Hey everyone, I've been thinking about this since my bio class last week when the prof zoomed through the ATP stuff super fast. Back in high school I remember cramming for a test and just memorizing that glycolysis gives you a couple ATP quick, but then mitochondria do the heavy lifting—yet I never really got why the chemiosmosis part is way more efficient than those direct substrate-level steps. Like, is it mostly because it pumps out so much more ATP overall from the same glucose, or something about energy capture? Anyone have a simple way to wrap their head around it? Kinda frustrating when it feels like the cell's wasting effort otherwise.
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Man, I totally get where you're coming from—those early stages always seemed kinda underwhelming to me too. In my experience rereading notes from uni, substrate-level phosphorylation is straightforward and fast, just slapping a phosphate onto ADP directly during reactions like in glycolysis or bits of the Krebs cycle, but it only nets a handful of ATP total. Chemiosmosis steps in during the electron transport chain and uses that proton gradient across the membrane to power ATP synthase, basically harvesting way more energy from the electrons carried by NADH and FADH2. That's why the bulk of ATP comes from there. If you're trying to visualize the whole pathway, I sometimes refer back to this cellular respiration chart that breaks down the stages clearly—it really helped me see the numbers side by side without getting lost in textbooks. Just my two cents, but it clicks better when you see how much more "bang for your buck" the gradient method gives.