CourseCourseQ BankQuestion BankDocsDocuments

D2.3.4—Changes in plant tissue

Plant tissue changes mass in sucrose or salt solutions, allowing isotonic concentration to be estimated from zero percent change in experiments.

Syllabus
First assessment 2025
Objective
D2.3.4
Level
HL

Exam analysis

Chance of appearing3%of analysed past papers
Latest appearanceMay 2024
Most common paperPaper3
Typical marks1–3

Common command terms

  • Identify
  • Describe
  • Explain
  • Suggest
  • Evaluate
  • Outline

Scoring notes

Common mistake
Using raw mass change instead of percentage change when initial masses differ.

Recent exam appearances

May 2024Paper3 ["HL"] · TZ22(c)[ 2 ]D2.3.4—Changes in plant tissue
November 2019Paper3 ["HL"] · TZ03(c)[ 2 ]D2.3.4—Changes in plant tissue
November 2019Paper3 ["HL"] · TZ03(a)[ 1 ]D2.3.4—Changes in plant tissue
May 2018Paper3 ["HL"] · TZ11(b)[ 3 ]D2.3.4—Changes in plant tissue
Practice this objective

Coverage 2018–2024 · Updated 16 Jul 2026

Estimate Isotonic Concentration with Plant Tissue

Changes in plant-tissue mass or length across a series of sucrose concentrations can be used to estimate the isotonic concentration.

Prepare equal tissue pieces, record initial mass or length, incubate them for the same time in known sucrose solutions, blot consistently, record final values and calculate change.

%\text{ change}=\frac{\text{final value}-\text{initial value}}{\text{initial value}}\times100

Plot mean percentage change against sucrose concentration. The x-intercept, where change is 0%, estimates the isotonic concentration. Replicates allow standard deviation to compare spread and standard error/error bars to compare uncertainty in means.

Positive mass change at 0.20 mol dm⁻³ and negative change at 0.30 mol dm⁻³ place the isotonic estimate between those concentrations; interpolate from the fitted graph rather than choosing the nearest raw point.

Zero mean change estimates isotonic conditions; it does not mean water molecules stopped moving. Consistent blotting, initial size and incubation time are needed for a fair comparison.

Changes in plant tissue

Assessment in practice

1–2 marks
How it is assessed

This objective is assessed through experimental design, commonly using Identify / Describe / Explain.

Command terms

Identify / Describe / Explain / Suggest / Evaluate / Outline

What earns marks

Build the answer around this relationship: Percentage change in mass shows relative water gain or loss.

Watch for

Using raw mass change instead of percentage change when initial masses differ.

Representative question

Question 1

[Maximum number: 2]

Student osmosis experiments often involve putting plant tissue such as potato cylinders in several salt solutions of different concentrations and measuring the mass before and after immersion. Outline how data collected from such an experiment could be used to estimate the osmolarity of the plant tissues.

Core Osmosis Effects

Water forms hydration shells around ions and polar solutes; hydrogen bonding and charge attraction reduce free water movement. Water moves by osmosis across partially permeable membranes from hypotonic/lower solute solutions toward hypertonic/higher solute solutions. Osmosis direction depends on internal and external solute concentration; isotonic conditions have dynamic water movement but no net osmosis. Plant tissue changes mass or length in sucrose solutions; percentage change graphs estimate isotonic or osmotic concentration. Animal cells can lyse in hypotonic solutions and crenate in hypertonic solutions; freshwater protists use contractile vacuoles to expel excess water. Plant cells become turgid in hypotonic solutions as vacuoles swell; hypertonic solutions cause flaccidity and plasmolysis from water loss. Isotonic saline prevents harmful water gain or loss in body cells; IV fluids and transplant organ baths must match tissue osmotic concentration.

Concept essentials

  • Percentage change in mass shows relative water gain or loss.
  • The isotonic concentration is where mass change is zero.
  • Hypotonic solutions cause plant tissue to gain water.
  • Controlled variables make osmolarity estimates more reliable.