Unlike Photosynthesis, Cellular Respiration Occurs In 2023

Unlike Photosynthesis, Cellular Respiration Occurs In 2023
Diagram showing process of photosynthesis and cellular respiration from www.vecteezy.com


Cellular respiration is a vital process that occurs in living organisms to produce energy in the form of ATP. Unlike photosynthesis, which is the process by which plants convert light energy into chemical energy, cellular respiration takes place in the mitochondria of both plant and animal cells. In this article, we will explore the key differences between photosynthesis and cellular respiration, as well as delve into the various stages and mechanisms involved in cellular respiration.

The Process of Cellular Respiration

Cellular respiration can be divided into three main stages: glycolysis, the Krebs cycle (also known as the citric acid cycle), and oxidative phosphorylation (electron transport chain and chemiosmosis).


Glycolysis is the first stage of cellular respiration and occurs in the cytoplasm of cells. It involves the breakdown of glucose into two molecules of pyruvate. This process does not require oxygen and is therefore considered anaerobic.

The Krebs Cycle

The Krebs cycle takes place in the mitochondria and involves the further breakdown of pyruvate into carbon dioxide. This stage generates high-energy molecules such as NADH and FADH2, which are essential for the next stage of cellular respiration.

Oxidative Phosphorylation

Oxidative phosphorylation occurs in the inner mitochondrial membrane and involves the transfer of electrons from NADH and FADH2 to oxygen through a series of protein complexes in the electron transport chain. This process generates a large amount of ATP, which is the main energy currency of the cell.

Differences between Photosynthesis and Cellular Respiration

While both photosynthesis and cellular respiration are crucial processes for sustaining life on Earth, they are fundamentally different in several ways:

Source of Energy

Photosynthesis utilizes light energy from the sun to convert carbon dioxide and water into glucose and oxygen. In contrast, cellular respiration breaks down glucose molecules to release stored chemical energy.


Photosynthesis primarily occurs in the chloroplasts of plant cells, specifically in the thylakoid membrane and stroma. Cellular respiration, on the other hand, takes place in the mitochondria of both plant and animal cells.

Reactants and Products

Photosynthesis requires carbon dioxide, water, and sunlight as reactants and produces glucose and oxygen as products. Cellular respiration, in contrast, utilizes glucose and oxygen as reactants and produces carbon dioxide, water, and ATP as products.


1. What is the main purpose of cellular respiration?

The main purpose of cellular respiration is to generate ATP, the energy currency of the cell, through the breakdown of glucose molecules.

2. Can cellular respiration occur without oxygen?

Yes, the initial stage of cellular respiration, glycolysis, can occur without oxygen. However, the subsequent stages, such as the Krebs cycle and oxidative phosphorylation, require oxygen and are therefore considered aerobic processes.

3. How does cellular respiration differ in plant and animal cells?

Cellular respiration occurs in both plant and animal cells, but plant cells also undergo photosynthesis. Plant cells have both mitochondria and chloroplasts, allowing them to generate energy through cellular respiration and produce their own food through photosynthesis.

4. Is cellular respiration an efficient process?

Cellular respiration is highly efficient in terms of energy production. Through oxidative phosphorylation, a large amount of ATP is generated from the breakdown of glucose molecules.

5. Can cellular respiration occur in single-celled organisms?

Yes, cellular respiration occurs in both single-celled and multicellular organisms. It is an essential process for all living organisms to generate energy for various cellular activities.

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