# Explain how the structure of the Golgi apparatus is related to its function in the processing and secretion of proteins.

> IB DP Biology Higher Level (2023 syllabus) — A2.2 Cell structure · Explain · 4 marks

## Mark scheme (4 marks)

1. The Golgi apparatus is composed of a stack of flattened membrane-bound cisternae, providing a series of distinct compartments in which sequential modification of proteins can occur.
2. Vesicles arriving from the rough endoplasmic reticulum fuse with the cis face of the Golgi, delivering proteins for processing, ensuring a directional flow through the organelle.
3. As proteins pass through the cisternae, enzymes within each compartment add or modify carbohydrate chains (glycosylation) and cleave signal peptides, so the stack provides spatially separated enzymatic environments.
4. At the trans face, modified proteins are packaged into secretory vesicles that bud off and fuse with the plasma membrane (exocytosis), enabling export from the cell; the membrane-bound nature of the vesicles prevents degradation of proteins during transit.

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