4.6.2Additional lessons
Osmosis in Cells — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 52 of 101
Curriculum Equation Key قوانين الرقم الهيدروجيني والاتزان الأيوني - pH & Acid-Base Equilibrium FormulasFast Exam Solution
pH = -log[H⁺] | pOH = -log[OH⁻] | pH + pOH = 14 | [H⁺][OH⁻] = 10⁻¹⁴
Word Equation & Conditions: الرقم الهيدروجيني = -لوغاريتم تركيز أيون الهيدروجين | pH + pOH = 14
Location & Specifications: الاتزان الأيوني، كيمياء 3 ثانوي، التحصيلي، و AP Chemistry.
Part 1 of 5Animal Cells
In a hypotonic solution
- In a hypotonic solution Water enters, the cell swells and may burst, which is called lysis because there is no cell wall to resist.
In a hypertonic solution
- In a hypertonic solution Water leaves, the cell shrinks and the membrane looks scalloped;
- red blood cells in this state are crenated.
Capillary problems
- Capillary problems Crenated or lysed red blood cells cannot carry oxygen or pass through capillaries properly.
Control
- Control The kidneys and blood regulate plasma concentration so that body fluid stays close to isotonic with cells.
Part 2 of 5Plant Cells
Turgid
- Turgid In a hypotonic solution water enters the vacuole, pushing the membrane against the wall, and turgor pressure rises.
Cell wall
- Cell wall The inelastic wall prevents bursting, and the pressure helps support stems and keep leaves held out to the light.
Flaccid
- Flaccid In an isotonic solution there is no net movement, and the cell is limp, with little turgor.
Plasmolysed
- Plasmolysed In a strongly hypertonic solution the protoplast shrinks away from the wall, leaving a gap, and the plant wilts.
| Solution | Animal cell | Plant cell |
|---|---|---|
| Hypotonic | Swells, may lyse | Turgid |
| Isotonic | No change | Flaccid |
| Hypertonic | Shrinks (crenation) | Plasmolysed |
Part 3 of 5Organisms in Fresh Water
Problem
- Problem Freshwater protozoa live in water more dilute than their cytoplasm, so water enters constantly.
Contractile vacuole
- Contractile vacuole This organelle collects excess water and expels it, which uses ATP and prevents bursting.
Cell walls
- Cell walls Plants, fungi and bacteria rely on strong walls to resist the pressure of incoming water.
Part 4 of 5Medical Uses
Saline drips
- Saline drips Solutions given by injection or infusion are made isotonic to blood so that blood cells are not damaged.
Organ transplants
- Organ transplants Donated organs are bathed in an isotonic solution so that their cells neither swell nor shrink during storage.
Why not pure water
- Why not pure water Injecting pure water would make blood cells swell and burst, while concentrated solutions would shrink them.
Part 5 of 5Exam Checklist & Tips
4.6.2 – Key Points for the Exam
- Lysis Bursting of a cell caused by excessive water uptake.
- Crenation Shrinkage of an animal cell with a notched edge in a hypertonic solution.
- Turgor pressure The pressure exerted by the cell contents on the wall of a plant cell.
- Plasmolysis Shrinking of the plant protoplast away from the cell wall.
- Contractile vacuole An organelle that pumps excess water out of a single-celled organism.
Common Mistakes
- Saying that plant cells burst in pure water because of their cell wall; they become turgid.
- Using plasmolysis for animal cells.
- Thinking that a flaccid cell has lost its cell wall.
- Forgetting that animal cells have no wall to resist swelling.
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Cambridge 9700 AS Biology
Core Formula
Magnification Triangle & Unit Conversion
Formula: M = I / A ⇔ A = I / M ⇔ I = M × A
Units: 1 mm = 1,000 μm = 1,000,000 nm.
Rule: Convert Image size (ruler mm) to μm by ×1,000 before dividing by Actual size.