Chapter 29 - The Working Plant

• Sap -watery solutions moving through vascular system.

• In xylem it carries water and nutrients from roots to leaves and stems.

• In phloem it transports sugar already made, from leaves to other parts of plants.

• Sap is made in Spring by converting starch that was made the previous summer into sugars.

• It takes 40 liters of maple tree sap to produce 1 liter of maple syrup.

• Plants get CO2 from air (through stomata), minerals and H2O from soil,(through root hairs) and O2 from soil.(through stomata).

• A plant releases more O2 from photosynthesis than it consumes by respiration

• Plant nutrition: all minerals that enter a plant root are dissolved in water

• Go through epidermis & cortex of root; plasma membrane of root cells (selectively permeable); to xylem.

• Mycorrhiza (fungi) help in absorption

• Macronutrients-need in large amounts: carbon, oxygen, hydrogen, nitrogen, sulfur, phosphorus, calcium, potassium, and magnesium

• Micronutrients - need in extremely small amounts: iron, chlorine, copper, manganese, zinc, molybdenum, boron, nickel. Mainly components of enzymes.

• See p. 641-642 for uses of all nutrients

• Deficiencies - quality of soil affects our own nutrition - Corn on left grown in nitrogen rich soil; on right in nitrogen poor soil

• Bacteria help with nitrogen nutrition: 3 types of soil bacteria:

1. Nitrogen-fixing bacteria - converts N2 in air to ammonium

2. Ammonifying bacteria - adds ammonium by decomposing organic matter

3. Nitrifying bacteria - converts soil ammonium to nitrate - plants take this up

• Plants then convert nitrate back to ammonium to make proteins/organics.

• Legumes (soybean, clover, peas, alfalfa) have root nodules that contain nitrogen-fixing bacteria called Rhizobium.

• Symbiotic relationship - bacteria have a place to live and receive carbohydrates/organics from plant. Plants get ammonium ions released into soil.

• Why do some farmers rotate their crops? Ex: One year corn, the next year soybeans? ___________________________________

The Transport of Water:

• Pulled up plant through transpiration (loss of water vapor from plant,) through the stomata

• Cohesion = water molecules stick together, are pulled up together

• Adhesion = water molecules adhere to cellulose molecules in walls of xylem cells

• A continuous string of water molecules move up tube

• Molecules of water break off from the top of the string as they leave the leaf. String is kept tense and pulled upward as long as transpiration continues.

• No energy expenditure by plant

• Called: Transpiration-cohesion-tension mechanism