Water potential
International Baccalaureate · IB Diploma · Biology · SL Topic 28 4:31 English narration · English + 中文 subtitles burned in
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Plant tissue can gain or lose mass in different solutions.
植物组织在不同溶液中可能增重或减重。
The direction of net water movement depends on the water-potential 水势 difference, not on whether water molecules move at all.
净水分移动的方向取决于水势差，而非水分子是否发生移动。
Water moves through a water-permeable membrane from higher toward lower water potential.
水通过透膜从较高水势向较低水势移动。
Dissolved solute lowers the tendency of water to leave a solution relative to the chosen reference.
溶解的溶质降低了相对于选定参照系的水离开溶液的倾向。
A plant cell wall allows pressure to develop as water enters; tissue behaviour cannot always be explained by solute concentration alone.
植物细胞壁允许在进水时产生压力；组织行为不能仅用溶质浓度来解释。
Water potential is a measure used to compare the tendency of water to move between systems.
水势是用于比较水在不同系统间移动倾向的度量。
Turgor is the pressure of plant-cell contents against the cell wall.
膨压是植物细胞内容物对细胞壁施加的压力。
A zero mass change suggests no net transfer over the measured interval under the experimental conditions.
质量变化为零表明在实验条件下，测量区间内没有净转移。
It does not imply that every individual cell has the same potential or that molecular exchange stops.
这并不意味着每个细胞的电势都相同，也不意味着分子交换停止。
Compare percentage change when initial sample masses differ.
当初始样品质量不同时，比较百分比变化。
In the lab: Use repeated equal-sized plant samples in teacher-approved solutions.
在实验室中，使用重复的等大小植物样本，置于教师批准的溶液中。 保持组织来源、温度、体积和时间一致。
Keep tissue source, temperature, volume and time consistent; blot consistently before weighing.
称重前统一吸干水分。 记录初始质量和最终质量。
Record initial/final mass and plot percentage change against solution concentration, retaining variation and the uncertainty of any interpolated zero-change point.
以溶液浓度为横坐标，绘制百分比变化曲线。 保留变异性和任何插值零变化点的不确定性。
Known: a five point zero zero gram tissue sample becomes five point four zero grams.
已知：5.00 g 组织样本变为 5.40 g。
Percentage mass change equals five point four zero minus five point zero zero, divided by five point zero zero, times one hundred, which is plus eight percent.
质量变化百分比 = (5.40 - 5.00) / 5.00 × 100 = +8%。
This supports net water entry under the measured conditions.
这表明在测量条件下存在净水分进入。
A separate sample with zero change is consistent with balanced net transfer, but this mass method does not independently measure cell pressure.
另一个无变化的样本与净转移平衡一致，但此质量法不能独立测量细胞压力。
Your turn: A tissue sample changes from 4.00 g to 4.20 g.
轮到你了。 一个组织样本的质量从4.00克变为4.20克。
Calculate percentage mass change.
请计算质量变化的百分比。
Pause the video and work it out.
请暂停视频，自己算一算。
Check: 0.20 divided by 4.00 is a gain of 5 percent.
核对：(4.20 − 4.00) ÷ 4.00，增加 5%。
This SL preparation focus uses qualitative water-potential reasoning and mass-change evidence.
本SL备考重点采用定性的水势推理及质量变化证据。
Quantitative solute-pressure equations are kept in the separate HL preparation case pending exact guide review.
定量的溶质与压力方程保留在独立的HL备考案例中，待精确指南审查后处理。
Blotting variation or tissue damage can change the observed result.
吸水纸擦拭的差异或组织损伤可能改变观察结果。
Not true: A zero net mass change proves that all movement of water molecules has stopped.
这种说法不正确。 净质量变化为零，并不能证明水分子的所有运动都已停止。
Zero NET change is a balance of two continuing flows.
净变化为零是两种持续流动相互平衡的结果。
Water molecules never stop moving; equal rates in both directions produce no net change.
水分子永远不会停止运动。 两个方向上的速率相等时，就不会产生净变化。
Water moves through a water-permeable membrane from higher toward lower water potential.
水通过透水的膜从高水势向低水势移动。
A zero mass change suggests no net transfer over the measured interval under the experimental conditions.
零质量变化表明在实验条件下，在测量的时间间隔内没有净转移。
Watch for: this SL preparation focus uses qualitative water-potential reasoning and mass-change evidence.
注意：这个SL备考重点使用定性的水势推理和质量变化证据。
A tissue sample changes from 3.00 grams to 3.36 grams.
组织样本的质量从3.00克变为3.36克。
Find the percentage mass change.
请计算质量变化的百分比。
A zero net change does not mean water molecules have stopped moving.
净变化为零并不意味着水分子停止了运动。
The result is a gain of 12 percent.
结果是增加12%。
The sample rose from 5.00 to 5.40 grams, an eight percent gain.
样品从5.00克增加到5.40克，增加百分之八。
That supports net water entry under these conditions.
这支持在此条件下水分净进入。
Fictional tissue gains 6 percent in solution A and loses 3 percent in solution B.
虚构的组织在溶液 A 中质量增加 6%，在溶液 B 中减少 3%。
What does each result support, and why is neither an independent measurement of cell pressure?
每个结果分别支持什么结论？ 为什么两者都不能独立测量细胞压力？
A supports net water entry and B net loss under comparable conditions.
在条件可比时，A 说明水分净进入，B 说明水分净流失。
Mass change combines tissue responses; it does not separately determine pressure.
质量变化综合了组织的各种反应，并不能单独确定压力。
Use repeats and a zero-change series.
应进行重复实验，并设置一组零变化的浓度系列。
Pause and check yourself. Explain each point on screen in your own words, then change one number in the last example and say which assumption must still hold.
暂停一下，自我检查：用自己的话解释屏幕上的每个要点，再改动最后一个例子中的一个数字，说明哪个假设仍然必须成立。