Chapter 9 - Transport in Plants

Question 1

Adaptations of plants to increase SA: V ratio

Answer 1

Plants have a branching body shape
Leaves are flat and thin
Roots have root hairs

Question 2

Xylem & Phloem

Answer 2

➜ vascular tissue that carries dissolved minerals and water up the plant
➜ food storage
➜ structural support
➜ xylem tissue found in vascular bundles
➜ only up (water)

➜ transport organic compounds, particularly sucrose, from the source (eg. leaf) to the sink (up and down)

Question 3

Xylem made up of:

Answer 3

➜ Tracheids (long, narrow tapered cells with pits)
➜ Vessel elements (large with thickened cell walls and no end plates when mature)
➜ Xylem parenchyma
➜ Sclerenchyma cells (fibres and sclereids)

Question 4

Xylem structure and function:

Answer 4

➜ lignified cell walls - adds strength to withstand hydrostatic pressure so vessels dont collapse and impermeable to water
➜ no end plates - allows the mass flow of water and dissolved solutes as cohesive and adhesive forces are not impeded (prevent)
➜ no protoplasm (dead cells) - doesn’t impede mass flow of water and dissolved solutes
➜ pits in wall (non lignified) - lateral movement of water allows continual flow in case of air bubbles
➜ small diameter - helps prevent water column from breaking and assists with capillary action

Question 5

Root

Answer 5

➜ endodermis - one cell thick - get water to xylem
➜ pericycle - layer of meristems in endodermis
➜ xylem - towards middle as X
➜ phloem - outside
➜ collenchyma and sclerenchyma provide support to plant (lignin)
➜ cortex and medulla made of parenchyma - starch storage & transport nutrient to core of root

Question 6

Stem

Answer 6

➜ endodermis - get water to xylem
➜ xylem - found towards inside
➜ phloem - outside
➜ collenchyma and sclerenchyma provide support to plant (lignin)
➜ cambium - meristem cell layer between xylem and phloem

Question 7

Phloem structure and function

Answer 7

➜ transport proteins in plasma membrane - moves assimilates into and out of sieve tube elements
➜ large number of mito - to provide ATP for active transport of assimilates into or out of the companion cells
➜ plasmodesmata - link to sieve tube elements which allow organic compounds to move from companion cell to sieve tube elements

Question 8

Phloem - sieve tube elements

Answer 8

➜ living cells - form tube of phloem
➜ joined end to end - form sieve tubes
➜ sieve parts = end walls - lots of holes = allow solutes to pass through
➜ no nucleus, think layer of cytoplasm and few organelles
➜ cytoplasm of adjacent cells connected through holes in sieve plates

Question 9

Phloem - companion cells

Answer 9

➜ comp cell for every sieve tube element because no nucleus
➜ carry out living functions for itself and sieve tube cells
➜ e.g provide energy for active transport of solutes

Question 10

Transpiration

Answer 10

➜ loss of water vapour down a water potential gradient through stomata in leaves
➜ consequence of gas exchange - H2O lost when stomata opens to exchabge gases
➜ water uptake = passive process = osmosis
➜ uptake of minerals = passive or active and occurs by diffusion or active transport

Question 11

Transpiration advantages

Answer 11

➜ provides a means of cooling the plant via evaporative cooling
➜ transpiration stream (movement of water from root to leaves) is helpful in the uptake of mineral ions
➜ turgor pressure of the cells provides support to leaves

Question 12

Factors affecting rate of transpiration

Answer 12

➜ light intensity
- stomata is open during the day so transpiration ↑
- stomata close in dark so ↓ transpiration
➜ temp
- warm water = ↑ KE = evaporate, so water diffuses faster
- high temp can also cause stomata to close
➜ humidity
- at high humidity, reduces H2O vapour conc grad between leaf and air (lots of water molecules in air) so transpiration ↓
➜ wind - lots of air = blow away H2O from stomata - ↑ water potential grad = ↑ transpiration

Question 13

Symplast (slower than apo)

requires water to cross partially permeable membranes

Answer 13

➜ goes through living parts of cell - CYTOPLASM - diffusion
➜ cytoplasms of neighbouring cells connect through PLASMODESMATA - osmosis
➜ root hair cells has ↑ water potential than next cell
➜ water makes the cell dilute so it moves to the next one

Question 14

Apoplast (lol apo from kiNNPORSCHE MY BELOVED)

Answer 14

➜ goes through non living - CELL WALLS
➜ walls are adsorbent (allows gas,liquid or solid to ADHERE to it) and water can diffuse through them
➜ cohesive forces between water molecules creates tension so continuous flow of water - no resistance
➜ when water gets to endodermis in root, it is blocked by casparian strip (band of waxy suberin)
➜ so water will now travel via symplast
➜ as plant ages, Casparian strip thickens

Question 15

Vacuolar

Answer 15

➜ water travels through cytoplasm THEN vacuole
➜ REPEATS HEHEHE
➜ DIFFUSION!

Question 16

role of stomata

Answer 16

➜ controlled by pairs of guard cells
➜ guard cells open the stomata when they are turgid and close when they lose water
➜ stomata usually open during day due to CO2, O2 gas exchange

Question 17

transpiration pull

Answer 17

➜ water evaporates from a mesophyll cell wall into the air sacs which creates trans pull

Question 18

Potometer

Answer 18

➜ cut shoot underwater to prevent air entering xylem (no air bubbles)
➜ assemble potometer and insert shoot (UNDERWATER)
➜ remove apparatus from water but keep end of capillary tube submerged
➜ check apparatus is airtight and watertight (to stop evaporation of water)
➜ dry leaves - allow time for shoot to acclimatise and shut tap
➜ lift capillary tube from water to form an air bubble and replace
➜ record starting position of air bubble
➜ start a stopwatch and record distance moved by bubble per unit time (minutes)
➜ only change one variable at a time keeping rest constant
➜ rate of movement = rate of transpiration

Question 19

Translocation

Answer 19

➜ movement of assimilates from source to sink and requires the input of metabolic energy (ATP)
➜ liquid that is being transported (found within phloem sieve tubes) is called phloem sap
➜ phloem sap consists not only sucrose but also water and substances such as amino acids, hormones and minerals

Question 20

Phloem loading

Answer 20

➜ via apoplastic or symplastic pathway
➜ modified companion cells pump hydrogen ions out of cytoplasm via proton pump into cell walls = active process so ATP needed
➜ large conc of H⁺ in the cell wall of the companion cell so H⁺ move down the con grad back to the cytoplasm of the companion cell
➜ H⁺ diffuses back into CC via co-transport with sucrose
➜ sucrose diffuse from CC to sieve tube element through plasmodesmata (low H20 potential inside)
➜ H20 moves into STE by osmosis + generate turgor pressure for mass flow

Question 21

Phloem unloading

Answer 21

➜ at sinks
➜ similar to loading
maintain a conc grad by converting sucrose to other molecules = metabolic reaction so enzymes used
THATS ALL U NEED TO KNOW

Question 22

Mass flow

Answer 22

➜ assimilates flow from source to sink down pressure gradient

Question 23

Phloem unloading

Answer 23

➜ passive
➜ sucrose diffuse from phloem into sinks
➜ sucrose is moved to other cells to maintain conc gradient
➜ loss of assimilates: ↑ H20 potential in STE
➜H20 moves out by osmosis

Question 24

Dicotyledonous (dicots) plants

Answer 24

➜ Seeds that contain two cotyledons (seed leaves)
➜ Network of veins
➜ Leaves that typically have broad blades (leaf surface) and petioles (stalks)
➜ Tap root with lateral branches
➜ Herbaceous dicots have a relatively short life cycle (one growing season) and non-woody tissue

Question 25

Xeromorphic features

Answer 25

➜ adapted for dry conditions and adapted to maximise water conservation
➜ fleshy succulent leaves = water stores for times of low availability
➜ leaves reduced to scales, spines or needles, leaves curled or rolled = reduced transpiration due to reduced surface area
➜ hinge shells shrink when flaccid = causes leaves to rill exposing thick waterproof cuticle to area and creates a humid space in rolled leaf
➜ stomata closed during light and open in dark = CAM (Crassulacean acid metabolism just need to know CAM) metabolism to minimise photorespiration, CO2 fixed at night, day time water loss is minimised
➜ sunken stomata = water loss minimised by trapping moist air lose to area of water loss reducing diffusion grad
➜ low stomata = less water lost
➜ stomata only found in upper epidermis = open into humid space created by hairs and rolled shape
➜ thick waxy cuticle = waterproof

Question 26

Hydrophytes features

Answer 26

➜ adapted to living in freshwater
➜ cell wall prevents too much water being absorbed
➜ challenge - receiving enough CO2 during the day and enough O2 during the night
➜ floating leaves = leaves are thin and flat and large air spaces inside to give them buoyancy so they’re closer to surface for more light during photosynthesis
➜ thin waterproof waxy cuticle = little need to prevent water loss
buoyancy
➜ reduced root system = only small roots are required as they can also extract nutrients from surrounding water through tissues
➜ reduced veins in leaves = xylem is less as no need to transport water in plant
e.g water lily