Question 1

Which organelles belong to the endomembrane system?

Accepted Answer

The endoplasmic reticulum, Golgi apparatus, lysosomes and vacuoles are connected through vesicle budding, fusion and cargo transport. The outer nuclear membrane is also continuous with the ER, although the nuclear envelope itself is a double-membrane structure.

Question 2

What is the difference between rough and smooth ER?

Accepted Answer

Rough ER consists of flattened cisternae with ribosomes attached to the cytosolic surface, while smooth ER is a network of membrane tubules without attached ribosomes. Both are part of the single-membrane endomembrane system.

Question 3

How does a protein move from the ER to the Golgi apparatus?

Accepted Answer

A protein synthesized by a ribosome attached to rough ER enters the ER lumen and moves through an ER cisterna. A transport vesicle buds from the ER and docks at the cis-forming face of the Golgi apparatus.

Question 4

Why is a lysosome lumen acidic?

Accepted Answer

A lysosome contains hydrolytic enzymes that work in an acidic lumen maintained at about pH 4.5–5.0 by proton pumps. This environment supports digestive reactions inside the lysosome.

Question 5

How does a mature plant central vacuole differ from animal-cell vacuoles?

Accepted Answer

A mature plant cell usually has one large central vacuole bounded by the tonoplast. It stores cell sap and helps maintain turgidity. Animal-cell vacuoles are generally smaller and can include food vacuoles and contractile vacuoles.

Endomembrane System 3D Lab — ER to Golgi to Lysosome & Vacuole

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