Roots and water absorption
Stand young plants in measuring cylinders of water sealed with oil, compare intact roots, damaged root hairs and cut-off roots, and try salty water.
Core concept
Roots absorb water mainly through their root hairs, by osmosis; salty water stops absorption
Topic: Plants
Plants absorb water from the soil through their roots. Near each root tip are thousands of tiny root hairs, which give the root a huge surface area for taking in water. Water moves into the root hair cell: The tiny building block that every living thing is made of. All key words by osmosis: from the soil water, where there is more water, into the cell sap, where there is less. If the soil water is very salty, it has less water than the cell sap, so water cannot enter the roots and may even leave them, and the plant wilts.
What you will learn
- Show that roots absorb water.
- Explain the importance of root hairs.
- Explain why plants wilt in salty water.
Before you start
- Know that water moves into and out of cells.
Materials
- Young bean or mustard plants, cooking oil, salt, candle wax
Equipment
- Measuring cylinders
Procedure
- Stand a plant with intact roots in fresh water under a layer of oil. Record the water absorbed after 6, 12 and 24 hours.
- Repeat with a plant whose root hairs were damaged by rough washing.
- Repeat with a plant whose roots were cut off and the cut sealed with wax.
- Repeat with intact roots in salty water.
How this simulation is simplified
- A plant with healthy roots in fresh water absorbs 1.5 mL an hour; the oil stops evaporation from the cylinder.