CH9 transpiration Flashcards
1
Q
Stomata
A
- carbon dioxide move into leaf and oxygen moves out of leaf
- opened by guard cells
- water vapour moves out by diffusion
2
Q
Transpiration stream
A
- water enters root by osmosis and is transported up in xylem until reaches leaves
- evaporates from freely permeable cellulose cell wall
3
Q
How does transpiration stream work
A
- water molecules evaporate from surface of mesophyl cells into the air spaces in ;eaf and move out of stomata into surrounding air by diffusion
- loss of water from mesophyll lowers water potential of cell, so water moves into cell from adjacent cell by osmosis
- process repeated across leaf to xylem
- water molecules form bonds with carbohydrates in walls of narrow xylem vessels - cohesion and adhesion results in capillary action
- transpiration pull created as water drawn up xylem in continuous stream
- pull results in tension in xylem which helps move water across roots from soil
4
Q
Evidence for cohesion-tension theory
A
- when transpiration at highest, ttension in xylem is high and treee shrinks in diameter and vice versa
- if a xylem vessel is broken air is drawn into xylem rather than water leaking out
5
Q
Opening and closing of stomata
A
- when turgor is low, stomata close
- cellulose hoops prevent cell from swelling in width, so extend lengthways
- inner wall less flexible than outer wall so cells become bean shapes
6
Q
Factors affecting transpiration
A
- light
- temperature
- humidity
- air movement
- soil water availability
7
Q
Why does light affect transpiration
A
- increased light means increased photosynthesis
- leads to increased open stomata
- rate of water vapour diffusing out increases
8
Q
Why does humidity affect transpiration
A
- humidity is the amount of water vapour in the air
- high humidity will lower concentration gradient of air and leaf
- rate of diffusion will decrease
9
Q
Why does temperature affect transpiration
A
- increases kinetic energy
- increases amount of water the air can hold until it becomes saturated, decreasing the airs relative humidity
10
Q
Why does air movement affect transpiration
A
- increases concentration gradient
11
Q
Why does soil water availability affect transpiration
A
- amount of water available changes
