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

Ex Input:
Passage: Some molecules, such as proteins, are too large to pass through the plasma membrane, regardless of their concentration inside and outside the cell. Very large molecules cross the plasma membrane with a different sort of help, called vesicle transport . Vesicle transport requires energy, so it is also a form of active transport. There are two types of vesicle transport: endocytosis and exocytosis. Both types are shown in Figure below and described below. Answer: active transport

Ex Output:
What type of transport is vesicle transport considered to be?

Ex Input:
Passage: Plants in the haploid generation are called gametophytes . They form from haploid spores. They have male and/or female reproductive organs and reproduce sexually. They produce haploid gametes by mitosis. Fertilization of gametes produces diploid zygotes. Zygotes develop into the diploid generation. Answer: through mitosis

Ex Output:
How do gametophyte plants form haploid gametes?

Ex Input:
Passage: Toxic heavy metals include mercury and lead. Mercury is used in some industrial processes. It is also found in fluorescent light bulbs. Lead was once widely used in gasoline, paint, and pipes. It is still found in some products. Answer: toxic heavy metals

Ex Output:
Mercury and lead, which was once widely used in paint and gasoline, are examples of what type of metals?