What Are The Reactants Of Photosynthesis And Cellular Respiration?

The reactants of photosynthesis are carbon dioxide and water, meaning during photosynthesis carbon dioxide and water are taken in to create energy. The reactants of cellular respiration are glucose (sugar) and oxygen, these are taken in by animals and humans to produce energy.

The cells found in both plants and animals need to produce energy. Trees produce energy via the process of photosynthesis which takes the raw solar energy from the sun and converts it into carbohydrates, or usable chemical energy.


Meanwhile, the cells found in animals, including the cells in your body, perform the process of cellular respiration which makes ATP (a form of usable energy).

Cellular respiration and phtosynthesis are opposite of one another and part of the carbon cycle. Photo: OpenStax College, Biology/CC-BY 4.0

The Relationship Between Photosynthesis and Cellular Respiration

Apart from both being processes that cells use to create energy, is there any relationship between the two processes? As it turns out, yes there is. To find out what it is, let’s take a look at the chemical equations which happen in both cellular respiration and photosynthesis.

Here’s the equation for photosynthesis: 6CO2 + 6H2O → C6H12O6+ 6O2

The reactants of photosynthesis are:

  • Carbon Dioxide (CO2)
  • Water (H2)

The products of photosynthesis are:

  • Energy (C6H12O6)
  • Oxygen (O2)

The reactants of cellular respiration are:

  • Glucose (sugar)
  • Oxygen (O2)

The products of cellular respiration are:

  • Carbon Dioxide (CO2)
  • Water (H2)
  • ATP (Energy)

This equation means that plants take C02 (carbon dioxide) and water, and with the assistance of solar energy, turn it into glucose and oxygen (O2).

The equation for cellular respiration is as follows: C6H12O6 + 6O2 → 6CO2 + 6H2O


This means that cellular respiration utilizes glucose and oxygen and releases carbon dioxide and water as a result. Essentially, the two equations are the exact opposite of one another. Animal cells combine oxygen and hydrogen to form water as a byproduct, while the glucose they use to create the ATP (energy) they need is transformed back into carbon dioxide. Plants use both this water and carbon dioxide to power photosynthesis, and as a byproduct, they release oxygen and glucose.

The complex and intertwined relationship of photosynthesis and respiration are part of what is known as the “carbon cycle,” which is what allows carbon molecules to be recycled and work their way through the entire biosphere. Carbon is released into the atmosphere by respiration from animals in the form of carbon dioxide, while photosynthesis from plants absorbs the carbon dioxide and gets it out of the atmosphere.

Photosynthesis reactantsPhotosynthesis productsCellular respiration reactantsCellular respiration products
Carbon Dioxide (CO2)Energy (C6H12O6)Glucose (sugar)Carbon Dioxide (CO2)
Water (H2)Oxygen (O2)Oxygen (O2)Water (H2)
ATP (Energy)

Let’s take a closer look at the reactants involved in the carbon process.

Reactants of the Carbon Process

  • C6H12O6 – While the formula can technically apply to a number of different molecules, depending on how the individual atoms within the molecule are connected, most of them are various types of sugars. The most famous formation of C6H12O6 is known as glucose, which can be known by other names including dextrose and even blood sugar. In the cells of animals, the process known as glycolysis converts glucose into pyruvate which generates two molecules of ATP along with it.
  • O2 – Dioxygen, frequently just referred to as oxygen, is what vertebrates used to breathe. In vertebrates, the oxygen is brought into the lungs and is picked up by the red blood cells. The use of oxygen enables the more efficient conversion of glucose into ATP, although ATP can also be generated without oxygen in anaerobic conditions. Oxygen accounts for almost 21% of all our atmosphere.
  • CO2 – Carbon dioxide is produced by a variety of different microorganisms during both cellular respiration and fermentation. Carbon dioxide can enter the cells of plants through tiny holes in the leaves of plants called stomata. Once the carbon dioxide is inside the cells of the plant, the chloroplasts in the cell use it to undergo photosynthesis and create carbohydrates. Carbon dioxide is a greenhouse gas when it is in the atmosphere, and it contributes to global climate change.
  • H2O – Water is found everywhere on earth, and it also exists in the cells of most living things. Plants need water in addition to carbon dioxide and sunlight to produce energy for photosynthesis. Plant cells hold the water in structures called vacuoles.

The Photosynthetic Process

Photosynthesis requires several different components. The photosynthetic process requires the use of pigments and plastids.

Photosynthetic organisms have organelles referred to as plastids floating around in the cytoplasm of their cells. Plastids are multi-membraned organelles that can contain both pigments and other structures like fats and starches. Chloroplasts are examples of plastids. Like mitochondria in animal cells, they have their own collections of genes within them, and in plants, they are responsible for the conversion of solar energy into carbohydrates.

Plants cells have both chloroplasts and mitochondria. Photo: Public Domain

Pigments are what give plants their color, but they also allow plants to trap sunlight. The different colors of pigments can trap different wavelengths of light. There are three primary groups of pigments and these groups are carotenoids, phycobilins, and chlorophylls.

Carotenoids are typically colored yellow, orange, or red. These colors are responsible for absorbing green/blue light. You can think of cartone, which is colored orange, as an example of a carotenoid. In fact, it is how carrots get their color. Phycobilins are either red or blue, and they can absorb the wavelengths of light outside of blue, red, and orange. Examples of organisms employing phycobilins include red algae and cyanobacteria. Finally, chlorophylls are the most famous example of pigments for plants, and they are colored green. Chlorophylls are able to absorb light in the blue and red wavelengths, and they can be further subdivided into three different classes. Chlorophyll can be found in every photosynthesizing plant, and it exists alongside a variant called bacteriochlorophyll which is capable of grabbing light that exists in the infrared spectrum. Bacteriochlorophyll is only found in bacteria, as the name implies.

Differences Between Plant and Animal Cells

An animal cell has mitochondria which produces ATP for the cell. Photo: Public Domain

Plant and animal cells both have designated cell structures that are collectively responsible for the production of energy. Plants have chloroplasts, while animal cells have a structure known as mitochondria which utilize glucose and oxygen to produce carbon dioxide, water, and energy (as well as heat). It is important to note that plant cells have mitochondria as well, but animal cells do not have chloroplasts. However, the mitochondria that are in plants function a little differently from the mitochondria that are found in animal cells. The mitochondria in animal cells are used for both aerobic respiration and energy production, while the mitochondria in plant cells are only used to respire.

Plant and animal cells exist in a complex and delicate balance. The two types of organisms rely on substances output by the other organism, and one type of organism could not exist without the other.



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