什麼是藻類
一群主要是水生的、能行光合作用而無法精確定義的有機體。大小不一,從顯微鏡下的單細胞鞭毛蟲,到長達60公尺的大型褐藻。藻類提供了地球上大部分的氧氣,是幾乎所有的水生生物的食物基地,並提供食品和工業產品,包括石油產品。它們的光合作用色素比植物的更為多樣,它們的細胞中具有植物和動物所沒有的特點。隨著新的分類法資訊的發現,藻類的分類也在迅速改變。以前,藻類按它們葉綠體裡的色素分子分成紅藻、褐藻與綠藻三類。現在辨認出的種類遠遠多於這三類,每一種都有共同的色素型別。從演化的意義上看,藻類彼此間的關係並不密切。某些種群與原生動物和真菌的區別只在於它們有葉綠體以及能行光合作用的能力,因此從演化上來看,它們與原生動物或真菌的關係比與其他藻類的關係更為接近。利用藻類的歷史或許與人類的歷史一樣悠久,沿海的居民食用海藻,許多餐館裡都提供藻類食品。它們常見於溪流中「黏滑的」岩石上(參閱diatom),是池塘上綠色光輝之源。
algae
Any of a group of mostly aquatic, photosynthetic organisms (see photosynthesis) that defy precise definition. They range in size from the microscopic flagellate Micromonas to giant kelp that reach 200 ft (60 m) in length. Algae provide much of the earth's oxygen, serve as the food base for almost all aquatic life, and provide foods and industrial products, including petroleum products. Their photosynthetic pigments are more varied than those of plants, and their cells have features not found among plants and animals. The classification of algae is changing rapidly as new taxonomical information is discovered. Algae were formerly classified into three major groups—the red, brown, and green seaweeds—based on the pigment molecules in their chloroplasts. Many more than three groups are now recognized, each sharing a common set of pigment types. Algae are not closely related to each other in an evolutionary sense. Specific groups can be distinguished from protozoans and fungi (see fungus) only by the presence of chloroplasts and their ability to carry out photosynthesis, and thus have a closer evolutionary relationship with the protozoa or fungi than with other algae. Use of algae is perhaps as old as mankind; seaweeds are eaten by coastal societies, and algae are served in many restaurants. They are common on “slimy” rocks in streams (see diatoms) and as green sheens on pools and ponds.
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什麼是浸潤
組織內侵入了異常的細胞或出現了正常情況下不應出現的機體細胞,以及某些病變組織向周圍擴充套件的現象。在細胞內或間質中出現異常的物質、或原有的某些物質的堆積過多也稱為浸潤。有的變性或沉積也稱為浸潤。浸潤大多為病理性的,但有時是為了治療目的而人為的。它們...
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什麼是細菌性感染
細菌引起的感染。包括醫院外感染和醫院內感染。引起醫院外感染最常見的細菌為革蘭氏陽性菌如金黃色葡萄球菌、肺炎鏈球菌、化膿性鏈球菌和革蘭氏陰性的大腸桿菌、流感嗜血桿菌等;引起醫院內感染的則多為有耐藥性的金黃色葡萄球菌、表皮葡萄球菌、腸球菌、克雷伯...
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什麼是腎性骨營養不良
由慢性腎功能衰竭導致的骨代謝病,表現為鈣磷代謝障礙、酸鹼平衡失調、骨骼畸形,並可引起繼發性甲狀旁腺功能亢進。腎性佝僂病常由慢性腎小球腎炎、慢性腎盂腎炎、腎結核、腎腫瘤、腎結石或先天性腎盂積水引起。由於腎小球遭到破壞,間質纖維化、腎小管萎縮、尿濃縮...
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什麼是三叉神經痛
面部三叉神經感覺支分佈區出現的短暫發作性疼痛。多發病於中年以上,40歲以上佔70~80%,而70歲以上又逐漸減少。患者中女性多於男性,兩者之比為3:2。多為一側性,雙側受罹者在5%以下。以三叉神經第二支(上頜支)受侵犯者最常見,其次為第三支(下頜支),第二、三支同時患病者亦常見...