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

> IB DP Biology Standard 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 compartments in which sequential modification of proteins can occur.
2. Vesicles from the rough endoplasmic reticulum (rER) fuse with the cis face of the Golgi, delivering newly synthesised proteins for processing.
3. As proteins move through the cisternae from cis to trans, they are chemically modified (e.g. glycosylation / addition of carbohydrate chains), producing the final functional form.
4. Secretory vesicles bud off from the trans face and carry the processed proteins to the cell surface membrane for exocytosis, enabling secretion.

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