9 - transport in plants Flashcards
What are reasons for the need of plant transport systems?
METABOLIC DEMAND - Green parts of plant photosynthesis and make their own glucose, however internal and underground plants don’t and need glucose transported to them - Mineral ions must be transported from roots to rest of plants to make proteins for enzymes and cell structure - Hormones must be transported - Waste cell metabolism products must be removed SIZE - Large perennial plants need effective transport systems to move substances up and down plant (roots to leaves) SA:V RATIO - Leaves have large SA:V, but stems trunks/roots make plants overall ratio small.
What are herbaceous dicots?
Soft tissue plants with short life span (leaves and stems that die down at the end of growing season)
Define vascular system.
Series of transport vessels that run through leaves, roots and stem of a dicot plant.
Define vascular bundle.
The vascular system of herbaceous dicots comprising of xylem and phloems.
label the structure of the stem
Parenchyma - In the middle, packing and supporting tissue Phloem vessel on outside - for translocation
Xylem vessel on inside - for transpiration
Vascular cambium - new xylem and phloem cells divide from it.
In a stem the vascular bundles around the edge provide structural support.
label the structure of a root (dicot)
Root hair on the outside protruding
From root hair
Exodermis, epidermis, cortex, endodermis Phloem as 4 dots Xylem as a cross
label the structure of a leaf (dicot)
Midrib of the leaf gives structural support as it is the main vein carrying the vascular tissue through the organ
Xylem and phloem
Palisade mesophyll - main photosynthetic tissue
What is the function and structure of a xylem?
End walls removed forming a long tube
No cytoplasm or organelles - non-living tissue
Cell walls lignified (impregnated with lignin)
Makes wall waterproof and prevents xylem collapsing
Spiral, annular (ring-like) and reticulate (mesh-like) thickening to strengthen walls and prevent collapsing
Bordered pits to allow lateral water flow between xylem vessels
E.g. if the xylem has an obstruction, water can still flow but in another xylem vessel
What is the function of a phloem vessel and what are its components?
Transports assimilates actively by mass flow - involves 2 cells
Sieve Tube Elements (STE) - long sieve tubes transporting assimilates
Companion Cells - supports metabolic function of STE, also involved in actively loading the phloem
What are the adaptations of the sieve tube element?
Few organelles and no nucleus - long hollow tubular structure
Has end walls with sieve plates (perforated walls)
Thin layer of cytoplasm
Not lignified as the cell is not under tension
What are the adaptations of companion cells?
ste = sieve tube element
Closely linked to STE
Connected to STE by plasmodesmata
microscopic channels of cytoplasm through cellulose cell walls linking cytoplasm to adjacent cells
Dense cytoplasm with many mitochondria and a large nucleus
Mitochondria gives energy to move sucrose into STE
What are the roles of water in plants?
Turgor pressure (hydrostatic) as a result of osmosis in plant cells, gives a hydrostatic skeleton - supports stem and leaves.
Loss of water by transpiration keeps plants cool
Water is a transport medium for mineral ions and assimilates
Water is a raw material for photosynthesis.
What is the role and what are the adaptations of a root hair cell?
Exchange surface where water is taken into plant
Long thin extension from root hair cell is root hair
Adaptations
Small size - can penetrate soil particles
Each hair has a large SA:V ratio
Each hair has a thin surface layer to reduce diffusion and osmosis distance to quicken the process
Solute concentration in root hair cell cytoplasm maintains water potential gradient between soil and cell.
What is the symplast pathway?
Symplast - continous cytoplasm of living plant cells that are connected through plasmodesmata
Water moves by osmosis down the water potential gradient from cell to cell, starting at the root hair cell until the xylem
What is the apoplast pathway?
Apoplast - cell wall and extracellular spaces of the cell
Carries water through cell wall and between cells
Water does not enter the cytoplasm or pass the plasma membranes
Describe the movement of water into the xylem.
After water move by symplast and apoplast it reaches the endodermis (layer of cells surrounding xylem and phloem
Casparian Strip
Band of waxy material (suberin) that surrounds endodermal cells forming a water proof layer.
It stops water from entering via the apoplast pathway, it is forced into the symplast pathway
For water to enter the symplast pathway from apoplast, it must pass the selectively permeable membrane which stops toxic solutes from entering from the soil as there are no carrier proteins to admit them
After entering the xylem does the water stay in the symplast pathway?
No it re-uses the apoplast pathway
What is root pressure?
Root endodermis uses metabolic energy to pump mineral ions into root medulla
Reducing water potential in medulla and xylem to lower than the cortex, so water moves across the endodermis into the xylem
Water cannot move back to the cortex as it is blocked by the Casparian Strip, creating pressure in the cortex pushing water up the xylem
Define transpiration.
Loss of water vapour from the upper segments of the plant (mainly leaves)
Occurs through evaporation from leaf surface and through stomata