Edexcel IGCSE Biology

Revision Notes

2.8.1 The Requirement for Transport Systems

Unicellular Organisms

  • In order for any organism to function properly, it needs to exchange substances, such as food molecules and waste products, between itself and its environment
  • This exchange of substances occurs across the cell membrane
  • There are three transport processes that living organisms use for exchange: diffusion, osmosis and active transport
  • Unicellular (single-celled) organisms like amoeba have very large surface areas (SA) in comparison to their volumes
    • This means that the distance between the surface of the organism to its centre is very small
  • As a result, unicellular organisms do not need to have specialist exchange surfaces or transport systems; as diffusion, osmosis and active transport through the cell membrane occur at a sufficient rate to meet the organisms needs

Transport in unicellular organisms, downloadable IGCSE & GCSE Biology revision notes Unicellular organisms such as amoeba do not require transport systems due to their large surface area to volume ratio

Multicellular Organisms

  • Large, multicellular organisms like humans have relatively small surface areas (SA) in comparison to their volumes
  • This means that the distance between the surface of the organism to its centre is relatively long
  • As diffusion, osmosis and active transport cannot occur at a sufficient rate to meet the needs of the organism, larger organisms usually have exchange surfaces and transport systems
  • Exchange surfaces in animals include:
    • The lungs and alveoli for gas exchange
    • The small intestines and villi for absorption of digested food
  • Transport systems in animals include
    • The blood and circulatory system carries the necessary substances around the body
  • Exchange surfaces in plants include:
    • Roots and root hairs where mineral ions and water are absorbed
    • The leaves for gas exchange
  • Transport systems in plants include:
    • The xylem moves water and mineral ions from roots to shoots
    • The phloem moves sugars and amino acids to where they are needed in the plant

Cell Adaptations for Diffusion, IGCSE & GCSE Biology revision notesSome examples of exchange surfaces in plants and animals

Transport systems in plants and animals, downloadable IGCSE & GCSE Biology revision notes Some examples of transport systems in plants and animals

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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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