MBIO 2230 - Topic 4 (oxygen)

Oxygen is a strong , meaning it is being itself

Ozygen is a strong oxidizer, meaning it is being reduced itself

Oxidation releases…

Energy

Burning vs. respiration (differences)

Burning: Release of C in an uncontrolled way
Respiration: Release of C in a controlled way

Burning vs. respiration (similarities)

They both release C by reacting with O2

Spontenous redox reactions 

Electrons move from atoms with a low affinity for electrons, to atoms with a high affinity for electrons

Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

Half reaction: Zn⁰ → Zn²⁺ + 2e⁻

--> What happened to the zincs oxidation state and solubility

Zinc was oxidized (loss electrons) and its solubility changes in a way that it became aqueous

Zn(s) + Cu²⁺(aq) → Zn²⁺(aq) + Cu(s)

Half reaction: Cu²⁺ + 2e⁻ → Cu⁰

--> What happened to coppers oxidation state and solubility

It was reduced (gained electrons) and its solubulity changed in a way that it became solid

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The temp increases, since energy is released during the movement of electrons 

The _ changes along with the change in oxidation state

Solubility

Where do organisms collect energy from?

From carefully controlled redox reactions 

Aerobic respiration

It is the reaction that most animals use to derive energy from food, starting with glucose and oxygen

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"C #1 = 0
C #2 = +4 "

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C is the electron _"

Donor 

Which ever molecule is the electron donor is also the source

Energy

If 1 thing is oxidized, something else must be _

Reduced

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O is the electron "

Acceptor

Gibbs free energy 

The potential energy that an electron can hold and therefore the energy it releases when a redox reaction occurs 

Activation energy

The amount of energy needed to overcome the energy barrier that allows for a chemical reaction to occur

Gibbs free energy formula 

""

ΔE

The difference in electrical potential (V) between the oxidation and reduction half reactions

"ΔE formula "

"ΔEº = E cathode (reduction) - E anode (oxidation)"

The apart the electrical potential is, the ΔE is, meaning the ____ energy that is released

The further apart the electrical potential is, the higher ΔE is, meaning the more energy that is released

ΔGº vs. ΔG

ΔGº = It is under standard conditions
ΔG = It is under real world conditions, which are often not in standard conditions

Common terminal electron acceptor 

O2

Electron donor in cellular respiration 

Glucose 

Electron transport chain 

It builds up and captures energy in the form of ATP and a proton gradient 

What is a terminal electron acceptor (i.e. O2)?

It's kind of like a garbage truck, such that it absorbs electrons that have already given away its energy and therefore is at a lower energy state, in order to clear them out of the way

Assimilation of carbon

Carbon to build with

Dissimilation of carbon

Carbon to burn (i.e. acts as the electron donor)

Across the diversity of life, organisms have acquired means of mixing & matching different ____________ of electron ______ and terminal electron _________. 

Across the diversity of life, organisms have acquired means of mixing & matching different combinations of electron donors and terminal electron acceptors. 

What happens if reduced carbon is not available for oxidation?

Other substances can be used as the electron donor, such as iron 

Iron replacing glucose

The iron acts as the energy source, as its electrons are taken from it and given to oxygen

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Significance of distance between electron acceptor and donor "

The further away the two are from each other, the more energy that is released in the reaction

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Which reaction releases more energy?"

The red one, since the electron acceptor and donor are further apart

Aerobic respiration dominates in _________ environments, but not so much in _______ environments

Aerobic respiration dominates in terrestrial environments, but not so much in aquatic environments 

Why is aerobic respiration less prominent in aquatic environment

This is becayse the water acts as an effective barrier against oxygen, as the diffusion rate of oxygen in standing water is very slow

What do organisms do when O2 is not available for aerobic respiration?

They use other molecules as the terminal electron acceptor

Alternative terminal electron acceptor that is not oxygen

Nitrogen 

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Energy difference between the two reactions"

The energy released is roughly the same

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If the energy difference is not that great, what is the problem with using N instead O as a terminal electron acceptor "

The constraint is the source of N and the fact that it has to be in solution

Rapid + Slow ___ = Limited amount of O2

Rapid consumption + Slow replenishment = Limited amount of O2

Adaptation that allows aquatic plants to make up for the lack of O2

They have pores that allows O2 to diffuse inside in the gas phase so that it can get to the roots, rather than it having to go through water

Dead zones that lead to fish kills

1.) This refers to areas with high decomposition, leading to a rapid consumption of O2 that causes the water to be hypoxic
2.) This kills the living organisms (i.e. the fish) in the area as a result, due to suffocation

Dead zones leading to fish kills usually occur when? 

It often occur after winter, due to the long duration of ice cover

ASK PROF

O2 availability as a net outcome --> Flux in vs. flux out

Flux in = Local production or transfer from atmosphere
Flux out = Consumption by respiration 

Determining O2 concentration in a soil aggregate (how)

Penetrate into the soil aggregate to measure the O2 levels

Determining O2 concentration in a soil aggregate (results)

The amount of O2 decreases the deeper we go, meaning that the deeper we go, the more that rates of consumption exceeds replenishment 

O2 levels in microbial colonies

The area at the surface has the highest concentration, but the deeper you go into the colony, the less O2 there is

Aerobic respiration vs. photosynthesis reaction

Their reactions are the complete inversion of each other 

Input of energy in photosynthesis 

Sunlight 

Why is it weird that we have so much O2 in our atmosphere

Geochemical forces usually want O2 to react with other chemicals and form oxides

Two mechanisms for the generation of O2

1.) Use of solar energy 
2.) Photosynthesis 

Generation of O2: using solar energy

This invovles the photolysis of water vapour into O2 (but it's only a small source of O2)

Photolysis

The process of breaking something apart using light

Generation of O2: photosynthesis 

Oxygen is a byproduct of photosynthesizers making chemical energy

Photosynthesis reaction 

It involves using water and CO2 as substrates, resulting in O2 and CH2O products 

Seasonal dynamics of O2 

This refers to the fact that O2 levels are directly proportional to the amount of actively growing plants 

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What is the graph showing us "

Dotted line = Capacity of O2 that water can hold
Above line = It represents the level of O2 being ejected from water, coming from photosynthesizers in the water

Banded iron formations 

It represents the transition of earth from a low oxygen environment to a high oxygen environment, based on the massive amounts of iron that precipitated out of ancient oceans

Atmosphere then vs. now (in relation to oxygen + iron)

Then = Atmosphere used to be anoxic, therefore most/all of the iron was reduced in water
Now = As O2 became more available because of photosynthesizers, the iron became oxidized, which is less soluble, causing the iron to precipitate out of the water

Use the terms ‘flux’ and ‘steady state’ to describe oxygen dynamics in the atmosphere for the period of time following the evolutionary innovation known as oxygenic photosynthesis. 

1.) Photosynthetic organisms acted as the source of oxygen, allowing it to flux out into the environment 
2.) It started off as being in a steady state, as it was constantly being used up by iron so that it can be oxidized, all while the photosynthesizers continued to make more

Aerobic respiration is essentially the _______ of photosynthesis

Reverse

Significance of aerobic respiration being the reverse reaction of photosynthesis 

In order for photosynthesis to drive the accumulation of molecular oxygen, some of the reduced carbon that is formed by photosynthesis must be stored as organic matter

"""In order for photosynthesis to drive the accumulation of molecular oxygen, some of the reduced carbon that is formed by photosynthesis must be stored as organic matter"" --> WHY? "

1.) If the reduced carbon made in photosynthesis is immediately oxidized, the formation of O2 is just reversed, before it could be utilized in aerobic respiration
2.) Therefore, it must first be stored in/as organic matter

Negative vs. positive feedback 

Negative feedback has a dampening/countering effect, while positive feedback has a re-inforcing effect

Negative feedback example

When the temperature in a room drops, it is sensed by the thermostat, which brings the temperature back up

Negative and positive feedback are esssential for what?

They are essential for maintaining balance/stability

Feedback example involving oxygen 

As O2 levels increase in the atmosphere, the penetration of O2 into the ocean is deeper, allowing respiration to happen in more places, which allows O2 to be used up at a faster rate 

How has life shaped the chemical environment of Earth? 

1.) It has made Earth's surface a highly oxidizing environment
2.) Which in turn, helps in the formation of the shield against UV radiation

Earth's surface is now a highly environment, due to the splitting of via _

Earth's surface is now a highly oxidizing environment, due to the splitting of water via photosynthesis

Ozone 

A thick layer O3 that shields the earth from UV radiation

High altitude 

Stratospheric ozone

Low altitude 

Tropospheric 

Ozone in the lower atmosphere

It contributes to air pollution 

Ozone _______ & __________ is a continuous and dynamic process 

Ozone creation & destruction is a continuous and dynamic process 

Production of ozone 

1.) UV radiation (light) splits O2 into individual oxygen atoms 
2.) The individual oxygen atom can then react with O2 to form O3 

Destruction of ozone 

1.) UV radiation splits O3 into O2 and an individual atom
2.) The individaul atom can then react with another O3 molecule and form two O2 molecules 

UV radiation splitting O2 or O3 is similar to…

The formation of O2 from the photolysis of water

Ozone is only created when…

When O2 levels become enriched in the atmosphere

Ozone is the primary constituent of the __________ that _______ incoming light in the ultraviolet wavelengths. 

Ozone is the primary constituent of the atmosphere that absorbs incoming light in the ultraviolet wavelengths. 

What makes O3 so good at acting as a barrier against UV radiation

Because it is able to absorb UV very well

Ozone is a _______ in the troposphere 

Pollutant

What impacts the fate of the ozone in the stratopheric vs. troposcheric atmosphere

It depends on the prescence of water

Water availability in the lower vs. upper atmosphere

Stratosphere = Low water 
Troposphere = High water

What happens to the ozone in the trophospheric region 

1.) There are lots of water, which can interact with an excited oxygen atom to form a hydroxyl radical 
2.) A series of reactions then occur that result in the formation of O2 from O3

Significance of high water availability in the tropospheric region 

The water helps clean up the air, as it forms O2, which helps control the fact that ozone is a pollutant in this region 

Hydroxyl radicals 

1.) The main source of oxidizing power in the troposphere
2.) It has a lifespan of seconds 

More ozone is formed in the ___

Stratosphere

Ozone in the stratosphere (stability)

It is more stable and therefore has a longer residence time in the stratosphere

What happens to the ozone when other chemicals are present in the atmosphere 

They can accelerate ozone destruction, as many of them act as catalysts that can be regenerated during intermediate reactions 

Example of chemical that acts can as a catalyst to accelerate ozone destruction 

Chlorine 

What causes chemicals to be present in the atmosphere

It is caused by human activity, such that it causes chemicals to be in the atmosphere that are not usually there

Chlorine significance to the ozone 

It can react with O3, convering it into O2 

CFC significance to the ozone 

1.) UV light causes one of its chlorine to be cleaved
2.) The chlorine can now reaction with O3 to form O2 

How does chlorine act as a catalyst 

It does not get used up, it can be used again to react with O3 again 

NaCl vs. CFC residence times

NaCl = Short RT
CFC = Long RT

Tropopause 

The barrier that separates the stratosphere and troposphere from mixing 

Is there stratification in the atmosphere

Yes, via the tropopause