| Core | Supplement |
|---|---|
| 1 State the functions of xylem and phloem: (a) xylem – transport of water and mineral ions, and support (b) phloem – transport of sucrose and amino acids | 3 Relate the structure of xylem vessels to their function, limited to: (a) thick walls with lignin (details of lignification are not required) (b) no cell contents (c) cells joined end to end with no cross walls to form a long continuous tube |
| 2 Identify in diagrams and images the position of xylem and phloem as seen in sections of roots, stems and leaves of non-woody dicotyledonous plants |
植物体内的运输
IGCSE 生物 · 第 8 主题
8.1
木质部与韧皮部
大纲
来源:剑桥国际大纲
植物有两种贯穿根、茎和叶的运输组织:
- 木质部(xylem)——把水和矿物质离子(mineral ions)从根往上运,并给植物支撑(support)。
- 韧皮部(phloem)——把蔗糖(sucrose)和氨基酸(amino acids)运到任何需要它们的地方。
在一个根、茎或叶中,木质部和韧皮部并排位于维管束(vascular bundles)中。
Xylem structure (Supplement)
木质部由叫导管(vessels)的长管构成,很适合运水:
- 它们的壁厚,并用木质素(lignin)加强,它也帮助支撑植物。
- 细胞是死的、空的(它们没有细胞内容物),所以水自由地流过。
- 细胞端端相连,管内没有壁横跨,构成一根长的、连续的管道。
探索
Xylem and phloem route
Watch water and sugar move through different plant transport tissues.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| xylem | 木质部 | mù zhì bù |
| mineral ions | 矿物质离子 | kuàng wù zhì lí zi |
| support | 支撑 | zhī chēng |
| phloem | 韧皮部 | rèn pí bù |
| sucrose | 蔗糖 | zhè táng |
| amino acids | 氨基酸 | ān jī suān |
| vascular bundles | 维管束 | wéi guǎn shù |
| vessels | 导管 | dǎo guǎn |
| lignin | 木质素 | mù zhì sù |
8.2
水分的吸收
大纲
| Core | Supplement |
|---|---|
| 1 Identify in diagrams and images root hair cells and state their functions | |
| 2 State that the large surface area of root hairs increases the uptake of water and mineral ions | |
| 3 Outline the pathway taken by water through the root, stem and leaf as: root hair cells, root cortex cells, xylem, mesophyll cells | |
| 4 Investigate, using a suitable stain, the pathway of water through the above-ground parts of a plant |
来源:剑桥国际大纲
水和矿物质离子通过根毛细胞(root hair cells)进入植物。巨大数量的根毛(root hairs)给一个非常大的表面积(surface area),它加速水和矿物质离子的吸收。
水随即跟随这条途径:
根毛细胞 → 根皮层(cortex)细胞 → 木质部 → 叶中的叶肉(mesophyll)细胞。
你可以通过把一株植物或一朵白花立在含有一种有色染色剂(stain)的水中来显示这条途径。染色剂被沿木质部往上运并给叶脉着色。
探索
Water uptake by root hairs
Root hair cells take in water by osmosis — water moves from the dilute soil into the more concentrated cell.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| root hair cells | 根毛细胞 | gēn máo xì bāo |
| root hairs | 根毛 | gēn máo |
| surface area | 表面积 | biǎo miàn jī |
| cortex | 皮层 | pí céng |
| mesophyll | 叶肉 | yè ròu |
| stain | 染色剂 | rǎn sè jì |
8.3
蒸腾作用
大纲
| Core | Supplement |
|---|---|
| 1 Describe transpiration as the loss of water vapour from leaves | |
| 2 State that water evaporates from the surfaces of the mesophyll cells into the air spaces and then diffuses out of the leaves through the stomata as water vapour | |
| 4 Explain how water vapour loss is related to: the large internal surface area provided by the interconnecting air spaces between mesophyll cells and the size and number of stomata | |
| 5 Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull that draws up a column of water molecules, held together by forces of attraction between water molecules | |
| 3 Investigate and describe the effects of variation of temperature and wind speed on transpiration rate | 6 Explain the effects on the rate of transpiration of varying the following factors: temperature, wind speed and humidity |
| 7 Explain how and why wilting occurs |
来源:剑桥国际大纲
蒸腾作用(transpiration)是水蒸气(water vapour)从叶的流失。
- 水从叶肉细胞的湿表面蒸发(evaporates)到叶内部的气腔(air spaces)中。
- 水蒸气随即通过气孔(stomata)扩散(diffuses)出叶。
What changes the rate of transpiration
| 因素 | 蒸腾在……时更快 | 为什么 |
|---|---|---|
| 温度(temperature) | 更热 | 水蒸发更快 |
| 风速(wind speed) | 更有风 | 风把水蒸气带走 |
| 湿度(humidity,补充) | 空气更干 | 一个更大的差使水扩散出去更快 |
例题。 在一个蒸腾计中,气泡在 5 分钟内移动了 60 mm。求水分吸收的速率,并说明打开风扇后会怎样。速率 = 距离 ÷ 时间 = 60 ÷ 5 = 每分钟 12 mm。速率一定要写完整的单位"每分钟 mm",不能只写"12"。风扇提高风速,把水蒸气从叶片带走,所以蒸腾加快,同样 5 分钟内气泡移动得更远。
How water rises up the xylem (Supplement)
当水蒸气离开叶时,它把更多的水拉上来跟在它后面。这个拉叫蒸腾拉力(transpiration pull)。水分子通过吸引力(forces of attraction)互相粘连,所以它们作为一根长的水水柱(column)一起被沿木质部拉上来。
Wilting (Supplement)
若一株植物失去水比它能吸收的更快,它的细胞变软,而植物萎蔫(wilts)——叶和茎下垂。这往往在一个炎热、干燥、有风的天发生。
探索
The transpiration stream
Water is pulled up the plant in a continuous stream, from the roots to the leaves where it evaporates.
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| transpiration | 蒸腾作用 | zhēng téng zuò yòng |
| water vapour | 水蒸气 | shuǐ zhēng qì |
| evaporates | 蒸发 | zhēng fā |
| air spaces | 气腔 | qì qiāng |
| diffuses | 扩散 | kuò sàn |
| stomata | 气孔 | qì kǒng |
| temperature | 温度 | wēn dù |
| wind speed | 风速 | fēng sù |
| humidity | 湿度 | shī dù |
| transpiration pull | 蒸腾拉力 | zhēng téng lā lì |
| forces of attraction | 吸引力 | xī yǐn lì |
| column | 水柱 | shuǐ zhù |
| wilts | 萎蔫 | wēi niān |
8.4
有机物的运输
大纲
| Core | Supplement |
|---|---|
| 1 Describe translocation as the movement of sucrose and amino acids in phloem from sources to sinks | |
| 2 Describe: (a) sources as the parts of plants that release sucrose or amino acids (b) sinks as the parts of plants that use or store sucrose or amino acids | |
| 3 Explain why some parts of a plant may act as a source and a sink at different times |
来源:剑桥国际大纲
转运(translocation)是蔗糖和氨基酸在韧皮部中的移动,从源(sources)到库(sinks)。
- 源是释放蔗糖或氨基酸的部分——例如叶,它通过光合作用制造糖。
- 库是使用或储存它们的部分——例如生长的根,或一个储存器官。
探索
Translocation in the phloem
Phloem carries dissolved sugars from where they are made (the source) to where they are used or stored (the sink).
词汇表
训练
| 英文 | 中文 | 拼音 |
|---|---|---|
| translocation | 转运 | zhuǎn yùn |
| sources | 源 | yuán |
| sinks | 库 | kù |
8.4
考试技巧
- 木质部:水和矿物质离子,只向上,加上支撑——它的细胞是死的,带厚木质素壁。韧皮部:蔗糖和氨基酸,在活细胞中。
- 学习水的途径:根毛细胞 → 皮层 → 木质部 → 叶肉。
- 蒸腾 = 从叶肉蒸发,然后从气孔扩散出去。它在更热、更有风或更干时更快。
- 水通过蒸腾拉力上升;水分子作为一根水柱保持在一起。
- 转运从一个源(糖被制造或储存的地方)到一个库(它被使用的地方)。方向能随季节改变。
本主题的互动课程
逐步学习,并即时检测练习。