instruction:
Given a scientific passage and an answer, generate a question for the given answer.
question:
Passage: Pea plants are naturally self-pollinating. In self-pollination , pollen grains from anthers on one plant are transferred to stigmas of flowers on the same plant. Mendel was interested in the offspring of two different parent plants, so he had to prevent self-pollination. He removed the anthers from the flowers of some of the plants in his experiments. Then he pollinated them by hand with pollen from other parent plants of his choice. When pollen from one plant fertilizes another plant of the same species, it is called cross-pollination . The offspring that result from such a cross are called hybrids. Answer: cross-pollination
answer:
What is it called when pollen from one plant fertilizes another plant of the same species?

question:
Passage: Many important biological processes involve redox reactions, which frequently store and release energy. For example, photosynthesis involves the reduction of carbon dioxide into glucose and the oxidation of water into oxygen. This process stores the energy of sunlight in the bonds of sugars. The reverse reaction, cellular respiration, converts the energy in glucose into ATP. Cellular respiration involves the oxidation of glucose to carbon dioxide and the reduction of oxygen gas to water. This process depends on the reduction of NAD + to the electron carrier NADH, and the reverse oxidation of NADH to NAD + . The reduction of NAD + leads to the formation of a proton (H + ) gradient, which drives the synthesis of ATP. NADH (nicotinamide adenine dinucleotide) and NADPH (Nicotinamide adenine dinucleotide phosphate) are electron carriers in biological systems. The term redox state is often used to describe the balance between NAD + /NADH and NADP + /NADPH (Nicotinamide adenine dinucleotide phosphate). Answer: cellular respiration
answer:
What reaction is considered the reverse of photosynthesis?

question:
Passage: A colloid is a homogeneous mixture with medium-sized particles. Examples include homogenized milk and gelatin. The particles of a colloid are large enough to reflect light, so you can see them. But they are too small to settle or filter out of the mixture. Answer: particles
answer:
A colloid is a homogeneous mixture with medium-sized what?