3.3 Transports in plants

Question 1

Why do plants need transport systems?

Answer 1

Metabolic demands - Photosynthesis
Size
Sa:Vol ratio

Question 2

Transport system in dicotyledonous plants:

Answer 2

Contains vascular system:
Phloem
Xylem

Question 3

Draw a root tissue of a dicotyledonous plant, annotate

Answer 3

Exodermis
Cortex
Endodermis
Cambium
Xylem = + shape structure
Phloem = triangle shape structures surrounding xylem

Question 4

Draw and annotate a stem tissue of a dicotyledonous plant

Answer 4

Epidermis
Cortex
Phloem - (outside tissue of vascular bundle)
Cambium - separating phloem and xylem
Xylem - (inside tissue of vascular bundle)

Question 5

Draw and annotate a leaf tissue of a dicot leaf

Answer 5

Upper epidermis
Palisade mesophyll
Spongy mesophyll
Inside spongy mesophyll - xylem - towards top, phloem - underneath xylem
Lower epidermis

Question 6

What is the xylem function

Answer 6

Transport of water and mineral ions
Support

Question 7

What is the structure of Xylem

Answer 7

Hollow tube
Non-living tissue
Lignified walls - spiral shape
+ bordered pits
Xylem parenchyma - around xylem vessels

Question 8

What is the purpose of lignified wall in the xylem

Answer 8

provide structure

Question 9

What is the purpose of Xylem parenchyma in xylem

Answer 9

storing food
Tannin deposits - bitter substance - prevent against animal attacks

Question 10

What is and what is the purpose of bordered pits in the xylem

Answer 10

un-lignified areas in the xylem, that allow for water to leave the xylem and move to other areas of the plant

Question 11

What is the purpose of phloem?

Answer 11

Transport assimilates up and down the the cell

Question 12

What is the structure of the phloem?

Answer 12

Contains sieve tube elements
Perforated walls form sieve plates
No nucleus, tonoplast, or other organelles
supporting tissues - fibres and sclereids

Question 13

What is the function of companion cells

Answer 13

Cells linked to sieve tube elements, by plasmodesmata
Active cells ‘life support system’ - maintain organelles

Question 14

How is water transported in plants?

Answer 14

Turgor/hydrostatic pressure

Question 15

Why is water needed in plants

Answer 15

Photosynthesis

Question 16

How are root hair cells adapted for efficient exchange

Answer 16

Microscopic hairs - large SA:V
Hairs have thin surface layers
High concentration of solutes in cytoplasm, maintaining a water potential gradient

Question 17

Where does water exchange into a root of a plant

Answer 17

Root hair cells

Question 18

How does water move into the root hair cell

Answer 18

Via osmosis
Down a water potential gradient

Question 19

What is the symplast pathway

Answer 19

Water moves through the cytoplasm of plants

Question 20

How is water moved in the symplast route

Answer 20

Water diffuses in, making the cytoplasm more dilute. so water moves into the next cell along. This makes the water potential fall, maintaining a steep concentration gradient

Question 21

What is the apoplast pathway

Answer 21

Water moves between intercellular spaces

Question 22

How is water moved in the apoplast route

Answer 22

Water molecules are pulled through due to cohesive forces between the water molecules, creating tension

Question 23

How does water move close to the xylem

Answer 23

Water moves to endodermis, across the casparian strip, into the xylem

Question 24

What is the casparian strip

Answer 24

Waterproof wax band that runs around cells

Question 25

What is the function of the casparian strip

Answer 25

Forces water into the symplastic route. This filters the water, removing any toxic solutions, as cell surface membranes have no carrier proteins

Question 26

How does water move into the xylem

Answer 26

endomeral cells move mineral ions into the xylem via active transport, Water potential in xylem cells is much lower, water move into xylem via osmosis

Question 27

What happens after water enters the xylem

Answer 27

Water returns to apoplast pathway, pumping of minerals into the xylem and the osmosis of water into the xylem results in root pressure, giving water a push up the xylem

Question 28

Evidence for role of active transport in root pressure:

Answer 28

Some poisons that affect mitochondria are applied to roots, removing root pressure Root pressure increases with a rise in temperature If oxygen or respiratory substrates fall, root pressure falls

Question 29

What is transpiration

Answer 29

Loss of water vapour from the leaves

Question 30

What structure allows for gas loss in plants

Answer 30

Stomata Opened and closed via guard cells

Question 31

Why are guard cells important

Answer 31

Control amount of water loss Varies day and night seasonally

Question 32

What is the transpiration stream

Answer 32

stream of water, moving from roots to leaves,

Question 33

Water leaving via stomata:

Answer 33

Water molecules evaporate out of mesophyll cells into air spaces, moving out of stomata, down a concentration gradient, this lowers the water potential of the cell, water moves in from other cells via osmosis.

Question 34

Capillary action:

Answer 34

Water molecules for hydrogen bonds with carbohydrates in xylem vessels (adhesion), and hydrogen bonds with other water molecules, so stick together (cohesion), resulting in capillary action

Question 35

Transpiration pull:

Answer 35

Water is drawn up into xylem in a continuous stream to replace water lost via evaporation

Question 36

Cohesion tension theory:

Answer 36

water moving from the soil in a continuous stream up the xylem and across the leaf

Question 37

Evidence for cohesion tension theory

Answer 37

Changes in diameter of tress - during the day, transpiration is at the highest, xylem is tense, so tree shrinks. At night, transpiration is at the lowest, xylems are not under tension, diameter increases. If a xylem vessel is broken and put in water, air is drawn into xylem, water can no longer be drawn up, continuous stream is broken

Question 38

Factors impacting transpiration:

Answer 38

Light intensity Humidity Temperatures water availability Wind/air movment

Question 39

How do stomata close and open

Answer 39

When turgor is low, guard cell walls close the pores When conditions are good, solutes are actively pumped, increasing their turgor

Question 40

How are guard cells adapted

Answer 40

Inner walls of guard cells are more flexible then the outer walls Cellulose hoops prevent width extension, so they extend lengthways

Question 41

What is translocation

Answer 41

Movements of assimilates around the plant

Question 42

Where do assimilates need to move in a plant

Answer 42

From source to sink

Question 43

What is the main assimilate needed to be transported in plants

Answer 43

Sucrose

Question 44

Sources:

Answer 44

Leaves and stems Storage organs unloading their stores at the beginning of a growth period Germination of food stores in seed

Question 45

Sinks:

Answer 45

Roots that are growing and actively absorbing mineral ions Meristems that are dividing Parts of plants that are using food stores (seeds, frits or storage)

Question 46

Active loading:

Answer 46

At the source, companion cells actively pump hydrogen ions into the source tissue, increasing the concentration. Hydrogen ions diffuse back into companion cells via facilitated diffusion along with sucrose molecules (Co-transport). Sucrose molecules build up in companion cells, then move into sieve cells via simple diffusion, across the plasmodesmata and cytoplasm bridge

Question 47

Mass flow: At the source

Answer 47

At the source, the active loading of sucrose into sieve tissue lowers the water potential in the sieve tube. Water moves into sieve tubes via osmosis from xylem and source. Increasing the volume and thus hydrostatic pressure withing sieve tissues.

Question 48

Mass flow: At the sink

Answer 48

At the sink, sucrose moves into the sink tissue, via simple diffusion, across plasmodesmata into companion cells, then facilitated diffusion into sink, increasing water potential. Water movves out of sieve tues, into xlem, decreasing volume of water and hydrostatic pressure.

Question 49

Why is Mass flow important

Answer 49

Sucrose and water is forced from the source tissue into the sink, quicker then normally, down a hydrostatic pressure gradient

Question 50

Evidence for translocation:

Answer 50

Microscopy If mitochondria are poisoned, translocation stops Flow of sugars is very fast compared to diffusion Aphids show that there is pressure in the phloem that forces the sap out, pressure is lower at the sink then nearer the source

Question 51

What are xerophytes

Answer 51

Plants that live in low water availability areas hot, dry, breezy Cold, icy

Question 52

Ways of conserving water:

Answer 52

Thick, waxy cuticle Sunken stomata - reduce air movement Reduced number of stomata Reduced leaves Hairy leaves - catches lost water, creating humidity, reducing excess water loss Curved leaves - increases humidity Leaf loss Deep roots or widespread, shallow roots

Question 53

Adaptations of marram grass:

Answer 53

Curled leaves Sunken stomata Hairs Vertical and horizontal roots

Question 54

What are hydrophtes

Answer 54

Plants that live in water

Question 55

Adaptations of hydrophtes

Answer 55

Thin or little waxy cuticle Open stomata / inactive guard cells Stomata on upper surface Reduced structure - supported by water Wide flat leaves Small roots Large SA of stems and roots underwater Air sacs / Aerenchyma - tissue with many air spaces

Question 56

Adaptations of water lillies:

Answer 56

Stomata on upper surface REduced structure Wide, flat leaves