transport in plants Flashcards
Why do plants need a transport system?
to get water and minerals from the roots up to the rest of the plant;
to carry assimilates made at the leaves down through the plant
What is the role of collenchyma and sclerenchyma?
to provide mechanical strength and support plant
Where is sclerenchyma and collenchyma found?
in the vascular bundles
Direction of flow in phloem and xylem
xylem - up
phloem - up or down as needed
Describe the vascular bundle in the young root
Bundle in centre, xylem x shaped and phloem between arms of x shape
Where is the endodermis in the young root?
surrounds the vascular bundle and medulla
Where is the pericycle found?
Layer cells just inside the endodermis in young root
What is the pericycle?
layer meristem cells able to differentiate
Where are vascular bundles located in the stem?
Found around the outside of the stem
How are vascular bundles organised in the stem?
phloem on outside, xylem inside, cambium layer between them. sclerenchyma on outer edge of vascular bundle
Adaptations of xylem to its function (5)
aligned dead cells, continuous column;
thin tubes;
bordered pits;
lignification
no walls/contents to obstruct water
How is capillary action maintained in the xylem?
thin tubes, water column doesn’t break easily - adhesion
What are assimilates?
mainly sucrose and amino acids, dissolved in water to form sap, products of photosynthesis
Describe the structure of the phloem (3)
sieve tube elements elongated;
perforated sieve plates between them;
companion cells between tubes
What do companion cells do?
load assimilates into phloem
How are sieve tube elements adapted for mass flow?
no nucleus and little cytoplasm
How are companion cells adapted?
dense cytoplasm and large nucleus, many mitochondria to produce ATP for active processes
What are plasmodesmata?
gaps in cell wall connecting cells by their cytoplasm
Describe the apoplast pathway
- water enters cellulose cell wall by cohesive forces in water molecules
Describe the simplest pathway
- water moves through plasmodesmata and cells
- enters cytoplasm
- using osmosis
Describe the apoplast pathway
- water moves through molecules in cell wall
- by cohesive forces in water molecules
- does not enter cell
How does water move between water potential?
from area of high potential to low
What happens if plant cell placed in pure water/higher potential?
water moves in by osmosis until becomes turgid, cell wall prevents bursting, pressure potential between water and cell wall
What does turgid mean?
plant cell intake lots of water, swells and cell membrane exerts pressure on cell wall
