Tài liệu Sinh Học

The most important active transporter in the plasma membrane of plant cells is the proton pump. It hydrolyzes ATP and uses the released energy to pump hydrogen ions (H+) out of the cell. This creates a proton gradient because the H+ concentration is higher outside the cell than inside. It also creates a membrane potential or voltage because the ...

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The plant body is a hierarchy of structural levels, with emergent properties arising from the ordered arrangement and interactions of component parts. The plant body consists of organs that are composed of different tissues, and these tissues are teams of different cell types.

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2. The dorsal, hollow nerve cord develops in the vertebrate embryo from a plate of ectoderm that rolls into a tube dorsal to the notochord. Other animal phyla have solid nerve cord, usually located ventrally. The nerve cord of the chordate embryo develops into the central nervous system: the brain and spinal cord.

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Most sponges are hermaphrodites, with each individual producing both sperm and eggs. Gametes arise from choanocytes or amoebocytes. The eggs are retained, but sperm are carried out the osculum by the water current. Sperm are drawn into neighboring individuals and fertilize eggs in the mesohyl. The zygotes develop into flagellated, swimming larv...

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(5) The transformation of a zygote to an animal of specific form depends on the controlled expression in the developing embryo of special regulatory genes called Hox genes. These genes regulate the expression of other genes. Many of these Hox genes contain common “modules” of DNA sequences, called homeoboxes. Only animals possess genes that are ...

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Parasitic fungi usually have some hyphae modified as haustoria, nutrient-absorbing hyphal tips that penetrate the tissues of their host. Some fungi even have hyphae adapted for preying on animals.

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In seeds plants, the delicate female gametophyte and young embryos are protected from many environmental stresses because they are retained within the moist sporangia of the parental sporophyte. The gametophytes of seed plants obtain nutrients from their parents, while those of seedless vascular plants are free-living and fend for themselves.

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Ferns and other pteridiophytes are sometimes called seedless plants because there is no seed stage in their life cycles. The evolution of the seed in an ancestor common to gymnosperms and angiosperms facilitated reproduction on land. A seed consists of a plant embryo packaged along with a food supply within a protective coat. The first seed plan...

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Reproduction and life cycles are highly varied among protists. Mitosis occurs in almost all protists, but there are many variations in the process. Some protists are exclusively asexual or at least employ meiosis and syngamy (the union of two gametes), thereby shuffling genes between two individuals. Others are primarily asexual but can also rep...

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Molecular evidence accumulated over the last two decades has led to the conclusion that there are two major branches of prokaryote evolution, not a single kingdom as in the five-kingdom system. These two branches are the bacteria and the archaea. The archaea inhabit extreme environments and differ from bacteria in many key structural, biochemical...

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