Transport in plants Flashcards
Why do large plants need a transport system
have a small SA:V
Plants not active and have low respiration so demand for O2 is low
Large demand for sugars and water
What do plants need a transport system to move
water and minerals from the roots to the leaves
sugars from the leaves to the rest of the plant
What does the vascular tissue consist of
xylem - water and soluble mineral ions travel upwards
Phloem - assimilates (sucrose) travel up and down
How is vascular tissue distributed
xylem and phloem are found together in vascular bundles
- may also contain other types of tissues i.e. collenchyma/ sclerenchyma) that give bundle strength and help support the plant
How is the xylem and phloem arranged in a young root
- at the centre
- central core of xylem often shaped in an ‘X’ where the phloem is found in between the arms of the ‘X’ shaped tissue
arrangement provides strength and support to pulling forces to which root is exposed
-around vascular bundle is endodermis which plays key role in getting water into the xylem vessels - in endodermis is layer of meristem cells (can divide) called the pericycle
How is the xylem and phloem arranged in a stem
Vascular bundle found near the outer edges of the stem
Non woody: bundles separate and discrete
Woody: separate in young stems but becomes continuous rings in older stems
Arrangement provides strength and flexibility to withstand pulling forces stems and branches are exposed
- xylem towards inside of vascular bundle and phloem towards the outside
- in between xylem and phloem is a layer of cambium tissue
What is the cambium
- in between xylem and phloem vessels
- layer of meristem cells hat divide to produce new xylem and phloem
How is the xylem and phloem arranged in a leaf
- vascular bundles form the midrib and veins of a leaf
- dicotyledonous leaf had branching network of veins that gets smaller as spread away from mid-rib
- with in each vein the xylem is located at the top of the phloem
What is the structure and function of the xylem
vessel used to transport water and mineral ions from roots up to the leaves and other parts of the plant
Consists of:
-vessels to carry water and dissolved mineral ions
- fibres to help support the plant
- living parenchyma cells which act as packing tissue to separate and support vessels
What does lignin do to the xylem
- as xylem develops lignin impregnates the walls of the cells making them waterproof
- this kills the cells - end walls and contents of the cells decay leaving long tube of dead cells with no contents (xylem vessel)
- lignin strengthens the walls and prevents from collapsing - keeps vessel open even when there is short water supply
What does the lignin thickening cause in the xylem wall
forms patterns in the wall
- may be spiral, annular (rings) or reticulate (a network of broken rings)
prevents the vessel becoming too rigid and allows some flexibility of the stem/branch
What happens where lignification is incomplete
leaves gaps in the cells
- gaps form pits/ bordered pits which in two adjacent vessels that are aligned allows water to leave one and pass on to the next vessel
Allows water to leave the xylem and pass into he living parts of the plant
Adaptations of the xylem to its function
- made from dead cells aligned end to end to form a continuous column
- tubes are narrow so water column does not break and capillary action is effective
- bordered pits in lignified walls allows water to move sideways from one vessel to another
- lignin deposited in the walls spiral, annular, reticulate patterns allow xylem to stretch as plant grows and enables the stem/branch to bend
What is the structure and function of the phloem
Phloem is a vessel used t transport assimilates (sucrose and amino acids i.e.) around the plant
- sucrose is dissolved in water to form a sap
Consists of sieve tubes made up of sieve tube elements and companion cells
Features of the sieve tube elements
-elongated sieve tube elements are lined up end to end to form sieve tubes
- contain no nucleus and little cytoplasm leaving space for mass flow pf sap to occur
- at end of the sieve tubes elements are perforated cross walls called sieve plates
- perforations into the sieve plates allow movements of the sap from one element to the next
- sieve tubes have very thin walls
Features of the companion cells
In between sieve tube elements are small cells which with large nucleus and dense cytoplasm
- numerous mitochondria to produce ATP needed for active processes
- carry out metabolic activities needed to load assimilates into sieve tubes
How are plant cells linked
Many plant cells joined by cytoplasmic bridges, where the cytoplasm of cells is connected to the cytoplasm of another cell through a gap in their walls.
These gaps are called plasmodesmata
What are the three different pathways water can take into a plant
apoplast pathway
symplast pathway
vacuolar pathway
How does the Apoplast pathway work
Water passes through spaces in the cell wall and between the cells
DOES NOT pass through any plasma membranes into cells
- water moves my mass flow rather than by osmosis
- dissolves mineral ions and salts can be carried with the water
How does the Symplast pathway work
Water enters the cell cytoplasm through the plasma membrane
- can pass through the plasmodesmata from one cell to the next
How does the Vacuolar pathway work
Similar to the Symplast pathway but water is not confined to the cytoplasm of the cells
- able to pass through the vacuoles as well
