the need for transport systems in plants

• Why do plants require specialised transport systems?

  • Increasing transport distances
  • Surface area: volume ratio
  • Increasing levels of activity
• Why do plants need to increase transport distances?

  • Every cell in a plant requires water, glucose and mineral ions
  • The roots of a plant take in water and mineral ions while the leaves produce glucose by photosynthesis
  • These molecules need to be transported to the other parts of the plant
  • Glucose is transported as sucrose in plants
  • This large transport distance makes simple diffusion a non-viable method for transporting substances all the way from the exchange site to the rest of the organism
  • Diffusion wouldn’t be fast enough to meet the metabolic requirements of cells
• What adaptations do plants have to increase SA:V ratio?

  • Plants have a branching body shape
  • Leaves are flat and thin
  • Roots have root hairs
• What level of activity to larger plants have?

  • Larger organisms are not only more physically active but they also contain more cells than smaller organisms
  • A larger number of cells results in a higher level of metabolic activity
  • As a result, the demand for oxygen and nutrients is greater and more waste is produced
  • Plant cells and tissues have a much lower metabolic rate than animal cells
  • Therefore their demand for oxygen for aerobic respiration is reduced
• What is mass flow?

  the bulk movement of materials
• What do mass transport systems help to do?

  • Bring substances quickly from one exchange site to another
  • Maintain the diffusion gradients at exchange sites and between cells and their fluid surroundings
  • Ensure effective cell activity by keeping the immediate fluid environment of cells within a suitable metabolic range
• What two separate mass flow systems have flowering plants evolved?

  • The xylem which transports water and mineral ions
  • The phloem which transports sucrose and other nutrients (assimilates)
• Why do plants not have a specialised transport system for oxygen and carbon dioxide?

  • They do not need one because:
  • They have adaptations that give them a high SA: V ratio for the absorption and diffusion of gases
  • The leaves and stems possess chloroplasts which produce oxygen and use up carbon dioxide
  • There is a low demand for oxygen due to plant tissues having a low metabolic rate
• why do plants require a transport system?


  to ensure all cells receive a strong supply of the nutrients require

  it's especially important as a plant must be able to transport substances up their stem against gravity!
• Why do large multicellular plants need a transport system?

  there is a long distance from the external surface to cells, thus some cells won't receive substances needed e.g sucrose

  they have a small surface area to volume ratio

  they cannot rely on diffusion alone as it's not fast enough
• What are the formulas for volume and surface area of a sphere?

  volume= 4/3 π r^3

  surface area= 4 πr^2
• What is the benefit to plants of internal transport systems?

  allows for a high metabolic rate

  ensures nutrients, sugars, water etc reaches all tissues
• what is the formula for surface area and volume of a sphere?

  surface area= 4 pi r^2

  volume= 4/3 pi r^3
• why do large multicellular plants need a transport system?

  as there is a long distance from the external surface to cells

  large plants have a small surface area to volume ratio thus diffusion isn't fast enough

  e.g sucrose needs to be transported
• what is the benefit to plants of internal transport systems?

  diffusion from the external surface to cells isn't sufficient

  internal transport systems ensures molecules such as nutrients, sucrose, water etc reach all tissues and cells

  allows for high metabolic rate
• example of something a root hair cell transports?

  nitrate ions
• why do plants require a transport system?


  to ensure all cells receive a strong supply of the nutrients they require

  especially important as a plant must be able to transport substances up their stem against gravity
• why do large multicellular plants need a transport system?


  long distance from external surface to cells (1) small surface area to volume ratio (1) diffusion not fast enough (1) named example of substance that is transported e.g. sucrose
• volume of a sphere?


  4/3 x pi x r^3
• surface area of a sphere?


  4 x pi x r^2
• benefits to plants of internal transport systems?

  (transport system) ensures molecules / nutrients / sugars / water, reach all tissues s ✓ (allows) high metabolic rate