Chapter 29 The Working Plant
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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.
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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
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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
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Plants then convert nitrate back to ammonium to make proteins/organics.
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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-cohesiontension mechanism