Membranas e transporte membranar
International Baccalaureate · IB Diploma · Biology · SL Tópico 9 4:14 Narração em inglês · Legendas em inglês + 中文 gravadas
Capítulos
Transcrição
A potato cylinder gains mass in one solution and loses mass in another.
土豆圆柱体在一种溶液中增重，在另一种溶液中减重。
Its mass change provides evidence about movement of water, rather than movement of potato tissue.
其质量变化为水的移动提供了证据，而非土豆组织的移动。
Osmosis is the net movement of water through a partially permeable membrane from a more dilute solution to a more concentrated solution.
渗透作用是水分子通过半透膜从稀溶液向浓溶液的净移动。
Dissolved solutes can change the direction of net water movement.
溶解的溶质可以改变水分子的净移动方向。
Osmosis is defined as net water movement through a partially permeable membrane.
渗透作用是指水分子通过半透膜的净移动。
A control variable is a factor kept constant for a fair comparison.
控制变量是指在公平比较中保持恒定的因素。
Use percentage change to compare samples with different initial masses.
使用百分比变化来比较初始质量不同的样本。
A zero percentage change estimates a solution concentration with no net water movement.
零百分比变化估算出一种没有净水分移动的溶液浓度。
This is an estimate from a trend, not proof that water molecules stop moving.
这是基于趋势得出的估算，并非证明水分子停止了移动。
In the lab: Use equal-length cylinders from similar tissue, fixed solution volume, temperature and immersion time.
在实验室中，使用来自相似组织的等长圆柱体，保持固定溶液体积、温度和浸泡时间。
Blot each cylinder in the same way before weighing.
称重前以相同方式吸干每个圆柱体表面水分。
Repeat each concentration and plot mean percentage change against concentration.
对每种浓度重复实验，并绘制平均百分比变化与浓度的关系图。
Known: initial mass 2.50 g; final mass 2.75 g.
已知：初始质量 2.50 g；最终质量 2.75 g。
Use percentage change equals final minus initial, all over initial, times 100.
使用公式：百分比变化等于（最终值减初始值）除以初始值，再乘以 100。
Percentage change equals 2.75 minus 2.50, all over 2.50, times 100, which is plus 10 percent.
百分比变化等于 2.75 减 2.50，除以 2.50，再乘以 100，结果为正 10%。
A positive value means net water entry.
正值表示净水进入。
Interpolate the concentration where the plotted trend crosses zero.
通过插值法找出绘制曲线穿过零点时对应的浓度。
Your turn: A 4.00 g cylinder ends at 3.60 g.
请开始练习。 一个质量为 4.00 克的圆柱体，最终质量为 3.60 克。
Find percentage mass change.
求质量变化的百分比。
Pause the video and work it out.
请暂停视频，自己算一算。
Check: minus 0.40 divided by 4.00 is a change of minus 10 percent, a loss.
核对：(3.60 − 4.00) ÷ 4.00，变化为 −10%，即质量减少。
Blotting removes surface solution.
吸纸可去除表面溶液。
Weighing a wet cylinder without blotting adds liquid that did not enter the cells.
若未吸纸直接称量湿圆柱体，则会将未进入细胞的液体重量一并计入。
Repeats reduce random variation but do not correct a miscalibrated balance.
重复测量虽可减少随机误差，但无法修正天平校准偏差。
Not true: At zero net water movement no water molecules cross the membrane.
不正确。 在净水通量为零时，并非没有水分子穿过膜。
Zero NET movement means water molecules cross the membrane in both directions at equal rates.
净通量为零意味着水分子以相同的速率双向穿过膜。
Molecules never stop moving; only the net transfer is zero.
分子运动永不停止；只是净转移量为零。
Osmosis is the net movement of water through a partially permeable membrane from a more dilute solution to a more concentrated solution.
渗透作用是指水分子通过半透膜，从较稀溶液向较浓溶液的净移动。
Use percentage change to compare samples with different initial masses.
使用百分比变化来比较初始质量不同的样本。
Watch for: blotting removes surface solution.
注意：吸纸会去除表面溶液。
A five point zero zero gram cylinder ends at four point seven five grams.
一个5.00克的圆柱体最终变为4.75克。
Find the percentage mass change.
求质量变化的百分比。
Zero net water movement is not zero movement.
净水量为零并不等于没有水分移动。
The result is a loss of 5 percent.
结果是减少5%。
The cylinder rose from 2.50 to 2.75 grams, a ten percent gain.
圆柱体从2.50克增加到2.75克，增加百分之十。
A positive change means net water entry by osmosis.
正的变化表示水通过渗透作用净进入。
Fictional tissue changes are +4% at 0.20 mol/L and −2% at 0.50 mol/L.
虚构组织的变化在0.20 mol/L时为+4%，在0.50 mol/L时为−2%。
Estimate the zero-change concentration by local linear interpolation and state its limitation.
请通过局部线性插值估算零变化浓度，并说明其局限性。
Zero lies four sixths of the way along the interval, so the estimate is 0.20 plus four sixths of 0.30, which is 0.40 moles per litre.
零点位于该区间的六分之四处，所以估计值为 0.20 加上 0.30 的六分之四，即每升 0.40 摩尔。
This assumes local linearity and comparable conditions; repeat around the crossing.
这假设局部呈线性且条件可比；应在交叉点附近重复实验。
Zero net mass change does not mean molecules stop moving.
净质量变化为零并不意味着分子停止运动。
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。