Q.Describe why mitochondria is called the powerhouse of the cell.
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You have probably heard that the mitochondria is the "powerhouse of the cell." That is a good start, but it tells you nothing about how it makes power. The secret is in its structure — a structure that is not random, but perfectly engineered for its job: extracting energy from food and packaging it into ATP.
Imagine a factory that needs to generate electricity. You wouldn't just dump the generator in the middle of an open room. You would build a dedicated power plant with a secure outer wall, a controlled inner chamber, and a huge surface area of machinery to maximise energy production. That is exactly what a mitochondrion is.
The Two Membranes: The Outer Wall and the Inner Factory Floor
A mitochondrion is wrapped in two membranes, not one. This is the first critical point.
The outer membrane is the security fence. It is smooth and porous, containing large protein channels called porins. These make it freely permeable to small molecules like ions, ATP, and nutrients. Anything small can pass through without a ticket. This membrane simply separates the mitochondrion from the rest of the cell (the cytoplasm).
The inner membrane is the real machinery. It is highly selective — almost nothing crosses it without a specific transporter. This is where the action happens. If the outer membrane is the factory wall, the inner membrane is the factory floor where the generators are bolted down.
The space between the two membranes is called the intermembrane space. The space inside the inner membrane is the matrix. These two compartments have very different chemical compositions, and that difference is the engine of ATP production.
The Cristae: Why Folding Matters
Here is the intuitive leap. The inner membrane is not a simple balloon inside the outer one. It is heavily folded into shelf-like structures called cristae (singular: crista).
Why fold it? Surface area. A flat inner membrane would be too small to hold enough machinery. By folding, the mitochondrion packs an enormous amount of membrane into a tiny volume. Think of it like a concertina — you can fit a long strip of metal into a small space by folding it back and forth. The cristae increase the surface area of the inner membrane by a factor of 5 to 10.
The cristae project into the matrix, so the matrix is a dense, gel-like substance filling the irregular spaces between the folds.
The F1 Particles: The ATP Generators
If you look at the inner membrane under an electron microscope, you will see tiny, mushroom-shaped knobs sticking out into the matrix. These are F1 particles (also called ATP synthase complexes).
Each F1 particle is a molecular motor. It uses the flow of protons (H⁺ ions) from the intermembrane space into the matrix to spin a rotor, and that mechanical energy is used to attach a phosphate group to ADP, making ATP. The stalk of the mushroom anchors it in the membrane, and the head (the F1 part) does the chemical work.
The entire process of aerobic respiration (Krebs cycle in the matrix, electron transport chain on the inner membrane) is designed to pump protons into the intermembrane space, creating a gradient. The F1 particles then let those protons flow back down the gradient, using the energy to make ATP.
Putting It All Together …
Mitochondria carry out cellular (aerobic) respiration, releasing most of the cell's usable energy. …
Mitochondria make most of the cell's ATP, so they are its powerhouse.
Mitochondria are called the 'powerhouse of the cell' because it is here that the energy-releasing steps of respiration — the Krebs cycle (in the matrix) and the electron transport chain/oxidative phosphorylation (on the inner membrane/cristae) — take place. During these processes food (glucose) is oxidised and a large amount of energy is trapped in the form of ATP, the energy currency of the cell. Since the mitochondria generate most …
- CBSE 2026Set ANNUAL1 markQ._______ is produced in mitochondria.
›Reveal solutionSolution
Mitochondria are the site of aerobic respiration, and the ATP generated there powers the cell's energy needs.
Each mitochondrion has a double membrane: a smooth outer membrane, and an inner membrane thrown into folds called cristae, which greatly increase the surface area available for the electron transport chain. The fluid matrix enclosed by the inner membrane contains the enzymes of the Krebs (citric acid) cycle.
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- CBSE 2026Set ANNUAL1 markMCQQ.Which of the following is a double membrane-bound organelle ?(a) Lysosome(b) Golgi apparatus(c) Mitochondria(d) Ribosome
›Reveal solutionSolution
Mitochondria are double membrane-bound organelles, so the answer is (C).
Membrane organisation of organelles:
- Mitochondria — double membrane (outer smooth membrane and inner membrane folded into cristae); the site of aerobic respiration.
- Lysosome and Golgi apparatus — single membrane-bound.
- Ribosome — not membrane-bound at all. …
- CBSE 2025Set ANNUAL1 markMCQQ.Which cell organelle is called as power house of the cell?(a) Mitochondria(b) Ribosome(c) Golgi bodies(d) Lysosome
›Reveal solutionSolution
Mitochondria are called the power house of the cell because they are the primary site of aerobic cellular respiration and ATP synthesis.
Mitochondria are double membrane-bound organelles. Their inner membrane is folded into cristae, which house the electron transport chain and ATP synthase enzyme complexes. The matrix contains enzymes of the Krebs cycle. Through oxidative phosphorylation, mitochondria convert the chemical energy of food (via pyruvate and acetyl-CoA oxidation) into ATP, the energy currency of the cell.
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- CBSE 2024Set ANNUAL1 markMCQQ.Assertion (A) : Mitochondria and chloroplast are semi-autonomous organelles. Reason (R) : They are formed by division of pre-existing organelles and contain DNA but lack protein synthesizing machinery.(a) Both Assertion (A) and Reason (R) are true and Reason (R) is correct explanation of Assertion (A).(b) Both Assertion (A) and Reason (R) are true but Reason (R) is not correct explanation of Assertion (A).(c) Assertion (A) is true but Reason (R) is false.(d) Both Assertion (A) and Reason (R) are false.
›Reveal solutionSolution
Mitochondria and chloroplasts are semi-autonomous because they contain their own circular DNA, ribosomes (70S type) and RNA, allowing them to synthesise some of their own proteins — they do not lack protein-synthesising machinery, they simply cannot function fully independently of the nucleus.
The Assertion — that mitochondria and chloroplast are semi-autonomous organelles — is true. They are called 'semi-autonomous' because they have some genetic autonomy but are not completely independent of nuclear control.
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- CBSE 2022Set TERM11 markMCQQ.Which cell organelle is also known as 'Powerhouse of the cell'?(a) Golgi apparatus(b) ER(c) Lysosome(d) Mitochondria
›Reveal solutionSolution
Mitochondria generate the ATP that powers the cell, earning the nickname 'powerhouse of the cell'.
Mitochondria are double-membrane-bound organelles; the inner membrane is folded into cristae that increase surface area for the electron transport chain and ATP synthase. Through the processes of the Krebs cycle and oxidative phosphorylation, mitochondria oxidise pyruvate (derived from glucose) in the presence of oxygen to release large amounts of energy, most of which is captured as ATP. Because ATP is the cell's usable energy currency and mitochondria are the primary site of its aerobic pro …
- CBSE 2020Set ANN1 markQ.Choose the correct answer. The organelle known as power house of the cell is :
›Reveal solutionSolution
The mitochondrion is the "power house of the cell" because it is the main site of aerobic cellular respiration, where most of the cell's ATP is generated.
Every living cell needs a continuous supply of energy in a usable form, and that form is ATP (adenosine triphosphate). Among the four options:
- Ribosome: builds proteins from amino acids; it does not generate energy.
- Vacuole: mainly a storage sac (water, ions, waste products); no major role in energy release.
- Chloroplast: traps light energy and makes food (glucose) by photosynthesis, but this is energy CAPTURE, not the day-to-day energy-currency-generating engine common to all cells (plant and animal alike). …
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