16 votes
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Why don't McDonald's fries decompose?

This controlled experiment of burger decomposition explains in detail why fast food burgers do not decompose easily. The same can be applied to fries, which are smaller and come dehydrated from the ...
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  • 9,314
12 votes
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If red blood cells have no mitochondria how are they able to metabolize glucose?

In humans (and all mammals), red blood cells lack mitochondria and therefore has no functional TCA cycle. They metabolize glucose mainly via glycolysis, forming lactate which is released from the ...
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  • 5,595
11 votes
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Are carbohydrates an essential component of human diet?

From a theoretical perspective this is a very interesting question, mostly because it is difficult to completely abstain from carbohydrate intake on a normal diet. Even the popular low carb diets of ...
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10 votes
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What is the relationship between the light and dark reactions of photosynthesis?

ATP is a bad medium for storing energy as detailed here. ATP has a molecular weight of 507 Da Glucose has a molecular weight of 180 Da, and contains the same amount of energy as 31 ATP ...
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  • 2,494
9 votes

Why is carbon dioxide produced in alcohol fermentation but not in lactic acid fermentation?

Glycolysis needs a steady supply of NAD+ to happen - this is the driver for the anaerobic oxidation to lactate and ethanol, although this is energetically much less favorable than the complete ...
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6 votes

Why do animals use glycogen for their polysaccharide storage whereas plants use starch?

well glycogen can be broken down into sugars a lot faster, many more branches means many more ends to clip individual sugars off of, that's how you mobilize the sugar for use, it is clipped of the end ...
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6 votes

Can fructose take multiple forms ? Which of these structures of fructose is correct?

The two structures on the left are correct; the one on the upper left is the alpha-D-fructofuranose form, while the one on the lower left is the beta-D-fructofuranose form. Fructose is a ketohexose (a ...
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  • 240
5 votes

Can a human being live without any carbohydrates?

The Atkins diet is based on that. Without carb intake, however, the citric acid cycle (CAC) eventually basically stops and proteins will be utilized to be converted to carb intermediates to feed the ...
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5 votes
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Where do lost membrane proteins go after exocytosis?

In the process of exocytosis materials which are about to be released are transported in small vesicles to the plasma membrane. The plasma membrane fuses with these vesicles and this sets the ...
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  • 49.2k
4 votes

If red blood cells have no mitochondria how are they able to metabolize glucose?

While hemoglobin makes up about 90% of the protein in an RBC, there are many other proteins present as well, including enzymes in the anaerobic pentose phosphate pathway, which is responsible for ...
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4 votes
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Chitin, homo or heteropolysaccharide?

Even teachers are sometimes wrong. ;) Chitin is a homopolysaccharide. This just means that it is made up of repeating units of the same monosaccharide - in this case that monosaccharide is N-...
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  • 2,462
4 votes
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Is aquafaba readily digestible?

Much of it is not readily digestible. According to this chemical analysis: Finally the results presented here also indicate that the amount of digestible carbohydrates in aquafaba is minimal. For ...
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  • 628
4 votes

Carbohydrates in acidic stomach

As for the digestion of fats there are two digestive enzymes active in the stomach: Lingual lipase (produced with saliva) Gastric lipase (produced in the stomach chief cells) Both have activity ...
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  • 2,048
4 votes
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Why do animals use glycogen for their polysaccharide storage whereas plants use starch?

Summary The key difference between glycogen and amylopectin (the main constituent of starch) is not the number of α l,6-glycosidic branches, but their arrangement. In glycogen branches are ...
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4 votes
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Why is it possible to make yoghourt with lactose-free milk?

Conversion of lactose to galactose and glucose is a part of the bacterial metabolism of lactose. So digested lactose would work. In fact, it should work for all kinds of 6-carbon sugars as lactic ...
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  • 35.1k
4 votes
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How can cane sugar sucrose be different from beet sugar in regard to carbon-13 content?

The differential uptake of different isotopes of carbon is covered well at: https://en.m.wikipedia.org/wiki/Fractionation_of_carbon_isotopes_in_oxygenic_photosynthesis Plants have a lower proportion ...
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4 votes
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Why is fructolysis independent of glycolysis?

Summary The mechanistic reason why fructose is converted to fructose 1-phosphate by fructokinase rather than fructose 6-phosphate by hexokinase is explained in terms of the Km values of fructose and ...
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3 votes

Solubility of Amylopectin and Glycogen in water

The answer is relatively simple: Amylopectin is watersoluble, and this seems to be a classical textbook error, which has been propagated now for decades. As you say yourself, the only difference is ...
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3 votes
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Living on pure glycogen?

You asked three questions here, so I'll answer them one by one. Yes, you can survive with glycogen as the only source of carbohydrates, assuming that you also take other nutrients like proteins, fats,...
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3 votes

What is the relationship between the light and dark reactions of photosynthesis?

Apology This question has a very simple answer which was provided in a comment by @EliKorvigo (and acknowledged by the poster) two years before writing this answer. However the commenter did not post ...
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3 votes

Sugars which are Carbohydrates and vice-versa?

You need to make a distinction between polymers and monomers (or dimers). Typically, sugars are monomers like glucose, maltose, or fructose. Sucrose (table sugar) is a dimer. These are all ...
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  • 3,422
3 votes

How does it make thermodynamic sense for photosynthesizers to turn CO₂ into O₂?

Oxygen in photosynthesis does not come from carbon dioxide. It comes from water and this is the step that actually requires light: Photolysis of water. The proton produced in this process is used to ...
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3 votes

Why are we carbon-based?

Too long for a comment. Just extending the answer from @prooffreader slightly. It's true that long carbon chains are present in lipids, but in proteins and nucleic acids there are chains of carbon ...
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  • 22.7k
3 votes

Why are we carbon-based?

We are carbon-based because carbon is the only molecule that is able to form the long, long chains of hundreds of molecules that are required to from proteins, DNA, etc. Absolutely no other molecule ...
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3 votes
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What is the carbohydrate found in almonds, cashews, pecans, hazlenuts and pistachios?

Firstly you must realize that all the above mentioned nuts are actually the seeds of plants. So the question now is which carbohydrate is mainly found in seeds of plants. During the double ...
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  • 1,247
3 votes

What allows grass eaters to digest cellulose?

No there is something else missing besides bacteria humans often already have the right bacteria but they don't digest most of the cellulose they ingest because digesting cellulose with bacteria is ...
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  • 13.2k
3 votes

Why is beta- D fructofuranose two different structures when in free form and as part of sucrose?

I'll try to explain this to you, but you should really look it up here: https://pubchem.ncbi.nlm.nih.gov/compound/beta-Levulose#section=3D-Conformer&fullscreen=true This is the structure of beta-...
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2 votes

Error in textbook

In case of oligosaccharides, only the final ends matter and not the ends of the individual monosaccharides involved in glycosidic linkage. As a consequence, most oligosaccharides have only one ...
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  • 4,619
2 votes
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Do plants need O₂ to consume energy they've stored via sugar?

Plants need sugar not only for energy but also for synthesizing essential metabolites and building blocks including cellulose (used in cell wall), glycoproteins and 5-carbon sugars for nucleotides. ...
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