Biophysics

Biology: Nasta Edition (PART 2 of 2) by Campbell, Reece

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By Campbell, Reece

Biology: Nasta version [Hardcover]

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But plants and soil have a two-way relationship. Dead plants provide much of the energy needed by soil-dwelling microorganisms, while secretions from living roots support a wide variety of microbes in the near-root environment. Here we'll focus on some mutualistic, or mutually beneficial, relationships between plants and soil bacteria or fungi. Then we'll look at some unusual plants that form nonmutualistic relationships with other plants or, in a few cases, with animals. Soil Bacteria and Plant Nutrition Bacteria in the Nitrogen Cycle Some beneficial bacteria are found predominantly in the rhizosphere, the soil layer that is bound to the plant's roots.

The spore wall, which consists of material produced by both the microspore and the anther, usually exhibits an elaborate pattern wlique to the species. During maturation of the male gametophyte, the generative cell passes into the tube cell and the spore wall is completed. The tube cell now has a completely free-standing cell inside it. After the microsporangium breaks open and releases the pollen, a pollen grain may be transferred to a receptive surfare of a stigma. uces the pollen tube, a long cellular protuberanre that delivers sperm to the female gametophyte.

The remaining two nuclei, called polar nuclei, are not partitioned into separate cells but instead share the cytoplasm of the large central cell of the embryo sac. The ovule, which will eventually become a seed, now consists of the embryo sac and m'o surrounding integuments. • Figure 38A Exploring Flower Pollination Some angiosperm species can self-pollinate, but such species are limited to inbreeding in nature. Most angiosperm spedes rely on a living (biotic) or nonliving (abiotic) pollinating agent that can move pollen from the anther of a stamen of a flower on one plant to the stigma of a carpel of a flower on another plant.

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