Transport In Plants

Question 1

Need for water

Answer 1

Mineral ions and sugars are transported
Raw material for photosynthesis
Cooling effect, via transpiration
Turgor pressure

Question 2

Water potential

Answer 2

Is the tendency for water molecules to move within and between cells.
Highest water potential is zero
Presence of solute lowers water potential

Question 3

Root hair cell adaptations

Answer 3

Very thin permeable cellulose cell wall that are permeable to water and minerals
Microscopic
Large SA;V
concentration of solutes in cytoplasm of root hair cells maintains water potential gradient between soil water and cell

Question 4

3 water pathways, and what they mean

Answer 4

Symplast- through the cytoplasm and plasmodesmata
Vacuolar- through vacuoles
Apoplast- through the cell walls

Question 5

What is the Casparian strip

Answer 5

Impermeable layer of Suberin, waxy material.
Continuous cylinder of endodermal cells which surround the central vascular tissue, xylem and phloem
Forces water in the apoplast pathway into symplast pathway

Question 6

Use of the casparian strip

Answer 6

• when water reaches the endodermis of the root it’s path is blocked
• endodermis has impermeable layer called caspairan strip
• in order to cross the endodermis the water is moved into the apoplast pathway. Water now moves through the cell surface membrane and into the cytoplasm
• this is a selectively permeable plasma membrane, this removes toxins

Question 7

3 processes to move the water up the stem

Answer 7

Root pressure, active process
Transpiration pull
Capillary action
( all happens due to gas exchange at the top of the plant)

Question 8

Define transpiration

Answer 8

The loss of water vapour from the stems and leaves of a plant as a result of evaporation from cell surfaces inside the leaf and diffusion down a concentration gradient out through the stomata

Question 9

How is water transported up the stem to the leaves

Answer 9

• Water is lost from the leaves as water vapour, through the stomata
• this creates a low hydrostatic pressure at the top of the plant compared to the higher hydrostatic pressure at the bottom.
• due to the pressure gradient a transpiration stream/tension is created causing the water in the xylem to be drawn up into the leaves
• water sticks to the walls of the xylem vessel due to adhesion and water molecules stuck to each other due to hydrogen bonds allowing the water to move against gravity upwards.

Question 10

Evidence for the cohesion tension theory

Answer 10

Tree rings- when transpiration is at its highest tree diameter decreases due to the tension in the xylem vessels being higher.

Broken xylem vessel- when a vessel breaks air is drawn in stead of water leaking out

Question 11

Factors affecting the rate of transpiration

Answer 11

Light intensity - required for photosynthesis therefore stomata open for gas exchange, open stomata increase the rate of transpiration
Relative humidity - if volume of water in the air is high this reduces the conc gradient between the inside of the leaf and the outside air meaning transpiration rate decreases
Soil water availability -
Air movement - sweeps water molecues off leaf surface maintaining conc graidents
Temperature - increases KE of water particles meaning they move out of the leaf at a faster rate ( if temp gets too high stomata close to prevent excess water loss)

Question 12

What is the gap between the companion cell and the phloem sieve tube called

Answer 12

Plasmodesmata

Question 13

Function / adaptations of xylem

Answer 13

• transports dissolved minerals and water around the plant
  Lignified cell walls - add strength to withstand the hydrostatic pressure of transpiration pull so that the vessels do not collapse
  No end plates - allows the mass flow of water to cohesive and adhesive, these forces are not impeded (continuous forces)
  Cells are dead - cells do not need the minerals that are being transported
  Bordered pits - allows movement of water into the phloem
  Small diameter- helps prevent colum from breakig and assists with capillary action

Question 14

Function / adaptations of phloem

Answer 14

Transports assimilates from source to sink, Assimilates are disolved in water to form sap
No vacuole or nucleus - to maximise space for assimilates
Sieve tube elements line up end to end to form a continous tube
Sieve plates with sieve pores - allow phloem content to flow through whilst removing preventing movement of unwated stubstances. Can also become signified to prevent spread of disease
Companion cells linked by plasmodesmata ( channels through the cell wall which allow sucrose to enter)
Celluose cell wall - withstands hydrostatic pressure

Question 15

What is facilitated diffusion

Answer 15

Diffusion that takes place through the use of protein channels

Question 16

effect temperature has on sugar transportation

Answer 16

Higher temp means cells have more KE.
Higher KE means rate of photosynthesis is higher meaning more ATP is available for companion cells to facilitate diffusion of h+ ions and sucrose

Question 17

Structures and function of companion cells

Answer 17

Have role in loading and unloading sugars from phloem
Large number of mitochondria
Plasmodesmata - link to sieve tube elements which allow organic compounds to move from the companion cells to seive tube

Question 18

Charged particles are move out of companion cells by ————

Answer 18

Active transport

Question 19

How are guard cells adapted to their function

Answer 19

Unevenly thickened cell wall ( side beside pore thicker )
Meaning cell is able to bend and change shape
Contains lots of transporter proteins in plasma membrane
Presence of chloroplasts to provide energy

Question 20

Why is lignin essential for xylem vessels

Answer 20

Provides strength and support 
Prevent collapse
Transpiration produces tension 
To waterproof the cell, adhesion of water 
So cell dies to create a hollow tube 
Spiral allows flexibility

Question 21

Why is cartilage essential

Answer 21

support to keep airway open
Provides strength to prevent collapse during inspiration as the volume of thorax increases meaning the pressure in the tranche drops

Question 22

Need for transport system in plants

Answer 22

Metabolic demands- glucose and oxygen made in the plant must be transported to other areas that do not photosynthesise
Size- increasing transport distances
SA:V - relatively small SA:V despite adaptions such as leaves, this means they cannot rely on diffusion alone to supply cells with everything they need
Plants need to take carbon dioxide and nutrients in
Waste products generated need to be released

Question 23

Structure of the stem

Answer 23

Vascular bundles around the edge to give strength and support

Question 24

Structure of root

Answer 24

Vascular bundles are in the middle to help the plant withstand the tugging strains that result as the steams and leaves are blown in the wind

Question 25

Structure/function of dicot leaf

Answer 25

Midrib is the main vein carrying the vascular tissue through the organ.
It also helps to support the structure of the leaf
Many small branching veins spread through the lead functioning both in transport and support

Question 26

Movement of water into the root, due to root hair cells

Answer 26

Microscopic size means they can penetrate easily between soil particles
Each microscopic hair has a large SA:V
Each hair has a thin surface layer, giving a short distance for diffusion and osmosis to take place
Concentration of solutes in cytoplasm maintains water potential gradient

Question 27

Symplast pathway

Answer 27

Continuous cytoplasm of living plant cells that is connected through plasmodesmata
Root hair cell has high water potential than the next cell along so water moves along my osmosis

Question 28

Apoplast pathway

Answer 28

Through cell walls and intracellular spaces
Water fills the spaces between the loose open network of fibres in the cellulose cell wall
As more water molecules move into the xylem more are pulled through the apoplast due to cohesion forces, creating a tension and a continuous flow of water

Question 29

Sources of assimilates

Answer 29

Green leaves and green stems
Storage organs such as tubers and tap roots that are unloading their stores at the begging of growth periods
Food stores seeds when they germinate

Question 30

Sinks of a plant

Answer 30

Any part of the plant that is removing sucrose from the phloem for :
Roots that add growing
Meristem that are actively diving
Metabolic activity

Question 31

Translocation process

Answer 31

• h+ ions move from the companion cell into the source cell from an area of high conc to low conc
• h+ ions and sucrose molecules bind to the transporter protein and are transported across into the companion cell via active transport
• sucrose diffuses into the phloem tube down the conc gradient
• this causes water to rush in from the xylem tube as the additional sucrose lowers water potential
• this mean hydrostatic pressure outside the source is higher than at the sink causes sucrose to move towards the sink
• sucrose is in high conc in the phloem tube and low in the companion cell meaning the sucrose diffuses in (unloading)

Question 32

How water is transported into the roots

Answer 32

Mineral ions enter via active transport decreasing the water potential.
Water then moves in by osmosis
Travels to the casperian strip,which forces water into the symplast pathway
Dissolved nitrates travel into the xylem decreasing water potential, water follows

Question 33

Structure of phloem tubes

Answer 33

Sieve tubes are elongated cells that line up to form tubes with thin cytoplasm and perforated cross walls / sieve plates
They form the phloem and allow the flow of sap

Question 34

Why transpiration is unavoidable during the day

Answer 34

Stomata are open allowing gaseous exchange
Photosynthesis occurs
Higher temperature during the day causes greater evaporation

Question 35

2 types of cell that can be found in the phloem tissue

Answer 35

Sieve tube elements
Sieve tube plates
Companion cells
Parenchyma

Question 36

Why may plant need lenticels (area found on trunk that allow diffusion)

Answer 36

No leaves in winter for diffusion of o2 into the plant

Stomata closed at night

Question 37

Location where growth occurs in plants

Answer 37

Cambium, situated between phloem and xylem
Apex of root/shoot
Meristem
Bud

Question 38

When does leaf/stem growth occur

Answer 38

Mitotic division in the cambium

Question 39

Source of plant

Answer 39

Any part of the plant that loads sucrose into the phloem

Question 40

Name one other part of the lead which water may be lost

Answer 40

Epidermis/ cuticle