Water Balance in Plants
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Plants take in water through their...?
The continuous passage of water (and ions) through a plant from root to leaf is called the...?
Briefly describe the route water takes through a plant
- Water in soil enters root hairs by osmosis from a HWC to a LWC down a concentration gradient
- Water moves across the root cortex through cells, cell walls and intercellular spaces by osmosis from a HWC to a LWC down a concentration gradient
- Water enters the xylem by osmosis
- Transpiration pull causes continuous, thin, tense columns of water to be drawn up xylem in stem and into leaves. Water pulled up in very thin columns without breaking is due to cohesion and adhesion
- Root pressure helps move water up the plant
- Water moves into leaf cells by osmosis froma HWC to a LWC down a concentration gradient
- Water evaporates into air spaces of leaf
- Water evaporates out of leaf through stomata
What is a root hair?
It is an extension of an epidermal cell which has a large surface area to absorb more water from the surrounding soil
What other function can a root hair have?
It can provide anchorage for the plant
How does water move through a plant?
- Water moves:
- between cells
- across cell walls
- across cell membranes through the root cortex by osmosis
The force by which water is pushed up the stem by the roots is called...?
What is transpiration?
The process by which water is lost by evaporation from the aerial parts of a plant
Where does most transpiration occur in a plant?
What ions are needed for the formation of chlorophyll?
Mg and Fe
How do ions enter the plant?
By active transport only
What is the importance of the transpiration stream?
- Provides water for photosynthesis (photolysis)
- Water keeps cells turgid which gives a plant structure and support
- Cooling effect for the plant
- Involved in uptake and transport of mineral ions to cells
How can the rate of transpiration from a leaf be measured?
Using a potometer
As temperature rises the rate of transpiration...?
As humidity increases the rate of transpiration...?
As wind increases the rate of transpiration...?
As light intensity increases the rate of transpiration...?
What effect does air pollution have on transpiration?
Soot blocks the stomata thus reducing transpiration
What are stomata?
Tiny pores on the surfaces of leaves
What do guard cells do?
They change shape to open and close the stomata
Describe briefly how stomata open
- Water enters the flaccid guard cells and so they become turgid
- The thin outer parts of the guard cells stretch more than the thick inner parts
- The two guard cells bulge out and the thick inner walls become pulled apart, opening the stomata
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