Different plants are different, aquatic (>90%) is greater than mesophytic, greater than terrestrial, greater than xerophytic (as low as 6%)

Plants of the same species live in different environments and have different water contents.

Different organs and tissues of the same plant have different water contents

The same organ has different water contents in different growth stages

Parts with strong life activities and high water content

Definition: Water molecules are polar due to uneven charge distribution. When H2O encounters charged ions or molecules, due to the action of charges, the water molecules will be oriented and arranged around the ions or molecules to form a water film.

Function: Stabilize the intracellular environment

Influencing factors: The smaller the ionic radius, the higher the number of charges, and the stronger the hydration ability

When it is higher: the plant protoplasts are in a sol state, the plant metabolism is active, the growth is fast, and the stress resistance is poor.

When it is low: the plant protoplasm is in a gel state, with low metabolic activity, slow growth and strong stress resistance.

The main mode of long-distance transport, concentration has a higher transport rate than diffusion and requires energy

How water moves within the cell membrane system

aquaporin

Definition: The phenomenon of diffusion of solute molecules through a semipermeable membrane, moving according to the water potential gradient

Thermodynamic definition: When the temperature, pressure and the amount of other substances are constant, the free energy of 1 mol of water in the system

In a system at the same temperature and pressure, the difference between the chemical formula of partial molar volume of water in the system and the chemical potential of pure water at the same temperature and pressure

Osmotic potential: related to solute concentration

Pressure potential: It is related to the state of cell wall separation. It is a positive value under normal circumstances. When the protoplast loses water rapidly during violent transpiration, it is a negative value when the cell wall and membrane are not separated. It is 0 when the cell wall is separated.

Lining potential: 0 for cells with a large central vacuole. Air-dried seeds and meristematic cells without a large central vacuole have a very low lining potential.

The cell's vacuole solution, protoplasm layer, and extracellular fluid constitute an osmotic system, which flows from high water potential to low water potential.

Under normal conditions: the pressure potential is greater than 0, under complete tension: the water potential is 0, initial mass wall separation: the pressure potential is equal to 0, severe transpiration: the pressure potential is less than 0

Swelling and water absorption: before the formation of vacuoles, it mainly relies on the lining potential; metabolic water absorption: using the energy of cellular respiration to allow water to enter the cells

Apoplast: A whole body composed of non-living substances other than the protoplasm, including cell walls, intercellular spaces, intercellular layers, xylem vessels and other non-living substances interconnected with each other. It does not cross membranes and moves quickly.

Symtoplast: The protoplasts in living cells are formed into a continuous whole through plasmodesmata. Because they need to cross the membrane, the resistance to water movement is large.

Production mechanism: Osmosis theory, metabolism theory, endothelial jump theory

Key point: temporarily withered, permanently withered