Chapter 37

Question 1

soil horizons

Answer 1

the layers soil is stratified into

Question 2

topsoil

Answer 2

consists of mineral particles, living organisms

Question 3

humus

Answer 3

the decaying organic material

Question 4

loams

Answer 4

the most fertile topsoils and contain equal amounts of sand, silt, and clay

Question 5

what cations are in soil?

Answer 5

K+, Ca2+, Mg2+ are cations in soil and they adhere to negatively charged soil particles; this prevents them from leaching out of the soil through percolating groundwater

Question 6

cation exchange

Answer 6

cations are displaced from soil particles by other cations

• displaced cations enter the soil solution and can be taken up by plant roots
• negatively charged ions do not bind with other negative soil particles and can be lost from the soil

Question 7

what are the marconutrients

Answer 7

carbon, oxygen, hydrogen, nitrogen, potassium, calcium, magnesium, phosphorus, and sulfur

Question 8

how can positively charged macronutrients enter the roots of the plants if they are connected to negative soil particles?

Answer 8

the root hair takes water and carbon dioxide to form HCO3- + H+ and the H+ ‘s are the ones that take the positively charged macronutrients place so then those macronutrients can go into the roots

Question 9

why is the hummus helpful

Answer 9

1. builds crumbly soil that still retains water and is still porous
2. increases soil’s capacity to exhchange cations
3. serves as resevoir of mineral nutrients

Question 10

what does agriculture do to soil?

Answer 10

depletes mineral content, taxes water reserves, and encourages erosion

Question 11

fertilization

Answer 11

replaces mineral nutrients that have been lost from the soil

Question 12

what do commercial fertilizers have

Answer 12

nitrogen, phosphorus, and potassium

Question 13

as organisms decompose what do they give to soil

Answer 13

nitrogen, phosphorus, and potassium

Question 14

does pH affect anything in soil?

Answer 14

yes, it affects cation exchange and the chemical form of minerals

• cations are more available in slightly acidic soil
• availability of different minerals varies with pH

Question 15

what do micronutrients function as?

Answer 15

function as cofactors, nonprotein helpers in enzymatic reactions

Question 16

nitrogen cycle

Answer 16

transforms nitrogen and nitrogen containing compounds

-most soil nitrogen comes from actions of soil bacteria

Question 17

conversion to NH4+

Answer 17

Ammonifying bacteria break down organic compounds and release ammonia (NH3)

• Nitrogen-fixing bacteria convert N2 into NH3
• NH3 is converted to NH4+

Question 18

nitrogen fixation

Answer 18

the conversion of nitrogen from N2 to NH3
-Symbiotic relationships with nitrogen-fixing Rhizobium bacteria provide some plant species (e.g., legumes) with a source of fixed nitrogen

Question 19

why is nitrogen unavailable to plants even though it is so abundant in the atmosphere?

Answer 19

because plants cant break down the triple bond between atoms in N2

Question 20

nodules

Answer 20

along a legumes roots are swellings called nodules, composed of plant cells “infected” by nitrogen fixing Rhizobium bacteria
-the plant obtains fixed nitrogen from Rhizobium and Rhizobium obtains sugar and an anaerobic environment

Question 21

crop rotation

Answer 21

A nonlegume such as maize is planted one year, and the next year a legume is planted to restore the concentration of fixed nitrogen in the so

Question 22

Mycorrhizae

Answer 22

-mutualistic associations of fungi
and roots
• The fungus benefits from a steady supply of sugar from the host plant
• The host plant benefits because the fungus increases the surface area for water uptake and mineral absorption

Question 23

Mycorrhizal associations consist of two major types

Answer 23

-Ectomycorrhizae – Arbuscular mycorrhizae

Question 24

ectomycorrhizae

Answer 24

he mycelium of the fungus forms a dense sheath over the surface of the root
• These hyphae form a network in the apoplast, but do not penetrate the root cells
• Ectomycorrhizae occur in about 10% of plant families including pine, spruce, oak, walnut, birch, willow, and eucalyptus

Question 25

arbuscular mycorrhizae

Answer 25

microscopic fungal hyphae extend into the root
• These mycorrhizae penetrate the cell wall but not the plasma membrane to form branched arbuscules within root cells
• Hyphae can form arbuscules within cells; these are important sites of nutrient transfer
• Arbuscular mycorrhizae occur in about 85% of plant species, including grains and legumes

Question 26

what are some types of plants that have nutritional adaptations that use other organisms in nonmutualistic ways (3)

Answer 26

– Epiphytes
– Parasitic plants
– Carnivorous plants

Question 27

epiphyte

Answer 27

grows on another plant and obtains water and minerals from rain

Question 28

Parasitic plants

Answer 28

absorb sugars and minerals from their living host plant

Question 29

Carnivorous plants

Answer 29

photosynthetic but obtain nitrogen by killing and digesting mostly insects
-evolved because their environment did and does not have sufficient amount of nitrogen ever