9.2 Transport In Phloem

Question 1

Where are the plant tissues in monocot and dicot stems?

Question 2

Where are the plant tissues in the roots of monocots and dicots

Question 3

In the summer where is the source of carbohydrates in a plant?

Answer 3

In the leaves

Question 4

In the summer where are the sink of carbohydrates in plants?

Answer 4

In the roots

Question 5

In the winter/spring where in the source of the carbohydrates?

Answer 5

In the roots

Question 6

What must the plants do to the glucose before transporting it?

Answer 6

Convert it to soluble sucrose

Question 7

What three things happen at the end of growing season?

Answer 7

Plant root/tubers become the source of glucose
Glucose production stops
Converts sucrose back to glucose for metabolic activities

Question 8

What are the two things which plants do during the growing season?

Answer 8

Plants produce glucose -> used to produce ATO for metabolic activities
Excess glucose is converted into sucrose

Question 9

What is the phloem composed of?

Answer 9

Sieve tubes along with companion cells

Question 10

Where are sieve plates found?

Answer 10

At either end of the sieve tubes

Question 11

What are the characteristics of sieve tubes?

Answer 11

They contain perforations in their walls called sieve plate pores

Question 12

What is hydrostatic pressure?

Answer 12

Pressure of liquid

Question 13

What happens when there is a high sucrose level in the sieve tubes? (6)

Answer 13

• It leads to an uptake of water by osmosis
• creates a low concentration of water in the sieve tube
• The concentration gradient shifts and water exists the sieve tubes by osmosis

Question 14

What are the two steps needed when sucrose is actively tranbsported into the phloem from leaf cells? (2)

Answer 14

1. ATP is used to pump H+ ions out of the phloem creating a concentration gradient of H+ ions
2. H+ passively move back to the phloem with the sucrose via the co-transport proteins

Question 15

How does the plant transport combine transpiration and translocation? (7)

Answer 15

1. Glucose is made in the palisade cells through the photosynthesis and is then converted into sucrose to make it soluble
2. The sucrose is then moved by active transport by the companion cell into the phloem cell
3. The transpiration of water is carried to the leaf, taken up by the roots through osmosis
4. This water is then moved to the sieve tube by osmnosis from the xylem due to the high sucrose concentration which has been created / the low water potentioal created in the phloem
5. The high hydroostatic pressure forces water and sucrose down the phloem due to low hydrostatic pressure at the bottom
6. The sucrose is then removed from the water through active transport and stored as starch in the sink
7. Now, thewater with high water potential, by osmosis, is moved back to the xylem

Question 16

What are the factors affecting translocation rate? (4)

Answer 16

The rate of photosynthesis
The rate of cellular respiration
The rate of transpiration
The diameter of sieve tubes

Question 17

How do you use aphids to measure phloem transport? (6)

Answer 17

1. The plant is grown in a lab with the leaves sealed within a glass container containing radioactively-labelled carbon dioxide
2. The leaves will convert the CO2 into radioactively-labelled sugar (via photosynthesis), which are transported by the phloem
3. Aphids are positioned along the plants length and encouraged to feed on the phloem sap
4. Once the feeding has commenced, the aphid stylet is severed as sap continues to flow from the plant at the selected positions
5. The sap is then analysed for the radioactively-labelled sugars
6. The rate of phleom transport (translocation) can be calculated based on the time taken for the radioisotope to be detected at different positions along the plant’s length