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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 NO3d. 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