Energy is released when chemical bonds are broken

[maize]

This is what my dd's biology teacher has taught her class. Dd was very proud of the 100% she got in her recent test, but glancing through the questions I found this answer marked correct. Dd says the teacher has been emphasizing this point all semester.

I explained that it is actually the formation of chemical bonds that releases energy and explained the application of this to biological processes like respiration but am now wondering what else is being mis-taught in this class.

[dirty ethel rackham]

It sounds like this teacher is confusing breaking and creating bonds with anabolic reactions (building larger molecules, which require energy) and catabolic reactions (breaking down larger molecules , which releases energy) as in ADP and ATP.  But I think you are right regarding most chemical bonds.

[prairiewindmomma]

Here's a one page quick review on exergonic v. endergonic reactions with re: to biology.  Your general response is correct with re: to chemistry & energy moving between levels/bonds forming. 

[maize]

The actual test question was: "Energy is released when bonds are? A) broken B) formed C) bonds don't carry energy D) both broken and formed"

With A) as the correct answer.

 

[Dicentra]

The teacher may have simply accidentally marked down the incorrect correct answer. 🙂  It's sometimes easy to do with multiple choice questions.  Did the teacher stick by the answer when the mistake was pointed out?  That would be more worrisome to me.  Because yes - energy is released when bonds are formed.

[prairiewindmomma]

I think that is a badly worded question.

[maize]

54 minutes ago, Dicentra said:

The teacher may have simply accidentally marked down the incorrect correct answer. 🙂  It's sometimes easy to do with multiple choice questions.  Did the teacher stick by the answer when the mistake was pointed out?  That would be more worrisome to me.  Because yes - energy is released when bonds are formed.

It is possible the answer was marked wrong, though dd seems confident that the teacher has taught them that you get energy by breaking bonds.

Haven't talked to the teacher about it yet.

[EKS]

Maybe this will help? https://apcentral.collegeboard.org/courses/ap-chemistry/classroom-resources/ending-misconceptions-about-energy-chemical-bonds

[Clemsondana]

Biology at all levels (including college) tends to have a lot of 'the energy to power X process comes from ATP' without teaching where the P goes when ADP is formed.  Explanations like this http://www.biologydiscussion.com/biochemistry/how-energy-is-stored-in-adenosine-triphosphate-atp-biochemistry/78815  are standard in most textbooks.  When I talk about metabolism, I put a lot of emphasis on the idea that redox reactions have to be coupled because the H has to go somewhere.  But, when we talk about something like active transport or motor proteins, all we tend to say is that the reactions 'happen because the energy comes from converting ATP to ADP'.  I may mention that the reactions occur because the protein gets phosphorylated, but a real understanding of phosphorylation of proteins isn't part of most regular high school classes.  

There a couple of topics that introduce by saying 'what I'm about to tell you isn't strictly accurate from a physics/chemistry perspective, but until you've got time to learn those subjects, this will have to do' - that explanation fits the material that's being taught in high school and non-majors college texts.  It's like when you use the summary reaction for photosynthesis - 

6 CO2 + 6 H2O <-> C6H12O6 + 6 O2     and then have to explain that cells don't literally connect 6 carbon dioxides and some water to make sugar - they actually use 1 CO2, combine with with RuBP, do a whole lot of shuffling around of molecules, and then produce G3P, which can then get made into sugar or something else.  

edited to say - As I think about this a little more, I think that biology is often guilty of these sorts of overstatements because, especially at the early levels, it only deals with a handful of reactions.  Converting ATP to ADP and shuffling H around from sugars to NAD+ for metabolism, dehydration and hydrolysis reactions...and that's about it for most general bio classes.  Students, many of whom haven't had chemistry of physics of any kind, don't have any idea of what a 'high energy bond' is or why some bonds are higher energy than others. And, for all practical purposes, as long as you know a bit about a few kinds of reactions, you know all that you'll encounter in most biology classes.  

Edited December 17, 2018 by ClemsonDana

[Clemsondana]

I've been pondering on this some more, because the only way that I've ever heard metabolism taught is that 'energy from the sun is converted into a usable form of energy (macromolecules) which can be stored or used to build cells and broken down when energy is needed'.  

I did some digging around and found 3 articles that might be interesting.

https://chem.libretexts.org/Textbook_Maps/Biological_Chemistry/Metabolism/ATP%2F%2FADP

I think that because the only reactions many bio students work with is ATP/ADP, this is how they come to think of all chemical bonds.

Then there's this...

http://ptexphys.utorontoeit.com/energy-metabolism/atp-and-stored-sources-of-energy/

specifically this paragraph  

The potential energy within the bonds of macronutrients (carbohydrates, lipids and proteins) is transferred into the energy stored in anhydride phosphate bonds of ATP through a series of stepwise redox reactions. Subsequently, energy from ATP hydrolysis may be transferred to other compounds to raise them to a higher activation level or it may be used to power mechanical, chemical and transport work. In exercise for example, ATP is required for muscular work as well as for maintaining ion gradients across the muscle and nerve cell membranes.

and then also the more chemistry/physics oriented 

https://www.wired.com/2015/12/we-need-to-talk-about-the-energy-in-chemical-bonds/

Edited December 18, 2018 by ClemsonDana