Overview
This lecture explains how osmosis impacts living organisms, particularly focusing on plants, animal cells, and real-world examples involving salt and water balance.
Effects of Salt on Plants
- Road salt in winter lowers water's freezing point but harms roadside plants via salt exposure.
- Saltwater flooding from hurricanes can kill trees and plants over time due to salt in the soil.
Osmosis: Core Concepts
- Osmosis is water movement through a semi-permeable membrane from high to low water concentration.
- It is a form of passive transport and does not require energy.
- Water moves toward areas with higher solute concentration (lower water concentration).
U-tube Example and Tonicity
- In a U-tube with a membrane, adding salt to one side causes water to move to the saltier (hypertonic) side.
- Hypertonic means higher solute concentration compared to another side; hypotonic means lower solute concentration.
- Osmosis continues until equilibrium is reached, but water molecules still move.
Medical and Biological Applications
- Pure water in an IV would cause red blood cells (which are hypertonic) to swell and burst due to osmosis.
- Hospitals use isotonic solutions to prevent cell swelling or shrinking.
- Saltwater fish in freshwater encounter water rushing into their cells, which can be fatal.
Adaptations and Plant Water Uptake
- Some animals (like salmon) can adapt to both salt and fresh water, managing osmosis effectively.
- Plant root hair cells have higher solute concentration than saturated soil, causing water to enter roots by osmosis.
Water Potential and Pressure in Plants
- Water potential combines solute potential (lowered by added solute) and pressure potential (increased by internal pressure).
- Water moves to areas of lower water potential.
- In potato core experiments, water enters cells until internal pressure (turgor pressure) increases water potential.
- Turgor pressure maintains plant structure and prevents wilting.
Key Terms & Definitions
- Osmosis — movement of water across a semi-permeable membrane from higher to lower water concentration.
- Solute — substance dissolved in a solvent (e.g., salt or sugar in water).
- Hypertonic — higher solute concentration compared to another solution.
- Hypotonic — lower solute concentration compared to another solution.
- Isotonic — equal solute concentrations between two solutions.
- Water potential — measure of water’s tendency to move, combining solute and pressure potential.
- Turgor pressure — internal pressure in plant cells due to water intake.
Action Items / Next Steps
- Review how osmosis and water potential apply to living organisms.
- Explore turgor pressure and its role in plant structure.
- (Optional) Research potato core labs to see water potential calculations in practice.