topic 12 plant exchange and transport

water

• 90-95% of the weight of soft tissues

• Present in cell walls, cytoplasm, organelles, cells sap, intracellular spaces and vascular bundles • Water as polar molecule

• Excellent solvent

• Forms hydrogen bond

• High heat storage capacity

• Transmits visible light and absorbs long wave radiation

turgor pressure

• a force within the cell that pushes the plasma membrane against the cell wall

• growth water

• metabolic water

• transpiration water

• transport water

• excretion and secretion

Physiological Functions

EXTRAFASCICULAR

• Description: This type of water conduction involves short-distance movement of water.

• Location/Mechanism:

  • Within the cell itself (cellular transport).

  • Between neighboring cells and tissues (radial transport).

  • Diffusion and osmosis along the symplast (interconnection of cells through plasmodesmata).

FASCICULAR

• Description: This type of water conduction involves long-distance, vertical movement of water.

• Location/Mechanism:

  • Occurs only along the longitudinal axis via vascular bundles.

  • Example: Bulk Flow Transport via the Xylem.

Cohesion tension hypothesis

• explains how water moves from the roots to the leaves in tall plants/trees.

  Water moves

Transpiration

• Water evaporates from the leaves through tiny pores called stomata.

• This evaporation creates a pulling force that drags water upward.

Cohesion

• Water molecules stick to each other (like tiny magnets).

• This makes a continuous column of water inside the xylem.

Adhesion

Water molecules stick to the walls of the xylem tubes, helping prevent the water from falling back down.

Apoplastic pathway

• Water moves around the cells, not through them.

• It flows through the cell walls and spaces between cells.

• This path is fast because water doesn’t have to go inside the cells.

Symplastic pathway

• Water moves inside the cells.

• It travels through the cytoplasm and passes from cell to cell through tiny connections called plasmodesmata.

• This path is slower because it must cross cell membranes.

Casparian strip

waterproof band in the root’s endodermis that controls what enters the plant’s vascular system.