8.2Transport in Plants
Water uptake — Cambridge IGCSE Biology 0610 Revision Notes & Topical Questions
5 min read 15 parts Lesson 5 of 9 1 quiz
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.
Lesson summary
8.2 Water uptake — IGCSE BIOLOGY notes: Describe root hair cells and the pathway of water from the soil into the leaf.Structure — Single-celled extensions of the root epidermis cells.Position — They grow between soil particles.Function — They absorb water and minerals from the so…
- No chloroplasts
- Large surface area
- Active transport
- Root cortex
- Function — They absorb water and minerals from the soil
- Osmosis — Water enters root hair cells by osmosis
Section 1 of 15Root hair cells
Root hair cells
Structure
- Single-celled extensions of the root epidermis cells.
Position
- They grow between soil particles.
Function
- They absorb water and minerals from the soil.
No chloroplasts
- Root hair cells are underground and do not photosynthesise.
Section 2 of 15Surface area
Large surface area
- The root hair increases the surface area of the cell significantly.
Effect
- It increases the rate of absorption of water by osmosis and mineral ions by active transport.
Section 3 of 15Water entering the root hair
Osmosis
- Water enters root hair cells by osmosis.
Reason
- Soil water has a higher water potential than the cytoplasm of the root hair cell.
Section 4 of 15Pathway of water
1
Water is taken up from the soil into root hair cells.
2
It moves across the root cortex cells by osmosis.
3
It enters the xylem vessels.
4
It is carried in the xylem up the stem to the leaves.
5
It enters the leaf mesophyll cells.
Section 5 of 15Tracing the pathway with a stain
1
Place a plant stem, such as celery, in a beaker of water containing a stain.
2
Leave for a few hours until the leaves turn the colour of the dyed water.
3
Cut a cross-section of the stem.
4
View the dye: it marks the location of the xylem vessels.
Section 6 of 15More from the specification
Transpiration stream
- Continuous movement of water up the xylem from roots to leaves.
Transpiration
- Loss of water vapour from leaves by evaporation and diffusion through stomata.
Phloem
- Tissue carrying sucrose and amino acids.
Humidity
- The amount of water vapour in the air.
Translocation
- Movement of sucrose and amino acids in phloem from sources to sinks.
Sucrose
- The sugar mainly transported in phloem.
Section 7 of 15Root hair cells
Root hair cells
Structure
- Structure epidermal cells of the root with a long single-celled extension that grows between soil particles.
Large surface area
- Large surface area the thin hair greatly increases the area for absorption.
Thin cell wall
- Thin cell wall gives a short diffusion distance.
Cell sap
- Cell sap dissolved solutes keep the water potential lower than the soil water.
Many mitochondria
- Many mitochondria provide energy for active transport.
Section 8 of 15How water enters the root
Soil water
- Soil water a dilute solution with a high water potential.
Root hair cell
- Root hair cell its cytoplasm and vacuole contain sugars, salts and proteins, so it has a lower water potential.
Osmosis
- Osmosis water therefore moves into the cell across the partially permeable membrane.
Section 9 of 15Pathway of water across the root
1
Water enters the root hair cell by osmosis.
2
It passes across the cortex cells down a water potential gradient, through cells and along cell walls.
3
It enters the xylem in the centre of the root.
4
It is drawn up the xylem by the transpiration stream to the leaf mesophyll cells.
Section 10 of 15Uptake of mineral ions
Concentration
- Concentration mineral ions such as nitrate are usually at lower concentration in soil than inside the root cell.
Active transport
- Active transport carrier proteins move them in against the gradient using energy from respiration.
Section 11 of 15Factors affecting uptake
Soil water content
- Soil water content less water means a smaller water potential difference.
Temperature
- Temperature low temperatures slow respiration and so active transport.
Oxygen supply
- Oxygen supply needed for aerobic respiration;
- waterlogged soil has little oxygen, so active transport slows and mineral deficiency appears.
Salty soil
- Salty soil if the soil solution is more concentrated than the root cells, water leaves the roots by osmosis and the plant wilts.
- This is why too much fertiliser can damage plants.
Section 12 of 15Routes across the root in more detail
1Apoplast pathway
- Apoplast pathway water travels in the spaces within cell walls.
2Symplast pathway
- Symplast pathway water moves through the cytoplasm of linked cells via channels called plasmodesmata.
3Vacuolar route
- Vacuolar route some water passes from vacuole to vacuole.
4Endodermis
- Endodermis a ring of cells with a waterproof band, so water must enter the cytoplasm there.
- This lets the plant regulate which ions enter.
5Root pressure
- Root pressure ions actively pumped into the xylem make water follow by osmosis, pushing water up a short distance.
- Transpiration pull does most of the lifting in tall plants.
Section 13 of 15Investigating mineral ion uptake
Investigating mineral ion uptake
Grow seedlings in solutions with and without the ion (for example nitrate), keeping all else identical.
Measure growth, leaf colour and dry mass after several weeks.
Compare the deficient plants with the control that has all minerals.
Section 14 of 15Key terms
| Term | Meaning |
|---|---|
| Root hair cell | An epidermal root cell with a long extension that absorbs water and minerals. |
| Osmosis | Net movement of water down a water potential gradient through a partially permeable membrane. |
| Active transport | Movement of ions against a concentration gradient using energy from respiration. |
| Root cortex | The tissue that water crosses between the root hair and the xylem. |
| Stain | A dye used to trace the pathway of water. |
| Term | Meaning |
|---|---|
| Root hair cell | An epidermal root cell with a long extension for absorption. |
| Water potential | The tendency of water to move; higher in dilute solution. |
| Osmosis | Net water movement from higher to lower water potential across a partially permeable membrane. |
| Active transport | Movement of ions against a gradient using respiratory energy. |
| Cortex | The tissue between the root epidermis and the xylem. |
Section 15 of 15Exam technique
1
Saying mineral ions enter by osmosis — they enter by active transport.
2
Saying water enters by active transport — water enters root hair cells by osmosis.
3
Leaving out the cortex from the pathway — water crosses the root cortex cells before the xylem.
4
Thinking root hairs are separate cells from the epidermis — they are extensions of epidermal cells.
1
Saying roots absorb water by active transport — water enters by osmosis.
2
Saying all of the root absorbs equally — absorption is mainly by root hair cells.
3
Forgetting that mineral ions need energy — they enter by active transport.
4
Saying water moves from low to high water potential — it moves from high to low.
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