. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. CHAPTER 17. Amoeboid Movement ROTOPLASMic STREAMING occurs in many living cells, possibly in all. Diffusion is too slow a process for the transport of solutes from one part of a cell to another, and active cytoplasmic movement provides a rapid transport mechanism. Streaming may proceed in a fixed path and may be fast enough for direct microscopic observation, as the cyclosis around the vacuole of some plant cells, or the transport of food vacuoles and granules about the body of a ciliate protozoan. In other cell
. Comparative animal physiology. Physiology, Comparative; Physiology, Comparative. CHAPTER 17. Amoeboid Movement ROTOPLASMic STREAMING occurs in many living cells, possibly in all. Diffusion is too slow a process for the transport of solutes from one part of a cell to another, and active cytoplasmic movement provides a rapid transport mechanism. Streaming may proceed in a fixed path and may be fast enough for direct microscopic observation, as the cyclosis around the vacuole of some plant cells, or the transport of food vacuoles and granules about the body of a ciliate protozoan. In other cells streaming may be slow and may be more of a churning than a fixed current; such cytoplasmic activity is best seen by accelerated motion pictures, as of tissue cultures (fibroblasts, ^), or of tips of growing nerve fibers.''"- ''•^ The cellular mechanism of protoplasmic streaming is unknown. Its dependence on colloidal properties, particularly on viscosity changes, is shown by the effects of hydrostatic pressure; streaming in Elodea is slowed in proportion to a decrease in ^ TYPES OF AMOEBOID CELLS AND OF PSEUDOFODS Amoeboid movement has a colloidal basis, as does protoplasmic stream- ing; amoeboid movement is also accompanied by changes in cell shape and often by progressive motion. Amoeboid movement may be directed locomo- tion, as in the rhizopod Protozoa (Sarcodina), in the plasmodium of myxo- mycetes, in amoeboid leucocytes (particularly vertebrate lymphocytes), in amoeboid or wandering cells of many kinds of animals (such as the archeo- cytes of sponges), and in growing nerve fibers; or amoeboid movement may consist in the extension, flexion, and retraction of processes (pseudopods) concerned primarily in feeding, as in most Foraminifera, Heliozoa, Radio- laria, vertebrate macrophages, and various phagocytes such as reticuloendo- thelial cells (, Kupffer cells of the liver). Locomotory amoeboid move- ment requires attachment to some substrate; n
Size: 1256px × 1990px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisher, booksubjectphysiologycomparative
