Transport in plants

Question 1

Why do plants require a transport system?

Answer 1

• to ensure all cells recieve a strong supply on nutrients they require
• especially important as plants must be able to transport up their stem (against gravity)

Question 2

Relate the structure of xylem to it’s function?

Answer 2

• long continuous columns made of dead tissue allowing water transportation
• contain pits allowing water to move sideways between vessels
• thickened with a tough substance providing structural support

Question 3

Relate the structure of phloem to it’s function?

Answer 3

• sieve tube elements transport sugars around the plant
• companion cells designed for active transport of sugars into tubes
• plasmodesmata allow flow of substances between cytoplasm of different cells

Question 4

Describe the structure and function of the vascular system in roots?

Answer 4

• consists of xylem and phloem
• xylem arranged in an x shape to provide resistance against force
• surrounded by endodermis a wat supply

Question 5

Describe the structure and function of the vascular system in stem?

Answer 5

• consists of xylem and phloem
• xylem on the inside of the bundle provide support and flexibility (phloem on outside)
• layer of meristem cells that provide new xylem and phloem tissue when needed

Question 6

Describe the structure and function of the vascular system in leaves?

Answer 6

• consist of xylem and phloem
• forms the midrib and veins
• involved in transport and support

Question 7

Define transpiration?

Answer 7

• evapouration of water from the leaves of a plant
• consequence of gaseous exchange , occurs when the plant opens the stomata to exchange O2 and CO2

Question 8

Name factors affecting the rate of transpiration?

Answer 8

• increased light = increased transpiration
• increased temp = increased transpiration
• increased humidity = decrease transpiration
• waxy cuticle = prevents transpiration
• increased air movement = increased transpiration

Question 9

How can we measure transpiration rate?

Answer 9

• potometer where plant cutting is placed in a water-filled tube containing an air bubble
• rate of transpiration calculated by measuring movement of air bubble over time

Question 10

Define water potential as a mechanism of movement in plants?

Answer 10

• water potential = tendency of water to move by osmosis from a high to low water potential
• pure distilled water = 0
• basis by which water moves to where it’s needed in the plant

Question 11

Explain what is meant by the apoplastic pathway?

Answer 11

Water moves through cell walls and intercellular spaces by mass flow until water reaches the casparian strip

Question 12

Explain what is meant by the symplastic pathway?

Answer 12

• a method of osmosis through the root hair cells where water moves through the cytoplasm via plasmodesmata
• starts when water is actively transported into the cells

Question 13

Explain the cohesion-tension theory?

Answer 13

• water molecules form hydrogen bonds with each other causing them to ‘stick together’
• surface tension also creates this sticking affect
• therefore is water is lost through transpiration more can be drawn up the stem from roots

Question 14

Give adaptions of xerophytes that allow them to live in dry conditions?

Answer 14

• small/rolled leaves
• densely packed mesophyll
• thick waxy cuticle
• stomata often closed
• hairs to trap moist air

Question 15

Give adaptions of hydrophytes that allow them to live in wet conditions?

Answer 15

• thin/absent waxy cuticle
• stomata often open
• wide flat leaves
• air spaces for buoyancy

Question 16

Summarise the mechanism of translocation?

Answer 16

• sucrose produced in leaves loaded into sieve tubes via active transport (with energy)
• lowers water potential causing water to move in from xylem
• assimilates move along the sieve tube to areas of lower hydrostatic pressure (sinks)
• sucrose diffuses into surrounding cells where it’s needed