrons during the process.

20. How do C4 and CAM plants adapt to reduce photorespiration?

C4 plants spatially separate initial CO2 fixation and the Calvin cycle, while CAM plants temporally separate these processes. Both strategies concentrate CO2 around rubisco, reducing its oxygenase activity and thus minimizing photorespiration, allowing these plants to thrive in hot, dry environments.

21. What is the relationship between photosynthesis, cellular respiration, and photorespiration?

Photosynthesis produces glucose, which cellular respiration breaks down for energy. Photorespiration occurs when rubisco fixes oxygen instead of CO2, reducing photosynthetic efficiency. C4 and CAM photosynthesis are adaptations to minimize photorespiration, enhancing overall energy production in certain conditions.

22. What is the role of water in photosynthesis and cellular respiration?

In photosynthesis, water is a reactant, providing electrons and protons for the light-dependent reactions. In cellular respiration, water is a product of the electron transport chain and serves as a medium for many reactions. Both processes rely on water for maintaining cellular structures and functions.

23. How do photosynthesis and cellular respiration affect a plant's water balance?

Photosynthesis requires stomata to be open for CO2 uptake, leading to water loss through transpiration. Cellular respiration produces water as a byproduct. The balance between these processes, along with root water uptake, determines the plant's overall water status and turgor pressure.

24. What is the importance of redox reactions in photosynthesis and cellular respiration?

Redox reactions are central to both processes. In photosynthesis, they drive electron flow from water to NADP+, producing NADPH. In cellular respiration, they transfer electrons from glucose to oxygen through various carriers, driving ATP production. These reactions are key to energy transformation in both processes.

25. How do photosynthesis and cellular respiration contribute to a plant's ability to respond to environmental stress?

Both processes are crucial for stress response. Photosynthesis provides the energy and carbon skeletons needed for producing stress-response molecules. Cellular respiration ensures energy availability for stress-related processes like repair mechanisms and osmolyte production, enhancing plant resilience.

26. What are the key enzymes involved in photosynthesis and cellular respiration, and what are their roles?

In photosynthesis, key enzymes include rubisco for CO2 fixation and ATP synthase for ATP production. In cellular respiration, important enzymes include pyruvate dehydrogenase, enzymes of the citric acid cycle, and ATP synthase. These enzymes catalyze specific reactions in their respective pathways.

27. How do environmental factors affect the rates of photosynthesis and cellular respiration?

Factors like light intensity, CO2 concentration, and temperature affect photosynthesis rates. Cellular respiration is influenced by oxygen availability, substrate concentration, and temperature. Both processes are also affected by water availability and nutrient status of the organism.

28. What is the significance of the compensation point in plants?

The compensation point is when the rate of photosynthesis equals the rate of cellular respiration, resulting in no net CO2 exchange. It's important for understanding plant energy balance and determining the minimum light intensity needed for plant growth and survival.

29. How do photosynthesis and cellular respiration contribute to a plant's overall energy budget?

Photosynthesis provides the energy input by producing glucose, while cellular respiration allocates this energy for various cellular processes. The balance between these processes determines the plant's net energy gain, influencing growth, reproduction, and survival.

30. What are the main differences between substrate-level phosphorylation and oxidative phosphorylation?

Substrate-level phosphorylation directly transfers a phosphate group from a substrate to ADP, occurring in glycolysis and the citric acid cycle. Oxidative phosphorylation uses an electron transport chain and chemiosmosis to produce ATP, occurring in the inner mitochondrial membrane.

31. How do the energy yields of photosynthesis and cellular respiration compare?

Photosynthesis requires energy input (from light) to produce glucose, storing about 470 kJ/mol of glucose. Cellular respiration releases this stored energy, producing about 30-32 ATP molecules per glucose molecule, equivalent to about 1260 kJ/mol of glucose.

32. How do photosynthesis and cellular respiration differ in their use of electron carriers?

Photosynthesis primarily uses NADP+ as an electron acceptor, producing NADPH for the Calvin cycle. Cellular respiration mainly uses NAD+ and FAD as electron acceptors, producing NADH and FADH2 for the electron transport chain. The specific carriers reflect the different energy needs of each process.

33. What is the significance of the proton gradient in both photosynthesis and cellular respiration?

In both processes, proton gradients are established across membranes (thylakoid in photosynthesis, inner mitochondrial in respiration). These gradients drive ATP synthesis through chemiosmosis, coupling electron transport to ATP production in a similar mechanism despite the different overall goals of each process.

34. What are the main differences between cyclic and non-cyclic photophosphorylation?

Non-cyclic photophosphorylation involves both photosystems I and II, produces ATP and NADPH, and results in oxygen evolution. Cyclic photophosphorylation involves only photosystem I, produces only ATP, and does not evolve oxygen. Plants use both to balance their ATP and NADPH production.

35. How do the carbon fixation steps differ between C3 and C4 photosynthesis?

In C3 photosynthesis, CO2 is fixed directly by rubisco in the mesophyll cells. In C4 photosynthesis, CO2 is initially fixed by PEP carboxylase in mesophyll cells, forming a 4-carbon compound that is then transported to bundle sheath cells where rubisco fixes CO2 in a CO2-rich environment.

36. How do the energy storage forms differ between photosynthesis and cellular respiration?

Photosynthesis primarily stores energy in the chemical bonds of glucose and other carbohydrates. Cellular respiration transfers this energy to ATP, which serves as the immediate energy currency of the cell. This difference allows for long-term energy storage and rapid energy utilization as needed.

37. What is the role of oxygen in photosynthesis and cellular respiration?

In photosynthesis, oxygen is a byproduct of water splitting in the light-dependent reactions. In cellular respiration, oxygen serves as the final electron acceptor in the electron transport chain, enabling the high ATP yield of aerobic respiration. Oxygen thus links these processes in the global oxygen cycle.

38. How do photosynthesis and cellular respiration contribute to a plant's circadian rhythms?

Both processes are influenced by and contribute to circadian rhythms. Photosynthesis is naturally rhythmic due to light availability, while cellular respiration rates may fluctuate to match energy demands. These rhythms help coordinate metabolic activities with environmental cycles, optimizing plant function.

39. What are the main differences in carbon dioxide utilization between photosynthesis and cellular respiration?

Photosynthesis consumes CO2 as a reactant, incorporating it into organic compounds through carbon fixation. Cellular respiration produces CO2 as a waste product from the oxidation of organic compounds. This opposite CO2 utilization forms the basis of the carbon cycle in ecosystems.

40. How do the energy transformation processes differ between photosynthesis and cellular respiration?

Photosynthesis transforms light energy into chemical energy stored in glucose. Cellular respiration transforms the chemical energy in glucose into ATP through a series of oxidation reactions. While both involve energy transformations, they operate in opposite directions in terms of energy storage and release.

41. What is the significance of the Calvin cycle in relation to cellular respiration?

The Calvin cycle in photosynthesis produces glucose, which serves as the primary substrate for cellular respiration. This cycle links the two processes, as the products of photosynthesis become the reactants for respiration, establishing a crucial energy flow in living systems.

42. How do photosynthesis and cellular respiration contribute to a plant's nitrogen metabolism?

Photosynthesis provides carbon skeletons and energy for nitrogen assimilation into amino acids and nucleotides. Cellular respiration generates ATP necessary for nitrogen uptake and assimilation. Both processes are thus essential for synthesizing nitrogen-containing compounds crucial for plant growth and function.

43. What are the main differences in the regulation of photosynthesis and cellular respiration?

Photosynthesis is primarily regulated by light availability and CO2 concentration, with additional control by end-product inhibition and circadian rhythms. Cellular respiration is mainly regulated by energy demand (ADP/ATP ratio) and substrate availability, with allosteric regulation of key enzymes playing a crucial role.

44. How do photosynthesis and cellular respiration affect a plant's mineral nutrient requirements?

Photosynthesis requires minerals like magnesium (in chlorophyll) and iron (in electron transport proteins). Cellular respiration needs minerals such as iron and copper for electron transport chain components. Both processes influence overall plant metabolism, affecting the demand for various nutrients.

45. What is the role of feedback inhibition in photosynthesis and cellular respiration?

In photosynthesis, feedback inhibition helps regulate the Calvin cycle when there's excess product (e.g., glucose inhibits phosphofructokinase). In cellular respiration, high ATP levels inhibit key enzymes like phosphofructokinase in glycolysis. These mechanisms help balance energy production with cellular needs.

46. How do photosynthesis and cellular respiration contribute to a plant's defense mechanisms?

Photosynthesis provides energy and carbon skeletons for producing defense compounds like alkaloids and phenolics. Cellular respiration ensures energy availability for activating defense responses, such as the hypersensitive response. Both processes are crucial for maintaining the plant's overall health and resistance to pathogens and herbivores.

47. What are the main differences in the membrane systems involved in photosynthesis and cellular respiration?

Photosynthesis primarily occurs in the thylakoid membranes of chloroplasts, while cellular respiration mainly takes place in the inner mitochondrial membrane. Both membranes are specialized for their respective electron transport chains and ATP synthesis, but differ in their protein complexes and specific functions.

48. How do photosynthesis and cellular respiration affect a plant's response to climate change?

Rising CO2 levels may enhance photosynthesis in some plants, but increased temperatures can reduce efficiency through photorespiration. Higher temperatures also increase cellular respiration rates, potentially leading to carbon loss. The balance between these processes influences plant adaptation to changing climates.

49. What is the relationship between photosynthesis, cellular respiration, and plant growth rates?

Photosynthesis determines the potential for growth by producing glucose and other organic compounds. Cellular respiration provides the energy needed for cell division, elongation, and differentiation. The balance between these processes, influenced by environmental factors, ultimately determines the plant's growth rate.

50. How do C3, C4, and CAM plants differ in their integration of photosynthesis and cellular respiration?

C3 plants have the simplest integration, with both processes occurring in the same cells. C4 plants spatially separate initial carbon fixation and the Calvin cycle, while CAM plants temporally separate these processes. These differences affect how energy from respiration is used to support photosynthesis in varying environmental conditions.

51. What is the role of alternative oxidase in plant respiration and how does it relate to photosynthesis?

Alternative oxidase provides an alternate route for electrons in the respiratory chain, producing heat instead of ATP. This can help protect photosynthetic machinery from damage under high light conditions by dissipating excess energy. It also allows continued respiration when the cytochrome pathway is saturated.

52. How do photosynthesis and cellular respiration contribute to a plant's ability to compete with other plants?

Efficient photosynthesis allows