3.1.3 Transport in plants Flashcards
Why do multicellular plants need a transport system?
-Metabolic demands
-Size
-Surface area: volume ratio
What is the function of the xylem?
To carry water and dissolved minerals up the plant.
What material is found in the xylem cell walls?
Lignin.
What do the lignified cell walls of the xylem do?
Withstand the hydrostatic pressure so the vessels do not collpase.
Why is the fact that the xylem has no end plates a benefit?
This allows a mass flow of water and minerals in a continous column.
Are xylem cells alive or dead?
Dead
Why do xylem have pits in their wall?
These unlignified pits allow water and minerals to pass through into other vessels.
Which direction can the water and minerals in the xylem flow in?
Upwards.
State some physical properties of xylem vessels.
Lignified cell walls.
Dead cells.
Pits in walls.
No end plates.
What is the function of the phloem?
To transport organic compounds, particularly sucrose from the source (e.g the leaf) to the sink (e.g the roots).
Which direction can the assimilates in the phloem travel?
Both directions (up and down).
Name the two types of cell in the phloem?
Sieve cell elements companion cells.
What are some benefits of transpiration?
It cools the plant down. It causes the transpiration stream It delivers h20 and mineral ions.
Why must plants take in a constant supply of water?
Plants are constantly losing water via the stomata in the leaves and so they must constantly take water up their roots to compensate.
Define translocation.
Translocation is the movement of dissolved solutes through a plant e.g surcrose and amino acids.
Is the unloading of sucrose from the source to the phloem an active or passive process?
An active process.
Explain how sucrose is loaded into the phloem.
1) Hydrogen ions are actively pumped out of the source, via a transport protein into the sieve tube elements and this requires ATP.
2) The ions diffuse back into the companion cell via co-transport proteins via facilittated diffusion.
3) Sucrose moves from a high concentration in the companion cell to a low concentration in the sieve tube element by diffusion through the plasmodesmata. 4) As the sucrose concentration increases in the sieve tube elements, the water potential becomes more negative so water enters from the xylem through the pits in the walls. 5) As water moves into the phloem, the turgor pressure of the phloem increases while pushing the contents of the phloem vessel down the sieve elements.
6) The contents of the phloem vessel move down to the sink.
7) The sucrose concentration is low in the sink and high in the source and so sucrose diffuses into the sink.
8) The loss of assimilates in the phloem increases the water potential so water moves into cells by osmosis or back into the xylem.
Why do the hydrogen ions in the mass flow hypothesis need to be pumped back into the companion cells before they can enter the sieve tube elements with sucrose?
Co-transport proteins cannot just transport one thing therefore hydrogen ions need to move with sucrose.
Is the unloading of phloem into the sink an active or passive process?
A passive process.
What is a xerophyte?
Plants which are adapted to live in dry climates so have adaptation to prevent them from losing too much water.
Give an example of a xerophyte.
cacti -marram grass
What is a hydrophyte?
Plants which live in aqautic habitats and as they grow in water, they do not need adaptations to mimise water loss but instead they need to cope with low oxygen levels.
Give an example of a hydrophyte.
Water lillies
Name some adaptations of xerophytes.
Rolled leaves
Thick waxy cuticle
Stomata in Pits
Small number of Stomata Stomata surrounded by hairs.
Name some adaptations of hydrophytes.
Thin waxy cuticle
Large airspaces in leaves
Stomata on upper surface of leaves
Reduced veins on leaves.
Why does having rolled leaves reduce transpiration rate?
Rolled leaves create a pocket of air around the stomata and reduce exposure to air therefore the water potential gradient is reduced.
