Plants 9.2 Transport in the phloem

Question 1

Where are the phloem tissues found?

Answer 1

throughout plants, including the stems, roots and leaves

Question 2

What are phloem composed of?

Answer 2

Sieve tubes

Question 3

What are sieve tubues composed of?

Answer 3

columns of specialized cells called sieve tube cells; are living; no nucleus (closely associated with companion cells)

Question 4

What are individual sieve tube cells separated by?

Answer 4

Perforated walls called sieve plates with pores

Question 5

What do phloem do?

Answer 5

transport organic compound through the plant down the plant from source to sink

Question 6

What is translocation?

Answer 6

the transport of organic solutes in a plant from source to sink

Question 7

Why is the function of the phloem (transport organic compounds) so important in a plant?

Answer 7

Links parts of plant that need supply of sugars and other solutes like amino acids to parts that have a surplus

Question 8

What is a source in terms of translocation?

Answer 8

areas where sugars and amino acids are loaded into the phoem/provide

Question 9

What is a sink in terms of translocation?

Answer 9

where sugar and amino acids are unloaded and used/needed

Question 10

In what direction does the phloem flow?

Answer 10

Flows in either direction (no valves/pumps) as sinks can turn into sources sometimes

Question 11

What is a similarity between blood vessels and phloem?

Answer 11

both systems a fluid flows inside tubes because of pressure gradients. For both energy is needed to generate meaning both are active processes

Question 12

What is an example of a source?

Answer 12

photosynthetic tissues: mature green leaves, green stems; storage organs that are unloading: storage tissues in germinating seeds, tap roots or tubers at the start of the growth season

Question 13

What is a part of a plant that is a sink?

Answer 13

roots that grow or absorb mineral ions using energy from cell respiration; parts of the plant that grow or develop food stores (fruits, seeds, leaves)

Question 14

What is the most prevalent solute in phloem sap?

Answer 14

Sucrose

Question 15

Why is sucrose a good transport form of carbohydrates?

Answer 15

Sucrose is not as readily available for plant tissues to metabolize directly in respiration, so it will not be metabolised during transport

Question 16

What is phloem loading?

Answer 16

This is the mechanism by which plants bring sugars into the phloem. this differs for different plants

Question 17

What is the apoplast route?

Answer 17

When a significant amount of sucrose travels through CELL WALLS from mesophyll cells to the CELL WALLS of companion/sieve cells where a sucrose transport protein then actively transports the sugar in

Question 18

How is the concentration gradient of sucrose established between phloem and cell walls companion cells ?

Answer 18

active transport where H+ ions are actively transported out of the companion cell from surrounding tissues using ATP as an energy source; ATP is broken down into ADP +Pi that is used to carry sucrose into the cell; Because H+ concentration outside of the sieve tube is higher, it goes down concentration gradient into the sieve tube

Question 19

What is the symplast route?

Answer 19

much of sucrose travels between cells through connections (cytoplasm) between cells called plasmodesmata;

Question 20

What happens to sucrose after it reaches the companion cell?

Answer 20

is converted to an ogliosaccharide to maintain the sucrose concentrations gradient

Question 21

How is water drawn into the companion cell?

Answer 21

sucrose/carbohydrates is high concentrated inside the companion cell and draws water in by osmosis.

Question 22

What results in a build -up of pressure inside a phloem?

Answer 22

the rigid cell walls combined with the incompressibility of water causes pressure

Question 23

What happens to the water inside the phloem once sucrose is withdrawn from it and used?

Answer 23

Loss of solute causes less osmotic pressure and the water that carried the solute to sink is then drawn to the xylem

Question 24

What can the sucrose be used for in a plant?

Answer 24

energy source for processes (like growth) or conversion into starch

Question 25

Why do sieve cells have to be living?

Answer 25

They depend on the membrane to help maintain the sucrose and organic molecule concentration that has been established by active transport

Question 26

Why are sieve cells closely associated with companion cells?

Answer 26

they share the same parent cell

Question 27

What does a companion cell do?

Answer 27

perform many of the genetic and metabolic functions of the sieve tube cell and maintain the viability of the sieve tube cell

Question 28

How can the companion cell increase the phloem loading capacity?

Answer 28

The infolding of the plasma membrane increases capacity using the apoplastic route

Question 29

What are plasmodesmata?

Answer 29

they are connections between the cytoplasm of companion cells and sieve tube cells

Question 30

What do plasmodesmata do?

Answer 30

accommodates the movement of oligosaccharides and genetic elements between the companion and sieve tube cells

Question 31

How are oligosaccharides produced?

Answer 31

The presence of active transport proteins or enzyme activity causes accumulation of sucrose in the sieve tube/companion cell pair

Question 32

How are sieve tube cells separated?

Answer 32

Perforates (with pores) walls called sieve plates

Question 33

What animal consumes the soluble molecules in a phloem as their main part of their diet?

Answer 33

Insects belonging to a group called Hemiptera like aphids, whitefly, mealybugs and psyllids

Question 34

How can phloem transport rates be measured?

Answer 34

using aphid stylets and radioactively labelled carbon dioxide (that is converted during photosynthesis into carbon compounds and then translocated inside the plant) using radioisotopes

Question 35

How can you tell xylem apart from phloem in micrographs?

Answer 35

xylems are generally larger cells; in a vascular bundle. phloem cells are closer to the outside of the plant

Question 36

Identify phloem and xylem

Answer 36

Xylem is larger

Question 37

Identify phloem and xylem

Answer 37

Question 38

identify phloem and xylem

Answer 38

Question 39

identify xylem and phloem

Answer 39