Key Difference – Phototrophs vs Chemotrophs
 

Organisms are categorized based on the nutritional requirements. Some organisms are able to produce their own food while some organisms depend on the other food products produced by other organisms. Some organisms show different relationships to obtain foods. Therefore, various kinds of organism categories are available, and among them, phototrophs and chemotrophs are two main categories. Phototrophs are the organisms that use sunlight as their energy source to carry out their cellular functions. There are two types of phototrophs; photoautotrophs and photoheterotrophs. Chemotrophs are the organisms that depend on energy produced by the oxidation of inorganic or organic molecules. Chemotrophs are two main types namely chemoautotrophs and chemoheterotrophs. The key difference between the phototrophs and heterotrophs is the energy source that they use. Phototrophs rely on sunlight to obtain energy while chemotrophs do not rely on sunlight to obtain energy instead rely on chemicals for energy production.

CONTENTS

1. Overview and Key Difference
2. What are Phototrophs
3. What are Chemotrophs
4. Similarities Between Phototrophs and Chemotrophs
5. Side by Side Comparison – Phototrophs vs Chemotrophs in Tabular Form
6. Summary

What are Phototrophs?

Phototrophs are the group of organisms that utilize energy from sunlight to produce ATP to carry out cellular functions. In other words, phototrophs are the organisms that rely on sunlight to produce their own foods or oxidize organic molecules to produce energy for cellular functions. The prefix “Photo” refers to the light, and the word “trophs” refers to the way of obtaining food or the nourishment. Hence, phototrophs are the organisms that fulfil their nutritional requirement using the sunlight.

There are two types of phototrophs namely photoautotrophs and photoheterotrophs. Photoautotrophs can be defined as the organisms that make their own foods by the use of sunlight and inorganic carbon source that is carbon dioxide. The process they carry out is photosynthesis. They possess special organelle and pigments to capture energy from sunlight and utilize it to produce organic molecules from carbon dioxide and water. Examples of the photoautotrophic organisms are green plants, algae, photosynthetic bacteria, cyanobacteria, etc. All most all green plants are photosynthetic. They serve as an important food source for the terrestrial ecosystems. Photoautotrophs are extremely important for the healthy functioning of most of the ecosystems and the survival of the heterotrophs. Heterotrophs depend on the foods produced by autotrophs. And also phototrophs are important since they are able to remove carbon dioxide from the atmosphere and release oxygen to the atmosphere of the animal respiration.

Figure 01: Phototroph – Green Plants

Photoheterotrophs are organisms that make energy from sunlight and use organic materials as their carbon sources. They are not photosynthetic, and they are not able to use carbon dioxide. Instead, they use organic carbon products produced by other organisms. Photoheterotrophs produce ATP via the process called photophosphorylation.

What are Chemotrophs?

Chemotrophs are organisms that obtain energy from chemical oxidation or the chemosynthesis. They cannot use sunlight as their energy source. Instead, they use inorganic or organic compounds and obtain the energy through oxidation.  The prefix “chemo” refers to the chemical and the word “troph” refers to the nourishment. Hence, these organisms are totally dependent on the chemicals for the energy source.

Chemotrophs can be two groups namely chemoautotrophs or chemoheterotrophs. Chemoautotrophs are able to produce their own foods through chemosynthesis. They use inorganic compounds such as H2S, S, NH4+, Fe2+ as reducing agents and synthesize carbohydrates from carbon dioxide. These organisms are found in extreme environments such as deep sea, etc. where sunlight cannot be reached. Examples of chemoautotrophs include methanogens, halophiles, nitrifiers, thermoacidophiles, sulfur oxidizers, etc.

Figure 02: A Black Smoker in the Atlantic Ocean providing energy and nutrients for Chemotrophs

Chemoheterotrophs are the organisms that depend on organic compounds for the energy and carbon source. These organisms ingest foods such as carbohydrates, lipids, proteins produced by other organisms. Chemoheterotrophs are the most abundant type of the organisms including most of the bacteria.

What are the Similarities Between Phototrophs and Chemotrophs?

• Both phototrophs and chemotrophs are groups of organisms based on the type of nutrition.
• Both phototrophs and chemotrophs groups include autotrophs and heterotrophs.
• Both phototrophs and chemotrophs groups can be found in same ecosystems.

What is the Difference Between Phototrophs and Chemotrophs?

Summary – Phototrophs vs Chemotrophs 

Phototrophs and chemotrophs are two main groups of organisms that are categorized based on the type of nutrition. Phototrophs make energy for their cellular processes using sunlight (solar energy). Chemotrophs are unable to use solar energy. Hence they depend on the energy produced by the chemosynthesis. Chemicals are oxidized by chemotrophs to produce energy for their cellular functions. Both groups include organisms that make their own foods and organisms depend on foods produced by other organisms. Chemotrophs are the most abundant type of organisms. Phototrophs are important for the functioning of many ecosystems. Photoautotrophs uptake carbon dioxide from the atmosphere and release oxygen to the atmosphere. The survival of other heterotrophic organisms is dependent on the photoautotrophs.  This is the difference between phototrophs and chemotrophs.

Reference:

1.Editors. “Photoautotroph – Definition, Function and Types.” Biology Dictionary, 29 Apr. 2017. Available here 
2.“Chemotroph.” Wikipedia, Wikimedia Foundation, 17 Feb. 2018. Available here 
3.Boundless. “Boundless Microbiology.” Lumen. Available here

Image Courtesy:

1.’60560′ (Public Domain) via pexels
2.’Blacksmoker in Atlantic Ocean’By P. Rona (Public Domain) via Commons Wikimedia 

ncG1vNJzZmivp6x7pbXFn5yrnZ6YsqOx07CcnqZemLyue8OinZ%2Bdopq7pLGMm5ytr5Wau268x6irqKyipL2pv4yapZ1lpqh6pLTEpqatqp%2BltbR7