Given a scientific passage and an answer, generate a question for the given answer.

[Q]: Passage: Most plant cells have a large central vacuole . It can make up as much as 90 percent of a plant cell's total volume. The central vacuole is like a large storage container. It may store substances such as water, enzymes, and salts. It may have other roles as well. For example, the central vacuole helps stems and leaves hold their shape. It may also contain pigments that give flowers their colors. Answer: vacuole
[A]: Most plant cells have a large central what?

[Q]: Passage: Nutrients are substances that the body needs for energy, building materials, and control of body processes. Carbohydrates, proteins, lipids, and water are nutrients needed in relatively large amounts. Vitamins and minerals are nutrients needed in much smaller amounts. Answer: nutrients
[A]: What are substances that the body needs for energy, building materials, and control of body processes?

[Q]: Passage: The electrochemical potential across a membrane determines the tendency of an ion to cross the membrane. The membrane may be that of a cell or organelle or other sub cellular compartment. The electrochemical potential arises from three factors:. Answer: cross the membrane
[A]:
The electrochemical potential across a membrane determines the tendency of an ion to do what?