9.1 Transport Systems in Plants Flashcards
Why do multicellular plants need transport systems?
Metabolic demands - some internal and underground parts of the plant don’t photosynthesise and so need oxygen and glucose transported to them and waste products transported away. Hormones made in one part need to be transported to an area where they have an effect. Mineral ions absorbed by the roots need to be transported to all cells to make proteins for enzymes and the structure of the cell.
Size - plants can grow continuously, and so need effective transport systems to move substances both up and down from the tip of the roots to the topmost leaves and stems.
Surface area to volume ratio - due to their size and complexity of the plants, their surface area to volume ratio is small and cannot rely on diffusion alone.
Describe and explain the distribution of vascular bundles in the stem, roots and leaves of plants.
Stem : around the edge to give strength and support.
Root : in the middle to help the plant withstand the tugging strains that result as the stems and leaves are blown in the wind.
Leaf : midrib of a dicot leaf is the main vein carrying vascular tissues. Helps support structure of leaf. Small, branching veins spread through the leaf functioning both in transport and support.
Describe the structure of the xylem
Xylem vessels are the main structure : long, hollow structures made by several columns of dead cells fusing together end to end.
Thick walled xylem parenchyma packs around the xylem vessels, storing food and containing tannin deposits.
Xylem fibres are long cells with lignified secondary walls that provide extra mechanical strength.
What is the function of the xylem?
Transport of water and mineral ions
Support
Describe the structure of the phloem
Main transporting vessels are the sieve tube elements.
Phloem siege tubes are made up of many cells joined end to end to form a long, hollow structure.
Between the cells, the walls become perforated to form sieve plates ( lets the phloem contents flow through ).
Companion cells are closely linked to the sieve tube elements by many plasmodesmata - microscopic channels through the cellulose cells walls linking the cytoplasm of adjacent cells. They maintain their nucleus and all their organelles.
Also contains supporting tissues including fibres and sclereids - cells with extremely thick cell walls.
What is the function of the phloem?
Transports food in the form of organic solutes around the plant from the leaves where they are made by photosynthesis.
Supplies the cells with the sugars and amino acids needed for cellular respiration and for the synthesis of all other useful molecules.
