Penn Foster Biology – The Cell Practice Test 2025 - Free Biology Practice Questions and Study Guide

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What is the composition of the outer membrane of mitochondria?

Protein only

Phospholipid bilayer

The outer membrane of mitochondria is primarily composed of a phospholipid bilayer, which is characteristic of all biological membranes. This bilayer consists of two layers of phospholipids, with hydrophilic (water-attracting) heads facing the outer environment and the cytoplasm, while the hydrophobic (water-repelling) tails are oriented inward, away from water. This structure allows the membrane to be selectively permeable, controlling the flow of ions and molecules into and out of the mitochondrion.

Additionally, the outer membrane contains various proteins, including porins that form channels, enabling the passage of small molecules and ions. However, the main structural composition that defines its nature and function is the phospholipid bilayer. This bilayer plays a crucial role in maintaining the integrity of the mitochondrion while also facilitating communication and transport between the mitochondria and the rest of the cell.

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Carbohydrate layer

Nucleic acid layer

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