IGCSE Biology: Movement Into and Out of Cells

Overview

• This chapter covers how substances move into and out of cells via:
  • Diffusion
  • Osmosis
  • Active Transport

Diffusion

• Definition: The net movement of particles from a region of higher concentration to a region of lower concentration (down a concentration gradient) due to their random movement.
• Mechanism: Occurs through the cell membrane, allowing molecules like glucose and proteins to move into the cell and waste products out.
• Factors Influencing Diffusion:
  • Surface Area: Larger surface area increases rate.
  • Temperature: Higher temperature increases rate due to increased kinetic energy.
  • Concentration Gradient: Greater difference increases rate.
  • Distance: Shorter distance increases rate.

Osmosis

• Importance of Water:
  • Acts as a solvent and medium for transport, digestion, and excretion.
• Definition: The 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.
• Mechanism:
  • Water moves into and out of cells through the cell membrane.
  • Water potential is used instead of concentration for water.
• Effects on Plant and Animal Cells:
  • Turgid: High water potential causes cells to swell.
  • Flaccid: Low water potential causes cells to shrink.
  • Plasmolysis: Excessive water loss in plant cells causing cytoplasm to shrink.
• Role in Plants:
  • Water uptake through roots via osmosis, maintaining turgidity.

Active Transport

• Definition: Movement of particles through a cell membrane from lower to higher concentration (against a concentration gradient) using energy from respiration.
• Mechanism:
  • Utilizes energy to transport molecules against the gradient.
  • Protein carriers in the cell membrane change shape to transport molecules.

Comparison of Processes

• Diffusion and Active Transport: Movement of particles
• Osmosis: Movement of water molecules
• Diffusion: Down a concentration gradient, uses kinetic energy
• Active Transport: Against a concentration gradient, requires respiration energy
• Osmosis: Movement across a partially permeable membrane

Hope these notes help in understanding the movement of substances in and out of cells. Don't forget to review these concepts and subscribe to IGCSE Study Buddy for more resources.