Chapter 6b Transport in plants

Question 1

What is the primary role of the transport system in multicellular plants?

Answer 1

To meet metabolic demands and cope with size requirements and SA:vol restrictions.

Question 2

What are the metabolic demands that the plant transport system needs to meet?

Answer 2

• Supply of oxygen and glucose to all cells
• Remove waste products of metabolism
• Transport growth plant regulators (‘hormones’)
• Take up and transport mineral ions

Question 3

What is turgor pressure and its role in plants?

Answer 3

Hydrostatic pressure that provides skeleton support and causes cell expansion.

Question 4

What is transpiration stream?

Answer 4

Movement of water from roots to leaves via mass flow and transpiration.

Question 5

What are the main components involved in the transpiration stream?

Answer 5

• Cohesion
• Tension
• Adhesion

Question 6

What is the role of phloem in plants?

Answer 6

Transports assimilates around the plant.

Question 7

What substances does xylem transport?

Answer 7

Water and mineral ions (nitrates, phosphates, sulphates, magnesium).

Question 8

What are the main types of cells found in phloem?

Answer 8

• Sieve tube elements
• Phloem fibres
• Phloem parenchyma
• Companion cells

Question 9

What unique features do xylem vessels have?

Answer 9

Hollow, dead cells supported by living parenchyma cells.

Question 10

What are the stages of transpiration?

Answer 10

• Transpiration at the leaves
• Water transport through the stem
• Water uptake in roots via root hair cells

Question 11

Fill in the blank: Transpiration is the loss of _______ from the underside of the leaf via the open stomata.

Answer 11

[water vapour]

Question 12

What are the characteristics of monocotyledons?

Answer 12

• Parallel leaf venation
• Fibrous roots
• Single-pored pollen

Question 13

What are the characteristics of dicotyledons?

Answer 13

• Reticulated leaf venation
• Main tap root with lateral branches
• Three-pored or furrowed pollen

Question 14

What factors affect the rate of transpiration?

Answer 14

• Temperature
• Light intensity
• Humidity
• Wind speed
• Number of leaves
• Cuticle thickness
• Arrangement of stomata
• Soil water availability

Question 15

How do guard cells control the opening and closing of stomata?

Answer 15

By changing turgidity through ion and water movement.

Question 16

True or False: Lenticels require ATP input to facilitate gas exchange.

Answer 16

False

Question 17

What is the main function of lenticels in plants?

Answer 17

To take in O2 for respiration and remove CO2.

Question 18

What adaptations do root hair cells have for their role in transpiration?

Answer 18

• Extended cytoplasm and cell wall for increased surface area
• Thin cell wall for reduced distance for water entry
• Higher number of mitochondria for active transport
• Absence of chloroplasts

Question 19

What is the main function of lenticels?

Answer 19

Take in O2 for respiration and remove CO2

Question 20

What is the main function of stomata?

Answer 20

Gas exchange for photosynthesis

Question 21

Why are lenticels necessary for woody stems?

Answer 21

Because stems develop bark which is impermeable to gases

Question 22

What do both lenticels and stomata have in common?

Answer 22

Carry out gas exchange by diffusion

Question 23

What is a potometer used for?

Answer 23

To estimate the rate of transpiration

Question 24

What does a potometer actually measure?

Answer 24

Water uptake and assumes it is related to transpiration

Question 25

What is the first step in the procedure for using a potometer?

Answer 25

Cut the shoot underwater to prevent air lock

Question 26

What angle should the shoot be cut at for a potometer?

Answer 26

45 degrees (oblique cut)

Question 27

What does the rate of air bubble movement in a potometer estimate?

Answer 27

The transpiration rate

Question 28

Fill in the blank: Volume of water absorbed (mm3) = _______.

Answer 28

πr² x distance moved (in mm)

Question 29

What is the formula for calculating rate of water uptake?

Answer 29

rate of water uptake (mm3 s-1) = volume of water absorbed (mm3) / time (s)

Question 30

What is translocation?

Answer 30

Movement of dissolved organic solutes through the phloem

Question 31

What are the main molecules transported by translocation?

Answer 31

* Sucrose * Amino acids

Question 32

What is the main source of sucrose in plants?

Answer 32

Sites of photosynthesis, primarily green leaves and stems

Question 33

Define 'sink' in the context of translocation.

Answer 33

Site of assimilate storage

Question 34

What are the main sinks in plants?

Answer 34

* Roots * Meristems * Developing seeds and fruits

Question 35

What is phloem loading?

Answer 35

The process of loading sucrose into phloem from source cells

Question 36

What are the two main routes for phloem loading?

Answer 36

* Symplast route * Apoplast route

Question 37

True or False: The symplast route for phloem loading is a passive process.

Answer 37

True

Question 38

What is the role of protons in the apoplast route of phloem loading?

Answer 38

Protons are actively pumped out and then co-transported back with sucrose

Question 39

What is phloem unloading?

Answer 39

The process of unloading sucrose from phloem into surrounding tissues

Question 40

What happens to sucrose during phloem unloading?

Answer 40

* Hydrolyzed into glucose and fructose * Condensed into starch

Question 41

What does the mass flow hypothesis explain?

Answer 41

The movement of solutes through the phloem due to pressure gradients

Question 42

What experimental evidence supports the mass flow hypothesis?

Answer 42

Contents of sieve tubes are under pressure and exude when cut

Question 43

What is a limitation of the mass flow hypothesis?

Answer 43

Sieve plates may act as barriers to mass flow

Question 44

How can aphids be used to measure phloem transport?

Answer 44

By extracting sap from phloem at various sites along the plant

Question 45

What is the significance of using radioactively-labelled CO2 in phloem transport studies?

Answer 45

It allows tracking of sucrose produced and transported in the plant