Sophia Nguyen
Period 5
Chapter 37 Worksheet Soil and Plant Nutrition A.P. Biology
Ms. Turner
Nutritional Requirements of Plants
1. Describe the chemical composition of plants, including the

Carbohydrate (carbon, hydrogen, oxygen) – most abundant elements in dry weight of a
plant.

Nitrogen, sulfur, and phosphorus – relatively abundant in plants.

A plant’s nutritional needs are met with water, minerals, and sunlight.
a. percent of wet weight as water: 80-85%
b. percent of dry weight as organic substances: 95%
c. percent of dry weight as inorganic minerals: 5%
2. Explain how hydroponic culture is used to determine which minerals are essential nutrients.

In a hydroponic culture, the roots of a plant are bathed in certain nutrients only to find
out what is really necessary for plant growth.

Water is aerated to provide oxygen to the roots.

Very exactly defined solutions will keep plants healthy. (Ex: potassium)

Leaving out a specific nutrient gives very specific symptoms. Most common symptoms
are little growth and discolored leaves.
3. Distinguish between macronutrient and micronutrient.

Macronutrient: elements that are required by plants in relatively large amounts (9
TOTAL)
-
6 major ingredients of organic compounds: carbon, oxygen, hydrogen, nitrogen,
sulfur, phosphorus. Other 3: potassium, calcium, magnesium.

Micronutrient: elements that plants need in very small amounts – function mainly as
cofactors of enzymatic reactions – deficiency of any of these can weaken or kill a plant.
(8 TOTAL)
-
iron, chlorine, copper, manganese, zinc, molybdenum, boron, nickel.
4. Recall the nine macronutrients required by plants and describe their importance in normal
plant structure and metabolism.
Carbon, oxygen, hydrogen: major components of plant’s organic compounds.
Nitrogen: component of nucleic acids, proteins, hormones, and coenzymes.
Sulfur: component of proteins, enzymes.
Phosphorus: component of nucleic acids, phospholipids, ATP, several coenzymes.
Potassium: cofactor that functions in protein synthesis, major solute functioning in water
balance, operation of stomata.
Calcium: important information and stability of cell walls and in maintenance of membrane
structure and permeability; activates some enzymes; regulates many responses of cells to
stimuli.
Magnesium: component of chlorophyll activates many enzymes.
5. List eight micro nutrients required by plants and explain why plants need only minute
quantities of these elements.

iron, chlorine, copper, manganese, zinc, molybdenum, boron, nickel.

These elements function in plants mainly as cofactors of enzymatic reactions Any
deficiency can weaken or kill a plant
6. Explain how a nutrient's role and mobility determine the symptoms of a mineral deficiency.

Role: Symptoms show in organ that uses that mineral the most. Mg is part of
chlorophyll, Mg deficiency causes yellowing of leaves, or chlorosis.

Mobility:
-
Deficiencies of mobile nutrients (move freely) show in older parts first because
young, growing tissues have more “pulling” power than old tissues for nutrients
that are in short supply. Ex: Mg deficiency will show chlorosis in older leaves
first.
-
Deficiencies of less mobile nutrients (does not move freely) show in younger
parts because older tissues may have enough amounts of mineral, which they
are able to retain during periods of short supply. Ex: deficiency of iron will cause
yellowing of young leaves first.
The Role of Soil in Plant Nutrition
7. Explain how soil is formed.
Soil forms by weathering solid rock. Water that seeps into crevices and freezes in winter
fractures the rock, and acids dissolved in the water also help to break down the rock. One
organism are able to invade the rock, they accelerate the breakdown. Lichens, fungi, bacteria,
mosses, and the roots of vascular plants all secrete acids, and the expansion of roots growing in
fissures cracks rocks and pebbles. The eventual result of all this is topsoil, a mixture of particles
derived from rock, living organisms, and humus, decomposing organic material.
8. Explain what determines the texture of topsoil and list the type of soil particles from coarsest
to smallest.
Topsoil = mixture of decomposed rock of varying texture, living organisms and humus
(decomposing organic material)
Depends on particle size: 1. Coarse sand 2. Sand 3. Silt 4. Clay
9. Describe the composition of loams and explain why they are the most fertile soils.

Soils are defined by proportions of sand, silt, clay. Loams have about equal amounts.

Reasons why they are the most fertile:
-
Clay has a large surface area for retaining water and minerals.
-
Coarse particles provide air spaces for gas exchange and drainage (cellular
respiration).
10. Explain how humus contributes to the texture and composition of soil.

It prevents clay from packing together

Builds a crumbly soil that retains water but is porous for root aeration

Helps to act as a reservoir of mineral nutrients that are gradually returned to the soil as
microorganisms decompose the organic matter.
11. Explain why plants cannot extract all of the water in soil.

Some water adheres so tightly to hydrophilic soil particles that it cannot be extracted by
plants

This happens because the soil has electrically charged particles
12. Explain how the presence of clay in soil helps prevent the leaching of mineral cations.

Many minerals in soil (Ca2+, K+, Mg2+) adhere by electrical attraction to the negatively
charged surfaces of clay particles.

This clay prevents the draining away of mineral nutrients during heavy rain or
irrigation because finely divided particles provide so much surface area for binding
materials.

Nitrates, phosphates, and sulfates (negatively charged) do not bind and tend to drain
away.
13. Define cation exchange. Explain why it is necessary for plant nutrition, and describe how
plants can stimulate the process.

Cation exchange: Protons are pumped out of the plant - Positive protons displace
positive ions bound to clay.

This is stimulated by the roots themselves, which secrete H+ and compounds that form
acids in the soil solution.
14. 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.


Need for soil management:
-
Natural ecosystems: mineral nutrients recycled by decomposition, soil covered.
-
Agriculture: mineral nutrients removed at harvest, soil stirred and exposed.
Mismanagement disasters:
-
Overgrazing, wheat cropping (+drought), Dust Bowl.
-
Soil exhaustion (crop rotation).
15. List the three mineral elements that are most commonly deficient in farm soils.
Nitrogen Phosphorus Potassium - mainly because they are leached away in rains and
irrigation.
16. Explain how soil pH determines the effectiveness of fertilizers and a plant's ability to absorb
specific mineral nutrients.

pH may prevent cation exchange

Altered pH may affect chemical form of a nutrient

Altered form may not be absorbable (A change may make one essential element more
available while causing another to adhere to soil and is not available)

Ex: pH 8 – plant can absorb calcium, but iron is almost completely unavailable.

If soil = too alkaline -> add sulfate to lower pH.

If soil = too acidic -> add calcium carbonate or calcium hydroxide (liming).
17. Describe problems resulting from farm irrigation in arid regions and list several current
approaches to solving these problems.


Problems:
-
Huge drain of water resources.
-
Can gradually make soil salty and infertile.
-
Aquifers are being depleted.
Approaches:
-
Drip irrigation avoids some evaporation.
-
Salt-tolerant varieties of crops.
18. Describe precautions that can reduce wind and water erosion.

Rows of trees to divide fields can act as windbreaks

Terracing hillsides helps prevent water erosion

Planting alfalfa and wheat provides good ground cover and protection

Goal: Sustainable Agriculture – farming methods that won’t harm environment but still
profitable.
19. Explain how phytoremediation can help improve polluted environments.

Phytoremediation is a nondestructive biotechnology that harnesses some plants ability
to extract soil pollutants and concentrate them in portions of the plant that can be easily
removed for safe disposal.

Ex: alpine pennycress can accumulate zinc in its shoots; shoots can then be harvested
and the contaminating zinc removed.
The Special Case of Nitrogen as a Plant Nutrient
20. Define nitrogen fixation and write the overall equation representing the conversion of
gaseous nitrogen to ammonia.


Nitrogen fixation is the conversion of atmospheric nitrogen (N2) into ammonia (NH3)
N2 + 8e- + 8H+ 16ATP č 2NH3 + H2 + 16ADP + 16Pi
21. Describe the important role of nitrogen-fixing bacteria.
Convert N2 into NH3
22. Recall the forms of nitrogen that plants can absorb and describe how they are used by plants.

Can absorb NH4+ and NO3-

Nitrate is converted into ammonia before incorporation into amino acids

Most plant species export nitrogen from roots to shoots, via the xylem, in the form of
nitrate or organic compounds that have been synthesized in the roots.
23. Explain why it is important to improve the protein yield of crops.

Most common form of malnutrition in human is protein deficiency.

Majority of people in the world have a predominantly vegetarian diet and thus depend
mainly on plants for protein

But many plants have low protein content – proteins that are present may be deficient
in one or more of amino acids that humans need from their diet.
24. Describe the challenges of raising crops enriched with protein.

New varieties of corn, wheat, rice -> high demand for nitrogen, which usually supplied
in form of commercial fertilizer.

Production of ammonia and nitrate = very expensive in energy costs

A chemical factory making fertilizer consumes large quantities of fossil fuels
Nutritional Adaptations: Symbiosis of Plants and Soil Microbes
25. Beginning with free-living rhizoidal bacteria, describe the development of a root nodule.

Roots emit chemical signals that attract Rhizobium bacteria  then signal for
development of infection thread

Cells of root cortex and the pericycle of stele begin diving  Bacteria in vesicles bud
from invaginated infection thread

Dividing cells of the pericycle and cortex surround cells containing bacteria  forms
nodule

Developing nodule sends new xylem/phloem into stele  vascular tissue supplies
nutrients to the nodule and carries nitrogenous compounds from nodule into the stele
for distribution to the rest of the plant.
26. Explain why the symbiosis between a legume and its nitrogen-fixing bacteria is considered to
be mutualistic.

Symbiotic nitrogen fixation results from intricate interactions between roots and
bacteria

Nodules form with the bacteria which supplies fixed nitrogen and the plant supplies
carbohydrates and other organic compounds
27. Recall the functions of leg hemoglobin and explain why its synthesis is evidence for
coevolution.
Coevolution is evident in their cooperative synthesis of leg hemoglobin, with the plant and the
bacteria each making part of the molecule. Leg hemoglobin is an iron-containing protein that,
like hemoglobin, binds reversibly to oxygen. The root nodule’s leg hemoglobin acts as an
oxygen “buffer”, regulating the supply of oxygen for the intense respiration required by the
bacteria to produce ATP for nitrogen fixation.
28. Describe the basis for crop rotation.
One year a nonlegume such as corn is planted, and the following year alfalfa or some other
legume is planted to restore the concentration of fixed nitrogen in the soil. Legume crop is
often plowed under instead of being harvested.
29. Explain how a legume species recognizes a certain species of Rhizobium. Explain how that
encounter leads to the development of a nodule.
1. The root secretes a signal in form of a specific flavenoid that is detected only by plant’s
Rhizobium partner
2. The flavenoid activates a gene-regulator named Nod D
3. Nod D, a transcription factor, then binds to a DNA region called the Nod box, activating
transcription of the nod genes (bacterial genes).
4. The products of nod genes are enzymes for a metabolic pathway that
5. Produces a chitin like substance called a Nod factor
6. The Nod factor functions as a specific signal between Rhizohium and the root,
triggering the development of infection thread and nodule.
30. Define mycorrhizae and explain why they are considered examples of mutualism. Explain
how mycorrhizae enhance plant nutrition.

Mycorrhizae are mutualistic combinations of fungi on plant roots.

Fungi increases root surface area and absorb minerals – also secrete growth factors that
stimulate roots to grow and branch – produce antibiotics that may help protect plant
from pathogenic bacteria and pathogenic fungi in the soil.

Plants protect and provide sugar.
31. Explain the significance of mycorrhizae in the evolution of terrestrial plants.
Primitive plants may have needed help gathering nutrients  fungi of mychorrhizae would
have helped because it’s more efficient at absorbing minerals than the roots themselves.
32. Compare the structure and properties of ectomycorrhizae and endomycorrhizae.

Ectomycorrhizae:
-
mycelium (mass of branching hyphae) forms a dense sheath, or mantle, over the
surface of the root.
-
Hyphae extend from mantle into soil  greatly increase surface area for water
and mineral absorption.
-
Fungal hyphae also grow into cortex of root but do not penetrate the root cells
 form a network in extracellular spaces that facilitates nutrient exchange
between fungus and plant.
-
Thicker, shorter, more branched than normal roots. Do not form root hairs.
-
Especially common in woody plants: pines, spruce, oak, walnut, birch, willow,
eucalyptus families.

Endomycorrhizae:
-
Do not have dense mantle
-
Hyphae extend inward and do not actually pierce the plasma membrane and
enter the cytoplasm of host cell, but instead grow into a tube formed by
invagination of root cell’s membrane.
-
Some fungal hyphae become highly branched to form dense knotlike structures
called arbuscles  important sites of nutrient transfer between the fungus and
plant.
-
Have root hair, which makes it look like normal root.
-
MORE common than ectomycorrhizae  found in 90% of plant species: corn,
wheat, legumes, etc.
33. Describe the agricultural importance of mycorrhizae.

Roots can be transformed into mycorrhizae only if they are exposed to the appropriate
species of fungus.

Fungi = in soil and seedlings develop mycorrhizae.

If seed are collected in one environment and planted in foreign soil, plants may show
signs of malnutrition resulting from absence of plants’ mycorrhizal partners.
34. Discuss the relationships between root nodule formation and mycorrhizae development. .

Both activate nodule genes in the host

Share components of a signal-transduction pathway
Nutritional Adaptations: Parasitism and Predation by Plants
35. Describe the modifications for nutrition that have evolved among plants, including parasitic
plants, carnivorous plants, and mycorrhizae.

Parasitic:
-
Mistletoe is green but supplements using penetrating haustoria.
-
Dodder taps host vascular tissue.
-
Indian pipe taps mycorrhizae
Parasitic plants extract nutrients from other plants

Carnivorous:
-
Photosynthetic.
-
Obtain minerals by killing and digesting bugs
-
live in poor soil conditions
Carnivorous plants supplement their mineral nutrition by digesting animals

Mycorrhizae:
-
helps plants absorb water and minerals
Key Terms
Mineral nutrient: essential chemical elements absorbed from the soil in the form of inorganic
ions. Ex: nitrogen.
Essential nutrient: a particular chemical element that is required for a plant to grow from a
seed and complete life cycle, producing another generation of seeds.
Macronutrient: elements required by plants in large amounts: carbon, oxygen, hydrogen,
nitrogen, sulfur, phosphorus, potassium. Calcium, magnesium.
Micronutrient: elements required by plants in small amounts: iron, chlorine, copper,
manganese, zinc, molybdenum, boron, nickel.
Topsoil: mixture of particles derived from rock, living organisms, and humus.
Humus: decomposing organic material formed by action of bacteria and fungi on dead
organisms, feces, fallen leaves, etc.
Horizons: other distinct soil layers that are often visible in vertical profile where there is a
roadcut. Loams: most fertile soils that are made up of roughly equal amounts of sand, silt, and
clay.
Cation exchange: Protons are pumped out of the plant - Positive protons displace positive ions
bound to clay.
Sustainable agriculture: farming methods that won’t harm environment and still profitable.
Phytoremediation: nondestructive biotechnology that harnesses some plants ability to extract
soil pollutants and concentrate them in portions of the plant that can be easily removed for safe
disposal.
Nitrogen - fixing: converting N2 to NH3
Bacteria nitrogen fixation: a metabolic process converting atmospheric nitrogen into ammonia
that could be used by plants.
Nitrogenase: an enzyme that catalyzes the entire reaction sequence – which reduced N2 to NH3
by adding electrons along with hydrogen ions.
Nodules: swellings of legume’s roots that are composed of plant cells that contain nitrogen
fixing bacteria of Rhizobium
Bacteroids: a form of Rhizobium that are contained within vesicles formed by the root cell.
Mycorrhizae: “fungus roots” – modified roots consisting of symbiotic associations of fungi and
roots.
Ectomycorrhizae & Endomycorrhizae: refer to #32