I. Water Movements in the Plant

the factors that affect water movement up the stem

- negative pressure in leaves
- gravity
- matrix effects in the soil

How do water columns stay together

- By cohesion (hydrogen bonds among molecules)
- Adhesion (water molecules are attracted to inner walls of tracheary elements)

how may the factors of water movement in the stem vary & how does variation affect water column movement and its integrity?

1: adequate transpiration + adequate water in soil + short plant = the water will continue moving upward

2: high humidity -> slower transpiration which means less negative pressure = the water movement will be slow or unable to move upward

3: very low humidity -> high transpiration -> very low negative pressure + little water in ground (increases matrix effect) -= can cause column to stop moving or break

4: very tall plant + long water column w/ high mass + significant gravity effect = may slow or stop upward movement

what is the anatomy of leaves?

- upper and lower epidermis
- stomata in bottom epidermis
- ground tissue: mesophyll

what's the primary function of the mesophyll in leaves?

photosynthesis

what are the two tissues found in the mesophyll (in leaves)?

- palisade parenchyma (on top)

- spongy parenchyma (on bottom)

what are the types of movement in and outside of the leaf?

- water moves out of the xylem
- layers of water surround cells
- Ions pumped into mesophyll cells
- Water evaporates; diffuses out via transpiration

how is negative pressure in leaves generated?

- thick layers of water surround cells

- Water evaporates; diffuses out

- water layers become thinner

- increased liquid surface which increases the surface --> That creates tension which causes water to be pulled from the xylem to replenish water and reduce surface tension.

My own further explanation: The water being pulled from the xylem is to replenish water that was lost during transpiration.

what's the structure of guard cells?

- attached at the ends
- thicker inner wall called ventral
- cellulose microfibrils wrapped around cells
- cell walls of guard cells can stretch when pressured (except inner wall due to it being thicker / lesser flexibility)

draw a guard cell

Physically draw it!

How do guard cells function to open and close stomata?

HINT: There's a 4 step process.

1. Night (most plants)
- Cells are depressurized
- stoma closed (less curving)


2. Sunrise
- Cells detect sunlight
- k+ ions pump in, osmosis occurs (brings water in concentration gradient), cell pressurized; cells bred/spread which opens the stoma

3. During day
- k+ slowly leaks out
- Sucrose content increases (made from breakdown of starch in cell)
- Cells remain pressurized and curved

4. Sunset
- k+ already low
- Sucrose disposed of somehow
- Cells depressurized, stoma closes