The Pine Life Cycle

The Pine Life Cycle - next year the pollen grain germinates...

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The Pine Life Cycle Pines have an interesting life cycle, shown in Figure 7, that takes two years to complete. Not all seed plants have such a long time span to complete their life history: some flowering plants manage to do it in as little as a few weeks. The sporophyte, as in all other vascular plant groups, is the dominant, photosynthetic part of the life cycle: when you are holding pine needles in your hand you are holding sporophyte parts. Pines have specialized reproductive structures in which meiosis occurs: pine cones. Pollen grains are produced in the male cones, and contain the male gametophyte (which consists of only a very few cells). Pollen released from the male cones is carried by wind to the female cones, where it lands. The cones close and the
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Unformatted text preview: next year the pollen grain germinates to produce a pollen tube that grows into the female gametophyte. The sperm cell (from the pollen grain) and egg cell fuse, forming the next generation sporophyte. The sporophyte develops into an embryo encased within a seed. The seed is later released to be transported by the wind to where (hopefully) it lands and germinates. If you have seen a large pine tree you realize there are hundreds or more female cones on such a tree. Pine pollen has been noted to travel great distances from the plant that produced it, if the wind is strong enough. To aid this transport pine pollen has two air sacs, and thus is quite distinctive, as shown in Figure 8....
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The Pine Life Cycle - next year the pollen grain germinates...

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