Tài liệu Khoa Học Tự Nhiên

The body plan of a hydra and other cnidarians makes a circulatory system unnecessary. A body wall only two cells thick encloses a central gastrovascular cavity that serves for both digestion and for diffusion of substances throughout the body. The fluid inside the cavity is continuous with the water outside through a single opening, the mouth. T...

Chia sẻ: huyhoang44 | Ngày: 18/03/2020 | Lượt xem: 561 | Lượt tải: 0

The liver performs a wide variety of important functions in the body, including the production of bile. Bile is stored in the gallbladder until needed. It contains bile salts which act as detergents that aid in the digestion and absorption of fats. Bile also contains pigments that are by-products of red blood cell destruction in the liver. Thes...

Chia sẻ: huyhoang44 | Ngày: 18/03/2020 | Lượt xem: 566 | Lượt tải: 0

Occurring in sheets of tightly packed cells, epithelial tissue covers the outside of the body and lines organs and cavities within the body. The cells of a epithelium are closely joined and in many epithelia, the cells are riveted together by tight junctions. The epithelium functions as a barrier protecting against mechanical injury, invasive mic...

Chia sẻ: huyhoang44 | Ngày: 18/03/2020 | Lượt xem: 603 | Lượt tải: 0

In general, plant hormones control plant growth and development by affecting the division, elongation, and differentiation of cells. Some hormones also mediate shorter-term physiological responses of plants to environmental stimuli. Each hormone has multiple effects, depending on its site of action, its concentration, and the developmental stage ...

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Flowers, the reproductive shoots of the angiosperm sporophyte, are typically composed of four whorls of highly modified leaves called floral organs, which are separated by very short internodes. Unlike the indeterminate growth of vegetative shoots, flowers are determinate shoots in that they cease growing once the flower and fruit are formed.

Chia sẻ: huyhoang44 | Ngày: 18/03/2020 | Lượt xem: 855 | Lượt tải: 0

Early ideas about plant nutrition were not entirely correct and included: Aristotle’s hypothesis that soil provided the substance for plant growth. Van Helmont’s conclusion from his experiments that plants grow mainly from water. Hale’s postulate that plants are nourished mostly by air. Plants do extract minerals from the soil.

Chia sẻ: huyhoang44 | Ngày: 18/03/2020 | Lượt xem: 563 | Lượt tải: 0

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 ...

Chia sẻ: huyhoang44 | Ngày: 18/03/2020 | Lượt xem: 617 | Lượt tải: 0

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.

Chia sẻ: huyhoang44 | Ngày: 18/03/2020 | Lượt xem: 560 | Lượt tải: 0

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...

Chia sẻ: huyhoang44 | Ngày: 18/03/2020 | Lượt xem: 598 | Lượt tải: 0