Edexcel IGCSE Biology 复习笔记 2.8.1 The Requirement for Transport Systems

Edexcel IGCSE Biology 复习笔记 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: diffusionosmosis 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 diffusionosmosis and active transport through the cell membrane occur at a sufficient rate to meet the organisms needs

 

 

Transport-in-unicellular-organisms

 

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 diffusionosmosis 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

 

Some examples of exchange surfaces in plants and animals

 

 

 

Transport-systems-in-plants-and-animals

 

Some examples of transport systems in plants and animals

转载自savemyexam

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