Xylem And Phloem

Question 1

What does xylem do

Answer 1

Transport water and mineral ions in solution
- These substances move up the plant from the roots to the leaves

Question 2

What does phloem tissue do?

Answer 2

Transport organic substances like sugars both up and down the plant

Question 3

What systems are both xylem and phloem

Answer 3

Mass transport systems

Question 4

What are xylem vessels structure like and how does this help the function

Answer 4

• Long tube black structures formed from dead cells joined end to end
• No end walls on these cells making an uninterrupted tube that allows water to pass through the middle easily

Question 5

Water moves up a plant against the force of gravity how does that happen?

Answer 5

• Cohesion and tension help water to move up plants from roots and leaves against the force of gravity
  1- water evaporates from the leaves at the top of the xylem
  2- this creates tension which pulls more water into the leaf
• Water molecules are cohesive so when someone pulled into the leaf others follow
• This means the whole column of water in the xylem from the leaves down to the roots moves upwards
  4- water enters the stem through the roots

Question 6

Transpiration is loss of water from a plant surface, where does transpiration occur most from?

Answer 6

The leaves

Question 7

How does transpiration happen?

Answer 7

1- water evaporates from the moist cell walls and accumulates in the spaces between the cells of the leaf
- When the stomata open it moves out of the leaf down the concentration gradient- due to there being more water inside the leaf than in the air outside

Question 8

How does light affect the transpiration rate?

Answer 8

The lighter it is the faster the transpiration rate because this is the tomato open when it is light to let in CO2
- When it is dark tomato tomato are closed and there is little transpiration

Question 9

How does temperature affect transpiration?

Answer 9

• The higher the temperature, the faster the transpiration rate
• Warmer water molecules have more energy so they evaporate from the cells inside the leaf faster
• This increases the concentration gradient between the inside and outside of the leaf making water diffuse out of the leaf faster

Question 10

How does humidity affect transpiration rate?

Answer 10

The more humidity there is the slower the transpiration rate as there is no concentration gradient for the water to move out the plant

Question 11

How does wind affect transpiration rate?

Answer 11

The wind it is the faster the transpiration rate has lots of air movement blows away water molecules from around the stomata
- This increases the concentration gradient

Question 12

How are phloem tissue adapted for transporting solute?

Answer 12

-sieve tube elements are living cells that form the tube for transporting solutes
- They have no nucleus and few organelles so there is a companion cell for each sieve tube element

Question 13

What do companion cells do for phloem tissue

Answer 13

• Carry out living functions for sieve cells for example, providing energy needed for active transport of solutes

Question 14

What is translocation?

Answer 14

Movement of solute

Question 15

Is translocation an energy requiring process?

Answer 15

Yes, and it happens in the phloem

Question 16

Where does translocation move solute from?

Answer 16

• Move ciliates from sources to sinks

Question 17

What is the source of a solute?

Answer 17

Where it’s made so it’s at a high concentration there

Question 18

What is the sink of a solute?

Answer 18

The sink is the area where it is used up
- So it has a lower concentration there

Question 19

What do enzymes do in translocation?

Answer 19

Enzymes maintain a concentration gradient from the source to the sink by changing the salt gates at the sink (breaking them down or making them into something else)
- Make sure the sink always has a low concentration

Question 20

Explain the mass flow hypothesis at the source end

Answer 20

• Active transport load solute from companion cells into sieve tubes of the phloem at the source
• thus lowers the water potential inside the sieve tubes so water enters the tubes by osmosis from the xylem and companion cells
• This creates a high-pressure inside the sieve tubes at the source end of the flow

Question 21

Describe the mass flow hypothesis at the sink end

Answer 21

1- so are removed from the phloem to be used up
2- this increases the water potential inside the sieve tubes so water leaves the tubes by osmosis
3- this lowers the pressure inside the sieve tubes

Question 22

What is created from the source end to the sink end in the mass flow hypothesis?

Answer 22

• A pressure gradient from the source to sink end.
• This gradient pushes solutes along the sieve tubes towards the sink
• When they reach the sink, the solute will be used or stored