9.1 Transport Systems In Dicotyledonous Plants Flashcards
Why do multicellular plants need transport systems?
Metabolic demands
Size
Surface area to volume ratio
Metabolic demands of plants
Non photosynthesising cells in plants require glucose and oxygen transported to them and waste products removed
Hormones made in one area of the plant need to be transported to the target area
Mineral ions absorbed by the roots need to be transported to all cells to produce proteins
Why does the size of plants mean they need a transport system?
They need effective transport systems to move substances up and down from the tip of the roots to the leaves and stems at the top
Why does SA:V ratio mean plants need a transport system?
Plants have a relatively small SA:V ratio when the stems and roots are included
They cannot rely on diffusion alone to supply the cells
What are dicotyledonous plants?
They make seeds with 2 cotyledons
What are cotyledons?
They are organs that act as food stores for the developing embryo plant and form the first leaves when the seed germinates
2 types of dicotyledons
Herbaceous dicots
Woody dicots
What are herbaceous dicots?
Plants with soft tissues and relatively short life cycle, as leaves and stems die down at the end of the growing season
What are woody/arborescent dicots?
Plants with hard, lignified tissues and a long life cycle
In herbaceous dicots, what is the vascular system made of?
Xylem and phloem tissue
Where are vascular bundles found in herbaceous dicots?
The leaves, stems and roots
Where are the vascular bundles found in the stem?
Around the edge - to provide strength and support
Where are the vascular bundles found in the roots?
The middle - to withstand the strains of stems and leaves being blown in the wind
Where are the vascular bundles found in the leaf?
The midrib of a leaf contains the vascular bundle
This helps to maintain structure of a leaf
Function of xylem
Transport of water and mineral ions
Providing the plant with support
What direction is the flow of material in the xylem?
Material flows up from the roots to the shoots and leaves
What type of tissue is the xylem made of?
Non living/dead tissue
Structure of xylem
Long hollow structures, made by many columns of cells joined together end to end
3 types of ground tissues
Parenchyma cells
Collenchyma cells
Sclerenchyma cells
Parenchyma cells
Perform primary metabolic functions in the plant (include palisade cells)
Have thin and flexible cell walls
Retain ability to divide and differentiate
Collenchyma cells
Support young parts of the plant shoot
Elongates with unevenly thickened cell wall
Grouped in strands
Sclerenchyma cells
Supporting elements
Thickened secondary walls containing large amount of lignin
Mature cells cannot elongate and occur in regions that have stopped growing
How do spirals of lignin surrounding the xylem help its structure?
Helps reinforce the xylem vessels, so they don’t collapse under the transpiration pull
What is tannin?
Bitter tasting chemical that prevents herbivores attacking plant tissues
Function of phloem
Living tissue that transports food in the form of organic solutes around the plant from the leaves where they are made during photosynthesis
Direction of flow in phloem
Up and down the plant (both directions)
Main transporting vessels of the phloem
Sieve tube elements
Phloem sieve tubes
Made of many cells joined end to end to form a long hollow structure
Not lignified
What are sieve plates?
Areas between cells where the wall becomes perforated
What happens as large pores appear in cell walls?
Tonoplast, nucleus and some other organelles break down
How are companion cells linked to the sieve tube elements?
By many plasmodesmata
What are plasmadesmata?
Microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells
What are sclereids?
Cells with extremely thick cell walls
