Transport in plants

Question 1

What is the function of the xylem in plants?

Answer 1

The xylem transports water and dissolved minerals from the roots to the rest of the plant.

Also provide structural support

Question 2

What is the function of the phloem in plants?

Answer 2

The phloem transports organic nutrients, particularly sucrose, from the leaves to other parts of the plant.

Question 3

What is transpiration?

Answer 3

Transpiration is the loss of water vapor from the aerial parts of the plant, mainly through the stomata in the leaves.

Question 4

What are the main factors affecting the rate of transpiration?

Answer 4

• light intensity
• temperature
• humidity
• wind
• leaf SA
• stomatal density

Question 5

Light

Answer 5

Increases transpiration by opening stomata.

Question 6

Temperature

Answer 6

Higher temperatures increase evaporation rates.

Question 7

Humidity

Answer 7

Lower humidity increases the rate of transpiration.

Question 8

Wind

Answer 8

Removes water vapor, increasing transpiration.

Question 9

Leaf SA

Answer 9

Larger areas increase transpiration.

Question 10

Stomatal density

Answer 10

More stomata increase transpiration rates.

Question 11

What is the process of water uptake by plant roots?

Answer 11

Water is taken up by plant roots primarily through osmosis, where water moves from an area of higher water potential in the soil to an area of lower water potential in the root cells.

Question 12

What is the cohesion-tension theory?

Answer 12

The cohesion-tension theory explains how water moves up through the xylem.
Cohesion refers to the attraction between water molecules, and tension is the pulling force generated by evaporation at the leaf surface.

Question 13

How does water move through the xylem?

Answer 13

Water moves through the xylem via bulk flow, driven by negative pressure (tension) generated by transpiration and the cohesive properties of water.

Question 14

What are stomata and their function?

Answer 14

Stomata are small openings on the leaf surface that allow gas exchange.
They play a critical role in transpiration and photosynthesis by regulating the movement of gases and water vapour

Question 15

What is the role of guard cells?

Answer 15

Guard cells surround stomata and regulate their opening and closing, thus controlling gas exchange and water loss.

Question 16

Define the term ‘root pressure.’

Answer 16

Root pressure is the osmotic pressure within the cells of a root system that causes sap to rise through a plant stem to the leaves.

Question 17

What is the significance of the Casparian strip?

Answer 17

The Casparian strip is a band of cell wall material in the roots that blocks passive flow of water and solutes, forcing them to cross the plasma membrane of endodermal cells, ensuring selective uptake.

Question 18

Describe the process of translocation.

Answer 18

Translocation is the movement of organic compounds (mainly sucrose) from sources (like leaves) to sinks (like roots, fruits, and growing tissues) via the phloem.

Question 19

What is the pressure-flow hypothesis?

Answer 19

The pressure-flow hypothesis explains the mechanism of phloem transport. It involves the generation of high pressure at the source end and low pressure at the sink end, causing sap to flow from source to sink.

Question 20

Explain the term ‘capillary action’ in plants.

Answer 20

Capillary action is the ability of water to flow in narrow spaces without the assistance of external forces, essential for the movement of water through the tiny pores in the cell walls of xylem vessels.

Question 21

Cohesion

Answer 21

Water molecules stick together due to hydrogen bonding.

Question 22

Adhesion

Answer 22

Water molecules stick to the walls of xylem vessels.

Question 23

Phloem translocation of sucrose mechanism

Answer 23

• loading
• mass flow
• unloading

Question 24

Loading

Answer 24

Active transport of sucrose into phloem sieve tubes at the source.

Question 25

Mass flow

Answer 25

High pressure at the source pushes the sap towards lower pressure at the sink

Question 26

Unloading

Answer 26

Sucrose is actively transported out of the sieve tubes at the sink.

Question 27

What are the key structural features of xylem vessels?

Answer 27

• made of dead cells aligned end to end to form continuous tubes.
• thick, lignified walls to provide support
• hollow to facilitate the upward movement of water and minerals.

Question 28

What are the key structural features of phloem tissue?

Answer 28

Phloem tissue consists of sieve tube elements and companion cells.

Question 29

Sieve tubes

Answer 29

have perforated end walls (sieve plates) and lack nuclei.

Question 29

Companion cells

Answer 29

have nuclei and dense cytoplasm to support the metabolic functions of the sieve tubes.

Question 30

What are some adaptations of plants to reduce water loss?

Answer 30

• thick cuticles
• reduced leaf surface area
• sunken stomata
• hairy leaves