Chapter 3 - Transport in Plants

Question 1

What is the role of lignin in xylem?

Answer 1

• Makes xylem walls waterproof
• Provides strength and support to prevent vessel from collapsing and keeping it open
• Lignification decays end of cells to make one long hollow tube

Question 2

What patterns can lignin form?

Answer 2

• spiral
• annular (rings)
• reticulate (network of broken rings)

Question 3

How are bordered pits formed?

Answer 3

Incomplete lignification forms gaps in cell walls. These gaps form bordered pits.

Question 4

What is the role of bordered pits?

Answer 4

The bordered pits in adjacent vessels are aligned so water can pass from one into the other. They also allow water to leave xylem and pass into living tissue.

Question 5

What are some adaptations of xylem?

Answer 5

• narrow tubes so it doesn’t break easily and capillary action is effective
• bordered pits allow water to move sideways between vessels
• lignin thickens walls to prevent collapse
• no cell contents (nucleus/ cytoplasm) to make cells hollow
• made from dead cells to form a collumn

Question 6

What is sap?

Answer 6

Sucrose dissolved in water

Question 7

What do sieve tubes consist of?

Answer 7

Sieve tube elements and companion cells

Question 8

What are sieve tube elements (+adaptations) ?

Answer 8

• Aligned end to end to form sieve tubes
• sieve plates between elements allow movement of glucose from one element to the next
• no nucleus and little cytoplasm so more space for mass flow of assimilates
• thin walls

Question 9

What are companion cells?

Answer 9

• small cells between sieve tubes
• numerous mitochondria and large nucleus
• Provide ATP for active processes such as loading assimilates into sieve tubes

Question 10

What is parenchyma?

Answer 10

Unspecialised packing tissue surrounding phloem and xylem

Question 11

What are plasmodesmata?

Answer 11

Gaps in the cell wall where cytoplasm of one cell is connected to another

Question 12

What are the 3 pathways taken by water?

Answer 12

• Apoplast pathway
• Symplast pathway
• Vacuolar pathway

Question 13

What is the apoplast pathway?

Answer 13

Water passes through spaces in cell walls and between the cells by mass flow. It doesn’t pass through any plasma membranes into the cells.

Question 14

What is the symplast pathway?

Answer 14

Water passes though the cell cytoplasm and plasma membrane and through plasmodesmata to pass from one cell to the next.

Question 15

What is the vacuolar pathway?

Answer 15

Water passes through the plasma membrane, cytoplasm and vacuole and through plasmodesmata to pass from one cell to the next.

Question 16

What is meant by turgid?

Answer 16

Water enters a plant cell via osmosis and it swells but does not burst due to a strong cellulose cell wall.

Question 17

What is meant by plasmolysis?

Answer 17

Water leaves the plant cell via osmosis and the cytoplasm and vacuole shrivel, causing the plasma membrane to pull away from the cell wall.

Question 18

What is a potometer?

Answer 18

Device that measure the rate of water uptake of a transpiring plant

Question 19

What is the importance of transpiration?

Answer 19

• Maintains cell turgidity
• Transports useful mineral ions up the plant
• Supplies water for growth, cell elongation and photosynthesis
• Water can keep the plant cool on a hot day as it evaporates

Question 20

How does increased temperature affects rate of transpiration?

Answer 20

• Increased rate of evaporation so water-vapour potential in the leaf increases
• Increased rate of diffusion through stomata as water molecules have more kinetic energy
• It will decrease water vapour in air, increasing water potential gradient, allowing more rapid diffusion out of leaf

Question 21

What is adhesion?

Answer 21

Attraction between water molecules and walls of xylem

Question 22

What is cohesion?

Answer 22

Attraction between water molecules due to hydrogen bonds

Question 23

What is the Casparian strip?

Answer 23

Located in endodermis and blocks apoplast pathway between the cortex and medulla so water must pass through symplast pathway

Question 24

How does water move up the xylem?

Answer 24

Mass flow (help from root pressure, transpiration pull and capillary action)

Question 25

What is root pressure?

Answer 25

The endodermis moves minerals into the medulla and xylem by active transport which draws water into the medulla by osmosis. Pressure in the medulla builds up, forcing water into and up the xylem.

Question 26

What is transpiration pull?

Answer 26

Cohesion-tension theory - Cohesion means the water molecules are attracted to each other, creating a column. Water is lost by evaporation from leaves, pulling the column of water up the plant. Adhesion allows water to be pulled up the sides of the xylem. This creates tension.

Question 27

What is capillary action?

Answer 27

The xylem vessels are very narrow so adhesion can pull water up the sides of the vessel.

Question 28

What are the steps in the process of translocation?

Answer 28

1. Companion cells use ATP to pump H+ ions out of the cell, increasing the concentration of H+ ions outside the cell, creating a concentration gradient
2. Facilitated diffusion of H+ ions back into the companion cell down a conc. gradient, carrying sucrose with them using cotransporter proteins
3. As the concentration of sucrose in the companion cell increases, it can diffuse through the plasmodesmata into sieve tube elements
4. Water enters the sieve tube elements by osmosis, increasing hydrostatic pressure
5. Sucrose and other assimilates move up and down the phloem by mass flow, down the pressure gradient
6. Sucrose leaves the sieve tube by active transport or via plasmodesmata where it is required
7. This increases water potential in the sieve tube so water moves out, reducing hydrostatic pressure

Question 29

What are xerophytes?

Answer 29

Plants adapted to living in dry conditions

Question 30

What are hydrophytes?

Answer 30

Plants adapted to living in water or where the ground is very wet

Question 31

What are 2 adaptations of xerophytes?

Answer 31

• Roots are very widespread to take advantage of any rain that does fall
• spines instead of leaves to reduce surface area so less water is lost by transpiration

Question 32

What are 2 adaptations of hydrophytes?

Answer 32

• Many large air spaces in leaves to keep the leaf afloat so they can absorb maximum oxygen and sunlight
• Stomata are on upper epidermis so they are exposed to the air to allow for gaseous exchange

Question 33

Why do large multicellular plants need a transport system?

Answer 33

• small surface area to volume ratio
• long distance from external surface to cells
• diffusion is not fast enough
• Needs to transport sucrose/ water/ minerals efficiently to all cells/ tissues

Question 34

For which macromolecule does a plant need both nitrogen and phosphorus?

Answer 34

DNA

Question 35

Why can water form hydrogen bonds?

Answer 35

It is polar and it forms between hydrogen and oxygen.

Question 36

What is the method of using a potometer?

Answer 36

1. Cut a shoot with leaves from a plant underwater
2. Immerse potometer underwater and place the shoot in a tight bung seal at the end of the potometer tube
3. Lift the potometer out of the water and allow one air bubble to form at the other end of the potometer before placing that end into a beaker of water
4. Record the starting position of the air bubble
5. Leave for a set time and measure the distance moved by the bubble
6. Reset the bubble using the tap of the reservoir
7. Repeat experiment after changing the factor being investigated