CellEnergySE | Cellular Respiration | Photosynthesis

Cellular respiration is also important in the movement of matter through living systems: As living things break down food molecules using cellular respiration, they release the atoms from the food molecules back out into the environment as carbon dioxide and water. Photosynthesis brings in carbon dioxide and water from the environment, and cellular respiration sends them out again, forming a circular matter pathway that scientists call the carbon cycle.

This very fact forms the basis of the relationship between cellular respiration and photosynthesis.

The fact that both resort to the 'electron transport chain' when it comes to the movement of electrons is perhaps one of the most prominent similarities between photosynthesis and cellular respiration.

The photosynthesis-cellular respiration relationship also explains why the two are necessary for the presence of life on the planet.


How are respiration and photosynthesis related to each other

But because of photosynthesis and cellular respiration, energy from the sun is converted into a ATP that fuels the work of plant cells.

The chemical equation for cellular respiration is C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy released (2830 kJ mol-1); wherein glucose (C6H12O6) and oxygen (O2) are reactants, whereas carbon dioxide (CO2), water (H2O) and energy are products.

How are Photosynthesis and Cellular Respiration Related?

In the information of each of these two processes, you must have noticed that the products of one process are reactants of another - and vice versa.


How is Photosynthesis Related to Cellular Respiration

In order to understand how photosynthesis is related to cellular respiration, one has to get well-versed with the basics of each of them.

Photosynthesis: Photosynthesis is a process wherein synthesis of sugar (glucose) is carried out using sunlight (which acts as the radiant energy), carbon dioxide and water.

How are photosynthesis and cellular respiration related?

During photosynthesis, a plant is able to convert solar energy into a chemical form. It does this by capturing light coming from the sun and, through a series of reactions, using its energy to help build a sugar molecule called glucose. Glucose is made of six carbon atoms, six oxygen atoms, and twelve hydrogen atoms. When the plant makes the glucose molecule, it gets the carbon and oxygen atoms it needs from carbon dioxide, which it takes from the air. Carbon dioxide doesn't have any hydrogen in it, though, so the plant must use another source for hydrogen. The source that it uses is water. There is a lot of water on the earth, and every water molecule is composed of two hydrogen atoms and one oxygen atom. In order to take the hydrogen it needs to build glucose molecules, the plant uses the energy from the sun to break the water molecule apart, taking electrons and hydrogen from it and releasing the oxygen into the air. The electrons it takes are put into an electron transport system, where they are used to produce energy molecules called ATP that are used to build the glucose molecule-- all made possible by the sun's energy. Thus, during photosynthesis a plant consumes water, carbon dioxide, and light energy, and produces glucose and oxygen.

The sugar glucose is important because it is necessary for cellular respiration. During cellular respiration, the chemical energy in the glucose molecule is converted into a form that the plant can use for growth and reproduction. In the first step of respiration, called glycolysis, the glucose molecule is broken down into two smaller molecules called pyruvate, and a little energy is released in the form of ATP. This step in respiration does not require any oxygen and is therefore called anaerobic respiration. In the second step of respiration, the pyruvate molecules are rearranged and combined and rearranged again in a cycle. While the molecules are being rearranged in this cycle, carbon dioxide is produced, and electrons are pulled off and passed into an electron transport system which, just as in photosynthesis, generates a lot of ATP for the plant to use for growth and reproduction. This last step requires oxygen, and therefore is called aerobic respiration. Thus, the final result of cellular respiration is that the plant consumes glucose and oxygen and produces carbon dioxide, water, and ATP energy molecules.

At first, this doesn't seem to make any sense! If the plant can use the energy from the sun to make ATP, why does it go through all the trouble of then using up the ATP to make glucose, just so it can get ATP again? There are two reasons why the plant does this. First, in addition to ATP, the plant needs materials to grow. Glucose is an important building block that is necessary to produce all of the proteins, DNA, cells, tissues, etc. that are important to life, growth, and reproduction. Second, one problem with the sun is that it goes away every night, and during winter it isn't very bright. The plant needs energy all of the time. So, by producing glucose, the plant can store this molecule and then use it to produce energy during the night and over winter when there isn't enough sun to provide good photosynthesis.

It is very interesting how photosynthesis and cellular respiration help each other. During photosynthesis, the plant needs carbon dioxide and water-- both of which are released into the air during respiration. And during respiration, the plant needs oxygen and glucose, which are both produced through photosynthesis! So in a way, the products of photosynthesis support respiration, and the products of respiration support photosynthesis, forming a cycle.

While plants can complete this cycle by themselves, animals cannot, since animals aren't capable of photosynthesis! This means that animals have to survive solely through respiration. Also, since we animals can't produce glucose by ourselves, we have to get it from somewhere else-- from eating plants. We produce carbon dioxide that the plants need, and they produce the oxygen that we need, and then we eat them to get the glucose that we need. It seems that we need the plants a lot more than they need us!

Answer to How are photosynthesis and cellular respiration related?

Autotrophs and heterotrophs do cellular respiration to break down food to transfer the energy from food to ATP. The cells of animals, plants, and many bacteria use oxygen to help with the energy transfer during cellular respiration; in these cells, the type of cellular respiration that occurs is aerobic respiration (aerobic means “with air”).