Cell structure: describe question

An electron micrograph of a eukaryotic cell reveals several structures with distinctive features. For each of the following features, name the organelle and describe how the feature relates to the organelle's function:

1. Inner membrane folded into cristae.
2. Ribosomes attached to the outer surface of flattened membrane sacs.
3. A large central sac bounded by a single membrane, occupying most of the cell's volume.
4. A double membrane enclosing internal membrane stacks (thylakoids).