Xylem and Phloem

Question 1

What is the different between the protoplast and the apoplast?

Answer 1

protoplast is everything inside the plasmodesma

apoplast is everything outside

Question 2

What is the xylem?

Answer 2

the dead cell walls part of the apoplast pathway which create the pathway of water, minerals and nutrients from the soil

Question 3

What is everything inside the endomersis called?

Answer 3

the stele

Question 4

Name the 3 structures outside the endodermis?

Answer 4

the cortex and the epidermis and hypodermis

Question 5

What is the role of cellulose and pectin in the cell wall?

Answer 5

• they control what can pass through teh wall from the outside to the inside as they are relatively permeable to water

Question 6

What does it mean when the plasmodesmata is open?

Answer 6

molecules can go between cells without crossing a membrane

Question 7

What is the role of the casprian strip? (3)

Answer 7

• block the cell wall pathway
• force molecules through the membrane
• control what goes into the xylem

Question 8

Name the 3 pathways of water movement across teh root

Answer 8

apoplastic
cell to cell
symplastic

Question 9

What is the difference between the apoplastic and the symplastic pathway?

Answer 9

apoplastic; involves the Caspian strip

symplastic; plasmodesmata are open and reach the stele

Question 10

Name the mechanisms of xylem transport

Answer 10

1) root pressure

2) transpiration pressure

Question 11

Describe the process of root pressure in xylem transport

Answer 11

• endormisis and caspiran strip make stele act like a single cell
• accumulation of ions increase osmotic pressure and lowering water potential
• this generates transport of water across the xylem

Question 12

What creates transpiration tension?

Answer 12

cohesion and adhesion create a negative pressure in the leaves under transpiration

Question 13

When is cavitation caused?

Answer 13

when water bubbles block the xylem

Question 14

When is cavitation greater?

Answer 14

when transpiration is high

Question 15

Why is there an absence of cavitation at night?

Answer 15

because the stomata is shut so there’s no tension
whereas during the day, teh sun comes up and there is more evaporation
more tension so more cavitation

Question 16

How can cavitation events be cleared out?

Answer 16

by root pressure

Question 17

What are tree rings a consequence of?

Answer 17

• CO2 fixation

- transport effiency vs cavitation resistance

Question 18

What is the key process decreased by cavitation

Answer 18

transport efficiency

Question 19

Define the phloem

Answer 19

the vascular tissue in plants which conducts sugars and other metabolic products downwards from the leaves.

Question 20

Name 3 differences in the structures of the phloem and the xylem

Answer 20

• xylem is made up of dead cells whereas phloem is made up of living cells
• xylem has a thick cell wall, phloem has a thin cell wall
• xylem cell wall made up of lignin whereas phloem is made up of cellulose

Question 21

What is the differences in transportation between phloem and xylem (2)

Answer 21

• xylem transport is passive, phloem transport is active
• xylem transport is unidirectional, phloem is bidirectional
• xylem carries water from roots to leaves, phloem carries solutes from leaves to growing parts

Question 22

What is phloem a generic term for?

Answer 22

the translocation system

Question 23

What is a source in these terms?

Answer 23

a plant organ in which sugar is being produced by either photosynthesis or the breakdown of starch

Question 24

What is a sink in these terms?

Answer 24

an organ that is a net consumer or store of sugar e.g. a photosynthesising leaf

Question 25

What is the role of the sieve tube?

Answer 25

specific tube that does teh transport in the translocation system and goes to teh xylem

Question 26

What is the role of the companion cell?

Answer 26

provides genetic information and proteins, and an important function in maintaining the sieve tube

Question 27

Why do the sieve tubes need the companion cell?

Answer 27

sieve tube doesn’t have a nucleus but it is alive

Question 28

What is the role of the plasmodesmata?

Answer 28

they connect cytoplasm of adjacent cells, not like gap junctions, very selective, can open or close

Question 29

What is the main mechanism of translocation in angiosperms?

Answer 29

pressure flow

Question 30

What creates a difference in hydrostatic pressure to drive phloem sap from the source to the sink?

Answer 30

• high levels of sugar at source lowers water potential and causes water to flow into the tube
• removal of sugar at the sink increases water potential and causes water to flow out of teh tube

Question 31

Name the two ways in phloem loading occurs

Answer 31

• apoplastic which involves membranes

- symplastic - no membranes involved