MTP

Question 1

Explain how water enters xylem then transported to the leaves.

Answer 1

• active transport by endodermis
• of ions/salts into xylem
• lower water potential in xylem
• evaporation from leaves
• cohesion tension between water molecules
• adhesion creates continuous columns of water

Question 2

What causes root pressure?

Answer 2

• active transport by endodermis
• ions/salts into xylem
• lowers water potential in xylem
• so water enters by osmosis

Question 3

Factors that affect transpiration.

Answer 3

• light intensity
• temperature
• air movement
• humidity

Question 4

Give precautions taken when setting up potometer.

Answer 4

• cut shoot under water
• cut shoot at a slant
• ensure no air bubbles
• dry off leaves
• note where bubble is at start

Question 5

Mass flow hypothesis.

Answer 5

• in source sucrose actively transported into phloem
• energy provided by companion cells (ATP)
• water potential lowered in xylem
• water enters by osmosis
• increase in hydrostatic pressure pressure causes mass movement toward sink
• unloaded by active transport

Question 6

Adaptations of root hair cells.

Answer 6

• extensions increase surface area = increase water uptake
• thinNER cellulose walls = shorter diffusion pathway
• actively transport ions using ATP hydrolysis from soil into cytoplasm = lowers water potential so water IN by osmosis

Question 7

Name xylem structures and functions.

Answer 7

• dead cells forming hollow tubes = faster water flow
• no end walls = continuous columns of water
• walls strengthened with lignin = waterproof and can withstand tension/rigid
• xylem pits = water can move laterally and get around blocked vessels

Question 8

Explain cohesion-tension theory.

Answer 8

• water evaporates from leaves
• lowers water potential in leaf cells
• water replaced from xylem
• water potential gradient creates tension
• hydrogen bonds maintain CONTINOUS COLUMNS

Question 9

What to use when measuring the rate of transpiration.

Answer 9

Potometer

Question 10

Limitations of using potometer.

Answer 10

• volume of water taken up does NOT ALWAYS EQUAL volume of water lost
• only measures water uptake THROUGH STEM (not roots)

Question 11

Xerophyte adaptations.

Answer 11

• reduced stomata
• stomata in pits
• hairs to trap water
• rolled leaves
• thick waxy cuticles

Question 12

What is translocation?

Answer 12

• movement of solutes from source to sink
• requires ATP = provided by companion cells
• enzymes maintain concentration gradient from source to sink

Question 13

Ringing experiment.

Answer 13

• if a ring of bark is removed from a woody stem, a bulge forms above ring
• fluid in bulge has a highER conc of sugars than below ring
• HOWEVER, sieve plate function unclear
• not all solutes move at same rate (should according to mass flow)

Question 14

APHID experiment.

Answer 14

• pierce the phloem, then bodies removed, leaving mouth = sap flows out
• sap flows out quicker nearer to leaves then at stem = pressure gradient

Question 15

Autoradiography (radioactive trackers).

Answer 15

• leaves supplied with with radioactive 14C
• converted to glucose and other organic substances
• tracked through plant as transported
• lack of oxygen inhibits translocation = active transport involved
• companion cells possess many mitochondria to readily produce ATP