How do you calculate percentage change in mass?
Reveal answer
(final mass − initial mass) ÷ initial mass × 100.
Key words: percentage change
2(d) MOVEMENT OF SUBSTANCES INTO AND OUT OF CELLS · RECALL
2.17 Diffusion and osmosis investigations
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How do you estimate cell sap concentration from potato results?
Reveal answer
Plot % change in mass against concentration; read off where the line crosses zero.
Key words: crosses zero
Give two control variables for a potato osmosis investigation.
Reveal answer
Same size of cylinder (same cork borer and length), same time, same temperature, same volume of solution, same potato.
Key words: same size · same time
Why blot potato cylinders before weighing?
Reveal answer
To remove surface liquid so only water taken in or lost by the cells is measured.
Key words: blot
What is meant by the term percentage change?
Reveal answer
(final value − initial value) ÷ initial value × 100.
Key words: percentage change
What is meant by the term isotonic?
Reveal answer
Having equal effective water potential across a membrane, causing no net water movement.
Key words: isotonic
What is meant by the term x-intercept?
Reveal answer
The point where a plotted relationship crosses the horizontal axis.
Key words: x-intercept
What is meant by the term model?
Reveal answer
A simplified representation used to investigate or explain selected features.
Key words: model
What is meant by the term biological variation?
Reveal answer
Natural differences among living samples.
Key words: biological variation
Two practical systems, two kinds of evidence: for System, give the indicator agar and the potato tissue.
Reveal answer
Indicator agar: Non-living gel. Potato tissue: Living multicellular tissue.
Key words: System
Two practical systems, two kinds of evidence: for Process emphasised, give the indicator agar and the potato tissue.
Reveal answer
Indicator agar: Acid diffusion through a volume. Potato tissue: Osmosis across cell membranes.
Key words: Process emphasised
Two practical systems, two kinds of evidence: for Independent variable, give the indicator agar and the potato tissue.
Reveal answer
Indicator agar: Cube size/SA:V or another defined diffusion factor. Potato tissue: External sucrose concentration.
Key words: Independent variable
Two practical systems, two kinds of evidence: for Dependent variable, give the indicator agar and the potato tissue.
Reveal answer
Indicator agar: Penetration distance or percentage decolourised. Potato tissue: Percentage mass change.
Key words: Dependent variable
Two practical systems, two kinds of evidence: for Major limitation, give the indicator agar and the potato tissue.
Reveal answer
Indicator agar: No cell membrane or metabolism. Potato tissue: Biological variation, cut damage and blotting inconsistency.
Key words: Major limitation
True or false, and why? “Acid moves by osmosis into agar.”
Reveal answer
False. The acid particles diffuse; osmosis specifically describes water through a partially permeable membrane.
True or false, and why? “A potato cylinder with zero mass change has no water movement.”
Reveal answer
False. Water moves both ways at equal rates, producing no net change.
True or false, and why? “A larger potato piece can be compared using mass change alone.”
Reveal answer
False. Percentage mass change standardises for different initial masses.
True or false, and why? “Agar proves exactly how a cell behaves.”
Reveal answer
False. It lacks a cell membrane, metabolism and active transport, so it is a limited diffusion model.