What does the point where the line crosses zero change in mass show?

The water potential of the external solution at which no net movement occurred, which equals the water potential of the tissue.

Why must each piece be blotted before reweighing?

Surface liquid would be weighed as if it were taken up, which would exaggerate any gain.

Name three variables that must be controlled in this investigation.

The temperature, the time in the solution, and the size and source of the tissue pieces.

Why must the tissue pieces come from the same source?

Different plants, and different parts of one plant, have different solute concentrations, which would introduce a difference not caused by the solution.

Eduqas A-Level Biology A400QS

Biological Molecules

Topic overview Inorganic ions and the properties of water Monosaccharides and disaccharides Polysaccharides, storage and structure Lipids, triglycerides and phospholipids Amino acids and protein structure Condensation, hydrolysis and the food tests

Cell Structure and Organisation

Topic overview The nucleus and the endomembrane system Mitochondria, chloroplasts and other organelles Prokaryotic cells and viruses Cell theory, microscopy and measuring cells Comparing cells and the levels of organisation

Cell Membranes and Transport

Topic overview The fluid-mosaic model Factors affecting membrane permeability Diffusion and facilitated diffusion Osmosis and water potential Active transport and bulk transport Determining water potential in practice

Enzymes

Topic overview Enzymes as biological catalysts The active site and induced fit Temperature, pH and buffers Substrate and enzyme concentration Inhibition and immobilised enzymes

Nucleic Acids and Their Functions

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Photosynthesis

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Sexual Reproduction in Humans

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Sexual Reproduction in Plants

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Inheritance

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Topic overview Vascular systems compared across animal groups The mammalian heart and blood vessels The cardiac cycle and its control Blood, haemoglobin and dissociation curves The Bohr effect, chloride shift and tissue fluid The root and the uptake of water The endodermis and the entry to the xylem Xylem, transpiration and cohesion-tension The potometer and xerophytes and hydrophytes Phloem and translocation

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The Nervous System

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Human Musculoskeletal Anatomy: Skeletal TissuesMusculoskeletal

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Human Musculoskeletal Anatomy: Structure and Function of the SkeletonMusculoskeletal

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Neurobiology and Behaviour: The BrainNeurobiology

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Neurobiology and Behaviour: NeuroscienceNeurobiology

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Neurobiology and Behaviour: BehaviourNeurobiology

Topic overview Innate behaviour: escape reflexes, kineses and taxes Habituation and imprinting Classical and operant conditioning Primate societies and the costs and benefits of group living Insect castes, dominance hierarchies, territory and courtship

Cell Membranes and Transport

Determining water potential in practice

3 things to know
Component 1

Overview

Recall questions on the change in mass and change in length methods, plotting percentage change and reading the value where the line crosses zero, blotting and the controlled variables, incipient plasmolysis, and the sources of error in both methods.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How is the water potential of plant tissue found by change in mass?

Key term

On a graph of percentage change in mass against water potential, what does the point where the line crosses zero show?

Key term

Why is percentage change in mass plotted rather than the change itself?

Questions from this subtopic

Each one with the model answer underneath.

1
How is the water potential of plant tissue found by change in mass?
Model answer
Identical pieces of tissue are placed in solutions of known water potential, left for a set time, blotted and reweighed, and the percentage change in mass is plotted against water potential.
2
What does the point where the line crosses zero change in mass show?
Model answer
The water potential of the external solution at which no net movement occurred, which equals the water potential of the tissue.
3
Why is percentage change in mass plotted rather than the change itself?
Model answer
The pieces of tissue are not exactly equal in mass, so only a percentage allows them to be compared.
4
Why must each piece be blotted before reweighing?
Model answer
Surface liquid would be weighed as if it were taken up, which would exaggerate any gain.
5
Name three variables that must be controlled in this investigation.
Model answer
The temperature, the time in the solution, and the size and source of the tissue pieces.
6
Why must the tissue pieces come from the same source?
Model answer
Different plants, and different parts of one plant, have different solute concentrations, which would introduce a difference not caused by the solution.

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