Transport in Flowering Plants
The Need for Transport Systems
In multicellular organisms, diffusion can be too slow to support the cells furthest away from the
surface.
- The larger the organism, and the more active it is, the greater this problem becomes.
- This is why large organisms have transport systems, to carry important substances
around the body to every cell that needs them
Transport Tissues in Plants
Water and dissolved substances are transported throughout the plant in a series of tubes or
vessels.
- There are two types of transport vessel in plants, called xylem and phloem
Xylem
Structure
● Xylem tissue contains hollow xylem cells that form long tubes through the plant.
● The tubes are the hollow remains of dead cells.
● The thick strong cell walls help to support the plant.
Xylem tubes are important for carrying water and dissolved mineral ions, which have entered the
plant through the roots, to all the parts that need them.
They are particularly important for supplying the water that the leaf cells need for photosynthesis.
Phloem
Phloem cells are living cells that are linked together to form continuous phloem tissue.
Dissolved food materials, particularly sucrose and amino acids that have been formed in the leaf,
are transported all over the non-photosynthesising plant from the photosynthesizing leaves.
- E.g. sucrose is carried to any cell that needs glucose for respiration
- This also means that movement can be in any direction around the plant
Structure
● The cells are living cells and are not hollow
● Substances move from cell to cell through pores in the end walls of each cell
Sucrose
● Sucrose is less reactive than glucose and is easier to transport without causing problems
for other cells.
● Sucrose may also be carried to parts of the plant where it is stored, often as another
carbohydrate such as starch, stored in seeds and root tubers.
○ This transport of sucrose and other materials through the phloem is called
translocation
, Xylem is always on the inside and the phloem is always on the outside.
The Need for Transport Systems
In multicellular organisms, diffusion can be too slow to support the cells furthest away from the
surface.
- The larger the organism, and the more active it is, the greater this problem becomes.
- This is why large organisms have transport systems, to carry important substances
around the body to every cell that needs them
Transport Tissues in Plants
Water and dissolved substances are transported throughout the plant in a series of tubes or
vessels.
- There are two types of transport vessel in plants, called xylem and phloem
Xylem
Structure
● Xylem tissue contains hollow xylem cells that form long tubes through the plant.
● The tubes are the hollow remains of dead cells.
● The thick strong cell walls help to support the plant.
Xylem tubes are important for carrying water and dissolved mineral ions, which have entered the
plant through the roots, to all the parts that need them.
They are particularly important for supplying the water that the leaf cells need for photosynthesis.
Phloem
Phloem cells are living cells that are linked together to form continuous phloem tissue.
Dissolved food materials, particularly sucrose and amino acids that have been formed in the leaf,
are transported all over the non-photosynthesising plant from the photosynthesizing leaves.
- E.g. sucrose is carried to any cell that needs glucose for respiration
- This also means that movement can be in any direction around the plant
Structure
● The cells are living cells and are not hollow
● Substances move from cell to cell through pores in the end walls of each cell
Sucrose
● Sucrose is less reactive than glucose and is easier to transport without causing problems
for other cells.
● Sucrose may also be carried to parts of the plant where it is stored, often as another
carbohydrate such as starch, stored in seeds and root tubers.
○ This transport of sucrose and other materials through the phloem is called
translocation
, Xylem is always on the inside and the phloem is always on the outside.
