transport in vascular plants

Question 1

what nutrients do shoots acquire above ground

Answer 1

carbon dioxide and sunlight

Question 2

what nutrients do roots acquire below ground

Answer 2

water and minerals

Question 3

describe the earliest plants

Answer 3

nonvascular and produced photosynthetic shoots above the shallow fresh water in which they lived
the shoots were leafless and had waxy cuticles and few stomata which allowed them to avoid excessive water loss while still permitting some exchange of CO2 and O2 for photosynthesis

Question 4

as plants evolved and increased in number competition for resources increased. what adaptations did plants have to make to survive

Answer 4

some became taller with broad, flat appendages to absorb more light but this lead to a greater need for water and stronger root anchorage
these needs favoured production of multicellular branching roots
natural selection favoured plants capable of efficient long distance transport of water, minerals and products of photosynthesis
evolution of vascular tissue consisting of xylem and phloem made this possible

Question 5

what are xylem

Answer 5

they transport water and minerals upwards from roots to shoots

Question 6

what are phloem

Answer 6

they transport products form where they are made or stored to where they are needed

Question 7

what is transpiration

Answer 7

the loss of water through leaves - mainly through the stomata
this creates a force within the leaves that pulls xylem sap upwards

Question 8

if a plant is a photoautotroph what is its success largely dependent on

Answer 8

their ability to photosynthesise

Question 9

why is there so much variation in branching patterns among different plants

Answer 9

plants only have a finite amount of energy to devote to shoot growth
if most of that goes into branching, there is less available for growing tall and the risk of being shaded by taller plants increases
on the other hand, if plants use all their energy in growing tall then the plants aren’t optimally harvesting sunlight

Question 10

in what kind of environment do plants usually have smaller leaves

Answer 10

dry or cold environments where liquid water is scarce and evaporative loss is more problematic

Question 11

what is phyllotaxy

Answer 11

the arrangement of leaves on a stem

Question 12

what is phyllotaxy determined by

Answer 12

the shoot apical meristem

Question 13

what is self pruning

Answer 13

when non productive leaves or branches undergo programmed cell death and are eventually shed

Question 14

what is the leaf area index

Answer 14

the ratio of the total upper leaf surface area of a single plant or an entire crop divided by the surface area on the land n which the plant or crop grows

Question 15

what factors affect light capture in plants

Answer 15

leaf area index

leaf orientation

Question 16

when is it advantageous to have vertical leaves

Answer 16

when there is a lot of sunlight exposure

Question 17

open stomatal pores allow diffusion of CO2 into photosynthetic tissues but what is a disadvantage of having open stomatal pores

Answer 17

they promote evaporation of water from the plant - this is why stomatal pore opening needs to be regulated and there needs to be a compromise between minimising water loss and enhancing photosynthesis

Question 18

what are the 2 major compartments of plants

Answer 18

the apoplast and the symplast

Question 19

what is the apoplast

Answer 19

consists of everything external to the plasma membrane of living cells and includes cells walls, extracellular spaces and the interior of dead cells

Question 20

what is the symplast

Answer 20

consists of the entire mass of the cytosol of all the living cells in a plant as well as the plasmodesmata - the cytoplasmic channels that interconnect them

Question 21

what are the 3 routes for transport in plants

Answer 21

apoplastic, symplastic and transmembrane routes

Question 22

what is the apoplastic route of transport

Answer 22

water and solutes move along the continuum of cell walls and extracellular spaces

Question 23

what is the symplastic route

Answer 23

water and solutes move along the continuum of cytosol. this requires substances to cross a plasma membrane once - when they first enter the plant

Question 24

what is the transmembrane route

Answer 24

water and solutes move out of the cell across the cell wall and into the neighbouring cell

Question 25

how is the voltage across the membrane (membrane potential) of a plant cell established

Answer 25

mainly through the pumping of hydrogen ions by proton pumps rather than by Na ions in animal cells

Question 26

describe cotransport in plants using hydrogen ions

Answer 26

plants use the energy in the H gradient and membrane potential to drive active transport of many different solutes
e.g. a H/sucrose cotransporter couples movement of sucrose against its concentration gradient with movement of H down it electrochemical gradient

Question 27

what is water potential

Answer 27

a physical property (considering solute concentration and physical pressure) that predicts the direction in which water will flow
measured in megapascals

Question 28

water moves from a higher/lower water potential to a higher/lower water potential

Answer 28

higher to lower

Question 29

what are the 4 main types of transport seen in plants

Answer 29

1. H and the membrane potential (proton pump)
2. H and the cotransport of neutral solutes (e.g. sucrose)
3. H and the cotransport of ions (e.g. nitrate)
4. ion channels (e.g. K channel)

Question 30

what is solute potential proportional to

Answer 30

molarity

Question 31

as solute concentration increases solute potential inc/dec

Answer 31

decrease

Question 32

why is water in living plant cells usually under positive pressure

Answer 32

due to the osmotic uptake of water (its being pushed into the cell)

Question 33

what decreases the permeability of aquaporin to water

Answer 33

an increase in cytosolic Ca or a decrease in cytosolic pH

Question 34

long distance transport in plants occurs by which process

Answer 34

bulk flow - the movement liquid in response to a pressure gradient (from higher to lower pressure) and is independent of solute concentration

Question 35

where does bulk flow occur

Answer 35

mainly in the vascular tissue i.e. the xylem and the phloem

Question 36

what about the xylem and phloem facilitate bulk flow

Answer 36

the lack of cytoplasm - this makes the diameter larger and the substance being transported is able to flow faster

Question 37

what is the equation for water potential

Answer 37

water potential = pressure potential + solute potential

Question 38

if the water pressure is negative what can happen to the plant cell

Answer 38

the cell can plasmolyze - there is a net loss of water so the cell shrivels and the plasma membrane pulls away from the cell wall

Question 39

what is the water potential of a turgid cell - explain

Answer 39

0 mpa - there is a net uptake of water - the cell wall creates a backwards pressure to offset the entry of water - water potential becomes for the cell and its surroundings