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7.4.1: Pine Life Cycle

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    This video is an extremely helpful narrated animation of the pine life cycle. I recommend watching this video or some other walkthrough of the pine life cycle before attempting to interpret the complex diagram below.

    Video \(\PageIndex{1}\): A narrated video of the pine life cycle, sourced from YouTube.

    Pine life cycle diagram
    Figure \(\PageIndex{1}\): This is an illustrated diagram of the pine life cycle. Starting at the bottom of the image, there is a pine tree. This is the mature sporophyte (2n). It will produce both seed cones and pollen cones because it is monoecious. Seed cones will produce two megasporangia on each ovuliferous scale, each one surrounded by an integument. Within the megasporangium, a megaspore mother cell (2n) undergoes meiosis to produce four megaspores (n). Three die and one remains, developing by mitosis into the megagametophyte. The megagametophyte produces two archegonia, each with an egg. This trajectory occurs through the center of the diagram. Jumping back to the pollen cone, microsporangia are produced on each microsporophyll of the pollen cone. Initially, they are filled with microspore mother cells (2n) that then undergo meiosis to produce microspores (n). These microspores grow by mitosis (though only two rounds) into 4-celled microgametophytes: pollen. Each pollen grain is composed of two ear-like air sacs on the outside, a large tube cell, a small generative cell, and two tiny prothallial cells. The mature pollen grains are dispersed on the wind to seed cones where the tube cell will form a pollen tube into the megagametophyte by entering through a gap in the integument called the micropyle. The generative cell divides to produce to sperm cells, which travel down the pollen tube to fertilize an egg. Once fertilized, the integument closes, forming the seed coat. The embryo develops within the seed, consuming the megagametophyte and the megasporangium (now called the nucellus) as it grows. The seed is dispersed and, if in the right conditions, the embryo emerges from the seed coat and develops into a mature sporophyte. Diagram by Nikki Harris CC BY-NC with labels added.

    This page titled 7.4.1: Pine Life Cycle is shared under a CC BY-NC 4.0 license and was authored, remixed, and/or curated by Maria Morrow (ASCCC Open Educational Resources Initiative) .

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