Plants 3 - Plants 3 Gymnosperms evolved 250-280 million...

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Plants 3 Gymnosperms evolved 250-280 million years ago. They developed the seed which made them successful. They produced cones. In the ferns, the fronds are the sporophylls, or they have sporangia which make spores. Under the fern leaf, there are sporangia which are born on the leaves, or sporophylls. The gymnosperms have taken all of these sporophylls and grouped them together into the cones. Gymnosperms have regular pine cones, and then they have small cones. These two cones produce two different kidns of spores. The small cone produces pollen grains=microspores. The small cone is a collection of microspores. One of the sporophylls in a cone has associated with it a sporangium. This sporangium is on a sporophyte. Sporangia make spores. Inside of the sporangium is meisois occurring. Then it produces spores which are N. One of these N spores, typically consists of the following: there are 4-6 cells inside of the microspore, or pollen grain. It represents the immature microgametophyte, or male gametophyte. So, a spore has undergone mitosis to make the immature microgametophyte which is a couple of cells. It is part of the other generation. This microgametophyte is called a pollen grain. Gymnosperms, in the male gamete, or microgametophyte we no longer need water for dispersal of the male gametes. The two ears are wings that allow the pollen grain to be transferred by the wind. The other thing that gymnosperms have done is that they don’t have more Antheridium. This pollen grain which is going to have gametes in it is being dispersed by the wind. It has to find the opposite sex. When you release your pollen, you go with the wind. With plants, in order to ensure that pollen will reach the female, the gymnosperm has to make a lot of pollen. For each successful transfer, the gymnosperm has to make 1,000,000 pollen grains. This pollen grain is carried towards the female. What does the female look like? She is part of a sporophyll system: Female sporophylls are grouped inside a cone. The pollen grain comes via the wind into a small female cone. The pollen grain wants to get inside the cone. The scales on the small female cone open up very slightly. Any pollen floating around can sift into the open
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This note was uploaded on 02/04/2010 for the course BIO 1B taught by Professor Carlson,mischel,power during the Spring '07 term at University of California, Berkeley.

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Plants 3 - Plants 3 Gymnosperms evolved 250-280 million...

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