Exchange And Transport; Plants

Question 1

Explain why root hairs are efficient surfaces for the exchange of water and mineral ions

Answer 1

• large SA; very long extensions

- thin surface layer

Question 2

How does water enter the root hairs?

Answer 2

By osmosis; water potential is higher in soil as roots have sugars, amino acids and mineral ions dissolved in them

Question 3

Describe the apoplastic pathway of water in the roots

Answer 3

• water moves through adjacent cell walls. Due to its cohesive properties, tension draws water along

Question 4

Describe symplastic pathway of water through roots

Answer 4

• water moves through cytoplasm of adjacent cells, moving through small gaps (plasmodesmata). Water moves by osmosis

Question 5

How is water moved into the xylem from the roots?

Answer 5

• casparian strip in cell walls forces water to move into cytoplasm (active transport can only occur in within living tissue)
• active transport of salts into xylem lowers water potential, water moves in by osmosis

Question 6

How is water moved up the stem?

Answer 6

• root pressure; AT of salts into xylem creates gradient and increases pressure
• transpiration pull; H bonds form between water molecules, so when water evaporates from leaves, more water molecules are drawn up. There is a continuous stream of water molecules

Question 7

Why cant the xylem actively move water around the plant?

Answer 7

• xylem vessels are dead; transpiration pull is a passive process

Question 8

How does water move across the cells of a leaf?

Answer 8

• Water evaporates from mesophyll cells into air spaces; is replaced by water moving up xylem
• mesophyll cells now have lower wp, water enters by osmosis and moves to neighbouring cells by osmosis

Question 9

What is transpiration and why is it important?

Answer 9

It is the the evaporation of water vapour from plants. It is important as transpiration pull moves mineral ions, nutrients and water around plant

Question 10

How does light affect the rate of transpiration?

Answer 10

• more light means more photosynthesis

- stoma are open, and therefore rate of transpiration increases

Question 11

How does a rise in temp affect transpiration rate?

Answer 11

• kinetic energy of water molecules is increased, rate of evaporation increases
• humidity decreases, which decreases wp of atmosphere, therefore gradient increases

Question 12

How does humidity affect transpiration rate?

Answer 12

Humidity is the number of water molecules in atmosphere; higher humidity means less gradient, lower transpiration rate

Question 13

How does increased air movement affect transpiration rate?

Answer 13

• increased air movement disperses humid layer of water vapour at surface of leaf, therefore decreasing wp of atmosphere and increasing gradient. Transpiration rate is increased

Question 14

Define xerophytic plants

Answer 14

• plants adapted to living in environment with low water availability

Question 15

Give examples of adaptations of xerophytic plants

Answer 15

• thick cuticle; longer pathway fro evaporation of water
• hairy leaves; trap moist air close to leaf, decreases gradient of wp
• rolling up of leaves; region of moist air is trapped, reducing gradient
• stomata in pits/grooves; moist air is trapped by stoma
• reduced SA to volume ratio; slower rate of diffusion