Notes
• This is a short chapter - read it thoroughly.
• Pay attention (in all the chapters) to the “Concept Check” questions.
One approach to“What are plants made of?” • Mostly water (except
woody parts)• Otherwise, mostly
carbohydrate, including cellulose
• But also phospolipids, nucleic acids, proteins, chlorophyll, other enzymes, coenzymes and cofactors
What is essential?
• Drying and burning plants only takes you so far.
• Plants incorporate minerals selectively, but the “filter” is imperfect.– This can be useful: “attack of
the metal-eating plants”
• How then to determine what’s essential?
Macronutrients
• Carbon• Oxygen• Hydrogen• Nitrogen• Sulfur• Phosphorus• Potassium• Calcium• Magnesium
..and Micronutrients
• Chlorine• Iron• Boron• Manganese• Zinc• Copper• Molybdenum• Nickel
• Often act as or with catalysts
• Cofactors - metal ions that enable enzymes
• Needed in very small quantities– Example - Mo
• Soil Origins• Soil Horizons• Soil Composition
– Sediment texture- clays vs. sands. Loam. – humus
SOILS
Nitrogen Fixation and Root Nodules
• Nitrogen is a limiting nutrient for much plant growth
• Atmospheric Nitrogen (N2) is unavailable to plants
• Plants rely on bacteria to fix Nitrogen into ammonia (NH4) and nitrate (NO3
-)• Some of these bacteria form symbiotic
relationships, living in nodules in plant roots (especially in legumes - peas, beans etc)
Mycorrhizae
• Symbiosis between plant roots and fungal myceliae
• Increases plant absorption of minerals greatly
• The fungus gets sugar, other nutrients• Occurs in 90% of plant species• Fungal species are specific to plant
species