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

Q: Passage: The first period of the Paleozoic Era was the Cambrian. By the beginning of the Paleozoic, organisms evolved shells. Shells could hold their soft tissues together. Shells could protect them from predators and from drying out. Some organisms evolved external skeletons. These are called exoskeletons . Organisms with hard parts also make good fossils. Fossils from the Cambrian are much more abundant than fossils from the Precambrian. Answer: cambrian

A: The first period of the paleozoic era was called what?
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Q: Passage: Saturated hydrocarbons contain only single bonds between carbon atoms. They are also called alkanes. They may form straight-chain, branched-chain, or cyclic molecules. Compounds with the same number of atoms but different shapes are called isomers. Answer: alkanes

A: What is another word for saturated hydrocarbons?
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Q: Passage: Plant Life Spans The length of time from the beginning of development to the death of a plant is called its life span. The life cycle, on the other hand, is the sequence of stages a plant goes through from seed germination to seed production of the mature plant. Some plants, such as annuals, only need a few weeks to grow, produce seeds and die. Other plants, such as the bristlecone pine, live for thousands of years. Some bristlecone pines have a documented age of 4,500 years Figure 32.29. Even as some parts of a plant, such as regions containing meristematic tissuethe area of active plant growth consisting of undifferentiated cells capable of cell divisioncontinue to grow, some parts undergo programmed cell death (apoptosis). The cork found on stems, and the water-conducting tissue of the xylem, for example, are composed of dead cells. Answer: life cycle

A:
Life span is distinct from what, which means the sequence of stages a plant goes through from seed germination to seed production of the mature plant?
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