Mass Transport In Plants Flashcards
1
Q
how is the xylem tissue adapted for its function?
A
- long cells with no end walls = continuous water columns
- no cytoplasm, organelles = no obstruction of flow, easier water flow
- lignin = provides support and withstands tension
- pits in walls = lateral movement, get around blocked vessels
2
Q
what is the function of the xylem?
A
transports water absorbed by the root hairs up the plant
3
Q
what is transpiration?
A
caused by the evaporation of water from the leaves
- transpiration stream causes water through xylem
4
Q
what are the factors affecting the transpiration rate?
A
- increased light = more stomata open, increases area for water to leave leaf
- increased temperature = increased kinetic energy of water molecules, increasing movement of water down the water potential gradient
- decreased humidity = lack of water vapour in air around leaf, increasing water potential gradient
- increased wind strength = removes water molecules around stomata, increases water potential gradient
5
Q
what is the cohesion-tension theory?
A
- water lost from the leaf sue to transpiration from the mesophyll of the leaves
- lowers water potential of mesophyll
- water is pulled up the xylem, due to the negative pressure in the leaf due to water leaving = tension
- water molecules cohere due to hydrogen bonds
- this forms a continuous water column = transpiration pull
- adhesion of water molecules to walls of xylem, furthered by positive root pressure generated by water moving into the roots from the soil by osmosis
6
Q
what is the phloem?
A
tissue that transports biological molecules
7
Q
what are sieve cells?
A
- nor organel;es
- very little cytoplasm
- large scale
- thick walls
- large vacuole
= so more flow, thick, strong walls to resist pressure
8
Q
what are companion cells?
A
w
9
Q
what is the mass flow theory?
A
- transfer of sucrose into sieve elements from the photosynthesing tissue
- mass flow of sucrose through sieve tube elements
- transfoer of sucros from the sieve tubes elemts into storage or other sinks
10
Q
what is the top of the phloem called?
A
source end
11
Q
what is the end of the phloem called?
A
sink end
12
Q
how is sugar transported in plant?
A
- at source, sucrose is actively transported into the phloem, sieve tube by the companion cells
- lowers water potential in the phloem and water enters by osmosis
- this produces a high hydrostatic pressure
- mass flow transports towards sink takes place
- at the sink sugars are the removed, unloaded
