# In which order did the following functions of organisms evolve?

## Main Question or Discussion Point

In which order did the following functions* of organisms evolve, from the very first life through to all extant organisms.

Respiratory; digestion/excretion; reproduction; peripheral nervous; endocrine; integumentary/exocrine; circulatory; renal/urinary; lymphatic/immune; skeletal; Muscular; central nervous.

*I’m thinking of how the human body functions, and the human body systems, but also thinking of analogous functions / systems in organisms all the way back to the first life forms. So, for example, we have a complex reproductive system but the first life forms also had to reproduce simply by dividing; we have a complex digestive system but some earlier life forms also had to digest their food; we have a complex nervous system but earlier life forms had a primitive version; etc.

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phinds
Gold Member
2019 Award
Is this homework?

BillTre
Gold Member
This is not a simple question.
Several of the terms can apply to single cells or to multi-cellular organisms.
Those that apply to single celled organisms would of course evolve first.

These pairs I would separate:
digestion/excretion
integumentary/exocrine
lymphatic/immune

These terms would only apply to multi-cellular organisms and therefore would arise later in evolution:
peripheral nervous
endocrine
integument (like skin)
exocrine
circulatory
renal/urinary
lymphatic
immune
skeletal
Muscular
central nervous

Very simple multi-cellular organisms (like sponges) would not need any of these.
Those that they would need would be expected to evolve before the others.

Before the division of the peripheral/central nervous system, there was a nerve net (cnidarians: corals, anemones, jellyfish).

Respiration cold mean that part of biochemistry involved in the cell acquiring energy from its food source (early in evolution) or it could (perhaps to a beginner) mean a multi-cellular organism acquiring oxygen from its environment through the use of things like lungs, gills, trachea, or other things (later in evolution, not needed by very small organisms or my sponges).

This question illustrates the difficulty in origin of life questions. Even in the simplest single cell organisms these systems are highly complex. Yet they must be present for the organism to survive. For example, every organism has to reproduce and every organism has to have a digestive system. You need biochemical pathways to extract energy ( ATP) from your food and you need the enzymes and co-factors that go with those pathways. You need systems for communicating with your environment. You have to have a way to transmit all of these processes to the next generation. No one has any clue how all this happened. If they tell you they do know--- well......it's just a guess.

Is this homework?
No, phinds, not homework. Just curious about evolution.

Thanks, guys. Couple of questions.

According to BBC Bitesize the correct word for what I earlier referred to as respiration, i.e, breathing, is ‘ventilation’; is that correct?

How might a monocellular organism communicate with its environment?

Is the nerve net of a cnidarian analogous to our peripheral nervous system (I know that our pns relays impulses to our cns and that a cnidarian hasn’t got a cns but I’m wonderin if the nerve net was the beginnings a pns to which a cns ‘hooked up’ with later)?

And, finally, would the archaea (prokaryotic microbes) that lived in hydrothermal vents (and are the earliest known life forms – according to Wiki) have had, in a sense, a primitive ‘skin’ (cell membrane); a primitive digestion system; a primitive respiration system (in the proper sense of respiration); a way of communicating with their environment; and, in a sense, a reproductive system?

jim mcnamara
Mentor
You are going to wreck your ship on the reef of confusing definitions.

Single cells have no lungs, right? But they do undergo the process of respiration. So do all of the cells in your body. And we have lungs.

Respiration is the process of creating usable energy from a molecule, like table sugar, or grape sugar (glucose is the name we want).
The process goes like this:
Code:
glucose + oxygen -> energy + Carbon dioxide.
In man on the street terms, we use respiration and breathing as synonyms. For that use and even for physicians the term is perfectly okay. Except when you start learning about what you asked.

You can see why we kind of play mix and match here. Our lungs bring in oxygen. Our lungs expel waste carbon dioxide.
But bottom line: most organisms use respiration just like the formula above. And lots of organisms have lungs. Plants do not.

Okay.

Except that "modern" cells and large living things inherited respiration using oxygen. The ancient parent was a single cell. What we see today came a series of steps over VERY long periods. Steps go from:
Code:
one cell (like bacteria) -> many cells (multicellular like filamentous algae) -> plants and animals
Let's break it down (I left out a lot of detail and terms):
1. First process:
The first pass at this process does not use oxygen, it does a partial breakdown. We can see remnants of this in brewing beer. One end product of this old fashioned process is not carbon dioxide, it is ethanol - the alcohol in beer and wine. Since it goes fine without oxygen, no air is required. Call it Anaerobic. Anaerobic means without air. This is anaerobic respiration. It happens inside single yeast cells. It also is not like the first formula. Confusing, I know.

2. Second process:
So, if there is something like anaerobic going on without air, how about with air?
Answer: Aerobic (means with air) respiration. This requires moving oxygen into a living cell and then disposing of the carbon dioxide. For us, breathing. This process is way more efficient than anaerobic.

So respiration happens in yeast/barley mash when we make beer. Also happens when people drink beer and metabolize it.
two different concepts: one name. Respiration.

(So you do not get confused: yeast can also turn sugar into carbon dioxide. But when there is lots of sugar to burn up, the yeast gets turned off by its own product - high alcohol levels. Kind of like a DIY pollution switch. This is why there is a maximum attainable alcohol level in the brewing process. Higher levels are achieved by adding more alcohol or by distillation. The final level varies primarily with the variety of yeast. Secondarily with all kinds of diddling by us humans)

Respiration happens while you are reading this, too.
So, a definition - respiration is the process that releases usable energy from simple carbohydrates like glucose.
Respiration is also the act of breathing.

Life is like that, not all simple answers....

BillTre
Gold Member
According to BBC Bitesize the correct word for what I earlier referred to as respiration, i.e, breathing, is ‘ventilation’; is that correct?
Breathing can be called ventilation. In a larger sense ventilation could apply to actions involving moving the environmental medium (air or water) over specialized gas exchange surfaces (lungs, gills, etc. (there are many)).

How might a monocellular organism communicate with its environment?
Communication with its environment would be across its cell membrane. In the simplest cells (archaea and bacteria) this would involve molecules diffusing across the membrane (not that efficient) or things like protein receptors in the membrane that either using energy or not move a bound molecule across the membrane.
more complex (eukaryotic) single cells could also draw in volumes of the surrounding media by sucking vesicles (making little cell membrane lined bubbles containing what was outside at the surface) into the cell.
Cells can also send things out to their environment, like proteins, enzymes and other molecules.

Is the nerve net of a cnidarian analogous to our peripheral nervous system (I know that our pns relays impulses to our cns and that a cnidarian hasn’t got a cns but I’m wonderin if the nerve net was the beginnings a pns to which a cns ‘hooked up’ with later)?
Analogous vs. homologous: a structure is homologous to another structure if it is derived in evolution from that earlier structure. Alternatively, two currently existing structure can be homologous if they are both evolved (derived) from the same earlier structure. Analogous can have a variety of meanings where the structures are not derived from a pre-existing structure but have evolved a similarity of function and/or structure. Much looser term.
I would think of the cniderian nerve net (basically its whole nervous system) as a precursor to both the CNS and the PNS. Part of it can be conceived as evolving into the CNS and part into the CNS. Here are some pictures. There are more nerve cells around the oral end (acts as both a mouth and anus). This is often called a condensation. Some might consider it as an analogue of the CNS. Others might not.

And, finally, would the archaea (prokaryotic microbes) that lived in hydrothermal vents (and are the earliest known life forms – according to Wiki) have had, in a sense, a primitive ‘skin’ (cell membrane); a primitive digestion system; a primitive respiration system (in the proper sense of respiration); a way of communicating with their environment; and, in a sense, a reproductive system?
Archaea and bacteria can both live in hydrothermal vents. They are usually considered equivalent with respect to which came first. An unknown and presumed to now be extinct predecessor (their common ancestor) is though to have existed before them. It would most likely have had those things which both archaea and bacteria have in common: a cell membrane, DNA, RNA, ribosomes, a cellular respiration system: a system to derive energy from environmental molecules that involved moving electrons through electron transport chain that pumps protons (or hydrogen ions, H+) out of the cells and which then uses the gradient of H+ to produce ATP (the predominant cellular energy source)).

The cell's membrane's function is to separate the cell from its environment (as well as provide a unit for selections and the site of much of cellular respiration (pumping of protons and the ATP synthatase).
The respiration system would be there to provide cellular chemical energy for the cell to use.
I would call a digestive system something to break down food into molecules that could be taken into the cell for processing by the respiration system. This may not have been necessary, depending on what the cells were living off of. Some primitive cells would just absorb molecules that could be used by respiration without the preliminary digestion step. I would guess this would be the case in the first cells,. Others might not.
Many origin of life scenarios place the origin events in environments where a simple usable food molecule is provided by the environment. There are several proposed sites for this (hydrothermal and geothermal vents (different things) are among those) where suitable molecules are present in the environment for use without digestion. These are favored as hypothetical sites of origins because it makes one less thing that the first life form would not have to achieve before normal biological evolution could take over.
Any living thing has to be able to reproduce. It would have to have genetic system of some kind to provide their progeny with the information to make more of the specific proteins they are largely made of. Some think the first genetic information storage was RNA and the use of DNA evolved later (this would be in an earlier life form than the immediate ancestor of bacteria and archaea). The genetic system would also require the presence of ribosomes, tRNAs in order to make specific proteins. The proteins of the respiration system would require this.
The combination of a genetic system and reproduction would provide the basis for evolution.