SPM Biology Form 4 Notes – Terminology and Concepts: Movement of Substances Across the Plasma Membrane (Part III – Final)

by BerryBerryTeacher

in Berry Reference (Notes)

Ever wondered why you need to drink isotonic drinks (100 Plus as an example) after doing sports? Okay, mainly because it tastes good as any sweetish cold drink after much exercise is appreciated. However, isotonic drinks does more than that as it replenish fluids after you lose some fluid through sports. Well, Berry Berry Teacher thinks that most of our knowledgeable Berry Readers knows about the isotonic part, but how about hypotonic and hypertonic? Hypertonic do not make you any more hyper, while hypotonic do not have anything to do with hippopotamus. So let us ride through the journey of substances across plasma membrane with Part 3 (final part) of this series.

SPM Form 4 – Terminology and Concepts: Movement of Substances Across the Plasma Membrane (Part 3 – Final)

Permeability of the fruit skin

Permeability of the fruit skin

Type of Solution

  1. Hypotonic
  2. Isotonic
  3. Hypertonic

1) Hypotonic

  • Solute concentration in the external solution is lesser than solute concentration inside the cell.
  • Water concentration outside the cell is higher than the water concentration inside the cell.

2) Isotonic

  • Solute concentration in the external solution is equal to the solute concentration inside the cell.
  • Water concentration inside and outside of the cell is the same.

3) Hypertonic

  • Solute concentration in the external solution is greater than solute concentration inside the cell.
  • Water concentration outside the cell is lower than the water concentration inside the cell.

Types of solutions:

Type of Solution Hypotonic Isotonic Hypertonic
Animal Cell The cell inflates due to the water molecules enter the cell. Eventually it bursts (thin plama membrane). Example: red blood cell in distilled water. No change in the size of cell. Net movement of water is zero. Example: red blood cell in 0.85% sucrose solution. The cell shrinks and becomes soft and dehydrated due to the water molecule leave the cell. Example: red blood cell in 5% sodium chloride solution.
Plant Cell The cell expands and becomes firm / turgid due to the water molecules enter the cell. The rigid cellulose cell wall expands slightly and prevents cell from bursting. Example: strip of potato in distilled water. No change in the size of cell. Net movement of water is zero. Example: strip of potato in 5% sucrose solution. The cell becomes flaccid (plasmolysis occurs), vacuole and cytoplasma shrink due to the water molecules leave the cell. Example: strip of potato in 30% sucrose solution.

Application

  1. Food is soaked in a concentrated salt solution to prevent bacteria and fungus to survive.
  2. Chemical fertiliser (dissolved ions) increases solute concentration (decrease water molecules) in soil. Therefore, water leaves from the cell sap of the plant which result the plant wither.

Finally, the end of the interesting substance movement over plasma membrane. Do keep note that this might be a popular essay question. Easy to answer but hard to score, so take note of the terminologies and concepts shown above.

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