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Questions and Answers
Hydrogen bonds provide a continuous intermolecular ______ between the water molecules from the leaf to the root.
Hydrogen bonds provide a continuous intermolecular ______ between the water molecules from the leaf to the root.
attraction
The water column in the xylem lumen is driven out of a region with a higher ______ potential, i.e. from the root and the stem, to a region with a lower ______ potential.
The water column in the xylem lumen is driven out of a region with a higher ______ potential, i.e. from the root and the stem, to a region with a lower ______ potential.
water
The way in which water from soil enters roots, particularly to the root ______, is called "mechanism of water absorption".
The way in which water from soil enters roots, particularly to the root ______, is called "mechanism of water absorption".
xylem
Active absorption refers to the absorption of water by roots with the help of ______, generated by the root respiration.
Active absorption refers to the absorption of water by roots with the help of ______, generated by the root respiration.
Only ______% of total water absorption is carried out in active absorption process.
Only ______% of total water absorption is carried out in active absorption process.
In active absorption, energy is ______.
In active absorption, energy is ______.
In passive absorption, ______ energy is utilized.
In passive absorption, ______ energy is utilized.
Most volume of water entering plants is by means of ______ absorption.
Most volume of water entering plants is by means of ______ absorption.
The force for absorption of water is created at the ______ end.
The force for absorption of water is created at the ______ end.
As ______ proceeds, simultaneously water absorption also takes place to compensate the water loss from leaf end.
As ______ proceeds, simultaneously water absorption also takes place to compensate the water loss from leaf end.
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Study Notes
Functions of Water in Plants
- Medium for biochemical reactions in cells, as many enzymes are dissolved in cell water
- Provides structural support through turgor pressure, giving many cells their shape
- Enables cell enlargement by providing the physical force needed to expand cells during growth
- Transports solutes between organs via xylem and phloem vessels
- Cools leaves during transpiration through evaporation
Diffusion
- Movement of molecules from a region of higher concentration to a region of lower concentration
- Occurs in gases, liquids, and solutes
- Factors influencing rate of diffusion:
- Temperature: increase in temperature leads to increase in rate of diffusion
- Pressure: rate of diffusion increases with increase in pressure
- Size and mass of diffusing substance: diffusion of solid is inversely proportional to size and mass of molecules and ions
- Density of diffusing substance: rate of diffusion is inversely proportional to density of the diffusion substance
- Density of the medium: rate of diffusion is slower if the medium is concentrated
Permeability
- Degree of diffusion of gases, liquids, and dissolved substances through a membrane
- Types of membranes based on permeability:
- Permeable membrane: allows free passage of solvent (water) and most dissolved substances
- Impermeable membrane: prevents entry of water, dissolved substances, and gases
- Semi-permeable membrane: permits movement of solvent molecules only
- Selectively or differentially permeable membrane: allows selective passage of solutes with solvent
Osmosis
- Special type of diffusion of a liquid through a semi-permeable membrane
- Solvent moves from a place of higher diffusion pressure to a place of lower diffusion pressure
- Importance in plants:
- Absorption of water by plants
- Cell-to-cell movement of water throughout the plant body
- Maintenance of rigidity of plant organs
- Growth of plant parts
- Resistance to drought and frost
- Movement of plants and plant parts
- Opening and closing of stomata
Plasmolysis
- Shrinkage of the protoplast of a living cell from its cell wall due to exosmosis under the influence of a hypertonic solution
Water Absorption in Plants
- Water is absorbed along with mineral solutes by root hairs
- Water moves deeper into root layers through two distinct pathways:
- Apoplast pathway: movement of water through intercellular spaces and cell walls
- Symplast pathway: movement of water through cytoplasmic strands and cell membranes
Ascension of Water Through Plant Vascular System
- Water flows from roots to shoot of the plant through xylem
- Cohesion-tension theory: hydrogen bonds provide continuous intermolecular attraction between water molecules from leaf to root
Mechanism of Water Absorption
- Active absorption: absorption of water by roots with the help of ATP, generated by root respiration
- Passive absorption: absorption of water without utilization of metabolic energy, occurs in rapidly transpiring plants during daytime
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