Edexcel IGCSE Biology

Revision Notes

2.7.1 Diffusion in Gas Exchange

Diffusion in Gas Exchange

  • Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration
  • Molecules move down a concentration gradient, as a result of their random movement

Diffusion across the cell membrane, IGCSE & GCSE Biology revision notes

Diffusion across the cell membrane

  • Diffusion is the process by which gas exchange occurs
  • Single celled organisms, such as amoeba, can exchange gases sufficiently by simple diffusion through the cell membrane

Gas exchange in amoeba, downloadable IGCSE & GCSE Biology revision notes
Gas exchange in single-celled organisms (such as amoeba) occurs through diffusion

  • Multicellular organisms (such as plants and animals), however, have exchange surfaces and organ systems that maximise the exchange of materials
    • Gills are the gas exchange organs in fish, lungs in humans and leaves or roots in plants
  • These organs increase the efficiency of exchange in a number of ways:
    • Having a large surface area to increase the rate of transport
    • A short diffusion distance for substances to move across. This short distance is created because the barrier that separates two regions is as thin as possible
  • In addition, animals have:
    • Gas exchange surfaces that are well ventilated to maintain steep concentration gradients

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Ruth graduated from Sheffield University with a degree in Biology and went on to teach Science in London whilst also completing an MA in innovation in Education. With 10 years of teaching experience across the 3 key science disciplines, Ruth decided to set up a tutoring business to support students in her local area. Ruth has worked with several exam boards and loves to use her experience to produce educational materials which make the mark schemes accessible to all students.

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