2.7.12Inquiry Process
The Roots and Water Transport — IB Biology HL Revision Notes & Topical Questions
5 min read 4 parts Lesson 84 of 160
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 4Absorption by the Root
Root hair cells
- Root hair cells Thousands of thin projections increase the surface area in contact with soil water, allowing rapid uptake.
Mineral ions
- Mineral ions Ions such as nitrate and potassium are taken in by active transport using protein pumps, which needs ATP.
Water uptake
- Water uptake Pumping ions in lowers the water potential inside the root cells, so water follows by osmosis from the soil.
Mycorrhizae
- Mycorrhizae Fungal hyphae associated with the root extend into the soil, absorbing water and ions, and in return receive sugars from the plant.
Part 2 of 4Pathways Across the Root
1
In the apoplast pathway, water moves through the cell walls and spaces between cells, without crossing membranes.
2
In the symplast pathway, water moves through the cytoplasm of connected cells via plasmodesmata.
3
On reaching the endodermis, a band of waterproof suberin called the Casparian strip blocks the apoplast pathway.
4
Water must therefore enter the cytoplasm, which allows the plant to control which solutes continue inwards.
5
Once through the endodermis, water enters the xylem and is carried upwards by the transpiration stream.
| Pathway | Route | Crosses membrane? |
|---|---|---|
| Apoplast | Cell walls | No, until the endodermis |
| Symplast | Cytoplasm through plasmodesmata | Yes, entering the cell |
Part 3 of 4Evidence and Effects
Evidence and Effects
Waterlogged soil
- Waterlogged soil Oxygen shortage reduces respiration and ATP, so active uptake of minerals falls.
Respiratory inhibitors
- Respiratory inhibitors Poisons that stop ATP production decrease the uptake of ions, showing that active transport is involved.
Root pressure
- Root pressure Ion pumping in the root can push water into the xylem, a small effect compared with transpiration pull.
Surface area
- Surface area A branching root system and root hairs maximise contact with water films around soil particles.
Part 4 of 4Exam Checklist & Tips
2.7.12 – Key Points for the Exam
- Root hair A tubular extension of an epidermal cell that increases surface area for absorption.
- Apoplast pathway The route water takes through cell walls and intercellular spaces.
- Symplast pathway The route water takes through the cytoplasm via plasmodesmata.
- Casparian strip A waterproof band in endodermal cell walls that blocks the apoplast route.
- Mycorrhiza A mutualistic association between fungal hyphae and plant roots.
Common Mistakes
- Saying that mineral ions enter roots by osmosis;
- they enter by active transport or diffusion through channels.
- Forgetting that the Casparian strip forces water into the symplast.
- Writing that root hairs are separate cells; each is an extension of a single epidermal cell.
- Confusing the apoplast (walls) with the symplast (cytoplasm).
Last updated:
\n