Transport in Plants

Question 1

How is water taken up by root hair cells?

Answer 1

• Mineral ions are taken up from soil by root hair cells by active transport
• Reduces cell water potentail - water moves into root hair cells via osmosis (down water potential gradient)

Question 2

What are the 3 ways water can move from cell to cell?

Answer 2

• apoplast pathway (movement through cell walls)
• symplast pathway (inside cell cytoplasm via plasmodesmata)
• vacuolar (similar to symplast, moves via vacuoles of cells)

Question 3

What is the casparian strip?

Answer 3

• impermeable suberin ring around cell wall which blocks water moving via apoplast pathway, to force water to move via symplast pathway
• also prevents backflow of mineral ions from vascular bundle

Question 4

How does water move into the vascular bundle? (xylem)

Answer 4

• mineral ions are actively transported into the xylem, lowers water potential
• water moves into xylem via osmosis (follows water potential gradient)
• creates a HIGH root pressure

Question 5

What is the endodermis layer?

Answer 5

the tissue surrounding the vascular bundle that contains the cells with the casparian strip

Question 6

How are xylem and phloem arranged in the root?

Answer 6

• Xylem in one large X

- Phloem tucked in the ‘armpits’ of the X

Question 7

What are some key features of Xylem tissue?

Answer 7

• made of lignified dead cells (cell wall that has lignin in it) - lignin strengthens + makes xylem impermeable
• contains bordered pits - gaps in the lignin that allows lateral movement of water (in + out of xylem)
• made via cells fusing end to end to form a continuous tube, with no cell contents.

Question 8

What are the properties of water that allows it to move up the xylem?

Answer 8

• Cohesion - hydrogen bonding between water molecules (attraction to each other)
• Adhesion - attraction of water molecules to xylem walls, allowing them to move up

Both actions contribute to capillary action

Question 9

How are vascular bundles arranged in a stem? (cross section)

Answer 9

• phloem closest to the surface (OUTSIDE)
• cambium (meristem cells) seperate phloem from xylem
• xylem on the INSIDE
• sclerenchyma on the far outside of the vascular bundle (atop phloem)
• vascular bundles arranged in a ring around a central medulla

Question 10

What is the structure of the leaf? (from top -> bottom)

Answer 10

• waxy cuticle - stops water loss
• upper epidermis - transparent to allow light through
• palisade mesophyll - photosynthetic layer
• spongy mesophyll - air space for water movement
• stomata + guard cells

Question 11

How does stomata power the transpiration stream?

Answer 11

water moves out of xylem down concentration gradient, causing water to evaporate into air space and out of stomata - powers whole process of transpiration by providing the ‘pull’

• remember - water EVAPORATES from cell into air space and DIFFUSES out of plant via stomata

Question 12

Why would guard cells close stomata?

Answer 12

When water levels are low within the plant

Question 13

Why is transpiration necessary?

Answer 13

• supplies water to the plant for photosynthetic processes

- cools down leaves via evaporation

Question 14

What instrument is used to measure transpiration?

Answer 14

potometer

Question 15

How is a potometer set up?

Answer 15

• Take a cutting with an oblique cut stem (increase transpiration surface area) underwater
• Seal cutting stem within potometer while still underwater
• Allow a bubble to enter the potometer, and then place the potometer in the water + start a stopwatch
• every 3 mins for 30 mins to an hour record the distance that the bubble has travelled

Question 16

What are some factors that can be changed for a potometer experiment?

Answer 16

• light intensity (lamp)
• air movement (put a fan next to plant leaves)
• humidity ( plastic bag around potometer)

Question 17

Whats the difference between a hydrophyte and a xerophye?

Answer 17

xerophyte = plant that lives in arid environment (e.g. cactus)
hydrophyte = plant that lives in largely water environment

Question 18

What are some adaptations of xerophytes?

Answer 18

• thick waxy cuticle for water storage
• curled leaves, to trap water vapour so it doesn’t diffuse out
• stomata in pits to reduce wind exposure so water vapour remains in leaf for longer

Question 19

What are some adaptations of hydrophyte?

Answer 19

• stomata on upper leaf surface for maximum gaseous exchange
• air spaces within leaf for buoyancy on surface - also allows oxygen to diffuse down the stem to the root for metabolic processes

Question 20

Where are sugars made in the plant?

Answer 20

the photosynthetic tissues of the palisade mesophyll layer

Question 21

What are the adaptations of phloem cells?

Answer 21

• living cells
• has most of organelles cleared out during development to make room for mass flow
• barrier between phloem cells = sieve plate (perforated with many plasmodesmata)

Question 22

What performs the metabolic processes for the phloem cells?

Answer 22

companion cells

Question 23

How are companion cells connected to phloem?

Answer 23

plasmodesmata

Question 24

What is the purpose of the companion cell?

Answer 24

• help load and unload sugars into the phloem from palisade mesophyll and unload at desired cells.

Question 25

How do companion cells load sugars into phloem?

Answer 25

• H+ ions pumped out of companion cells to create concentration gradient
• H+ ions move back into comp. cell with sucrose via cotransport
• sucrose moves into phloem by plasmodesmata

Question 26

How do sugars move from source to sink?

Answer 26

• when sugars move into the phloem, they reduce the water potential
• water moves via osmosis into phloem due to water potential gradient formation
• creates high hydrostatic pressure, which forces sugars towards sink

Question 27

What occurs when sugars reach sink?

Answer 27

• they are actively unloaded + converted to starch quickly

- water potential of phloem quickly raised - water moves back into xylem via osmosis.

Question 28

What is mass flow?

Answer 28

The movement of sugars as a result of a high hydrostatic pressure at the source.