Transcript 1. Describe the chemical composition of plants and explain how this

Chapter 37 Reading Quiz
1.
2.
3.
4.
5.
What is the general name for elements
that plants require in large amounts?
What are the most fertile soils called?
What is found in soil that is capable of
nitrogen fixation?
What are “mycorrhizae”?
Plants that grow on the surface of
another plant but are not parasitic are
called…?
1. Describe the chemical composition of
plants and explain how this leads to plants’
nutritional needs.
• Carbohydrate (carbon, hydrogen, oxygen)
• Nitrogen, sulfur, and phosphorus
• A plant’s nutritional needs are met with
water, minerals, and sunlight 
2. Explain how a 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 
3. Distinguish between macronutrient and
micronutrient.
• Macronutrient  elements that are
required by plants in relatively large
amounts
• Micronutrient  elements that plants
need in very small amounts 
4. List the nine macronutrients required by
plants.
1.
2.
3.
4.
5.
6.
7.
8.
9.
Carbon
Oxygen
Hydrogen
Nitrogen
Sulfur
Phosphorus
Potassium
Calcium
Magnesium 
5. List eight micronutrients required by
plants and explain why plants need only
minute quantities of these elements.
1.
2.
3.
4.
5.
6.
7.
8.
Chlorine
Iron
Boron
Manganese
Zinc
Copper
Molybdenum
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.
• The symptoms of a mineral deficiency
depend partly on the function of the
nutrient in the plant
• Ex: magnesium is necessary in the function
of chlorophyll, and when it is deficient, the
leaves turn yellow
• Mobility  deficiency will show up in older
tissues because younger tissues have a
stronger “pulling” power 
7. 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 
8. Describe the composition of loams and
explain why they are the most fertile soils.
• Loams  equal amounts of sand, silt, and
clay
 fine particles retain water and minerals
 Coarser particles provide air spaces with
oxygen for cellular respiration 
9. 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 
10. 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 
11. Explain how the presence of clay in soil
prevents 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
• Nitrates, phosphates, and sulfates do not
bind and tend to drain away 
12. Define cation exchange, explain why it is
necessary for plant nutrition, and describe
how plants can stimulate the process.
• Cation exchange  positively charged
minerals are made available to the plant
when hydrogen ions in the soil displace the
mineral ions from the clay particles
• This is stimulated by the roots themselves,
which secrete H+ and compounds that form
acids in the soil solution 
13. Explain why soil management is necessary
in agricultural systems but not in natural
ecosystems such as forests and grasslands.
• Agriculture is unnatural and depletes the
mineral content of the soil, making soil less
fertile
• Crops use more water than natural
vegetation
• Leads to “crop rotation” in farms
• Also “contour tillage”
14. List the three mineral elements that are
most commonly deficient in farm soils.
1.
2.
3.
•
Nitrogen
Phosphorus
Potassium
Mainly because they are leached away in
rains and irrigation 
15. Describe the environmental consequence
of overusing commercial fertilizers.
• Excess minerals from chemical fertilizers
may be leached from soil and may pollute
streams and lakes
• Often causes “algal blooms” and choke off
life in lakes 
16. Explain how soil pH determines the
effectiveness of fertilizers and a plant’s
ability to absorb specific mineral nutrients.
• Acidity affects cation exchange and the
chemical form of the minerals
• A change may make one essential element
more available while causing another to
adhere to soil and is not available 
17. Describe problems resulting from farm
irrigation in arid regions and list several
current approaches to solving these
problems.
• Huge drain of water resources
• Can gradually make soil salty and infertile
 use of drip irrigation (slow watering)
 use plant varieties that require less water

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 
19. Define nitrogen fixation and write the
overall equation representing conversion of
gaseous nitrogen to ammonia.
NH3 + H  NH4
• Nitrogen fixation  the process of
converting atmospheric nitrogen to
nitrogenous compounds that can be directly
used by plants (nitrate or ammonia) 
20. Distinguish between nitrogen fixing
bacteria and nitrifying bacteria.
• Nitrogen-fixing  restock nitrogenous
minerals in the soil by converting N2 to
NH3 (ammonia)
• Nitrifying  convert NO3- to N2 which
diffuses from the soil to the atmosphere

21. 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 
22. Discuss the relationships between root
nodule formation and mycorrhizae
development.
• Mycorrhizae are modified roots consisting
of symbiotic associations of fungi and
roots
• Lots of evolutionary similarities between
nodule formation and mycorrhizae (gene
activation, signal-transduction pathways) 
23. Describe modifications for nutrition that
have evolved among plants including parasitic
plants, carnivorous plants, and mycorrhizae.
• Mycorrhizae  helps plants absorb water
and minerals
• Parasitic  haustoria taps in to obtain
xylem or phloem
• Carnivorous  live in poor soil conditions,
obtain nitrogen and minerals by killing and
digesting insects 