9.1 Xylem transport

Question 1

Define transpiration

Answer 1

TRANSPIRATION: loss of water vapour thrpugh the stems and leaves of a plant

Question 2

Explain process of transpiration

Answer 2

Some light E converted into heat - water in spongy mesophyll into vapour - evaporate through stomata - new water is _absorbed by root_s from soil creating different pressure gradients in roots (high) and leaves (low) - water is pulled via xylem along the pressure gradient (in transpiration stream by transpiration pull)

Question 3

Define stomata

Answer 3

STOMATA: pores on the underside of the leaf which facilitate gas exchange needed for photosynthesis

Question 4

Leaf anatomy

Answer 4

Question 5

Stem anatomy

Answer 5

Question 6

Root anatomy

Answer 6

Question 7

What influences rate of transpiration?

Answer 7

• opening of stomata (levels of photosynthesis - gas exchnage)
• humidity of the environment
• wind
• light intensity

Question 8

How stomata regulate water loss?

Answer 8

Stomata open/close:

• dehydrated cells release plant hromone abscisic acid ABA - triggers efflux of K+ from guard cells - decrease water pressure (lose turgor) - stomata close

Question 9

What makes transpiration stream possible?

Answer 9

Water adhesive (xylem polar - intermolecular associations - additional tension) and cohesive (H bonds - continuous stream) peroperties

Question 10

Explain xylem

Answer 10

• from tracheids (exchange water via pits) and vessels (main traspiration stream)
• tubes composed of dead cells
• water movement passive
• many pores - pits - water transferred to cells
• walls thicker cellulose and lignin - strength as water creates tension

Question 11

Way in which lignin may be deposited

Answer 11

Question 12

Adaptation of roots

Answer 12

Roots - very branched off - root hairs - increase SA by which minerals, ions and water can be taken up

Question 13

Tissues in roots

Answer 13

Question 14

Explain mineral uptake by roots

Answer 14

Needed to take up: Mg2+, K+, Na+, NO3-, PO4-

Can be taken up by diffusion or active transport - root cells contain ion pumps that expel H+ - displace the cations in soil (indirect active transport) - diffusion along a gradient - anions may bind with H+ and reabsorbed

Question 15

Explain water uptake by roots

Answer 15

Via osmosis to higher solute conc - by aquaporins - once inside the cell will move into xylem:

• symplastic route: via cytoplasm, water moves continuously between cells and plasmodesmata,
• apoplastic route: via cell wall, cannot pass Capsarian strip - run through cytoplasm of endodermis

Question 16

Explain water conservation adaptations by two types of plants

Answer 16

Xerophytes: tolerate dry conditions: reduced SA, exposure of stomata for water loss, thickened cuticle, CAm open stomata at night

Halophytes: tolerate salty conditions: can isolate toxins, salts in vacuoles and cell walls, abscission, salt glands, flowering at humid seasons

Question 17

Experiments modelling the movement of water up the xylem

Answer 17

• capillary tubing: traspiration pull/stream, adhesion + cohesion
• filter paper: movement up xylem, adhesion + cohesion - paper and xylem from cellulose
• porous pots: loss of water through pores similar to trasnpiartion

Question 18

Explain potometer

Answer 18

POTOMETER: device that is used to estimate transpiration rates by measuring rate of water loss/uptake

Plant fixed to a potometer - water uptake assesed by movement of a air buble along a ruler - important to remember that not all water is lost due to transpiration - some used for metabolism

Question 19

Controlled variables of experiment with potometer

Answer 19

• temperature
• humidity
• wind
• light intensity