Why are mitochondria called the powerhouse of the cell?

They earn that name because they produce most of a cell’s ATP during aerobic respiration. In IB Biology, you should be specific: the electron transport chain and ATP synthase in the inner membrane generate ATP via oxidative phosphorylation. That ATP then fuels processes like active transport and biosynthesis. The key idea is efficiency: aerobic respiration yields far more ATP per glucose molecule than anaerobic pathways. Examiners like when you connect ATP output to cell demands, such as muscle or neuron activity. A strong answer also links structure to output, especially the cristae increasing surface area.

Do all cells have mitochondria?

No, not all cells contain mitochondria. For example, mature mammalian red blood cells lack mitochondria, which leaves more space for haemoglobin and prevents them from using the oxygen they transport. In IB Biology, that’s a great structure-function link: losing an organelle supports the cell’s specialized role. Some cells also contain fewer mitochondria if their energy demands are lower. The broader rule is that mitochondria are common in eukaryotic cells, but abundance varies widely by function. When asked, always give one clear example and one reason.

How does mitochondrial structure increase ATP production?

The inner membrane is folded into cristae, increasing surface area for the electron transport chain and ATP synthase. In IB Biology, surface area is not a decorative detail; it explains how more respiratory proteins can fit into the membrane at once. The intermembrane space enables a steep proton gradient to form quickly, storing potential energy. The matrix contains enzymes for the link reaction and Krebs cycle, keeping those reactions in the right chemical environment. The double membrane also creates compartments, which is essential for separating steps and maintaining gradients. A full-mark response ties each structure to a direct payoff in ATP yield.