3/23/11

Chapter 29 Continued

• Transpiration works greatest on sunny, warm, dry and windy days.
• Maple tree can lose more than 200 L of water per hour (that's a lot)!
• Leaf stomata can help plants adjust to transpiration rates by changing shape.
• Open during the day, closed during the night (saves water).
• The stomata may close during the day if the plant is losing water too fast.

The Transport of Sugars:

• Phloem saps move in various directions inside of a plant.
• Phloem moves sugar from a leaf to a root of fruit.
• They move through a pressure-flow mechanism.
• Pressure-flow mechanism is the building of water pressure at source end of phloem tube, and the reduction of water pressure at the sink end causes water to flow from the source (leaf) to sink (root or fruit), carrying sugar with it.

Plant Hormones:

• Plant hormones control the growth & development of a plant.
• It affects division, elongation, & differentiation in cells.
• Auxin - Produced by apical meristem, stimulates growth of the shoot -- causes the cell to elongate.
• Cells elongate on the darker side of the stem, causing the stem to bend on opposite sides.
• Requires certain concentrations: too much causes inhibition of stem elongation.
• Usually inhibits roots.
• Ethylene - A gas that triggers aging responses - fruit ripening, dropping of leaves.
• Why does "one bad apple spoil the whole bunch?" Because one causes all to spoil, it spreads out.
• Cytokinins - Regulates growth, promotes cell division in roots, embryos, and fruits. 
• Stimulates growth of axillary buds (makes it more bushy).
• Gibberellins - Stimulates cell elongation & cell division in stems.
• Can influence fruit development.
• Abscisic Acid - Slows growth.
• During droughts, causes stomata to close when wilted, preventing further water loss.

Photoperiods:

• Enviornment that plants use to detect the time of the year; Lengths of day & night.
• 2 Groups:
• Long-night Plants - chrysanthemum & poinsettias - flower in late summer, fall, or winter, when night lenghtens (Short-day).
• Short-night Plants - lettuce, iris, cereal grains, flower in late spring or early summer, when nights are brieft (Long-day).
• We are currently transitioning into short-nights.
• Some plants aren't affected by photoperiods -- dandelions.

HW: EC UP. 63-64, Study!

Next Scribe: Sonali P.