Plant transport

Question 1

2 plant vascular tissues

Answer 1

xylem and phloem

Question 2

Label vascular tissues in root, stem and leaf

Answer 2

diagrams

Question 3

Adaptations of xylem

Answer 3

-dead cells aligned from end to end to form tube
-tubes narrow so water column doesn’t break easily
-bordered pits in lignified walls allow water to move sideways from one vessel to another
-lignin allows xylem to stretch as plant grows

Question 4

Features of phloem

Answer 4

-sieve tubes made of sieve tube elements and companion cells
-sieve tube elements- lined end to end, no nucleus, thin walls, sieve plates so sap moves to next element
-companion cells- large nucleus, dense cytoplasm, lots mitochondria
-holes between tube and companion cell= plasmodesmata
-sieve plates can close part of phloem if damaged to reduce loss of sap

Question 5

Water pathways

Answer 5

Apoplast-passes through spaces between cells, moves by mass flow not osmosis
Symplast- water enters cytoplasm through membrane, then passes through plasmodesmata to the next cell
Vacuolar- water not confined just to cytoplasm, it can enter and pass through vacuole

Question 6

Plasmolysis

Answer 6

when so much water is lost, the membrane loses contact with the cell wall
-tissue is now flaccid

Question 7

Transpiration

Answer 7

-loss of water vapour from the upper parts of the plants
Pathway
-water enters leaf through xylem and moves by osmosis to cells of spongy mesophyll
-water evaporates from cells walls of spongy mesophyll
-water vapour diffuses out leaf through open stomata, down the water vapour potential gradient

Question 8

Purpose of transpiration

Answer 8

-transport mineral ions up the plant
-maintain cell turgidity
-supply water for growth, cell elongation and photosynthesis
-keep plant cool on a hot day

Question 9

Factors effecting rate transpiration

Answer 9

-Light intensity- higher rate as more photosynthesis, so stomata open for gaseous exchange
-Temperature- higher rate, as evaporation quicker, diffusion quicker and decreases water vapour in air (humidity)
-Humidity- lower humidity, higher rate
-Air movement- higher rate as maintains conc gradient
-Water availability- more water, higher rate

Question 10

Practical to measure transpiration rates

Answer 10

-use a potometer
Valid results
-set up potometer under water so no air bubbles
-ensure healthy shoot
-cut stem under water so air doesn’t enter the xylem
-cut at angle so large SA
-dry the leaves

Question 11

Water uptake at root

Answer 11

-root hair cells have large SA to absorb ions and water
-water moves across root cortex and down water potential gradient to the endodermis of the vascular bundle
-can travel via apoplast pathway, but then must enter symplast due to casparian strip

Question 12

Role endodermis

Answer 12

-casparian strip blocks apoplast pathway between the cortex and medulla
-ensures water and ions pass into cell cytoplasm
-membrane contains transporter proteins that pump mineral ions from the cytoplasm of cells in the cortex, to the medulla and xylem
-this decreases WP, so water moves in via osmosis
-once water enters medulla, it can’t move back as blocked casparian strip

Question 13

Root pressure

Answer 13

-action endodermis pumping minerals into medulla draws water in via osmosis
-pressure in medulla builds, pushing water up the xylem

Question 14

Transpiration pull

Answer 14

-water molecules in xylem are attracted to each other due to H bonding- cohesion
-so as one molecule evaporates, the whole chain is pulled up the xylem

Question 15

Capillary action

Answer 15

-same forces that hold water molecules together, attract them to the sides of xylem- adhesion
-xylem is narrow, so these forces can pull water up the sides of the vessel

Question 16

Marram grass adaptations

Answer 16

-leaf rolls so air trapped inside, making it humid, reducing water loss
-thick waxy cuticle, reduce water loss
-stomata on inner side of rolled leaf
-stomata are in pits in the lower epidermis and covered by hairs to reduce air movement
-dense spongy mesophyll so lower SA for evaporation

Question 17

Cacti adaptation

Answer 17

-succulents- store water in stems
-no leaves, only spines, so small SA
-stem green for photosynthesis
-roots widespread to catch any rain that does fall

Question 18

Xerophytes

Answer 18

-plants adapted to living in dry conditions eg. marram grass, cacti

Question 19

Hydrophytes-

Answer 19

plant adapted to living in water or where the ground is very wet eg. water lily

Question 20

Water lily adaptations

Answer 20

-many air spaces in leaf so they float
-stomata on upper epidermis so exposed to air
-leaf stem has many air spaces which helps float

Question 21

Hydathodes-

Answer 21

structures in plants that can release water droplets which can then evaporate from the leaf surface

Question 22

Translocation-

Answer 22

-occurs in phloem and is the movement of assimilates throughout the plant

Question 23

Active loading

Answer 23

-H+ actively transported out of companion cells
-this creates a concentration gradient, so H+ diffuse back in
-they diffuse through cotransporter proteins with sucrose= cotransport
-concentration of sucrose in companion cell increases, so diffuses through plasmodesmata and into sieve tube element

Question 24

Movement sucrose

Answer 24

-by mass flow
-sap= solution sucrose, amino acids and other assimilates
-flow caused by difference in hydrostatic pressure
-water enters at source, increasing pressure, then leaves at sink, decreasing pressure

Question 25

Process of translocation

Answer 25

-sucrose actively loaded into sieve tube element, decreasing WP
-water then follows by osmosis, increasing hydrostatic pressure
-sap moves down from high hydrostatic pressure to low hydrostatic pressure at the sink
-sucrose removed for sieve tube by surrounding cells, increasing WP
-water leaves sieve tube, reducing hydrostatic pressure