The Need for a Transport System (Edexcel IGCSE Science (Double Award)): Revision Note

Exam code: 4SD0

Unicellular Organisms

  • To function properly, organisms must exchange substances, like food molecules and waste, with their environment

    • This exchange happens via diffusion, osmosis, and active transport across the cell membrane

  • Unicellular organisms, like amoebas, have large surface areas relative to their volume, meaning the distance from the surface to the centre is small

  • Consequently, they don't need specialised exchange surfaces or transport systems, as diffusion, osmosis, and active transport through the cell membrane are sufficient for their 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

  • Multicellular organisms, like humans, have bodies composed of many cells

  • These organisms have multiple cell layers, making the distance from the surface to the centre too long for diffusion alone

  • Diffusion to all cells would be too slow to meet the organism's needs, so larger organisms require transport systems

    • In animals, the circulatory system carries essential substances in the blood

    • In plants, the vascular system transports substances:

      • the xylem moves water and minerals from roots to shoots

      • the phloem distributes sugars and amino acids throughout the plant.

Transport systems in plants and animals, downloadable IGCSE & GCSE Biology revision notes

Humans and some plants have specialised transport systems


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Lára Marie McIvor

Author: Lára Marie McIvor

Expertise: Biology, Psychology & Sociology Subject Lead

Lára graduated from Oxford University in Biological Sciences and has now been a science tutor working in the UK for several years. Lára has a particular interest in the area of infectious disease and epidemiology, and enjoys creating original educational materials that develop confidence and facilitate learning.

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