Structure of transport tissues in plants

Plants have 2 transport systems:

• xylem: transports water and inorganic ions from the roots to the leaves.
• phloem: transports food made in the plant (sucrose and amino acids) from the leaves to the rest of the plant. 

Both of these systems are rows of cells that make continuous tubes running the full length of the plant.

Plants can be very large, but they have a branching shape which helps to keep the surface area to volume ratio fairly large. Their energy needs are generally small compared with those of animals, so respiration does not take place so quickly.

They can therefore rely on diffusion to supply their cells with O₂ and to remove CO₂. Their leaves are very thin and have a large surface area inside them in contact with the air spaces. This means that diffusion is sufficient to supply the mesophyll cells with CO₂ for photosynthesis, and to remove O₂. Plant transport systems therefore do not transport gases.

Transverse section of roots, stems and leaves of herbaceous dicotyledonous plants

1. Root 

2. Stem 

3. Leaf

Xylem tissue

Xylem tissue contains dead, empty cells with no end walls. These are called xylem vessel elements. They are arranged in long lines to form xylem vessels. These are long, hollow tubes through which water moves by mass flow from the roots to all other parts of the plant.

Xylem tissue.

 

Syllabus 2015 (d) [PA] describe the distribution of xylem and phloem tissue in roots, stems and leaves of dicotyledonous plants; (e) [PA] describe the structure of xylem vessel elements, phloem sieve tube elements and companion cells and be able to recognise these using the light microscope; (f) relate the structure of xylem vessel elements, phloem sieve tube elements and companion cells to their functions;

Syllabus 2016 7.1    Structure of transport tissues Plants  have two transport tissues: xylem and phloem. a)   draw and label from prepared slides plan diagrams of transverse sections of stems, roots  and leaves of herbaceous dicotyledonous plants  using an eyepiece graticule  to show tissues in correct proportions (see  1.1c) b)   draw and label from prepared slides  the cells in the different tissues in roots,  stems and leaves of herbaceous dicotyledonous plants  using transverse and longitudinal sections c)   draw and label from prepared slides  the structure of xylem vessel elements, phloem sieve  tube  elements and companion cells and be able to recognise these using the light microscope d)   relate  the structure of xylem vessel elements, phloem sieve tube  elements and companion cells to their functions