National 5 Biology - Cell Biology: Transport Across Cell Membranes

Introduction

• Focus on transport across cell membranes
• Cell membranes are selectively permeable, controlling what molecules can pass through

Structure of the Cell Membrane

• Composed of:
  • Phospholipids: tadpole-like structures
  • Proteins: large blobs within the membrane
• Selectively permeable: some molecules can pass, some cannot

Molecules Passing Through the Cell Membrane

• Into the Cell:
  • Glucose
  • Oxygen
  • Amino acids
• Out of the Cell:
  • Carbon dioxide
  • Urea (waste products)

Experiment: Glucose and Starch

• Use a semi-permeable membrane (dialysis tubing) in a beaker of water
• Observe diffusion of molecules:
  • Glucose: small enough to pass through, detectable in water over time
  • Starch: too large to pass through

Diffusion

• Movement from high concentration to low concentration
• Passive process: does not require energy
• Example: Perfume spreading in a room

Osmosis

• Movement of water molecules from high to low water concentration
• Passive process: does not require energy
• Occurs across selectively permeable membranes

Active Transport

• Movement against a concentration gradient
  • From low concentration to high concentration
• Active process: requires energy and proteins in the cell membrane

Osmosis in Beaker Experiment

• Identifying Water Movement:
  • From higher water concentration to lower water concentration
  • Convert salt percentages to water percentages to determine osmosis direction

Effects on Cells

• Animal Cells:
  • In high water concentration: cell swells and bursts
  • In low water concentration: cell shrinks
• Plant Cells:
  • High water concentration: cells become turgid (do not burst due to cell wall)
  • Low water concentration: cells undergo plasmolysis (membrane pulls away)

Key Terms to Remember

• Selectively permeable
• Diffusion
• Osmosis
• Active transport
• Turgid
• Plasmolysis

Study and Revision Tips

• Take notes and consolidate with class notes
• Use quizzes and Kahoot for self-assessment
• Understand differences in cell reactions to water concentration changes

Conclusion: Ensure understanding of key concepts regarding cell membrane transport mechanisms and its impact on cell structure in various environments.