IB Biology Topic B2.2.4 Adaptations of the…

The Mitochondrion: Where Aerobic Respiration Happens

The mitochondrion is a double-membrane organelle found in nearly all eukaryotic cells.
It is the site of aerobic cell respiration, the reactions that transfer energy from organic molecules to ATP.
1. Every structural feature of the mitochondrion relates directly to this function.
Mitochondria are typically sausage-shaped, roughly 1 to 5 µm long and 0.5 to 1 µm wide.
1. Cells with high energy demands, such as muscle fibres, active-transport epithelia, and sperm cells, contain thousands of mitochondria, while less active cells have fewer.

The outer membrane is smooth and contains large channel proteins called porins.
1. Porins let small molecules (pyruvate, oxygen, CO2, ADP, ATP) pass freely between the cytoplasm and the intermembrane space.
2. Larger molecules and proteins cannot cross without specific transport.

Common Mistake

The inner membrane is folded into structures called cristae (singular: crista).
1. These folds massively increase the surface area for the electron transport chain (ETC) and ATP synthase.
2. More cristae means more surface area, which means more ATP production.
3. Cells with very high energy demands, like cardiac muscle cells, have mitochondria with densely packed cristae.

The mitochondrion is a double-membrane organelle found in nearly all eukaryotic cells.
It is the site of aerobic cell respiration, the reactions that transfer energy from organic molecules to ATP.
1. Every structural feature of the mitochondrion relates directly to this function.
Mitochondria are typically sausage-shaped, roughly 1 to 5 µm long and 0.5 to 1 µm wide.
1. Cells with high energy demands, such as muscle fibres, active-transport epithelia, and sperm cells, contain thousands of mitochondria, while less active cells have fewer.

The outer membrane is smooth and contains large channel proteins called porins.
1. Porins let small molecules (pyruvate, oxygen, CO2, ADP, ATP) pass freely between the cytoplasm and the intermembrane space.
2. Larger molecules and proteins cannot cross without specific transport.

Common Mistake

The inner membrane is folded into structures called cristae (singular: crista).
1. These folds massively increase the surface area for the electron transport chain (ETC) and ATP synthase.
2. More cristae means more surface area, which means more ATP production.
3. Cells with very high energy demands, like cardiac muscle cells, have mitochondria with densely packed cristae.