Nutrient uptake

Question 1

Nutrient movement to the root

Answer 1

• diffusion
• mass flow
• root interception

Question 2

Diffusion

Answer 2

is most important for N(NO3^-), P, K

Question 3

Mass flow

Answer 3

is most important for Ca, Mg, S, micronutrients

Question 4

root interception

Answer 4

is not important

Question 5

Minerals taken up by plant roots are in a_________

Answer 5

watery solution

Question 6

Water and minerals are absorbed through the ______ of the root and must be taken up by _______ before they enter the _______

Answer 6

epidermis
root cells
xylem

Question 7

What controls what minerals enter the xylem

Answer 7

-selective permeability of the plasma membrane of root cells

Question 8

What are the two pathways by which water and minerals enter the xylem

Answer 8

• Intracellular route

- extracellular route

Question 9

Intracellular route

Answer 9

-water and solutes are selectively taken up by a root epidermis cell, usually a root hair, and transported from cell to cell through plasmodesmata

Question 10

Extracellular route

Answer 10

water and solutes pass into the root in the porous cell walls of root cells; they do not enter any cell plasma membrane until they reach the root endodermis

Question 11

The cells of the endodermis contain a waxy barrier called the ________

Answer 11

Casparian strip

Question 12

Casparian strip

Answer 12

-regulates uptake of minerals that enter the root via the extracellular route (stopped by the strip)

• Water and solutes that have entered the root without crossing a cell plasma membrane are blocked
• specialized cells of the endodermis take up water and minerals selectively

Question 13

Soil particles and plant roots participate in ________

Answer 13

cation exchange

Question 14

Cation exchange

Answer 14

the transfer of positive ions such as Ca, Mg, K from soil to plant roots

Question 15

soil particles tend to _____ cations can make uptake by plants ______

Answer 15

bond

difficult

Question 16

______ are readily taken up by plants and not affected as much by soil

Answer 16

Anions

Question 17

How does a plant get nutrients

Answer 17

• mineral movement to root by diffusion or bulk or root growth
• uptake controlled at root endodermis
• uptake by either simple diffusion (no protein), facilitated diffusion (protein channel), or active uptake (requires energy and a protein carrier)

Question 18

simple diffusion

Answer 18

no protein

Question 19

facilitated diffusion

Answer 19

protein channel

Question 20

active up take

Answer 20

requires energy and a protein carrier, proton pump

Question 21

Active diffusion

Answer 21

active uptake

Question 22

Passive diffusion

Answer 22

• simple diffusion

- facilitated diffusion

Question 23

_______ is main way plants can increase nutrient uptake

Answer 23

root elongation

Question 24

root elongation

Answer 24

• increased root:shoot ratio
  
  • increased investment in roots
• root proliferation in nutrient hot spots
  
  • root growth occurs where it does the most good

-longer root hairs

Question 25

_______ increase soil volume sued by plants

Answer 25

mycorrhizae

Question 26

mycorrhizae

Answer 26

• trade carbohydrates for nutrients (balanced parasitism)

- most advantageous for immobile nutrients (e.g., phosphate)

Question 27

Mechanisms of nutrient uptake

Answer 27

• Active transport most important (requires energy, moves against concentration gradient
• Abundant nutrients may enter by diffusion or mass flow

Question 28

cation

Answer 28

an ion that carries a positive charge

Question 29

anion

Answer 29

an ion that carries a negative charge

Question 30

cation exchange

Answer 30

a process-cations in solution exchanged with cations on exchange sites if minerals and OM

Question 31

Cation exchange capacity (CEC):

Answer 31

the total amount of exchangeable cations that a particular material or soil can adsorb at a given pH

Question 32

Strength of adsorption

Answer 32

related to hydrated ionic radius and valence

-the smaller the radius and greater the the valance, the more closely and strongly the ion is adsorbed

strength=valance/radius

Question 33

Controls on ion exchange

Answer 33

• strength of adsorption
• Relative concentration in soil solution
• Valance

Question 34

valance

Answer 34

the combing power of an element, especially as measured by the number of hydrogen atoms it can displace or combine with

Question 35

Cation exchange capacity

Answer 35

• the sum total of all exchangeable cations that a soil can adsorb
• expressed in terms of positive charge adsorbed per unit mass

Question 36

if CEC = 10 cmol/kg

Answer 36

soil adsorbs 10 cmol of H^+, can exchange it with 10 cmol K^+, or 5 cmol Ca^2+

number of charges, not number of ions is what matters

Question 37

mole

Answer 37

the mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kg of C 12

1 centimole= 10^2 moles

Question 38

exchange affinity is referred to as the ______

Answer 38

Lyotropic series

Question 39

Lyotropic series

Answer 39

H^+ > Al^3+ > Ca^2+ > Mg^ 2+ > NH4^+ > K^+ > Na^+
Held more strongly Held more weakly

strength of adsorption proportional to valance/ hydrated radius

Question 40

CEC Depends on

Answer 40

• amount of clay and organic matter

- type of clay minerals present

Question 41

The interchange between a cation in solution and one on a colloid must be _____ balanced

Answer 41

charge

Question 42

CEC

Answer 42

-OM has highest CEC
-Clay has high but not all clays created equal
-As increase sand content decrease CEC
-sands don’t adsorbed cations, if do really weak
-

Question 43

Rule of thumb for estimation of a soil’s CEC

Answer 43

CEC= (% OM100)+ (%clay50)

but the CEC of clay minerals ranges from 3 to 150.

Question 44

CEC capacity

Answer 44

Soil humus:150-200 cmol/kg
Clay: 3-150
Silt loams, sandy loams, loamy sands: less than 25