2.8 Tonicity and Osmoregulation

• What does tonicity measure in a solution compared to a cell?

  Relative solute concentration
• Tonicity determines the direction and extent of water movement into or out of the cell through osmosis
• In a hypotonic solution, water moves into the cell.
• What happens to a cell in a hypotonic solution?

  It becomes swollen or turgid
• In a hypertonic solution, water moves out of the cell.
• What happens to a cell in a hypertonic solution?

  It becomes shrunken or shriveled
• In an isotonic solution, there is no net water movement across the cell membrane.
• What happens to a cell in an isotonic solution?

  It maintains its normal shape
• Match the tonicity type with its effect on a cell:

  Hypotonic ↔️ Water moves into the cell

  Hypertonic ↔️ Water moves out of the cell

  Isotonic ↔️ No net water movement
• Osmosis is the movement of water across a semipermeable membrane from higher to lower water concentration.
• Osmosis plays a crucial role in determining the effects of different tonicity conditions on cells.
• Order the osmoregulation mechanisms in freshwater fish from water intake to excretion:

  1️⃣ Water flows in due to hypotonic environment

  2️⃣ Large volumes of dilute urine are excreted

  3️⃣ Salts are actively absorbed through gills
• Match the organism with its osmoregulation mechanism:

  Freshwater Fish ↔️ Excrete dilute urine

  Saltwater Fish ↔️ Excrete concentrated urine

  Terrestrial Mammals ↔️ Kidney filtration and reabsorption
• Plant cells in a hypotonic solution become turgid due to water intake.
• What maintains the rigidity of plant cells in a hypotonic solution?

  Turgor pressure
• In a hypertonic solution, plant cells undergo plasmolysis as water is lost.
• What happens to animal cells in a hypertonic solution?

  They undergo crenation
• In an isotonic solution, both plant and animal cells maintain their normal shape.