Water Loss and Water Acquisition Flashcards
Where does the majority of water loss occur from?
Stomatal transpiration
Why are primitive plants restricted to wet environments?
Moss gametophytes have no true cuticle; liverworts’ pores tend to remain open, don’t have much control over water loss.
Why does transpiration occur?
Vapor pressure difference between inside of lead and surrounding atmosphere
How do plants control water loss?
Waxy cuticle with pores whose opening can be controlled.
What controls the size of the stomatal aperture?
Guard cells
How does transpiration occur?
Water is lost by evaporation from the substomatal space to the atmosphere via stomata
What determines the rate of transpiration?
Vapor pressure difference
What are radial micelles? What do they do?
Cellulose thickening of guard cell primary wall, restricts expansion of guard cells, allowing them to lengthen but not thicken
What happens when guard cells lengthen?
Stomatal pore opens
Explain the process of stomatal opening using potassium.
- K+ taken up into guard cell vacuoles from surrounding cells
- Water potential lowers, water drawn into guard cells
- Pressure increases inside guard cells, lengthen and separate to produce stomatal aperture
Explain the process of stomatal closing using potassium.
- K+ ions leak out
- Water leaves along potential gradient, guard cells lose turgor
- Guard cells shorten, micelles cause cells to close pore
What factors affect stomatal opening?
Light stimulates opening in many species
Lowering of CO2 due to photosynthesis
Overheating
What factors affecting stomatal closing?
Water loss increases ABA, which promotes K+ leaving guard cells
What is the leaf boundary layer?
Water vapor forms a boundary layer over leaf surface
What is the purpose of the leaf boundary layer?
Reduces vapor pressure difference between sub-stomatal space and surrounding atmosphere, lessening water loss without reducing CO2 uptake
Why does air movement affect transpiration?
Leaf boundary layer is disrupted by wind, even gentle movement
How do pollutants affect transpiration?
SO2 can cause stomata to remain open
Small dust particles can block pores
How does temperature affect transpiration?
Increase in leaf temperature increase vpd between inside and outside
What is the first step of the Calvin cycle?
C3 fixation. C from CO2 added to the 5C RuBP
What does the first step of the Calvin cycle?
2 3C (3-phosphoglycerate) molecules
What is the principle output of the Calvin cycle?
G3P (glyceraldehyde 3 phosphate)