Biology: Transpiration Flashcards
What vessel is involved in transpiration?
xylem
Why do plants need water?
-photosynthesis -mineral transport -maintain turgidity -regulate temperature
Where is water absorbed, by what process?
absorbed from soil via osmosis
Where are mineral ions absorbed, by what process?
from the soil via active transport
Give two examples of mineral ions absorbed by plants and their importance
-nitrates: component in producing DNA, amino acids and chlorophyll important to growth
-phosphates: component in producing DNA and ATP
Outline the structure of a xylem vessel
-elongated tubes from dead cells -no end walls (hollow) -thick walls of lignin -pits in cell wall
What is the function of the xylem vessel?
to transport water and mineral ions up a plant and to provide support
Why are hollow tubes/no end walls an important feature in xylem?
uninterrupted tube allowing continuous flow of water and mineral ions
Why is thick walls of lignin an important feature of the xylem?
-strong and prevents collapse -waterproof to prevent water from adhering too much
How are pits an important feature of the xylem system cell wall?
-allows water to leave vessels -allows water to pass between vessels
Which factors affect the rate of transpiration?
-light intensity -temperature -humidity -wind
What is transpiration?
loss of water from stomata through evaporation
How does an increase in light intensity affect rate of transpiration?
-more stomata open -need for CO2 in photosynthesis -large surface area for evaporation
How does the rate of transpiration change with an increase in temperature?
-more kinetic energy -greater evaporation
How does an increase in humidity affect the rate of transpiration?
-more water vapour in air -reduces water potential gradient
How does an increase in wind affect the rate of transpiration?
-more wind removes humidity -water potential gradient maintained
What does narrow xylem affect?
larger capillary impact therefore more adhesion
Outline the process of transpiration
step one:
water evaporates as vapour out of stomata
step two:
water from xylem lost through transpiration
more water pulled upwards to replenish supply
step three:
hydrogen bonding sticks water molecules
cohesion
continuous column of water
step four:
water molecules adhere to walls
helps continuous column pull upwards
step five:
as column up, tension created
xylem narrower
increases capillary impact
