Question

organelles such as mitochondria and the endoplasmic reticulum have membranes that compartmentalize reactions and other metabolic processes. to function properly, the organelles must move substances across their membranes. which of the following statements describes a feature shared by mitochondria and the endoplasmic reticulum that increases the efficiency of their basic functions? (a) they have rigid, nonfluid membranes. (b) they have highly folded membranes. (c) they have membranes composed of many carbohydrates. (d) they have double membranes, with one membrane enclosed within the other.

Explanation:

Mitochondria have highly folded inner membranes (cristae) which increase the surface area for chemical reactions (like ATP production). The endoplasmic reticulum (especially the rough ER with ribosomes and the smooth ER with its structure) also has a membrane structure that is folded or has a complex shape in some regions (in case of the smooth ER, its continuous network - like structure can be thought of in a way that allows for more area for metabolic processes). This folding or complex membrane shaping (in the case of mitochondria's cristae which are highly folded membranes and in some aspects of ER's membrane arrangement - though ER's is more about its network and in case of rough ER, the association with ribosomes on its membrane surface etc. but the key is the membrane's structural feature of being folded or having a shape that increases the area related to function) increases the efficiency of their basic functions (ATP synthesis in mitochondria, protein and lipid synthesis, detoxification etc. in ER).

• Option A: Cell membranes (including those of organelles) are fluid - mosaic models (fluid due to the movement of lipids and proteins in the membrane), not rigid non - fluid. So this option is incorrect.
• Option C: Membranes (of mitochondria and ER) are mainly composed of lipids (phospholipids) and proteins. Carbohydrates are present in smaller amounts (like in the cell membrane for cell - cell recognition, but not a major component of the membranes of these two organelles in terms of what is relevant for their function - related membrane structure). So this option is incorrect.
• Option D: While mitochondria have a double - membrane (outer and inner), the endoplasmic reticulum has a single - membrane (it is a continuous membrane - bound network). So this is not a shared feature.

Answer:

B. They have highly folded membranes.