rav65819_ch37_741-756

rav65819_ch37_741-756 - ; 37 chapter Vegetative Plant...

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Vegetative Plant Development introduction HOW DOES A FERTILIZED EGG DEVELOP into a complex adult plant body? Because plant cells cannot move, the timing and directionality of each cell division must be carefully orchestrated. Cells need information about their location relative to other cells so that cell specialization is coordinated. The developing embryo is quite fragile, and numerous protective structures have evolved since plants first colonized land. Only a portion of the plant has actually formed when it first emerges from the soil. New plant organs develop throughout the plant’s life. 37.3 Fruits Fruit morphology exhibits environmental adaptations Fruits allow angiosperms to colonize large areas concept outline 37.1 Embryo Development A single cell divides to produce a three-dimensional body plan A simple body plan emerges during embryogenesis Food reserves form during embryogenesis 37.2 Seeds Seeds protect the embryo Specialized seed adaptations improve survival 37.4 Germination External signals and conditions trigger germination Nutrient reserves sustain the growing seedling The seedling becomes oriented in the environment, and photosynthesis begins
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741 rav65819_ch37_741-756.indd 741 rav65819_ch37_741-756.indd 741 12/7/06 6:47:53 PM 12/7/06 6:47:53 PM 37.1 Embryo Development Embryo development begins once the egg cell is fertilized. As described briefly in chapter 30, the growing pollen tube from a pollen grain enters the angiosperm embryo sac through one of the synergids, releasing two sperm cells (figure 37.1). One sperm cell fertilizes the central cell with its polar nuclei, and the resulting cell division produces a nutrient source, the endosperm, for the embryo. The other sperm cell fertilizes the egg to produce a zygote, and cell division soon follows, creating the embryo. A single cell divides to produce a three-dimensional body plan The first division of the zygote (fertilized egg) in a flowering plant is asymmetrical and generates cells with two different fates (figure 37.2). One daughter cell is small, with dense cytoplasm. That cell, which is destined to become the embryo, begins to divide repeatedly in different planes, forming a ball of cells. The other, larger daughter cell divides repeatedly, forming an elongated structure called a suspensor, which links the embryo to the nutrient tissue of the seed. The suspensor also provides a route for nutrients to reach the developing embryo. The root–shoot axis also forms at this time; cells near the suspensor are destined to form a root, while those at the other end of the axis ultimately become a shoot. Investigating mechanisms for establishing asymmetry in plant embryo development is difficult because the zygote is embedded within the female gametophyte, which is surrounded by sporophyte tissue (ovule and carpel tissue) (chapter 30). To understand the cell biology of the first asymmetrical division of zygotes, biologists have studied the brown alga
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This note was uploaded on 10/15/2010 for the course BIO BIO1 taught by Professor Lipke during the Fall '09 term at CUNY Brooklyn.

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rav65819_ch37_741-756 - ; 37 chapter Vegetative Plant...

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