The surfaces of the cells that form the alveoli (small air spaces of the lung) are coated with surfactant, which decreases the alveolar surface tension. 

Lung surfactant contains 80 to 90% phospholipid by weight, and 70 to 80% of the phospholipid is phosphatidylcholine, mostly the dipalmitoyl species.

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In other cells, mitochondria remain fixed at points of high energy demand.

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#Unit 2. Cellular Organization

In mitochondria, the metabolism of sugars is complete: allows 15 times more ATP to be made from a sugar than by glycolysis alone.

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Functions of Mitochondria-

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mtDNA is located in the mitochondrial matrix, and in the rapidly growing cells, mtDNA is often seen in regions devoid of densely stacked cristae.

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A human cell has about 1000–2000 mtDNA molecules

A human egg has about 500,000 mtDNA molecules

A sperm has only about 100 mtDNA molecules