AP Biology, Chapter 37
Plant Nutrition 

SUMMARY
INTRODUCTION

NUTRITIONAL REQUIREMENTS OF PLANTS
	The chemical composition of plants provides clues to nutritional requirements
		1. Describe the chemical composition of plants, including the: a) percent of wet weight 
		as water, b) percent of dry weight as organic substances, and c) percent of dry weight as 
		inorganic minerals.
			a. 80-85% water
			b. 95% of dry weight is organic
			c. 5% of dry weight is inorganic 
	Plants require nine macronutrients and at least eight micronutrient
		2. Explain how hydroponic culture is used to determine which minerals are essential 
		nutrients.
			a. Hydroponics allows complete control over the chemical solution
			b. Very exactly defined solutions will keep plants healthy
			c. Leaving out a specific nutrient gives very specific symptoms
		3. Distinguish between macronutrient and micronutrient.
			a. Macro: required in large amounts; CHON, S, P, K, Ca, Mg
			b. Micro: small amounts; Cl, Fe, B, Mn, Zn, Cu, Mo, Ni
	The symptoms of a mineral deficiency depend on the function and mobility of the 
	element
		4. Explain how a nutrient's role and mobility determine the symptoms of a mineral 
		deficiency.
			a. Role
				i. Symptoms show in organ that uses that mineral the most
				ii. Mg is part of chlorophyll, Mg deficiency shows mostly in leaves
			b. Mobility
				i. Deficiencies of mobile nutrients show in older parts
				ii. Deficiencies of less mobile nutrients show in younger parts

THE ROLE OF SOIL IN PLANT NUTRITION
	Soil characteristics are key environmental factors in terrestrial ecosystems
		5. Describe the composition of loams and explain why they are the most fertile soils
			a. Soils are defined by proportions of sand, silt, clay
			b. Loams have about equal amounts
			c. Reasons why they are the most fertile
				i. Clay has a large surface area for retaining water and minerals
				ii. Coarse particles provide air spaces for gas exchange and drainage
		6. Explain how the presence of clay in soil helps prevent the leaching of mineral cations.
			a. Clay particles have a negative surface
			b. Attract positive ions
		7. Define cation exchange, explain why it is necessary for plant nutrition, and describe 
		how plants can stimulate the process.
			a. Protons are pumped out of the plant
			b. Positive protons displace positive ions bound to clay
	Soil conservation is one step toward sustainable agriculture
		8. Explain why soil management is necessary in agricultural systems but not in natural 
		ecosystems such as forests and grasslands. Describe several examples of human 
		mismanagement disasters.
			a. Need for soil management
				i. Natural ecosystems:  mineral nutrients recycled by decomposition, soil 
				covered
				ii. Agriculture: mineral nutrients removed at harvest, soil stirred and 
				exposed
			b. Mismanagement disasters
				i. Overgrazing, wheat moncropping (+drought) Dust Bowl
				ii. Soil exhaustion
		9. List the three mineral elements that are most commonly deficient in farm soils.
			a. N P K
		10. Explain how soil pH determines the effectiveness of fertilizers and a plant's ability to 
		absorb specific mineral nutrients.
			a. pH may prevent cation exchange
			b. Altered pH may affect chemical form of a nutrient
			c. Altered form may not be absorbable
		11. Describe problems resulting from farm irrigation in arid regions and list several 
		current approaches to solving these problems.
			a. Problems
				i. Repeated irrigation with evaporation leads to the build up of salts
				ii. Taking water from rivers kills them
				iii. Aquifers are being depleted
			b. Approaches
				i. Drip irrigation avoids some evaporation
				ii. Salt-tolerant varieties of crops

THE SPECIAL CASE OF NITROGEN AS A PLANT NUTRIENT
	Introduction
	The metabolism of soil bacteria makes nitrogen available to plants
		12. Define nitrogen fixation and write the overall equation representing the conversion of 
		gaseous nitrogen to ammonia.
			a. Nitrogen fixation is the conversion of atmospheric nitrogen into ammonia
			b. N2 + 8e- + 8H+ 16ATP  2NH3 + H2 + 16ADP + 16Pi
		13. Describe the important role of nitrogen-fixing bacteria.
			a. Convert N2 into NH3
		14. Recall the forms of nitrogen that plants can absorb and describe how they are used 
		by plants.
			a. Can absorb NH4+ and NO3-
			d. Nitrate is converted into ammonia before incorporation into amino acids
	Improving the protein yield of crops is a major goal of agricultural research

NUTRITIONAL ADAPTATIONS: SYMBIOSIS OF PLANTS AND SOIL MICROBES
	Introduction
	Symbiotic nitrogen fixation results from intricate interactions between roots and 
	bacteria
		15. Beginning with free-living rhizobial bacteria, describe the development of a root 
		nodule.
			a. Roots emit chemoattractant; bacteria signal for development of infection 
			thread
			b. Bacteria in vesicles bud from invaginated infection thread
			c. Dividing cells of the pericycle and cortex surround cells containing bacteria
			d. Developing nodule sends new xylem/phloem into stele 
		16. Explain how a legume species recognizes a certain species of Rhizobium. Explain how 
		that encounter leads to the development of a nodule.
			a. Specific flavenoid released by root activates Rhizobium Nod operon
			b. Nod enzymes make nod factors inducing the infection thread
	Mycorrhizae are symbiotic associations of roots and fungi that enhance plant 
	nutrition
		17. Define mycorrhizae and explain why they are considered examples of mutualism. 
		Explain how mycorrhizae enhance plant nutrition.
			a. Mycorrhizae are mutualistic combinations of fungi on plant roots
			b. Fungi increases root surface area and absorbs minerals
			c. Plants protect and provide sugar
		18. Explain the significance of mycorrhizae in the evolution of terrestrial plants.
			a. Primitive plants may have needed help gathering nutrients
	Mycorrhizae and root nodules may have an evolutionary relationship
		19. Discuss the relationships between root nodule formation and mycorrhizae 
		development.
			a. Both activate nodulin genes in the host
			b. Share components of a signal-transduction pathway

NUTRITIONAL ADAPTATIONS: PARASITISM AND PREDATION BY PLANTS
	Introduction
		20. Describe the modifications for nutrition that have evolved among plants, including 
		parasitic and carnivorous plants.
			a. Parasitic
				i. Mistletoe is green but supplements using penetrating haustoria
				ii. Dodder taps host vascular tissue
				iii. Indian pipe taps mycorrhizae
			b. Carnivorous
				i. Photosynthetic
				ii. Obtain minerals by killing and digesting bugs
	Parasitic plants extract nutrients from other plants
	Carnivorous plants supplement their mineral nutrition by digesting animals