B3.2 Transport in plants Flashcards
What is xylem and what’s it function?
vascular tissue in plants responsible for water transport from roots to shoots
How xylem pushes the water up?
when water evaporates, then due to cohesive forces it pulls the water molecules that stay behind and adhesive forces between water molecules and xylem wall
What is cohesion and adhesion?
cohesin - attraction between two water molecules
adhesion - attraction between molecules and surface
What are the adaptations of xylem?
- dead, hollow cells
- lignin
- pits
What’s the function of dead, hollow cells in xylem?
maintaining continuous water column
What is lignin and what is it’s function?
ring polysaccharide that waterproofs the xylem and prevents collapse
What are pits and what is their function?
areas with no lignin, water can pass in and out the xylem
What is a vascular bundle?
in transverse-section: xylem and phloem
How to recognize xylem and phloem from transverse-section image?
xylem is closer to the inside, phloem is closer to the outside
What is cortex and what is it’s function?
between vascular bundles and epidermis, provides support and maintain shape
What are the differences in roots and stem transverse-section?
Xylem: roots: middle, stem: in vascular bundle
Phloem: roots: surrounding phloem, stem: in vascular bundle
Epidermis: roots: has hairs, stem: doesn’t
When transpiration may stop (3)?
- air is humid
- stomata are close
- plant lost its leaves
How plants create a root pressure in xylem?
it is generated by active transport of mineral ions from the soil into the root which causes high solute concentration and move water inside to balance it out
Why plants create a root pressure?
when transpiration is insufficient to transport water through the xylem
How transpiration is initiated?
when water evaporates from stomata and water moves through the plant
What’s the function of phloem?
it transports carbon compunds from source to sink
What’s the source and sink for phloem?
source: where carbon compounds are made (leaf)
sink: where carbon compounds are stored/used (root, shoot)
What’s translocation?
movement of carbon compounds through the phloem
What is a sieve tube?
the tube part of the phloem made of sieve tube elements
What are sieve plates?
structures with holes that separate sieve tube elements
What’s the function of sieve plates?
so the fluid of water and compounds (sap) can flow
What are the adaptations of sieve tube elements (in terms of organelle structure)?
- no nucleus or ribosomes
- few mitochondria
- limited cytoplasm
What’s the reason behind sieve tube elements structural adaptation?
to create more space for transport of nutrients
What are companion cells and what are their functions?
cells in phloem that load and unload nutrients into or from phloem
