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Questions and Answers
What percentage of fresh weight does water constitute in herbaceous plants?
Water is absorbed from the soil through root hair cells.
True
What is the main process by which water moves from cell to cell in plants?
Osmosis
What is water's role during photosynthesis?
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What theory explains the upward movement of water in plants?
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What is the function of the Casparian Strip in plants?
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Water loss from cells can occur when the solute concentration of the membrane is high, such as in _____ water.
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What causes water stress in plants?
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Match the following terms with their definitions:
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Study Notes
Water in Plants
- Makes up 80-90% of fresh weight in herbaceous plants and 50% in woody plants
- Acts as a solvent for transporting gases, minerals, and solutes
- Important reactant in photosynthesis and the hydrolysis of starch to sugar
- Provides turgidity to growing cells, maintaining their form and structure
- Provides mechanical support and rigidity to non-lignified plant cells
- Essential for cell elongation during growth
- An important metabolic end product of respiration
Transpiration
- Loss of water from plants in the form of vapor
Water Movement in Plants
- Water is absorbed from the soil through root hair cells
- Water moves from root cell to root cell via osmosis until it reaches the xylem
- Transported through xylem vessels up the stem to the leaves
- Evaporates from the leaves (transpiration)
Water Potential
- Water moves from outside into the cell through a semi-permeable membrane
- Difference in osmotic pressure drives the movement of water into cells
- Water flows from high to low water potential
- When separated by a semi-permeable membrane, water moves from high osmotic pressure to low osmotic pressure
Transport in Plants: Movement Up the Xylem
Root Pressure
- Movement of water upwards through the plant body is mainly due to root pressure
- Osmotic mechanisms created by the active absorption of salt by the roots drive the movement of water up the stem
Cohesion-Tension Theory
- Cohesion and tension phenomena enable water to move into the root and up the plant from the soil
- An unbroken column of water exists between the soil water and the water of the leaf tissue
Summary of Xylem Transport
- Root pressure is caused by the influx of water into the roots
- Water adheres to the inside of the xylem
- Water is cohesive, and forms a column which is pulled up the xylem as a result of transpiration
Active & Passive Transport
Passive Transport
- Movement occurs along with water
- Occurs through the apoplast (non-living) compartment – cell walls & xylem vessels
Active Transport
- Movement occurs against the gradient of mineral concentration
- Occurs in the symplast
- Uses energy and a proton pump
Casparian Strip
- An impermeable waxy layer between the cells of the endodermis, preventing water and solutes from entering the xylem
- Water and solutes must pass through the cytoplasm of adjacent cells to enter the xylem
How the Casparian Strip Filters Solutes
- The plasmalemma is selectively permeable, allowing only permitted molecules inside
- Solute molecules cannot pass through the casparian strip
- Solute molecules must detour through the symplast to pass through the casparian strip
Water Loss
- Cells lose water when the solute concentration of the membrane is high (e.g., salty water)
- Cells also lose water via evaporation
- Cells shrink, membranes fold, and organelles become distorted (out of shape)
Water Stress in Plants
- Water deficit or water stress refers to situations where cells and tissues are less than fully turgid
- Causes of water stress:
- Drought
- Salinity
- High temperatures
- Flooding
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Description
Explore the crucial role of water in plants, focusing on its percentage in different types of plants, its functions in photosynthesis, and the importance of water movement through transpiration. Understand how water potential influences the absorption and transport of water in plant cells, from roots to leaves.
