Tìm hiểu về tảo Scenedesmus

[vuminhduong_88]

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[canh cut nd k16a]

Mình đang tìm hiểu về hình thức sinh sản của tảo Scenedesmus rất mong các bạn quan tâm giúp đỡ!
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Scenedesmus is a green alga that forms small colonies equipped with spines for flotation. The morphology varies with conditions and species, but this arrangement of 4 cells with 4 spines is quite
common. Each cell is about 10 micrometres long. [3D Pov-Ray model].


The spines are flotation devices, keeping the colony floating high in the water column near the source of light needed for photosynthesis. This may seem surprising, but at this microscopic scale water behaves much like treacle (low Reynold's number) and spines are efficient flotation devices.

Scenedesmus is a beautiful organism to observe under your microscope! The large pyrenoids (for starch synthesis) inside the large green chloroplasts are clearly visible. Flotation helps keep the cells at the surface near the valuable sunlight, and flotation will also help disperse the organism and the spines probably also provide some protection against predators by making the organism larger. Indeed, Scenedesmus often grows as single-cells in culture (each cell often possessing 4 spines) but chemicals released by predators are detected by Scenedesmus (which are too large for many predators) and this induces the formation of longer chains of cells and larger colonies, an effect which has been empirically shown to reduce losses to predation. However, the larger colonies sink more easily and so this defense comes at a cost, which is why in the absence of predators single cells dominate. As a further aid to dispersion, Scenedesmus produces wall-less biflagellate zoospores or gametes (smaller cells, about 5 micrometres long with a chloroplast but no pyrenoid) that swim in the water and if two compatible zoospores meet then they fuse in fertilisation to form a zygote and a new Scenedesmus. In addition to this mode of sexual reproduction, Scenedesmus reproduces asexually by producing a miniature autocolony by division of each protoplast inside the parent cell wall. The wall of the parent cell then splits and the autocolony emerges. In
addition to the spines, which are often confined to the end cells, the middle cells may bear long fine bristles. These bristles possibly assist in flotation.

 

[vuminhduong_88]

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