19 - Transport

Question 1

What is the function of the vascular system?

Answer 1

Distributes nutrients and water, heat management, waste management.

Question 2

What is the function of the spongy mesophyll?

Answer 2

Speeds movement of carbon dioxide from the stomata to the palisade mesophyll for photosynthesis to occur.

Question 3

Describe the three properties of water that make it possible to transport in plants.

Answer 3

1. Capillary action: Water draw through the system with the aid of cohesion and adhesion.
2. Hydrostatic pressure: water flows to lower pressure areas.
3. Diffusion pressure: solutes affect concentration and water flows to areas with higher concentration.

Question 4

What is the cortex?

Answer 4

Tissue surrounding the stele and consists of intracellular spaces (symplast) and extracellular spaces (apoplast e.g. xylem).

Question 5

Describe the use of the endodermis.

Answer 5

Water passes through to get to root. Screening of unwanted materials through plasma membrane. Prevents backflow of water from stele.

Question 6

What is the tension-cohesion theory?

Answer 6

When one water molecule is lost (e.g. by transpiration), another is pulled along by the process of cohesion and adhesion.

Question 7

Explain what transpiration does.

Answer 7

Evaporation of water through leaves. Allows plants to adjust to local conditions. Can stop in hot conditions to prevent water loss and xylem collapsing.

Question 8

What are the hypotheses for tree heights?

Answer 8

1. Limited by mechanical strength.
2. Limited by hydraulics: how high xylem can pull water. (More correct)
3. Carbon balance: leaves must grow to provide carbon dioxide to the entire growing tree.

Question 9

What limits tree height?

Answer 9

Gravitational forces create embolisms.
Vessel cavitation.
Branch or plant death.
Loss of hydraulic function around 120-130m.

Question 10

How does phloem function?

Answer 10

Transports sugar and requires energy.
Sucrose source (e.g. leaf) – high water potential sucrose sink (e.g. fruit) – low water potential
For a single sieve tube, the source end will be where the net result of sucrose production/ sucrose utilisation is great.

Question 11

Describe how sugar is transported.

Answer 11

1. Loading of sugars into sieve tube at source.
2. Positive pressure forces sap to flow along.
3. Pressure relieved by unloading sugar and water at sink.
4. Xylem recycles water from sink to source.