Cellular respiration is how your body converts glucose from food...
Biology69 views·Updated 27 Aug 2026·2 pagesComplete A Level Biology Notes: Glycolysis & Krebs Cycle
Oscar66@oscar66
1
of 2
Overview of Cellular Respiration
Think of cellular respiration as your body's power station - it's constantly running to keep your cells energised. The process breaks down glucose through three connected stages, each happening in different parts of your cells.
Glycolysis kicks things off in the cytoplasm (the jelly-like substance in cells). This ancient process existed before mitochondria evolved, which explains why it happens outside these organelles. Here, glucose gets broken down into pyruvate, producing some ATP through substrate-level phosphorylation.
The real energy production happens in the mitochondrion. The Krebs cycle occurs in the matrix (think of it as the mitochondria's interior), whilst the electron transport chain operates in the cristae (folded inner membranes).
Here's the clever bit: high-energy electrons help pump protons across membranes, creating a gradient. When these protons flow back, their energy drives ATP synthase to make ATP through oxidative phosphorylation. Oxygen is only needed at the very end of the electron transport chain, but without it, everything grinds to a halt!
Key Insight: Cyanide is deadly because it blocks cytochrome oxidase, the enzyme that uses oxygen at the final step - showing just how crucial this process is for life.
2
of 2
The Three Stages in Detail
Glycolysis transforms one glucose molecule into two pyruvate molecules in your cytoplasm. This process uses and produces ATP, but more importantly, it generates NADH - think of this as an electron carrier that's like a rechargeable battery.
The Krebs cycle (also called the citric acid cycle) is where things get interesting. Pyruvate enters the mitochondria and gets converted into acetyl-CoA, which then goes through a series of chemical reactions. Each turn of the cycle produces CO₂, more NADH, FADH₂ (another electron carrier), and a bit more ATP.
The electron transport chain is your cellular powerhouse. NADH and FADH₂ donate their high-energy electrons to a series of protein complexes in the inner mitochondrial membrane. As electrons pass through these complexes, protons get pumped across the membrane, creating a proton gradient.
When protons flow back through ATP synthase, it's like water turning a turbine - the energy drives the production of loads of ATP. This is why the electron transport chain produces about 32-34 ATP molecules, compared to just 2 from glycolysis and 2 from the Krebs cycle.
Exam Tip: Remember the electron carriers - NAD⁺/NADH switching is crucial, and FAD/FADH₂ works similarly. These are your energy currency exchange systems!
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Biology69 views·Updated 27 Aug 2026·2 pagesComplete A Level Biology Notes: Glycolysis & Krebs Cycle
Oscar66@oscar66
Cellular respiration is how your body converts glucose from food into usable energy (ATP) - it's literally what keeps you alive! This process happens in three main stages: glycolysis in the cytoplasm, the Krebs cycle in mitochondria, and the electron...
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Overview of Cellular Respiration
Think of cellular respiration as your body's power station - it's constantly running to keep your cells energised. The process breaks down glucose through three connected stages, each happening in different parts of your cells.
Glycolysis kicks things off in the cytoplasm (the jelly-like substance in cells). This ancient process existed before mitochondria evolved, which explains why it happens outside these organelles. Here, glucose gets broken down into pyruvate, producing some ATP through substrate-level phosphorylation.
The real energy production happens in the mitochondrion. The Krebs cycle occurs in the matrix (think of it as the mitochondria's interior), whilst the electron transport chain operates in the cristae (folded inner membranes).
Here's the clever bit: high-energy electrons help pump protons across membranes, creating a gradient. When these protons flow back, their energy drives ATP synthase to make ATP through oxidative phosphorylation. Oxygen is only needed at the very end of the electron transport chain, but without it, everything grinds to a halt!
Key Insight: Cyanide is deadly because it blocks cytochrome oxidase, the enzyme that uses oxygen at the final step - showing just how crucial this process is for life.
2
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The Three Stages in Detail
Glycolysis transforms one glucose molecule into two pyruvate molecules in your cytoplasm. This process uses and produces ATP, but more importantly, it generates NADH - think of this as an electron carrier that's like a rechargeable battery.
The Krebs cycle (also called the citric acid cycle) is where things get interesting. Pyruvate enters the mitochondria and gets converted into acetyl-CoA, which then goes through a series of chemical reactions. Each turn of the cycle produces CO₂, more NADH, FADH₂ (another electron carrier), and a bit more ATP.
The electron transport chain is your cellular powerhouse. NADH and FADH₂ donate their high-energy electrons to a series of protein complexes in the inner mitochondrial membrane. As electrons pass through these complexes, protons get pumped across the membrane, creating a proton gradient.
When protons flow back through ATP synthase, it's like water turning a turbine - the energy drives the production of loads of ATP. This is why the electron transport chain produces about 32-34 ATP molecules, compared to just 2 from glycolysis and 2 from the Krebs cycle.
Exam Tip: Remember the electron carriers - NAD⁺/NADH switching is crucial, and FAD/FADH₂ works similarly. These are your energy currency exchange systems!
We thought you’d never ask...
Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.
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