Section 3- Mass Transport Plants

Question 1

What are water and mineral ions transported through in plants?

Answer 1

Xylem

Question 2

Why does xylem have no end walls?

Answer 2

So water flow is uninterrupted

Question 3

Why are side walls lignified?

Answer 3

To increase strength, preventing collapse under pressure

Question 4

What does the latent heat of vaporisation being high allow for leaves?

Answer 4

Allows a cooling effect

So enzymes do not denature

Question 5

What does cohesion of water form?

Answer 5

Continuous column of water

Question 6

What is the cohesion-tension theory?

Answer 6

Transpiration stream occurs when water evaporates from surface of mesophyll cells in leaf

Question 7

What is transpiration?

Answer 7

When water vapour diffuses out of the stomata.

Question 8

What does transpiration cause in the leaf?

Answer 8

Tension which pulls more water up the xylem into the cell

Question 9

Why is a potometer not best for determining transpiration rate?

Answer 9

Due to photosynthesis occuring

Question 10

What does a plant being used with a potometer need to be cut on a slant?

Answer 10

To increase surface area

Question 11

Why does a plant need to be cut underwater?

Answer 11

Keeps a continuous column of water

Question 12

What is the method of using a potometer?

Answer 12

1. Leafy shoot cut under water
2. Potometer filled with water
3. Leafy shoot fitted to potometer
4. Air bubble introduced into capillary tube
5. Distance moved by air bubble recorded
6. Calculate volume of water lost

Question 13

What are the 3 components of phloem vessles?

Answer 13

Sieve tube elements: tube to transport sucrose in dissolved sap

Companion cells: involved in ATP production for active loading of sucrose into sieve tubes

Sieve plates: gaps between cell walls where cytoplasm links, allowing substances to flow

Question 14

What is the process where organic materials are transported around the plant?

Answer 14

Translocation

Question 15

What is the source and sink in plants?

Answer 15

Source: site of production of sugar

Sink: places where they will be used or stored

Question 16

How can ringing experiments be used to investigate transport in plants?

Answer 16

Bark and phloem of tree are removed in ring leaving behind xylem
Tissues above missing ring swell = accumulation of sucrose

-Therefore tissues must be transported in phloem

Question 17

How can tracing experiments be used to investigate transport in plants?

Answer 17

Plants grown in presence of radioactive carbon dioxide

Using autoradiography, areas exposed to radiation correspond to where phloem is can be seen

Question 18

How can aphids be used to investigate transport in plants?

Answer 18

When noses of aphids removed, phloem sap seeps out

Show phloem is under pressure

Question 19

Why is less water lost from the upper surface of a leaf?

Answer 19

More stomata at the lower surface

Waxy cuticle on the upper surface

Question 20

How would covering a leaf in epidermal hairs help xerophytes survive in their habitat?

Answer 20

Reduces water potential gradient

Hair trap water vapor

More humid air around leaf so less transpiration

Question 21

What is translocation at the source?

Answer 21

Sucrose is actively transported into the phloem

Reduces water potential

Water moves in by osmosis

Increases pressure at the source

Question 22

What is translocation at the sink?

Answer 22

Sucrose is actively transported out of phloem

Increases water potential

Water moves out by osmosis

Reduces pressure at the sink

Question 23

What is one way in which companion cells are adapted for the transport of sugars between cell?

Answer 23

Mitochondria: release energy for active transport

Ribosomes to produce proteins for protein carriers

Question 24

Describe the mass flow hypothesis for the mechanism of translocation in plants.

Answer 24

At the source sucrose is actively transported into the phloem by companion cells

Lowers water potential of sieve tube

Water enters by osmosis

Increasing pressure causes mass movement towards sink

Question 25

What are two features of root hair cells which adapt them for water uptake?

Answer 25

Large surface area

Low water potential

Question 26

What are two features why xylem vessels are adapted for water transport?

Answer 26

No end walls - allows for continuous column of water

Lignin in side walls - stops collapse

No cytoplasm - ease of flow

Question 27

Why can transpiration in plants not be avoided?

Answer 27

Open stomata

Large surface area

Water potential gradient