Saturday, December 8, 2007

Concept 30.2

Q1: Based on Figure 30.4, explain why the various types of gymnosperms can be described as being similar yet distinctive.

A1: Although gymnosperms are similar in having "naked" seeds, their seed bearing structure vary greatly. For instance, Cycads have larger cones compared to Ginkgo and Gnetum. Leaf shape also varies greatly, from the needles of many conifers to the palmlike leaves of cycads to Gnetum leaves that look like those of flowering plants.

Q2: Explain how the pine life cycle (see Figure 30.6) reflects basic characteristics of seed plant.

A2: The life cycle illustrates heterospory, as ovulate cones produce megaspores and pollen cones produce microspores. The reduced gametophytes are evident in the formof the microscopic pollen grains and the microscopic female gametophyte within the megaspore. The egg is shown developing within an ovule, and the pollen tube is shown conveying the sperm. The figure also shows the protective and nutritive features of a seed.

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