Respiration vs. Photosynthesis: What’s the Difference?

You may have heard the terms respiration and photosynthesis before, but you may not understand precisely what they mean and how they differ from one another. Are they the same process? What’s the difference between respiration and photosynthesis? Respiration Vs. Photosynthesis describes the key differences between these two processes so that you can clearly understand their key similarities and differences.

Main Difference

One must first understand each process to understand the difference between respiration and photosynthesis. Respiration is the process of breaking down organic matter to release energy. This process occurs in all cells and is necessary for survival. Photosynthesis, on the other hand, converts light into energy that plants can use to create food. Although both processes are essential for life, they are pretty different.


Respiration constantly occurs in all cells, even when a plant is not actively growing. This is because respiration is necessary to release the energy cells need to function. On the other hand, photosynthesis only occurs when a plant is exposed to light. This is because photosynthesis requires light to convert into energy plants can use.

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What is Respiration?

Photosynthesis is when plants use sunlight to convert carbon dioxide into glucose (a type of sugar). Plants take in carbon dioxide and water through their roots and use these elements and sunlight to create glucose. When we talk about respiration, we are referring to the process of taking in oxygen and releasing carbon dioxide. For a plant to survive, they need both approaches to coincide. The plant will not live long enough to reproduce if either process stops.


What is Photosynthesis?

Photosynthesis is when plants take carbon dioxide and water from the atmosphere and convert them into sugar molecules using sunlight. Respiration is the opposite process where plants use oxygen and sugar molecules to create energy. Both processes co-occur in the same plant. However, they have different effects on the plant’s growth.

Critical Differences Between Respiration and Photosynthesis

  • Respiration is a process that occurs in all living cells and is used to convert energy from food into a usable form for the cell.
  • Photosynthesis is a process that only occurs in plants and is used to convert energy from sunlight into food for the plant. – In photosynthesis, the chlorophyll molecules in the plant’s chloroplasts capture light, converting it into chemical energy.
  • Chlorophyll molecules can also use some of this stored chemical energy to make carbohydrates from carbon dioxide and water, creating oxygen as a byproduct.
  • In respiration, carbohydrates are broken down with enzymes to produce carbon dioxide, water, and chemical energy (ATP). ATP has the unique ability to store chemical energy when it is converted into adenosine diphosphate (ADP) and adenosine triphosphate (ATP).
  • ATP can be used immediately or combined with ADP to create more ATP.

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In this way, ATP acts like fuel in a car engine, being burned up to generate movement or power. The car would not run without gas but would run out quickly if there was no place to refuel. Similarly, our bodies cannot operate without using energy. Still, they will eventually burn out if we don’t consume enough food sources containing carbohydrates and other nutrients needed for the body to function correctly.

1. Carbon Dioxide

Carbon dioxide is a gas that is produced by respiration. In plants, carbon dioxide is used to produce glucose and oxygen. When carbon dioxide is not present, the plant cannot perform photosynthesis.

2. Water

Water is necessary for both processes. Photosynthesis requires water, while respiration does not.

3. Light

Light is required for both processes. Photosynthetic organisms need light to perform photosynthesis, whereas respiring organisms do not.

4. Oxygen

Oxygen is required for both processes, but only photosynthetic organisms require oxygen.

5. Glucose

Glucose is a product of photosynthesis.

6. ATP

ATP is the primary source of energy for all living things.

How do plants respire?

Plants respire 24 hours a day, but photosynthesis only occurs during the day when there is sunlight. Plant respiration is when plants take in oxygen and release carbon dioxide, water vapor, and heat. On the other hand, photosynthesis is when plants use sunlight to convert carbon dioxide and water into glucose and oxygen. However, it doesn’t just stop there. Oxygen and glucose are six water molecules with extra hydrogen or oxygen atoms. What do you think happens to all those molecules? They combine and break down into their original components so they can be reused for something else!

How plants photosynthesize: Respiration vs. Photosynthesis

Plants can photosynthesize due to the presence of chloroplasts in their cells. Chloroplasts are organelles that contain chlorophyll, which gives plants their green color. Plants use energy from the sun to convert water and carbon dioxide into oxygen and glucose. This process is known as photosynthesis. Plants release oxygen into the air as a byproduct of photosynthesis.

In contrast, animals rely on cellular respiration to release carbon dioxide and produce ATP (energy). Cellular respiration takes place outside the mitochondria, where glucose molecules are broken down with the help of enzymes to produce ATP. Respiration produces water and carbon dioxide as byproducts, while photosynthesis produces oxygen.

Process of Respiration in Humans: Respiration vs. Photosynthesis

The human body is composed of trillions of cells, each with its unique function. These cells need oxygen to survive and perform their duties. Oxygen enters the body through the lungs and circulates throughout the body via the blood. The respiratory system must work properly for the body to use oxygen effectively. When the respiratory system does not work correctly, oxygen cannot enter the bloodstream, and the body becomes hypoxic (low in oxygen). Hypoxia is a severe condition that requires immediate medical attention.

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Respiratory System: Respiration vs. Photosynthesis

The respiratory system consists of two major parts: the upper and lower respiratory systems. The upper respiratory system includes the nose, mouth, sinuses, pharynx, larynx, trachea, bronchi, and bronchioles. The lower respiratory system consists of the lungs, pleura, diaphragm, peritoneal cavity, and abdominal wall.

Air enters the body through the nostrils and travels down the nasal passages to the nasopharynx. From here, air passes through the oropharynx and oral cavity before entering the pharynx. Air then moves through the larynx and trachea before passing through the bronchi and bronchioles and reaching the alveoli. Alveolar gas exchange occurs in the alveoli, where carbon dioxide diffuses out of the blood and oxygen diffuses into the blood. Carbon dioxide is released into the atmosphere while the blood takes up oxygen.

Respiration Cycle: Respiration vs. Photosynthesis

During respiration, oxygen molecules diffuse across the alveolar membrane into the capillary network. Once inside the capillaries, they pass through the pulmonary circulation and reach the heart’s right atrium. They travel through the right ventricle and are pumped into the left atrium. Oxygen-rich blood flows through the coronary arteries and reaches the myocardium. The oxygenated blood returns to the left ventricle and is pumped throughout the body.

When the oxygen level in the blood drops below normal levels, the brain sends signals to the respiratory center in the medulla oblongata. The respiratory center then stimulates the muscles involved in breathing. As a result, the diaphragm contracts and pushes air into the lungs.


In short, respiration is breaking down organic matter to release energy. At the same time, photosynthesis uses light energy to convert carbon dioxide and water into organic matter. Though both processes are necessary for life on Earth, they couldn’t be more different.

About Jackson Roy

Content Writer and a Business Student. I Write About Living a Wonderful Life Without Hurry, Making Different Choices, and Finding Happiness.

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