Understanding Autotrophs: Do Plants Use Oxygen and CO2? | Explained

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In summary, plant cells have both Chloroplasts for photosynthesis and Mitochondria for cellular respiration. This means that plants use both oxygen and carbon dioxide for these processes. The first life on Earth lived in completely anaerobic conditions, with respiration using oxygen evolving later when it became available in the atmosphere. Mitochondria evolved from endosymbiosis of aerobic bacteria, meaning that the evolution of aerobic respiration predates the evolution of mitochondria and eukaryotes. The assumption that heterotrophs consume autotrophs is not necessarily correct, as there are heterotrophs that consume inorganic energy sources. The first organisms on Earth were thought to be chemoautotrophs, which fix carbon dioxide
  • #1
I understand that plant cells have both Chloroplasts for Photosynthesis and Mitochondria for cellular respiration (breaking down the glucose that photosynthesis creates?). Does this mean that plants use both oxygen and carbon dioxide? Most non-science people tend to think that we use oxygen, and plants use CO2. However, plants are really using both for those two processes, right?

And because autotrophs create their own food from the sun's energy, does that mean that autotrophs were the first living things? It seems as if heterotrophs consume autotrophs and so on, so wouldn't there have to first be autotrophs before heterotrophs could consume them?
 
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Short answer: first life on Earth lived in completely anaerobic conditions. Example: Methanogenic bacteria cannot live in the presence of oxygen. Respiration using oxygen evolved when free oxygen became available in the atmosphere. Oxygen arose from photosynthetic bluegreen cyanobacteria, which also do not use oxygen. They give it off more like a waste product.

So, your assumptions are backwards: anaerobic processes gave rise to oxygen which later gave rise to aerobic processes.

Generally aerobic processes are confined to eukaryotes - those cells with organelles like mitochdondria. The mitochondria as contained organelles looong ago arose as the result of two separate species "merging" into one more complex cell. Mitochondria still retain a tiny amount of DNA. Mitochondria are central to aerboic respiration.

There is lots more to this. Example: see http://evolution.berkeley.edu/evolibrary/article/_0/endosymbiosis_03
 
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  • #3
jim mcnamara said:
Generally aerobic processes are confined to eukaryotes - those cells with organelles like mitochdondria. The mitochondria as contained organelles looong ago arose as the result of two separate species "merging" into one more complex cell. Mitochondria still retain a tiny amount of DNA. Mitochondria are central to aerboic respiration.

This is incorrect. There are plenty of prokaryotes capable of aerobic respiration such as the E. coli commonly used in laboratory research. In fact, mitochondria are thought to have evolved from endosymbiosis of aerobic bacteria, so the evolution of aerobic respiration must necessarily predate the evolution of mitochondria and eukaryotes.
 
  • #4
NextElement said:
I understand that plant cells have both Chloroplasts for Photosynthesis and Mitochondria for cellular respiration (breaking down the glucose that photosynthesis creates?). Does this mean that plants use both oxygen and carbon dioxide? Most non-science people tend to think that we use oxygen, and plants use CO2. However, plants are really using both for those two processes, right?

And because autotrophs create their own food from the sun's energy, does that mean that autotrophs were the first living things? It seems as if heterotrophs consume autotrophs and so on, so wouldn't there have to first be autotrophs before heterotrophs could consume them?

You are assuming that heterotrophs consume autotrophs, which is not necessarily correct. There are heterotrophs that consume inorganic energy sources, such as the bacteria that live around "black smokers" under the sea, and the thermophlic bacteria that live in hot springs. Bacteria like this are thought to have dominated life on Earth before the autotrophs evolved. Try looking up archaebacteria.
 
  • #5
phyzguy said:
You are assuming that heterotrophs consume autotrophs, which is not necessarily correct. There are heterotrophs that consume inorganic energy sources, such as the bacteria that live around "black smokers" under the sea, and the thermophlic bacteria that live in hot springs. Bacteria like this are thought to have dominated life on Earth before the autotrophs evolved. Try looking up archaebacteria.

There seems to be a bit of confusion here regarding autotrophs vs heterotrophs and phototrophs vs chemotrophs. Whether an organism is an autotroph or a heterotroph depends on the carbon source of the organism: autotrophs fix carbon dioxide from their environment in order to obtain carbon for building cellular materials while heterotrophs obtain their carbon from organic sources.

How an organism obtains its main source of energy classifies it as either a phototroph (the organism uses energy from the sun) or a chemotroph (the organism obtains energy from the oxidation of organic or inorganic molecules). Thus, the bacteria you describe that derive their energy from inorganic materials are better classified as chemotrophs rather than heterotrophs.

Although most extant autotrophs are phototropic (using solar energy and water to create reduced carbon compounds from carbon dioxide) and most extant heterotrophs are chemotrophic (obtaining both their energy and carbon from organic molecules), there can be heterotrophs that are phototrophic (photoheterotrophs) and autotrophs that are chemotrophic. Indeed, the bacteria and archaea you describe, the chemoautotrophs that fix carbon dioxide by using inorganic compounds as the reducing agents, are thought to be some of the first organisms on Earth.

Semantics aside, your general point that chemotrophs evolved prior to phototrophs is correct.
 
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  • #6
Ygggdrasil,

You're right, I was confused on the nomenclature. Thanks for setting me straight.
 
  • #7
Thanks for the replies, guys.

I'm trying to decide what area of Biology to pursue, what does this fall under? Evolutionary and Ecology?
 
  • #8
I'm interested in this stuff too. I met a scientist this summer that studies methanogenic archea. It looked cool he had to keep his cultures in no oxygen air. I would classify this as microbial ecology, ecological theory, with a little of evolution thrown in.
 

What are autotrophs?

Autotrophs are organisms that are able to produce their own food using energy from the sun or inorganic substances. They are also known as producers in a food chain or food web.

What are the different types of autotrophs?

The two main types of autotrophs are photoautotrophs and chemoautotrophs. Photoautotrophs use energy from sunlight to produce their own food, while chemoautotrophs use energy from inorganic chemicals to create food.

What is the importance of autotrophs in the ecosystem?

Autotrophs play a crucial role in the ecosystem by providing a source of energy for all other organisms. They are the base of the food chain and without them, other organisms would not have a source of food and energy.

How do autotrophs reproduce?

Autotrophs reproduce through a process called photosynthesis, where they use sunlight, water, and carbon dioxide to produce glucose and oxygen. Some autotrophs also reproduce through binary fission, where they divide into two identical cells.

What are some examples of autotrophs?

Some examples of autotrophs include plants, algae, and some bacteria. These organisms are able to produce their own food and sustain themselves without relying on other organisms for energy.

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