Transport in plants Flashcards
What is transported in phloem?
Organic substances.
What is transported in xylem?
Water and ions.
Dissection of plants.
Cut a thin cross section with a sharp blade.
Stored in water to prevent drying.
Transferred with tweezers into a dish containing stain.
Cohesion tension mechanism.
Water is needed for metabolic reactions, transport of solutes and to generate pressure potential to help support the plant.
Roots.
Take up water in the roots.
Root hair cells provide a large SA:Vol ratio to absorb water.
Water enters root down a water potential gradient by osmosis.
3 pathways: apoplast, symplast and vacuolar.
Apoplast pathway.
Non-living parts of the plant (spaces between cells and walls).
Water flows through this part as there is less resistance.
Symplast pathway.
Living parts of the plant (cytoplasm).
Cytoplasm is continuous from cell to cell through plasmodesmata.
Water crosses the partially permeable membrane by osmosis.
Vacuolar pathway.
Some water moves through the vacuole to vacuole through neighbouring cells, crossing through the symplast and apoplast.
Moves down the water potential gradient through membranes and tonoplasts by osmosis.
Xylem function.
Carries dissolved minerals and water up the plant.
Structural support.
Food storage.
Xylem.
Tissue found in vascular bundles.
In the roots they are found in the centre and in the centre of this is xylem tissue, which helps the roots to withstand pulling from growth.
In the stems the vascular bundles are around the outside and xylem is on the inside to help with support.
In the leaves the vascular bundles form the veins and spread from the centre, xylem is on the upper side of the bundles.
Phloem function.
Transport organic compounds (sucrose) from the source to the sink. Transport goes up and down.
Phloem.
Mainly made form sieve tube elements and companion cells.
In the roots the vascular bundles are in the centre, on the edges of the centre is phloem tissue.
In the stem vascular bundle is around the outside and phloem tissue is on the outside.
In the leaves vascular bundles form veins and spread from the centre, phloem tissue is on the lower side of the bundles.
Xylem structure.
Made form tracheids, vessel elements, xylem parenchyma and sclerenchyma cells.
Majority made from tracheids and vessel elements which are water conducting
Lignified cell walls: strength, withstand pressure, impermeable to water.
No end plates: allows mass flow of water.
Cells are dead: doesn’t impede mass flow.
Pits in walls: allows lateral movement of water.
Small diameter of vessels: prevent water column from breaking.
Phloem structure.
Mainly made from sieve tube elements and companion cells. Also have parenchyma for storage and strength.
Mature cells are alive (opposite to xylem).
Sieve plates have sieve pores: to allow continuous movement.
Cellulose cell wall: strengthens wall to withstand hydrostatic pressure.
No nucleus, vacuole in mature cells: maximises space for translocation.
Thin cytoplasm: reduces friction to help movement
Companion cells.
Nucleus and other organelles present: provide metabolic support to sieve tube elements.
Transport proteins to plasma membrane: move substances in and out of sieve tube elements.
Lots of mitochondria: provide ATP for transport.
Plasmodesmata: Link to sieve tube elements to allow movement of compound.
