Diffusion and osmosis

Homeostasis and Cell Membranes

• Homeostasis is a self-regulatory process that maintains stability in biological systems while adjusting to optimal conditions for survival.
• Cells maintain homeostasis by moving materials through plasma membranes into and out of the cytoplasm.
• Cellular membranes are selectively permeable, consisting of phospholipid bilayers with embedded proteins.
• Phospholipid fatty acids are hydrophobic, limiting the movement of water.

Water and Molecule Transport

• Water can pass through the membrane by: • Freely by osmosis (small amount) • Selectively by aquaporins (large amount)
• Molecules can pass through the membrane by: • Most ions moving through protein channels • Larger molecules carried by transport proteins via active or passive transport

Active and Passive Transport

• Active transport requires transport proteins, energy output, and moves against a concentration gradient.
• Passive transport does not require energy and moves along the concentration gradient, including diffusion and osmosis.

Diffusion and Osmosis

• Diffusion is the net movement of molecules or atoms down/along a concentration gradient.
• Osmosis is a type of diffusion that involves the net movement of solvent from a region of low solute concentration to a region of high solute concentration.

Tonicity

• Tonicity refers to the relative solute concentrations of two solutions separated by a semipermeable membrane.
• A solution can be hypertonic, isotonic, or hypotonic.
• Hypertonic solution: [free water in cell] > [free water out of cell], [solutes in cell] < [solutes out of cell]
• Isotonic solution: [free water in cell] = [free water out of cell], [solutes in cell] = [solutes out of cell]
• Hypotonic solution: [free water in cell] < [free water out of cell], [solutes in cell] > [solutes out of cell]

Effects of Tonicity on Cells

• In a hypertonic solution, animal cells shrink or become crenated, while plant cells become plasmolyzed.
• In an isotonic solution, animal cells remain normal, while plant cells become flaccid.
• In a hypotonic solution, animal cells lyse or burst, while plant cells become normal or turgid.

Factors Influencing Diffusion

• The rate of diffusion is influenced by: • Mass of particle: ↑mass of particle = ↓rate of diffusion • Temperature: ↑temperature = ↑rate of diffusion

Practical Investigation

• The lab will investigate: • Diffusion of gases • Osmosis (diffusion of molecules through a selectively permeable membrane) • Osmotic behavior in plant cells