Diffusion and Osmosis

Diffusion

Diffusion is a fundamental process in biology, describing the movement of molecules from areas of high concentration to areas of low concentration. It is a passive process that does not require energy input from the cell.

• Definition: Diffusion is the movement of molecules from an area of high concentration to an area of low concentration.

• Measurement: In the lab, diffusion was monitored by measuring pH with a sensor/probe.

• pH: pH measures the concentration of hydrogen ions (H+) in a solution.

• Effect of Ammonia: Ammonia is a base, which reduces H+ concentration, causing pH to increase.

• Temperature: Higher temperature increases the rate of diffusion because molecules have more kinetic energy and move faster.

• Equilibrium: A slope of zero in pH change indicates equilibrium has been reached; the system is no longer changing.

• Sensor Placement: A probe closer to the ammonia source detects pH changes sooner, but eventually all probes read the same pH at equilibrium.

• Static vs. Dynamic Equilibrium:

  • Static equilibrium: No movement occurs.

  • Dynamic equilibrium: Molecules continue moving, but there is no net change because movement occurs equally in opposite directions.

Osmosis

Osmosis is a specific type of diffusion involving water molecules moving across a selectively permeable membrane. It is crucial for maintaining cellular homeostasis.

• Definition: Osmosis is the diffusion of water across a selectively permeable membrane.

• Comparison to Diffusion:

  • Diffusion: Movement of molecules from high to low concentration.

  • Osmosis: Movement of water specifically across a membrane.

  • Similarity: Both are passive transport processes and move substances from high to low concentration.

• Egg Experiment: Decalcified eggs (with shells removed) were placed in various solutions to model osmosis.

  • Distilled Water: Egg gained mass; water was hypotonic, so water moved into the egg.

  • 0.9% NaCl: Egg changed little in mass; solution was isotonic, so little net movement of water occurred.

  • 1.0 M Sugar: Egg lost mass; solution was hypertonic, so water moved out of the egg.

  • 2.0 M Sugar: Egg lost the most mass; solution was hypertonic, with a higher solute concentration pulling out more water.

• Greatest Change: The egg in 2.0 M sugar showed the greatest decrease in mass due to the largest concentration gradient.

• Modeling Cells: Decalcified eggs act as cell models, with the semipermeable membrane mimicking a cell membrane.

• Red Blood Cells in Solutions:

  • Isotonic (0.9% NaCl): Cells remain normal; water moves in and out equally.

  • Hypertonic (10% NaCl): Cells shrink; water moves out.

  • Hypotonic (Distilled Water): Cells swell and may burst; water moves in.

Cellular Respiration

Overview of Cellular Respiration

Cellular respiration is the process by which cells extract energy from glucose using oxygen, producing ATP, carbon dioxide, and water. It is essential for all aerobic organisms.

• Definition: Cellular respiration is the breakdown of glucose in the presence of oxygen to produce ATP, CO2, and H2O.

• Chemical Equation:

• Measurement: CO2 was measured with a gas sensor; increased CO2 indicates cellular respiration.

Germination and Cellular Respiration

Germination is the process by which seeds begin to grow, requiring water, oxygen, and proper temperature. Cellular respiration is necessary for germination.

• Requirements for Germination:

  • Water (moisture)

  • Oxygen

  • Proper temperature

• Role of Moisture: Water softens the seed coat, activates enzymes, and allows cellular respiration to begin.

• Reactants Source: Glucose from stored food in seeds; oxygen from air.

• Evidence of Germination: Increased CO2 (from 1140 ppm to 2094 ppm) indicates active cellular respiration and germination.

Stages of Cellular Respiration

Cellular respiration occurs in three main stages, each with distinct processes and cellular locations.

• Stage 1: Glycolysis

  • Glucose is broken into two pyruvate molecules.

  • Produces some ATP and NADH.

  • Occurs in the cytoplasm.

• Stage 2: Krebs Cycle (Citric Acid Cycle)

  • Breaks down products from glycolysis.

  • Produces CO2, ATP, NADH, and FADH2.

  • Occurs in the mitochondrial matrix.

• Stage 3: Oxidative Phosphorylation (Electron Transport Chain)

  • Uses NADH and FADH2 to make ATP.

  • Produces most ATP.

  • Occurs in the mitochondria.

• ATP Production: Most ATP is produced during oxidative phosphorylation.

• Organelle: Mitochondria are the site of cellular respiration.

Summary Table: Effects of Solutions on Eggs and Red Blood Cells

Additional info:

• Glycolysis, Krebs cycle, and oxidative phosphorylation are sequential stages in cellular respiration, each contributing to the overall production of ATP.

• Dynamic equilibrium is a key concept in understanding molecular movement in biological systems.

• Osmosis and diffusion are essential for nutrient and waste transport in cells.