Plant Nutrition pt 1

Question 1

what’s the cost of land plants being taller and having more SA for light absorption

Answer 1

• more SA meant more water loss as well
• larger plants needed larger roots
• greater distance to transport nutrients between the root and shoot systems

Question 2

evolution of what fixed the problem of tall land plants having a greater distance to transport nutrients between the root and shoot systems

Answer 2

vascular tissues (xylem and phloem)

Question 3

how does shoot architecture vary amongst land plants

Answer 3

• stem length and width - so plants can grow tall
• branching pattern -for better light harvesting
• leaves vary in size -adapting for specific habitats, preventing water loss and maximising photosynthesis

Question 4

what’s phyllotaxy, how is it determined?

Answer 4

the arrangement of leaves on a plant, determined and genetically controlled by the SAM

Question 5

what are the types of phylotaxy (leaf arrangement)?

Answer 5

• one leaf per node > alternate/spiral
• two leaves per node > opposite
• multiple leaves per node > whorled

node= each particular position

Question 6

what factors affect nutrient acquisition in leaves

Answer 6

• total leaf area -leaves can shade other leaves on same plant reducing photosynthesis
• leaf orientation -in low light > horizontal leaves are best. -in high light > vertical leaves prevent water loss and burning.
• roots -maximise absorbance of nutrients.

Question 7

roots won’t branch in areas of

Answer 7

low N availability

Question 8

roots branch more in

Answer 8

areas of high nutrient loads.

Question 9

why do roots associate with mycorrhizae

Answer 9

to increase surface area for more nutrient uptake

Question 10

what two main compartments do plant systems have?

Answer 10

• apoplast -everything external to the plasma membrane (includes cell walls and internal spaces of dead tracheids and vessels)
• symblast -consists of the cytosol, plasmodesmata (connections between cell walls), and cytoplasmic interconnections.

Question 11

what are the 3 main transport “routes”

Answer 11

• apoblastic - water and solutes move along the cell walls and extracellular spaces (outside cells).
• symplastic - water and solutes move through the cytosol, from cell to cell, (through plasmodesmata).
• transmembrane -water and solutes move cell to cell, (across the cell walls)

slide 7 diagram

Question 12

both active and passive transport occur in plant cells true or false

Answer 12

true

Question 13

what ion do plants use for membrane potentials with proton pumps (primary active transport)

Answer 13

H+

Question 14

what is secondary active transport in plants

Answer 14

H+ is co-transported (ex: sugar in phloem cells)

Question 15

by what process does absorption or loss of water occur

Answer 15

• osmosis (passive transport).
  -water potential will direct the flow of water
  -free water (not bound to ions/solute) moves from high water potential to low

Question 16

what determines water potential

Answer 16

solute potential and pressure potential.

Question 17

pure water has a solute potential of _ MPa. Everything moves in relation to this.

Question 18

water inside plant cells is usually under positive or negative pressure?

Answer 18

positive pressure due to water uptake (puts pressure on cell wall)

Question 19

the protoplast (living part of the cell) exerts positive or negative pressure on the cell wall, creating turgor pressure

Answer 19

positve pressure creates turgor pressure.

Question 20

water inside _ and _ is often under negative pressure (tension)

Answer 20

inside tracheids and vessels (to move water)

Question 21

what happens to cells when they lose water and cell pressure potential is 0

Answer 21

they become flaccid (limp)

Question 22

what happens when a flaccid cell (has lost water) is put into a solution that has a lower water potential

Answer 22

lower water potential means solution has more solute, hypertonic. So more water will flow out of the flaccid cell, resulting in plasmolysis.

Question 23

what happens when a flaccid cell (has lost water) is put into a solution of pure water (has a higher water potential)

Answer 23

water moves inside the cell since the cell has more solutes than the pure water, exerting turgor pressure and becoming turgid.

Question 24

most of absorption of nutrients and water start at the

Answer 24

root hairs -permeable to water and its associated ions.

Question 25

describe the steps and mechanisms of water uptake in the roots

Answer 25

* through cell walls (apoplastic transport) * then active transport allows root cortex cells to absorb essential minerals * which pass through the cortex until they reach the endodermis around the vascular stele * selective transport due to the casparian strip then forces water and minerals into the symplastic route * then return to the apoplastic route to get to the tracheids and vessel elements via bulk flow

Question 26

how does xylem sap move in the stem

Answer 26

up the stem via bulk flow into the leaf veins

Question 27

water is lost due to transpiration which is

Answer 27

water vapour exiting the leaf

Question 28

what must the roots do to counteract the loss of water through transpiration?

Answer 28

absorb water

Question 29

what happens if there is more water loss in leaves than root absorption

Answer 29

the plant wilts

Question 30

how does root pressure contribute to xylem sap transport to the leaves

Answer 30

* root pressure pushes it up the plant * root cells continuously actively pump mineral ions into the xylem sap * accumulation of minerals lowers water potential inside the vascular cyclinder (in the root), causing water to flow from the root into the vascular stele, generating root pressure.

Question 31

too much root pressure can cause

Answer 31

guttation, water droplets being forced out of leaves.

Question 32

explain how the cohesion-tension mechanism contributes to xylem transport.

Answer 32

* transpiration provides the pull - water potential is greatest when uptaking, lowest at the top of the tree, which causes water to go from high to low going up tree. * cohesion of water (from h bonding) transmits this pull from shoot to root * xylem sap under negative pressure (tension)

Question 33

Transpirational pull

Answer 33

Stomata on the leaves lead to internal air pockets, exposing mesophyll cells to CO2 for photosynthesis. * Air is saturated with water vapour. Air outside the leaf is drier, and has lower water potential than air inside. * Causes water to leave from inside of leaf to outside * The negative water potential develops on the mesophyll cells, resulting in tension.

Question 34

differnce between cohesion and adhesion

Answer 34

cohesion-attractive force between the same kind of molecules adhesion-attractive force between different molecules.

Question 35

what can disrupt the bulk flow of xylem sap

Answer 35

big air bubbles (cavitation/embolisms) can disrupt the bulk flow of xylem sap. if the plant can't fix this, (prolonged hydraulic failure) plant death.

Question 36

stomata are flanked by ___ which control ____

Answer 36

2 guard cells which control the diameter of the stomatal pore.

Question 37

what happens when guard cells (on sides of stomata) take in water vs lose water

Answer 37

* when taking in water, they become turgid, and uneven cell wall thickness causes them to bow. * when water lost they become flaccid and the pore closes.

Question 38

change in tugor of guard cells is a result of reversible absorption and loss of what ion

Answer 38

K+ * Accumulation of K+ inside the guard cell lows the water potential, forcing water inside the guard cell * Loss of K+ ions from the guard cell raises the water potential of the guard cell, forcing water out of the guard cell. * Both facilitated by active transport of H+ -> results in a gradient and generation of a membrane potential which drives K+ in/out of the cell

Question 39

opening and closing of stomata is regulated by

Answer 39

circadian rhythms and plant hormones (ex. ABA produced during water shortages)

Question 40

Xerophytic plants are adapted to areas of low free water availability. how?

Answer 40

how: * life cycles are completed during the rainy season. * fleshy stems store water * cacti-reduced elaves to resist water loss * CAM plants-special photosynthesis * Stomata can be in pits, containing trichomes to maintain humidity * Extra thick cuticles to reduce water loss

Question 41

translocation

Answer 41

Sugars must be “loaded” into sieve-tube elements before being exported to sinks

Question 42

Sugars are “unloaded” at sinks via

Answer 42

faciliated diffusion. conc of sugar in sink is always lower than the sieve tube elements.

Question 43

explain the pressure-flow hypothesis describing how phloem sap moves.

Answer 43

Bulk flow of phloem sap is via positive pressure (pressure flow) * Sugars are loaded into phloem sap by source cells, which lowers the water potential of the phloem sap in that region. * This causes water to move into the phloem sap from nearby cells or surrounding xylem tissue * The increase in water pressure forces phloem sap to move through the sieve tubes * At sink cells, phloem is unloaded, increasing water potential and causing water to leave the phloem sap and enter nearby cells and xylem.

Question 44

what happens when a plant has too many sinks.

Answer 44

abort buds, fruits, and seeds through self-thinning.