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

Q: Passage: Another barrier is the saliva in the mouth, which is rich in lysozymean enzyme that destroys bacteria by digesting their cell walls. The acidic environment of the stomach, which is fatal to many pathogens, is also a barrier. Additionally, the mucus layer of the gastrointestinal tract, respiratory tract, reproductive tract, eyes, ears, and nose traps both microbes and debris, and facilitates their removal. In the case of the upper respiratory tract, ciliated epithelial cells move potentially contaminated mucus upwards to the mouth, where it is then swallowed into the digestive tract, ending up in the harsh acidic environment of the stomach. Considering how often you breathe compared to how often you eat or perform other activities that expose you to pathogens, it is not surprising that multiple barrier mechanisms have evolved to work in concert to protect this vital area. Answer: by digesting their cell walls

A: How does lysozyme destroy bacteria?
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Q: 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

A: What reaction is considered the reverse of photosynthesis?
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Q: Passage: Internal Fertilization Internal fertilization occurs most often in terrestrial animals, although some aquatic animals also use this method. Internal fertilization may occur by the male directly depositing sperm in the female during mating. It may also occur by the male depositing sperm in the environment, usually in a protective structure, which a female picks up to deposit the sperm in her reproductive tract. There are three ways that offspring are produced following internal fertilization. In oviparity, fertilized eggs are laid outside the female's body and develop there, receiving nourishment from the yolk that is a part of the egg (Figure 18.7a). This occurs in some bony fish, some reptiles, a few cartilaginous fish, some amphibians, a few mammals, and all birds. Most non-avian reptiles and insects produce leathery eggs, while birds and some turtles produce eggs with high concentrations of calcium carbonate in the shell, making them hard. Chicken eggs are an example of a hard shell. The eggs of the egg-laying mammals such as the platypus and echidna are leathery. In ovoviparity, fertilized eggs are retained in the female, and the embryo obtains its nourishment from the egg's yolk. The eggs are retained in the female's body until they hatch inside of her, or she lays the eggs right before they hatch. This process helps protect the eggs until hatching. This occurs in some bony fish (like the platyfish Xiphophorus maculatus, Figure 18.7b), some sharks, lizards, some snakes (garter snake Thamnophis sirtalis), some vipers, and some invertebrate animals (Madagascar hissing cockroach Gromphadorhina portentosa). In viviparity the young are born alive. They obtain their nourishment from the female and are born in varying states of maturity. This occurs in most mammals (Figure 18.7c), some cartilaginous fish, and a few reptiles. Answer: internal

A:
When a male directly deposits sperm in a female during mating, this is considered what type of fertilization?
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