Osmosis: mass changes and rates use different denominators
도입됨| English | 의미 |
|---|---|
| osmosis/ɒzˈməʊsɪs/ | 삼투 |
| percentage mass change/pəˈsentɪdʒ mæs tʃeɪndʒ/ | 질량 변화 백분율 |
What would explain this observation?
- Two plant samples can gain the same mass but show different percentage changes. Starting mass and exposure time both matter when comparing uptake.
- Start with a prediction. State the quantities or features you would compare, then decide what evidence could distinguish two explanations.
Build the model
- Osmosis 渗透 is net movement of water from a dilute solution to a more concentrated solution through a partially permeable membrane. Plant tissue can gain water in a more dilute surrounding solution and lose water in a more concentrated one. A zero net change suggests balanced water exchange under the measured conditions.
- osmosis: Net water movement through a partially permeable membrane from dilute to more concentrated solution; percentage mass change 质量变化百分比: Mass change divided by initial mass, multiplied by one hundred.
Which denominator is used for percentage mass change?
난이도 1/5 · 100 코인 + 오늘 첫 완료 시 소액 보너스
Percentage change compares the change with where the sample STARTED, so the denominator is the initial mass. Using the final mass or the time gives a different quantity with a different meaning.
Match each technical term to its precise meaning.
난이도 2/5 · 140 코인 + 오늘 첫 완료 시 소액 보너스
Use the definitions to distinguish related quantities and processes.
Choose evidence that can test it
- Percentage change = (final−initial)/initial×100. Mean water-uptake rate compares an estimated water amount with elapsed time. These are different quantities: percentage change adjusts for starting mass, while a rate describes change per unit time. Plot a concentration series and estimate where the trend crosses zero rather than expecting every individual repeat to lie on one line.
- For required practical 3, use repeated equal-size pieces from comparable tissue in teacher-approved sugar or salt solutions. Keep solution volume, temperature and duration fixed; blot consistently before weighing. Record all raw masses and units. A range of concentrations allows a meaningful zero-change estimate and a check for anomalies.
Which two habits make the investigation or model in this case more defensible?
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Stating the conditions and assumptions lets others repeat the work exactly, and recording the supporting evidence lets them check the conclusion. Hiding disagreeing results removes the evidence that could challenge a wrong conclusion, and one measurement can never establish a wider claim.
Work from known quantities
- State the known values and their units. Choose the relation because its assumptions fit this case, then rearrange before substitution.
- Known: initial mass 3.00 g and final mass 3.30 g after 40 min. Gain=0.30 g. Percentage gain=0.30/3.00×100=10%. Mean gain rate=0.30/40=0.0075 g/min under the model that the mass change represents water. The two answers have different meanings and units.
A 2.00 g sample gains 0.20 g in 20 min. Calculate mean mass-gain rate. Use the same sequence: known quantities → model → relation → substitution → unit and interpretation.
A 2.00 g sample gains 0.20 g in 20 min. Calculate mean mass-gain rate.
난이도 2/5 · 140 코인 + 오늘 첫 완료 시 소액 보너스
The result is 0.01 g/min. Known: 2.00 g sample gains 0.20 g in 20 min. Use mean rate = gain / time. Rate = 0.20/20 = 0.01 g per minute. This rate is distinct from the percentage change, which would be 0.20/2.00 x 100 = 10%.
Check the conclusion and its limits
- Surface liquid adds mass without entering the cells, so blotting is essential. A negative percentage indicates loss. An estimated zero-change concentration does not mean water molecules stop moving or that every cell is undamaged and identical.
- Return to the original observation. Explain what the result supports, which conditions it assumes, and one way to test a competing explanation.
Percentage mass change and mass-gain rate always have the same units. This claim is false: Percentage change is dimensionless (change / initial mass); rate carries units of mass per time. The two answer different questions - how much relative to the start versus how fast.
Osmosis: mass changes and rates use different denominators: Percentage change = (final−initial)/initial×100. Mean water-uptake rate compares an estimated water amount with elapsed time. These are different quantities: percentage change adjusts for starting mass, while a rate describes change per unit time. Plot a concentration series and estimate where the trend crosses zero rather than expecting every individual repeat to lie on one line.
Percentage mass change and mass-gain rate always have the same units.
난이도 1/5 · 100 코인 + 오늘 첫 완료 시 소액 보너스
Percentage change is dimensionless (change / initial mass); rate carries units of mass per time. The two answer different questions - how much relative to the start versus how fast.
Net water movement through a partially permeable membrane from dilute to more concentrated solution: write the technical term.
난이도 1/5 · 100 코인 + 오늘 첫 완료 시 소액 보너스
osmosis means Net water movement through a partially permeable membrane from dilute to more concentrated solution.