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

Q: Passage: CHAPTER SUMMARY 30.1 The Plant Body A vascular plant consists of two organ systems: the shoot system and the root system. The shoot system includes the aboveground vegetative portions (stems and leaves) and reproductive parts (flowers and fruits). The root system supports the plant and is usually underground. A plant is composed of two main types of tissue: meristematic tissue and permanent tissue. Meristematic tissue consists of actively dividing cells found in root and shoot tips. As growth occurs, meristematic tissue differentiates into permanent tissue, which is categorized as either simple or complex. Simple tissues are made up of similar cell types; examples include dermal tissue and ground tissue. Dermal tissue provides the outer covering of the plant. Ground tissue is responsible for photosynthesis; it also supports vascular tissue and may store water and sugars. Complex tissues are made up of different cell types. Vascular tissue, for example, is made up of xylem and phloem cells. Answer: permanent tissue

A: A plant is composed of two main types of tissue: meristematic tissue and what other kind of tissue?
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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: There are about 10,000 living species of birds. Almost all of them can fly. Flying birds are classified in 29 orders. Most species belong to the order of perching birds. A few birds are flightless, such as the ostrich and penguin, but they evolved from a flying ancestor. Answer: flightlessness

A:
What important and unusual physical property (for birds) do ostriches and penguins share?
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