Cytoplasm and Membranes





Transport of Smaller Quantities through Membranes

Solutes, Solvents and Solutions

Passive Transport

Active Transport

  1. Phagocytosis (e.g. protozoans feeding, white blood cells engulfing invading bacteria)
  2. Pinocytosis (e.g. human egg taking in food such as oil in droplet form)

Comparison of Diffusion, Osmosis and Active Transport

Transport of gases or dissolved substances in solution from a region of high concentration to a region of low concentration Transport of water through a semi-permeable membrane from a solution of high concentration to a solution of low concentration Transport of a substance from low to high concentration regions, using energy from the cell, through a living membrane
1. Liquids and gases can diffuse over considerable distances Water only transported over a short distance Certain selected solutes, ions, glucose, sucrose, amino acid, etc., transported through short distances
2. Rapid in gases, but slow in solutions of substances Slow process Rapid process
3. Transport from high to low concentration Transport of water from solution of high to low concentration Transport of selected substances from region of low to high concentration
4. Occurs with or without a non-living permeable membrane Either a living or non-living semi-permeable membrane needed A living selective lipo-protein membrane is essential
5.No cell energy required No cell energy required Cell energy from ATP required

Surface Area to Volume Relationship

Side LengthSurface AreaVolumeS.A. to Volume Ratio
1 cm6 cm21cm36
10 cm600 cm21000 cm30.6