IGCSE Biology: Topic 3 - Movement Into and Out of Cells

Overview

• This chapter covers the movement of substances into and out of cells.
• There are three main processes:
  • Diffusion
  • Osmosis
  • Active Transport

Diffusion

• Definition: Net movement of particles from a region of higher concentration to a region of lower concentration (down a concentration gradient).
• Involves random movement and kinetic energy of particles.
• Factors Influencing Diffusion:
  • Surface Area: Larger surface area increases diffusion rate.
  • Temperature: Higher temperature increases kinetic energy, enhancing diffusion.
  • Concentration Gradient: Greater difference in concentration increases diffusion rate.
  • Distance: Shorter distance increases diffusion rate.
• Examples:
  • Movement of glucose and proteins into cells for metabolic reactions.
  • Waste products like CO2 and lactic acid moving out of cells.

Osmosis

• Role of Water:
  • Acts as a solvent and medium for transport.
  • Essential for digestion and excretion.
• Definition: Net movement of water molecules from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution) through a partially permeable membrane.
• Concepts:
  • Water Potential: High in dilute solutions and low in concentrated solutions.
  • Partially Permeable Membrane: Allows only certain molecules to pass.
• Experiments:
  • Dialysis Tubing: Demonstrates osmosis with sucrose solution.
• Effects on Plant Tissues:
  • Turgid: Cells swell with water entry.
  • Flaccid: Cells shrink with water loss.
  • Plasmolysis: Cytoplasm shrinks away from cell wall.

Active Transport

• Definition: Movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration (against a concentration gradient) using energy from respiration.
• Characteristics:
  • Utilizes energy to move particles against their concentration gradient.
  • Involves protein carriers in the cell membrane.
• Applications:
  • Important in plant roots and epithelial cells for nutrient absorption.

Comparison of Processes

• Diffusion: Particles move down a concentration gradient using kinetic energy.
• Osmosis: Water molecules move from high to low water potential across a membrane.
• Active Transport: Particles move against a concentration gradient using energy from respiration.

Summary

• Understanding these processes is crucial for comprehending how cells interact with their environment.
• Each process plays a specific role in maintaining cellular function and homeostasis.

Note: Subscribe to IGCSE Study Buddy for more biology revision videos!