Plant 2 - Plant 2 Algae evolved in the oceans for about 1...

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Plant 2 Algae evolved in the oceans for about 1 billion years. One of the things they tried out is that they developed a highly unique life cycle. We will talk essentially about the green algae. The human life cycle has males and females. Each are diploid, or 2N. The females through meiosis make eggs (the female gamete), and the males through meiosis make sperm (male gamete). Once these two gametes are made, if they are brought together we can get fertilization which results in the formation of the zygote which is 2N, and this is the beginning of the two individual. The algae invented a new life cycle. Lets begin with the 2N, green algae individual. This 2N individual goes through meiosis, but instead of making gametes it makes spores which are N because tey’ve come from a product of meiosis. These spores germinate and make a new N plant. This plant forms the gametes (sperm, and eggs) which fertilize to make a zygote which makes the 2N individual. What the algae have done is instead of 2N individual making gametes directly, it maks spores. These spores grow into a new plant which produces gametes. The algae have delayed the production of the gametes by making a new plant entirely. This plant is N. Because this 2N individual makes spores, its called the sporophyte. The N plant which produces gametes is called the gametophyte. If you look at an algal life cycle, we see the alternation of two separate plants, a sporophyte and a gametophyte, in order for the life cycle to be complete. We call this life cycle the alternation of generations because we have to alternate between two separate generations in order for the life cycle to be complete. This persists in all the plants that we will study. What do these two plants look like in the algae? The sporophyte and the gametophyte may look the same or they may look different. One may be bigger than the other. Both plants are free living, and make their own food; they are independent because they each go through photosynthesis. In the first billion years, the algae developed the alternation of generations. Some of the algae were moving from the ocean into freshwater lakes into bogs, and marshes. 490 million years ago, an ancestor which came from the algae moved onto the land; it became the first land plant. If you were going to move from a water environment onto a land environment, some of the problems that you would encounter would be: drying out,
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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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Plant 2 - Plant 2 Algae evolved in the oceans for about 1...

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