Transport systems plants (3.1.3)

Question 1

What can you find the Xylem wall and what are they for?

Answer 1

Non-lignified pits.

Allow H2O and mineral ions to leave the xylem.

Question 2

What else can be found in assimilates?

Answer 2

Sucrose
Ions
Amino acids
Hormones

Question 3

What does the Phloem do and what is the scientific name for this?

Answer 3

1) Transports assimilates up and down the plant.
2) Translocation

Question 4

Describe the two ways in which water travels from the roots to the xylem.

Answer 4

Apoplast pathway - water travels from cell to cell through the cell wall using tension.

Symplast pathway - water travels through the cytoplasm (diffusion) and plasmodesmata (osmosis) of each adjacent cells.

Question 5

What mechanism is in place to filter water that travels through the apoplast pathway?

Answer 5

Casperian strip - A waxy substance in the cell wall.

Water has to move into the cell where it then needs to pass through a partially permiable membrane.

Question 6

Where can you find the casperian strip?

Answer 6

Endodermal cells.

Question 7

Describe the movement of water and ions from the endodermis to the xylem.

Answer 7

Ions moved using active transport.

Water potential in xylem decreases.

Water potential in endodermis increases causing water to move into xylem by osmosis.

Root pressure pushes water up the xylem.

Question 8

Define transpiration.

Answer 8

The loss of water vapour by evaporation through stomata.

Question 9

What two benefits does transpiration provide?

Answer 9

1) Cools the plant.
2) Causes transpiration stream

Question 10

Draw and label the process of the transpiration stream.

Think of all the important keywords.

Answer 10

Include these words:

Osmosis
Diffusion
Water vapour
Stomata
Tension (suction)
Cohesion
Adhesion
Root cortex cells

Question 11

How does temperature affect transpiration rate?

Answer 11

Warm water molecules have more energy.

Evaporate from the cell walls and into the space between cell and leaf quicker.

The water potential gradient increases.

Water defuses out of the leaf faster.

Question 12

What effect does air movement have on transpiration rate?

Answer 12

The more air movement, the lower the humidity.

This maintains a steep water potential gradient.

Question 13

How does light intensity affect transpiration?

Answer 13

Light intensity increases the rate of photosynthesis.

More stomata open to allow CO2 to enter allowing more water vapour to diffuse out of the leaf.

Question 14

Picture and describe the process of active loading and mass flow.

Answer 14

Keywords:

Proton pump
Proton concentration gradient
Co-transporters (proteins that bind two molecules)
Active transport
Diffusion through plasmodesmata
Water potential, turgor pressure.
Mass flow

Question 15

Give two examples of xerophytic plants along with a description of their adaptations.

Answer 15

Cacti
Thick, waxy layer on the epidermis. Reduces water loss because the layer is waterproof.

Spines instead of leaves. Reduces surface area for water loss.

Closed stomata at the hottest times of the day when transpiration rates are the highest.

Marram Grass

Thick, waxy layer on the epidermis. Reduces water loss because the layer is waterproof.

Stomata sunken in pits / Hairs on the epidermis.
Traps moist air in the pits. Slows transpiration by lowering water potential gradient.

Roll their leaves when hot or windy.
Traps moist air. Reduces surface area. Protects stomata from the wind.

Question 16

How are hydrophytes adapted for their habitat?

Answer 16

Air spaces in the tissues help the plant to float. Leaves float increasing the amount of light they receive.

Air spaces in the tissues act as a store of oxygen for use in respiration.

Air spaces in the roots and stems allow for oxygen to move to the parts of the plant that are underwater.

Stomata are only present on the upper surface. Maximise gas exchange.

Flexible leaves and stems. Reduces damage by water currents.

Question 17

Define translocation

Answer 17

Translocation is the movement of assimilates to where they are needed in a plant.

Question 18

Sucrose is often required in constant supply. Give an example of how sinks ensure this happens?

Answer 18

In potatoes, sucrose is converted to starch in the sink.

This maintains a lower concentration of sucrose in the sink than the phloem.

In other sink areas, the enzyme invertase breaks down sucrose into glucose for use by the plant.

Question 19

Describe the processes of the mass flow hypothesis?

Answer 19

Active transport actively loads solutes into the sieve tubes.

Water potential lowers. Water moves in from Xylem and Companion cells by Osmosis.

HIGH PRESSURE AT THE SOURCE

Solutes diffuse from the Phloem in the sink end. Down a concentration gradient.

Water potential increases. Water flows to the Xylem.

LOW PRESSURE AT THE SOURCE

The resulting pressure gradient pushes solutes along the sieve tubes toward the sink.

Question 20

Explain Active loading.

Answer 20

H+ ions are actively transported out of the companion cell.

A concentration gradient is created.

Co-transport proteins transport an H+ ion, down the concentration gradient, back into the companion cell.

A sucrose molecule also binds to the carrier protein and moves into the companion cell, against its concentration gradient.

Sucrose molecules are moved into the sieve tubes by the same process.