Definition: A hypertonic solution is one that has a higher concentration of solute compared to another solution.
Effect on Potato Cells: When potato cells are placed in a 10% salt solution (hypertonic), they lose water, leading to cell shrinkage and flaccidity.
Observation and Characteristics:
Cells become more turbid when the solution is hypertonic.
This occurs because water moves out of the cells due to osmosis, as cells have a lower solute concentration compared to the surrounding solution.
Hypotonic Solutions
Definition: A hypotonic solution has a lower concentration of solute compared to another solution.
Effect on Potato Cells: Potato cells placed in a solution with 0% salt absorb water, leading to turgid cells.
Mechanism:
Water enters the potato cells because they contain a higher concentration of solute (approximately 0.9% salt).
As water enters, it fills the central vacuole, creating turgor pressure against the cell wall, causing the cells to swell but maintain their shape (turgid).
Turgidity:
Refers to the state of being distended or swollen, especially due to high fluid content. Turgid cells help maintain structure in plants.
Isotonic Solutions
Definition: An isotonic solution has an equal concentration of solute as another solution.
Effect on Potato Cells:
Example: A 0.9% sodium chloride solution is isotonic to potato sap.
Water moves in and out of the cells at the same rate, and potato cells maintain a good shape without significant swelling or shrinkage.
Observation: The potato strip in the isotonic solution is less turbid compared to strips in hypertonic solutions.
Experimental Observations
Benedict's Test and Diffusion Simulation
Setup: A beaker containing water and iodine was used to test for diffusion across a simulated semi-permeable membrane bag resembling a cell membrane.
Results of Benedict's Test:
A positive result indicates the presence of glucose. The bag containing glucose turned from blue to yellow-orange upon the addition of Benedict's undergo changes, confirming that glucose can pass through the bag's pores.
Starch vs. Glucose:
Glucose: A monosaccharide; small enough to diffuse through.
Starch: A polymer composed of many linked glucose molecules; too large to diffuse through the bag membrane.
Weight of Bags During Experimentation
Bag 1: Inside and outside solutions were isotonic, resulting in no net gain/loss of weight as water moved in and out consistently.
Bag 2: Contained 15% sucrose and was placed in a cup of water (hypotonic). The bag gained weight as water diffused in.
Bag 3: A more hypertonic solution showed a faster rate of weight gain due to stronger concentration gradients enhancing osmosis.
Bag 4: Lost weight as the external solution contained a higher solute concentration, leading to the osmotic movement of water out of the bag.
Factors Affecting Rate of Diffusion
Steepness of Concentration Gradient: A steeper gradient leads to a faster rate of diffusion.
Mass of Diffusing Particles: Smaller particles diffuse faster than larger particles. Observations showed potassium permanganate diffusing further than larger dyes, illustrating the inverse relationship between mass and diffusion rate.
Osmosis in Different Cell Types
Plant Cells vs. Animal Cells
Plant Cells: Prefer hypotonic solutions where water fills the vacuole and exerts pressure on the cell wall (turgor pressure). In hypertonic exposure, plasmolysis occurs, where the cell membrane detaches from the cell wall.
Animal Cells: Lack cell walls; thus, in a hypotonic solution, they may swell and burst (lyse). In hypertonic solutions, they shrivel (crenate).
Microscope Observations:
In hypotonic solutions, plant cells exhibit chloroplasts distributed away from the center due to turgidity.
In hypertonic solutions, animal cells displayed fragments and reduced size due to cell membrane collapse and loss of cell structure.
Isotonic solutions maintained the structural integrity and shape of red blood cells, as water maintained equal levels both incoming and outgoing in concentration.
Final Observations and Clean Up
Lab Summary: Emphasis on achieving a comprehensive understanding of osmosis, diffusion, and their impacts on various cell types in different solutions. Laboratory experiments provide practical evidence supporting theoretical concepts discussed during lectures.