2.3.2 Transport in Plants

Question 1

What is the arrangement of xylem in the root vascular bundle?

Answer 1

The xylem is arranged in an X-shape in the centre for mechanical strength.

Question 2

What surrounds the xylem in the root?

Answer 2

The endodermis surrounds the xylem, supplying it with water.

Question 3

Where is xylem found in the stem?

Answer 3

Xylem is located on the inside of the vascular bundle, providing support.

Question 4

What is the role of the cambium in the stem?

Answer 4

The cambium produces new xylem and phloem tissues.

Question 5

What do vascular bundles form in the leaf?

Answer 5

Vascular bundles form the midrib and veins in dicotyledonous leaves.

Question 6

What is the function of xylem vessels?

Answer 6

Xylem transports water and minerals and provides structural support.

Question 7

What are xylem vessels made of?

Answer 7

Xylem vessels are long tubes made of dead tissue, forming a continuous column.

Question 8

What is the purpose of pits in xylem vessels?

Answer 8

Pits allow water to move sideways between xylem vessels.

Question 9

How do xylem vessels remain flexible?

Answer 9

Xylem is thickened with lignin in spiral patterns, allowing flexibility.

Question 10

What is the function of phloem?

Answer 10

Phloem is involved in translocation, moving sugars like sucrose to growing parts and storage organs.

Question 11

What are the main components of phloem?

Answer 11

Phloem consists of sieve tube elements and companion cells

Question 12

How do sieve tube elements and companion cells communicate?

Answer 12

Plasmodesmata (gaps between cell walls) allow communication and the flow of substances between cells.

Question 12

What role do companion cells play in phloem?

Answer 12

Companion cells produce ATP to load sucrose into sieve tubes for active transport.

Question 13

What is transpiration in plants?

Answer 13

Transpiration is the process where plants absorb water through the roots, move it up through the plant, and release it as water vapour through stomata in the leaves.

Question 14

What is the role of transpiration in plants?

Answer 14

Transpiration supports photosynthesis, growth, and elongation by supplying water and minerals, and helps regulate plant temperature via evaporation.

Question 15

How does water move during transpiration?

Answer 15

Osmosis moves water from xylem to mesophyll cells, then evaporation from the mesophyll surface into intercellular spaces, followed by diffusion of water vapour out through the stomata.

Question 16

How is the rate of transpiration measured?

Answer 16

The rate of transpiration can be measured using a potometer, where the movement of the meniscus in a capillary tube replaces water lost by the leaf.

Question 17

What is the transpiration stream?

Answer 17

The transpiration stream is the movement of water from the roots to the leaves, driving important processes like photosynthesis and mineral transport.

Question 18

What factors affect the rate of transpiration?

Answer 18

Factors include number of leaves, size and position of stomata, waxy cuticle, light intensity, temperature, humidity, air movement, and water availability.

Question 19

How does water enter the root?

Answer 19

Water enters the root through root hair cells due to a water potential gradient, where the water potential is higher in the soil than in the root cells.

Question 20

Why do root hair cells have a large surface area?

Answer 20

Root hair cells have a large surface area to increase the movement of water into the root.

Question 21

How are minerals absorbed by root hair cells?

Answer 21

Minerals are absorbed via active transport, moving against the concentration gradient.

Question 22

What are the two pathways for water movement in the root?

Answer 22

Water moves through the root via the symplast pathway or the apoplast pathway

Question 23

What is the role of the Casparian strip in the root?

Answer 23

The Casparian strip (a layer of suberin) in the endodermis prevents water from moving through cell walls, forcing water to enter the symplast pathway to continue its journey.

Question 24

How does water enter the xylem after crossing the endodermis?

Answer 24

After crossing the endodermis, water moves down the water potential gradient from cell to cell until it reaches the xylem vessel through a pit.

Question 25

What is the symplast pathway?

Answer 25

water enters the cytoplasm through the plasma membrane and passes from one cell to the next through plasmodesmata the channels which connect the cytoplasm of one cell to the next.

Question 26

What is the apoplast pathway?

Answer 26

water moves through the water filled spaces between cellulose molecules in the cell walls. In this pathway, water doesn’t pass through any plasma membranes therefore it can carry dissolved mineral ions and salts.

Question 27

How does water move up the xylem?

Answer 27

Water moves up the xylem due to the water potential gradient, with water being removed from the top of the xylem vessels into mesophyll cells.

Question 28

What is root pressure and how does it help water movement?

Answer 28

Root pressure is caused by the active transport of minerals into the xylem, which drives water into the xylem by osmosis, pushing it upwards.

Question 29

How does cohesion help water move in the xylem?

Answer 29

Cohesion refers to the attractive forces between water molecules, which helps pull water up the stem.

Question 30

What is the tension-cohesion theory?

Answer 30

The tension-cohesion theory explains how water moves up the xylem due to cohesion (molecule-to-molecule attraction) and surface tension, supported by capillary action.

Question 31

How does capillary action contribute to water movement in the xylem?

Answer 31

Capillary action occurs when water molecules adhere to the walls of the xylem, aiding the upward movement of water through cohesion.

Question 32

What is translocation in plants?

Answer 32

Translocation is the energy-requiring process of transporting assimilates (like sucrose) in the phloem from sources (e.g., leaves) to sinks (e.g., roots, meristems).

Question 33

What is active loading in translocation?

Answer 33

Active loading is when companion cells use ATP to transport hydrogen ions (H⁺) into surrounding tissues, creating a gradient that helps sucrose enter the companion cells via cotransporter proteins.

Question 34

How does sucrose move from companion cells to sieve tube elements?

Answer 34

Sucrose diffuses from companion cells into sieve tube elements through plasmodesmata as the sucrose concentration increases in the companion cells.

Question 35

How does water enter the sieve tubes during translocation?

Answer 35

As sucrose enters the sieve tubes, it reduces the water potential, causing water to enter by osmosis, increasing the hydrostatic pressure inside the sieve tube.

Question 36

How is sucrose removed from the sieve tube elements?

Answer 36

Sucrose is removed from the sieve tubes by diffusion or active transport, which increases the water potential, causing water to leave by osmosis and reducing pressure at the sink.

Question 37

What drives the mass flow of water in the phloem?

Answer 37

The hydrostatic pressure gradient drives the mass flow of water from areas of high pressure (sources) to areas of lower pressure (sinks).